FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: mbrunson427 on August 23, 2017, 09:11:03 AM
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I've been searching this and there are quite a few discussions on different forums, but none specifically related to the FE. From the reading I've done, there's a pretty simple explanation for why people use dual pattern cams; to help the engine make up for unfavorable exhaust-side characteristics.
I had a cam ground by Elgin Cams for my 428 project. I sent him flow numbers for the BBM heads and a load of information about how the car was honestly going to be driven. He decided to grind me a single pattern cam. I've read some suggestions that a single pattern cam should help with low-mid range torque? In my info to him, I explained that it would be a street car and needed to have good vacuum for power brakes and good torque for stoplight to stoplight driving with the manual transmission.
Regardless, I wont be changing the cam to anything different, just trying to understand the theory in all this. Anyone with experience, chime in and teach me something!
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We could spend a few days on this subject, but I'll throw this out:
I rarely use a single pattern camshaft because all FE heads need at least a few degrees of split to help out a less than optimal exhaust side flow. Some cylinder heads are really good as far as exhaust flow goes, including your BBM heads, the Survival heads, CNC ported Edelbrocks, etc. These heads will usually be around a 70-75% ratio and I normally use a 2-6° split for most street engines. Some heads have very poor exhaust flow, like a factory Tunnel Port head for example. I have used 8-12° splits in the past for similar combinations.
A few side points:
1. Adding exhaust duration increases overlap. This can either help you or hurt you. If you have a large volume intake port (think 4V Cleveland or FE Tunnel Port), extra exhaust duration (overlap) will help scavenge the intake side and help intake port velocity. A lot of overlap, however, can prove to not be desirable for a street engine...low vacuum, rowdier idle, etc.
2. It all depends on the particular engine that you're dealing with at the time. There are tons of variables in an engine build and its application, which can affect the cam choice. It's really difficult to make ballpark statements.
3. A single pattern cam won't necessarily help with low-mid range hp or torque. Again, there's too many variables to make a broad statement like that, and it's entirely possible to grind a dual pattern cam that will increase hp/torque in the low-mid range, increase vacuum, increase street manners, etc. It just depends on the application and lobes that are chosen.
4. Most cam grinders don't know the engine they're grinding for on an intimate basis. Engine builders do. I cringe when someone tells me that they called up a cam tech line and ordered a cam for an FE, Cleveland, etc. Most guys that answer the phone have never seen an FE engine, much less built one, or built 100's of them. It's very easy for a cam grinder to grind a cam, send it out, and the end-user be happy with it, solely on the standpoint that they haven't tried anything else as a comparison. When you get to try 100 cams, you get to zero in on what works and what doesn't. The guy on the FE forum who's complaining about a noisy camshaft will probably learn the hard way that most of the Comp Cams out-of-the-catalog hydraulic roller cams are gonna have some noise to them.
I know that probably muddies the water, but this is a very difficult subject to throw out absolutes on.
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Brent covered it well. I have never put in a single pattern in any of the SBF engines I've done. Mostly because the exhaust ports a weak on stock heads even when ported. I have done a few 351Cs and the exhaust needs all the help it can get LOL. The ported 4Vs on the Mustang flow 340/199 - you'd think an exhaust port large enough to house a family of Gerbils would flow like a sewer pipe, but it doesn't. I see singles sold - Isky's catalog is full of them - for 351C and always wondered "eh?". I have used a lot of "catalog" cams but always worked the numbers to get an idea of what would work best in a particular setup - never relied on a tech line suggestion. However, The Howards hydro roller in the Mustang works well enough but the custom solid roller in the dragster from Brent's garage sale works great and sold me on the "call a builder that knows your motor and let that person order the cam".
Cams are a lot like carbs - everybody wants a "big one" and the companies will sell you a "smaller one" because they know good and well that it'll run better - generically - and that most people don't really know WTF they are trying to do. 850 double pumper on a station wagon with a stock converter and 3.08 gears, bitches on the internet that the carb is a POS. And so on.
BTW - the Howards hydro makes noise too, not that I care. If your cam makes noise but it runs good, maybe put less muffler on the car. ;)
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This should be interesting then. I'm going to dyno it and should have results posted on here by fall. So Brent, by not putting some split in the duration and running a single pattern, what do you think is being given up here? Don't worry about offending, I like learning and I like the theory.
Combo is a 428, std bore and stroke. BBM heads, Shelby 2x4 C7ZX intake, hydraulic roller cam (.609" lift, 112 lobe centers, 226 @.050, 282 advertised seat duration), 11:1 compression, 4 speed toploader with 3.50 gears, 3300 pound 67 Mustang Coupe
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mbrunson427,
My first comment regarding dual pattern cams is YES. The intake "charge" is fuel and air and the exhaust charge is still burning and expanding. Both very different "mediums" so why have the same timing events?
Brent is 100% correct in that familiarity with a specific engine is KEY to getting THE BEST cam for your application. Chevys, Oldsmobiles , Pontiacs , Fords, Mopars, etc ALL have their little quirks . Some thrive on lift and others love duration without giant lift. Nitrous cams have seen allot of changes in the last few years . Shorter intake duration with giant lifts and as much as a 20 ( or more) duration split on the exhaust. Why? Nitrous force feeds the cylinder beyond what normal vacuum would pull in , so it needs longer to evacuate. Yet there are "some" cylinder heads out there that are actually TOO good on the exhaust side and need to "choke" it by running a smaller exhaust lobe.
Again , it's all about getting the guy that knows a particular engine like the back of his hand , not what his catalog says. I was "a guy at the cam company" 40 years ago and saw co workers recommend stuff and they had never built an engine! If it wasn't in the book they didn't know.
Randy
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There is no "rule" when you should or shouldn't use a single pattern vs dual pattern cam. The intake to ex duration "split" is simply a result of proper valve events for the given combination. If the flow numbers show an intake to ex flow percentage, and the engine and application/combination warrant a single pattern cam, that's what you need. It happens VERY seldom. To put it simply, the bigger the difference between intake and ex flow numbers for the heads, the bigger the duration "split" will be. If whoever you're getting your cam from doesn't ask for flow numbers, or you aren't using flow numbers for your cam selection, you're missing out.
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This should be interesting then. I'm going to dyno it and should have results posted on here by fall. So Brent, by not putting some split in the duration and running a single pattern, what do you think is being given up here? Don't worry about offending, I like learning and I like the theory.
Combo is a 428, std bore and stroke. BBM heads, Shelby 2x4 C7ZX intake, hydraulic roller cam (.609" lift, 112 lobe centers, 226 @.050, 282 advertised seat duration), 11:1 compression, 4 speed toploader with 3.50 gears, 3300 pound 67 Mustang Coupe
My guess is about 20-25 hp. You only have about 58 degrees of overlap. You'll have great vacuum, but you'll be shy on horsepower.
Most importantly, you're gonna have trouble with that combo on pump gas, unless the ICL is set at 110. 11:1 compression with a 282 advertised duration and a 3.50 gear doesn't work well together if the cam is ahead much.
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guess I should mention.....I'm in Denver. Crappy air so we get away with more compression.
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Touche'......
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Touche'......
Haha, I'm not trying to argue here! Just trying to pick up on theory and understand why Dema thought this was the best approach for what I've got and what I asked for. I'd call him and ask him but I think he'd get annoyed with all my questions pretty quickly.
Similar to most of the things that I've read, it seems that people generally want to discuss this in terms of peak power. For this car I'm more concerned with it's manners, maintaining practicality, and really focusing on how it is to drive. Worried about the whole curve, rather than just the top.
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I don't think that any of us have been talking just in terms of peak horsepower. A lot of us build street engines and we look at the whole spectrum. As I mentioned up top, there's nothing about a single pattern cam that screams "max streetability" and there's nothing about a dual pattern cam that says you'll give up any of the things that you mentioned.
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Hey Mike, Mr. Dema Elgin is no green horn. Sounds like he listened carefully to what you described as your goals. It's easy to overdo it at 5000+ DA. Summer in Denver is not uncommon to see 9000 DA. I like the single pattern in your case. My favorite hyd roller for you would be 224/224. The 226/226 flat tappet would "act" a little smaller than 224 roller. He is trying to increase your cylinder pressure in an environment where pressure will be terminally low. The BBM head enjoys the 112. If you are willing to endure a proper break-in, I think you will like what he sent you. If you ran that same combo in Tennessee, I'd tell you to go 232/238-12 with power brakes, and progressively more as desired. I'd stay on the 112 with those heads with those kinds of cams. The really good exhaust does not benefit as much from the tighter centers, and wider separation will carry longer and have a broader power range.
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"hydraulic roller cam (.609" lift, 112 lobe centers, 226 @.050, 282 advertised seat duration)"
I think Elgin sent him a HR cam.
Can you explain why you can't grind a dual pattern and increase cylinder pressure too?
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I'm curious if you guys would call a 221/222 a dual pattern cam. HOw about a 222/221? What if the duration at .05 is the same but the lift is different? Is that a dual pattern cam? ::)
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Do you really feel the need to roll your eyes?
To answer your question, most camshaft manufacturers refer to it as a dual pattern camshaft when the intake lobe is different than the exhaust. So technically, yes, if the duration varied by just one degree, or the duration was the same and the lift was different between intake/exhaust, then it would be a dual pattern.
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I just overlooked the fact that it IS a hydraulic roller. I assumed flat tappet......I think that cam will do good. To your question Brent......it is just going to have more cylinder pressure if the exhaust opens later. Shorter duration will have to open later if the centrlines are a constant. The exhaust "blowdown" will have more energy. Like unplugging two airhoses......one at 50 psi, the other at 80 psi...same idea. That will move the exhaust gas with more energy initially, which will build torque at low rpm with restricted exhaust. As overlap grows with big cams, bottom end "pop" goes away and engines like less exhaust restriction or open headers because the exhaust becomes more of an event instead of a result of the pressure release from the valve cracking open under pressure. Scott, to your question....... it is certainly possible to have .050 numbers be the same or even flipped from the .200 relationship. "Dual pattern" in my book.....woops, don't have one, lol.....would refer to lobe design as much as duration numbers. I've seen many cams that have more advertised or more .050 on the exhaust, and then a look deeper at the .200 numbers shows a "smaller" or less aggressive lobe when you dig deeper. The same can happen in reverse. Lobes can be the same at .050 on paper, and the exhaust might have bigger .200 numbers. There are just an infinite number of ways to approach cam design. A person designing a cam should look at much more than just an advertised or .050 number on paper. Head flow characteristics, stroke of the engine, bla bla bla.......definitely lots of things to consider. The most important being to define the goals clearly, and then work the combo to the goals.
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Blair, I guess I was trying to be rhetorical with my question, and my thinking also involved Scott's question where he rolled his eyes at all of us: you can vary the characteristics between the intake/exhaust lobes just ever so slightly.
The beauty of a custom is that you can pick between an almost infinite number of lobe combinations in the catalogs and just because it's a "dual pattern" doesn't mean that you can't alter the ICLs and pick up some cylinder pressure. That refers back to the first few lines of your paragraph.
In theory, you could have a split duration and alter the lobe characteristics so that you would have even more cylinder pressure over a camshaft with the same lobes for both intake/exhaust.
All-in-all, I think we're all thinking the same thing, just using different terminology for it.
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Just a credit to everyone on here.....this is a much better conversation than any other forum/website I looked at. I'm glad I asked.
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Yes, it is certainly true that tighter centers, with everything else being a constant, will increase blowdown (cylinder pressure). If the cylinder head flows poorly, and more importantly, if the exhaust flows poorly...... tighter centers crutch things. That also roughs up the idle, and narrows the powerband. If the head flows good, tight centers send some of our potential to build a big fire right out the exhaust pipe. There are just lots of ways.....probably why there are lots of cam companies, and lots of guys with ideas. In my experience with the BBM heads and anything with better exhaust flow as a percentage of the intake, I lean toward spreading the lobes more than I used to. Lots of guys like the bumpity bump idle, but don't want their stick shift streeters bumping along in the lower gears.....so a wider separation smooths that out, and a better head with a happy valvejob (hopefully with a small intake port) gets the air moving without having to drag the intake charge through the exhaust. Just my thoughts, but everyone has ideas.
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Yep, and I was more directly referring to intake centerlines vs lobe centers.
In the OP's case, with just 58° of overlap, he could have went with a fairly noticeably duration split (4-6°) and either widened the LSA a degree or two, or to be honest, even kept it at 112 or 110 and still kept the overlap not far from where he is now. Making the intake events earlier would help with a loss of cylinder pressure.
When I look at grinding something for power brakes, or on a street application where you want something smoother, I keep a close eye on the overlap. You can vary the advertised durations, LSA, and ICL, so that you can still have the streetability, but still tweak for power too.
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I found that high altitude engines respond well to increased intake duration because of the lesser air density.
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Do you really feel the need to roll your eyes?
To answer your question, most camshaft manufacturers refer to it as a dual pattern camshaft when the intake lobe is different than the exhaust. So technically, yes, if the duration varied by just one degree, or the duration was the same and the lift was different between intake/exhaust, then it would be a dual pattern.
It was meant more as a rhetorical smile than an eye roll. I meant no disrespect. Point is, even if the numbers are the same at .05, the cam could very well be a dual pattern cam.
The problem here, for me, is the parroting of terms like "single" or "dual" pattern, "LSA", "LCL" and advertised .050 numbers as if they really mean anything. None of those tell you anything about a camshaft and are only terms that the industry has come up with for marketing. LSA numbers are simply a result of valve events. LSA is not a design criteria or something to choose a cam by. Intake or lobe centerline...same thing. If you have an asymmetric lobe, you'll be hard pressed to know where the centerline really is and as has already been talked about, .050 numbers don't really tell you much, if anything useful about the lobe. I never install a cam to the intake centerline. It's always to the intake opening event @ .05. That's about all that number is good for other than a very basic, fundamental reference.
I've been working with one of the best cam designers in the business going on 5 years now and I still wouldn't even come close to trying to design my own cam. I have enough understanding to be dangerous and maybe, just maybe, be able to know which cam to NOT use from a shelf.
If anyone has even a small investment in a performance engine, I would suggest calling someone that knows cams and cam design and talk to them about a cam you're thinking about using, or just get one made.
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Here's the cam that's going in my 390. Straub hyd roller. I asked for peak at around 5500. Used Stan Weis advertised flow numbers for a C6 head. I didn't flow the heads and since then have done a little work to them. 2.05 intake, 1.65 ex, 11/32 stems, good valve job, some minor bowl work but nothing major. No porting in the fronts of the ports and didn't touch the openings. Engine will have flat tops, performer RPM, 750 Holley DP and Doug's headers.
221/230 @ .05, 277/286 @ .006, .588/.554, 109 LSA. Intake opens at 4.5 BTDC.
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In my 428CJ I had my local grinder of 40 years make a dual pattern hydraulic flat tappet cam. 242@ .050 w.600 intake and 248w.575 lift on the exhaust. Because those lobes have the potential to rpm more than the 6,000 I want to use , I had him make it on a 106* lsa. My goal is to idle rough , have torque to melt tires and be "all done" by or before 6,000. I have yet to dyno it but it should be interesting. It's kind of like what I would have done in '68 when it was new. Nice set of NOS JR 1-7/8ths headers, again like a day 2 deal. I'm sure you guys will pick it apart but it is what I did against "modern thinking". LOL
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Here's the cam that's going in my 390. Straub hyd roller. I asked for peak at around 5500. Used Stan Weis advertised flow numbers for a C6 head. I didn't flow the heads and since then have done a little work to them. 2.05 intake, 1.65 ex, 11/32 stems, good valve job, some minor bowl work but nothing major. No porting in the fronts of the ports and didn't touch the openings. Engine will have flat tops, performer RPM, 750 Holley DP and Doug's headers.
221/230 @ .05, 277/286 @ .006, .588/.554, 109 LSA. Intake opens at 4.5 BTDC.
Nice street cam for a 390 ... 277/286 221/230 109 LSA on 106 ICL using our common speak.
Be real nice if you can hit a tight quench and true 10 - 10.2 static compression.
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Here's the cam that's going in my 390. Straub hyd roller. I asked for peak at around 5500. Used Stan Weis advertised flow numbers for a C6 head. I didn't flow the heads and since then have done a little work to them. 2.05 intake, 1.65 ex, 11/32 stems, good valve job, some minor bowl work but nothing major. No porting in the fronts of the ports and didn't touch the openings. Engine will have flat tops, performer RPM, 750 Holley DP and Doug's headers.
221/230 @ .05, 277/286 @ .006, .588/.554, 109 LSA. Intake opens at 4.5 BTDC.
Nice street cam for a 390 ... 277/286 221/230 109 LSA on 106 ICL using our common speak.
Be real nice if you can hit a tight quench and true 10 - 10.2 static compression.
I just finished the block @ 9.155. Pistons and rods are up and down a little but will average about .005 in the hole. Heads are C6 but haven't cc'd them. I don't think they've been surfaced before and it only took .002" to get them nice and flat. Pistons are Icon IC862 +.03. Compression "should" be right about 10.4 using a 73cc chamber. I think it should run pretty good.
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Here's the cam that's going in my 390. Straub hyd roller. I asked for peak at around 5500. Used Stan Weis advertised flow numbers for a C6 head. I didn't flow the heads and since then have done a little work to them. 2.05 intake, 1.65 ex, 11/32 stems, good valve job, some minor bowl work but nothing major. No porting in the fronts of the ports and didn't touch the openings. Engine will have flat tops, performer RPM, 750 Holley DP and Doug's headers.
221/230 @ .05, 277/286 @ .006, .588/.554, 109 LSA. Intake opens at 4.5 BTDC.
Nice street cam for a 390 ... 277/286 221/230 109 LSA on 106 ICL using our common speak.
Be real nice if you can hit a tight quench and true 10 - 10.2 static compression.
I just finished the block @ 9.155. Pistons and rods are up and down a little but will average about .005 in the hole. Heads are C6 but haven't cc'd them. I don't think they've been surfaced before and it only took .002" to get them nice and flat. Pistons are Icon IC862 +.03. Compression "should" be right about 10.4 using a 73cc chamber. I think it should run pretty good.
It should, especially if the heads are flowing decently. FYI - recommend you cc them though. Most FE iron heads come in high, and those heads can start well over 76cc. Also, not sure of the head gasket you are using, but a blue Felpro is over .051 thick. A 1020 is thinner, even though it has a bit big of a bore, it'll work. My hunch is, unless the heads were cut pretty well, you'll be close to 10 and as low as 9.8 if you run the blue gasket. A nice cam for a streeter.
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Here's the cam that's going in my 390. Straub hyd roller. I asked for peak at around 5500. Used Stan Weis advertised flow numbers for a C6 head. I didn't flow the heads and since then have done a little work to them. 2.05 intake, 1.65 ex, 11/32 stems, good valve job, some minor bowl work but nothing major. No porting in the fronts of the ports and didn't touch the openings. Engine will have flat tops, performer RPM, 750 Holley DP and Doug's headers.
221/230 @ .05, 277/286 @ .006, .588/.554, 109 LSA. Intake opens at 4.5 BTDC.
Nice street cam for a 390 ... 277/286 221/230 109 LSA on 106 ICL using our common speak.
Be real nice if you can hit a tight quench and true 10 - 10.2 static compression.
I just finished the block @ 9.155. Pistons and rods are up and down a little but will average about .005 in the hole. Heads are C6 but haven't cc'd them. I don't think they've been surfaced before and it only took .002" to get them nice and flat. Pistons are Icon IC862 +.03. Compression "should" be right about 10.4 using a 73cc chamber. I think it should run pretty good.
It should, especially if the heads are flowing decently. FYI - recommend you cc them though. Most FE iron heads come in high, and those heads can start well over 76cc. Also, not sure of the head gasket you are using, but a blue Felpro is over .051 thick. A 1020 is thinner, even though it has a bit big of a bore, it'll work. My hunch is, unless the heads were cut pretty well, you'll be close to 10 and as low as 9.8 if you run the blue gasket. A nice cam for a streeter.
I will CC and probably end up ordering a Cometic to get quench where I want it, probably around .027-.030". Not going to mill the heads for more compression...it'll be what it'll be. At some point I need to get this engine back together before the year is over. I'll start on my "good" NA motor this winter. Never really intended to do all this to this motor but you know how that goes... ::)
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You might not be competitive in Pro Stock with a single pattern cam but they'll work just fine on the street. In fact, a good single pattern cams work much better than a poorly designed dual pattern cam. There isn't anything magic about a dual pattern cam, the engine wants what the engine wants.
I had a 466 inch big block in my street car for a long time and I used that engine as a test bed for a lot of parts including cams. I was doing magazine articles in those days so I was hooked up with the cam mfgs and none of the cams they sent me other worked better than the old single pattern flat tappet that I had. Comp sent me three cams for that engine. The first one was too big. It made a tiny bit more top end power but gave up a bunch of torque. They followed up with a slightly smaller cam that worked better but still wasn't as good as my old single pattern. The third cam they sent me was pretty good but I still went back to the old single pattern. The Comp engineer was sure that their new fast rate lobes and dedicated exhaust lobes were better than my 40 year old design but it didn't turn out that way.
On a street engine it is easy to out-trick yourself and to use a bunch of race stuff that doesn't actually work on a street engine. The super fast rate cams wear out on the street and they don't necessarily work very well with a full exhaust system. So if you get a dual pattern cam with the latest lobe designs it might not work as well as an old factory type design with slower lobes. Bottom line is that I wouldn't turn up my nose at a single pattern cam for a street car. I run them all the time and they work just fine. A dual pattern cam might be better, but then again it might be worse. In my case the stuff that the cam engineers thought would be better wasn't. If the engineers at the cam company require 3 tries to get close to an old school cam then the odds of some guy picking the perfect cam out of a catalog are pretty low.
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As a follow on I'll add that I currently have 3 race engines and they all use dual pattern cams. From what I've seen over the years, a little extra duration on the exhaust side will help extend the power curve on a race engine with open headers. But as soon as you put mufflers on the engine the dynamics all change.
A street engine will usually make more power on the dyno with extra exhaust duration but it might not work better in the car with a full exhaust system. The extra duration on the exhaust side can hurt more than it helps with a full exhaust system since the back pressure can force the exhaust gases back into the engine. So the final words from me on the subject are "it all depends" and "you won't know until you try it".
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A street engine will usually make more power on the dyno with extra exhaust duration but it might not work better in the car with a full exhaust system. The extra duration on the exhaust side can hurt more than it helps with a full exhaust system since the back pressure can force the exhaust gases back into the engine. So the final words from me on the subject are "it all depends" and "you won't know until you try it".
That's interesting and I think I agree with it. The "prevailing wisdom" over the last few decades has been that if you had a restrictive exhaust system, then you needed more exhaust cam duration to make up for it. I think you're saying that adding more exhaust cam duration won't help if you physically can't flow it through the exhaust. Okay, it may help a tiny bit as you are giving it a few more milliseconds of time, but the payback of the increased overlap at lower rpms is much more severe. Something like that anyway
I asked Mike Jones a question like that a long time ago and the answer was similar, as I remember. I was asking about camming engines with restrictive exhaust manifolds vs. engines with headers and free flowing exhaust sytems. His answer was something to the effect that if you try to crutch a restrictive exhaust system with a lot of exhaust duration you essentially lose everywhere. The engine still won't make good top end power and you will lose the power in the rpm range that the engine could have made good power at. Basically he said concentrate on lower rpm power in such a situation, and likely use a single pattern (and smaller) cam.
Sometimes when you try to have your cake and eat it too, you end up with neither.
On the other other hand, why did the 428CJ cam work so well? It seems to follow the opposite theory. Or maybe the 428CJ would have been even better with a single pattern cam?
just jawin'
paulie
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A street engine will usually make more power on the dyno with extra exhaust duration but it might not work better in the car with a full exhaust system. The extra duration on the exhaust side can hurt more than it helps with a full exhaust system since the back pressure can force the exhaust gases back into the engine. So the final words from me on the subject are "it all depends" and "you won't know until you try it".
That's interesting and I think I agree with it. The "prevailing wisdom" over the last few decades has been that if you had a restrictive exhaust system, then you needed more exhaust cam duration to make up for it. I think you're saying that adding more exhaust cam duration won't help if you physically can't flow it through the exhaust. Okay, it may help a tiny bit, but the payback of the increased overlap at lower rpms is much more severe. Something like that anyway
I asked Mike Jones a question like that a long time ago and the answer was similar, as I remember. I was asking about camming engines with restrictive exhaust manifolds vs. engines with headers and free flowing exhaust sytems. His answer was something to the effect that if you try to crutch a restrictive exhaust system with a lot of exhaust duration you essentially lose everywhere. The engine still won't make good top end power and you will lose the power in the rpm range that the engine could have made good power at. Basically he said concentrate on lower rpm power in such a situation, and likely use a single pattern (and smaller) cam.
Sometimes when you try to have your cake and eat it too, you end up with neither.
On the other other hand, why did the 428CJ cam work so well? It seems to follow the opposite theory. Or maybe the 428CJ would have been even better with a single pattern cam?
just jawin'
paulie
I don't think the 428 CJ cam did all that well. I think a 428CJ with a better cam would likely do better everywhere, but I can't prove it :) It's basically a truck/Cadillac cam by today's standards, low lift, slow ramps, wide LSA, retarded for the added compression. It also was the off the shelf GT cam, not like it was engineered for the CJ. The CJ was "better exhaust manifolds, better exhaust, better heads, bigger valves, better intake (by a margin) and a bigger carb"...oh and 38 more cubes ;) All of those made it run pretty hard (sorta) compared to the 390 GT, not the cam IMO
That being said, remember, exhaust moves out (and the intake moves in) due to a couple of things, negative pulse in the primaries, a piston being jammed upwards, overlap, and some momentum, I am sure there are others. A little more exhaust duration will add overlap, which lets the exhaust do it's business a little better and it allows the piston to push for a little longer. Way simplified, and even to this day I am trying to wrap my head around exhaust valve timing in relation to blowdown and scavenging, but it is there. My hunch is, a restrictive set of manifolds likely will not benefit as much as a set of headers with a quite/small diameter intermediate pipe. So the "restrictive exhaust" IMHO doesn't mean bad manifolds, its more "bad mufflers and pipes behind the headers.
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I don't think the 428 CJ cam did all that well. I think a 428CJ with a better cam would likely do better everywhere, but I can't prove it :) It's basically a truck/Cadillac cam by today's standards, low lift, slow ramps, wide LSA, retarded for the added compression. It also was the off the shelf GT cam, not like it was engineered for the CJ. The CJ was "better exhaust manifolds, better exhaust, better heads, bigger valves, better intake (by a margin) and a bigger carb"...oh and 38 more cubes ;) All of those made it run pretty hard (sorta) compared to the 390 GT, not the cam IMO
That being said, remember, exhaust moves out (and the intake moves in) due to a couple of things, negative pulse in the primaries, a piston being jammed upwards, overlap, and some momentum, I am sure there are others. A little more exhaust duration will add overlap, which lets the exhaust do it's business a little better and it allows the piston to push for a little longer. Way simplified, and even to this day I am trying to wrap my head around exhaust valve timing in relation to blowdown and scavenging, but it is there. My hunch is, a restrictive set of manifolds likely will not benefit as much as a set of headers with a quite/small diameter intermediate pipe. So the "restrictive exhaust" IMHO doesn't mean bad manifolds, its more "bad mufflers and pipes behind the headers.
I mentioned the 428CJ cam mostly in a rhetorical way as it has been portrayed as helping the 428CJ run so well despite the "good (okay) exhaust manifolds" and horrible exhaust system after that.
The CJ cam has a huge split of around 206/220 degrees @ 0.050" Something like that anyway. The reason I brought it up was to point out that maybe the CJ would have run much better with the stock exhaust system with a very different cam. I dunno. Or maybe the CJ really came alive when fitted with headers and a modified (or no) exhaust system?
If true, has it really taken us almost half a century to figure this out? Holy cow.
just jawin'
paulie
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I have a cam here going in a 396 FE, 280/230 intake, 284/236 exhaust, on 112, I plan to put it in the engine at 106, we'll see what it does LOL
It's a neat cam, hydraulic, would have liked to see it tighter LSA, but it's out of another Forum members engine, and is what it is
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The guys who have this really figured out are the ones who run in FAST class. They have to run with stock appearing engines and full stock appearing exhaust. I know some of the tricks that they use but I don't know them all since I haven't done any of that stuff for years. But there is a fairly firm limit on how much duration you can run on the exhaust side when you have manifolds and a full exhaust system. Too much duration and you lose power everywhere. They compensate by running a lot of lift and a ton of compression but they don't run a huge amount of duration. I wouldn't recommend a FAST cam for street use, just bringing it up as an example that you don't want to get too excited with exhaust duration if you are using a full exhaust system.
If you want to see some crazy split cams take a look at what the Chevy engineers are using in the LS engines. The COPO 427 engines have 40 degrees more duration on the exhaust than the intake. Something like 230/270 for duration. I'm not sure how they came up with that. People always say "think outside the box" but I don't think I would've ever thought that far outside the box! Here is a link to a COPO data sheet: http://www.jegs.com/p/Chevrolet-Performance/Chevrolet-Performance-427ci-425hp-COPO-Crate-Engine-2012-2015/2804804/10002/-1
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Yes, high compression is your friend with factory exhaust manifolds and exhaust. Push it out hard and quick.
It also makes sense, I think, to have a high lift, aggressive exhaust lobe in the factory exhaust manifold situation we're talking about. Get done what you can while you can.
In most hot rod engines the intake lobe tends to be more aggressive (faster) than the exhaust. This makes sense based on the pressure differentials in the intake and exhaust tract. At least I think so. There is more "pull" on the intake port when the valve is further open, so you want to open it fast to get it in the sweet spot longer. The exhaust port has the highest pressure differential when the exhaust valve is just opening, so normally low lift flow is more important. So exhaust lobes tend to be less aggressive. In fact it is often the case that intake lobes become exhaust lobes as cam and valvetrain technology advances. One generation's intake lobe becomes the next generation's exhaust lobe, as a new more aggressive intake lobe is designed.
BUT, in a very exhaust restricted combination, all this might not be true. I bet those F.A.S.T cars have exhaust lobes at least as aggressive as the intake lobes. And super high compression. I don't know the rules. It is interesting, though.
JMO,
paulie
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The guys who have this really figured out are the ones who run in FAST class. They have to run with stock appearing engines and full stock appearing exhaust. I know some of the tricks that they use but I don't know them all since I haven't done any of that stuff for years. But there is a fairly firm limit on how much duration you can run on the exhaust side when you have manifolds and a full exhaust system. Too much duration and you lose power everywhere. They compensate by running a lot of lift and a ton of compression but they don't run a huge amount of duration. I wouldn't recommend a FAST cam for street use, just bringing it up as an example that you don't want to get too excited with exhaust duration if you are using a full exhaust system.
If you want to see some crazy split cams take a look at what the Chevy engineers are using in the LS engines. The COPO 427 engines have 40 degrees more duration on the exhaust than the intake. Something like 230/270 for duration. I'm not sure how they came up with that. People always say "think outside the box" but I don't think I would've ever thought that far outside the box! Here is a link to a COPO data sheet: http://www.jegs.com/p/Chevrolet-Performance/Chevrolet-Performance-427ci-425hp-COPO-Crate-Engine-2012-2015/2804804/10002/-1
When you have an intake tract as efficient as that, coupled to a full exhaust system and "OK" ex port, that's what it takes to make power. Lift is almost irrelevant on the ex side pother than to maintain a certain valve path. 90% of the work is done the second the ex valve cracks off the seat, not unlike your favorite beverage when you pop the top. The remainder is just "time" (duration) to get the rest of the exhaust out. Intake to ex duration is directly related to the ratio of the flow numbers. The closer you can get to real running conditions, ie: flow the heads with intake, carb, headers and exhaust system bolted on, the better the resutls will be with the cam. A bare head sitting on the flow bench can be WORLDS different than one with everything bolted on it. Not just in mean flow numbers, but also the ratio/percentage of intake to ex. but in the end, of the flow ratio heavily favors the intake side, you'll see a healthy split with duration favoring the exhaust. These duration numbers aren't a "guess", either. They're derived from math.
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As a follow on I'll add that I currently have 3 race engines and they all use dual pattern cams. From what I've seen over the years, a little extra duration on the exhaust side will help extend the power curve on a race engine with open headers. But as soon as you put mufflers on the engine the dynamics all change.
A street engine will usually make more power on the dyno with extra exhaust duration but it might not work better in the car with a full exhaust system. The extra duration on the exhaust side can hurt more than it helps with a full exhaust system since the back pressure can force the exhaust gases back into the engine. So the final words from me on the subject are "it all depends" and "you won't know until you try it".
I'd like to ask for more information about exhaust systems and cam choices. If you have a small engine bay, say like a 60's Mustang with a big block and have unequal length headers, that you need to be creative on making heads and not loose power, versus a car like mine, a 427 Shelby Cobra replica, where the header tube angle couldn't be straighter, and the flow into the side pipes with no real muffler. I would only assume, that this is one of the easiest systems to expell exhaust flow from the heads.
So, with the Mustang vs 427 Cobra's exhausts, does that mean the cam & exhaust port's would be way,....different for best performance ?
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As a follow on I'll add that I currently have 3 race engines and they all use dual pattern cams. From what I've seen over the years, a little extra duration on the exhaust side will help extend the power curve on a race engine with open headers. But as soon as you put mufflers on the engine the dynamics all change.
A street engine will usually make more power on the dyno with extra exhaust duration but it might not work better in the car with a full exhaust system. The extra duration on the exhaust side can hurt more than it helps with a full exhaust system since the back pressure can force the exhaust gases back into the engine. So the final words from me on the subject are "it all depends" and "you won't know until you try it".
I'd like to ask for more information about exhaust systems and cam choices. If you have a small engine bay, say like a 60's Mustang with a big block and have unequal length headers, that you need to be creative on making heads and not loose power, versus a car like mine, a 427 Shelby Cobra replica, where the header tube angle couldn't be straighter, and the flow into the side pipes with no real muffler. I would only assume, that this is one of the easiest systems to expell exhaust flow from the heads.
So, with the Mustang vs 427 Cobra's exhausts, does that mean the cam & exhaust port's would be way,....different for best performance ?
Most guys will never flow their heads let alone their exhaust systems. Induction flow factors are a very large part of good cam design. I know when Chris designs a high end cam, he tells the customer to get flow numbers with intake, carb and headers attached if they want the absolute best results. It really doesn't matter what configuration you're working with as long as it becomes a "known". If you don't have the ability to flow the exhaust system on the heads, then we have to make assumptions and "best guesses" based on experience...which Chris has a lot of. So to answer your question, the cam would most likely be different if you had the ability to flow everything in place. If the engines were the same and going to operate in the same rpm range and target the same power, then the cams could possibly be "tweaked" if one ex system was radically different from the other but at that point you're also picking pepper out of fly poop. Not sure if it's in your question or not, but I will tell you that any exhaust system is going to kill power, no matter how good the cam is. We ran the best dyno tested exhaust on our big block Cobras (which was the Loback) and it cost 60hp. The ex ports would (should) not be any different. There are tuned headers available for the 60's big block cars and the difference between those headers and your Cobra headers, which are most likely not tuned, are probably insignificant.
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I'll just add that on every car I knew of or actually worked on, dumping the cast iron manifolds and having dual exhausts and fairly efficient mufflers (some hardly muffled!) made a big difference, seat-of-the-pants wise. This included Boss 302's, Windsors, SBC's and BBC's (sorry!) some Chrysler 340's, 383's and even a 392 early Hemi.
My point is with a muffled street engine, once the exhaust side is well thought out, the difference between a single versus dual pattern cam, given they are off-the-shelf cams, is IMO minimal. Now, open headers and a race optimized engine IS a whole different story.
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I'll just add that on every car I knew of or actually worked on, dumping the cast iron manifolds and having dual exhausts and fairly efficient mufflers (some hardly muffled!) made a big difference, seat-of-the-pants wise. This included Boss 302's, Windsors, SBC's and BBC's (sorry!) some Chrysler 340's, 383's and even a 392 early Hemi.
My point is with a muffled street engine, once the exhaust side is well thought out, the difference between a single versus dual pattern cam, given they are off-the-shelf cams, is IMO minimal. Now, open headers and a race optimized engine IS a whole different story.
I will 100% disagree with that.
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While we are on camshafts, frankly I have never understood this (taken from another site & much proliferated);
"There is a very easy way to tell if the camshaft has been advanced by the cam company when the cam was machined. Look at the cam timing card and compare the lobe separation angle (LSA) with the intake centerline number. If the numbers are the same, then the camshaft has not been advanced.
When we look at the cam card, the intake centerline is listed at 107 degrees while the LSA is listed at 112 degrees. The numbers tell us the intake centerline has been advanced five degrees from 112 to 107 degrees after top dead center (ATDC)."
Never got this. Maybe I'm just stupid or missing the obvious.
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We were covering this very thing on another thread here.
When the LSA = ICL, it's called "straight up". When the ICL is smaller than the LSA it's considered "advanced" and when the ICL is greater than the LSA it's considered "retarded".
So, a 110 LSA with a 110 ICL is considered straight up.
A 110 LSA with a 104 ICL is considered 6 degrees advanced.
A 110 LSA with a 112 ICL is considered 2 degrees retarded.
The cam company can grind the cam with any amount of advance or retard built into it. Most of Comp Cams' off-the-shelf cams are usually 110 LSA on a 106 ICL, so they are all ground 4 degrees advanced.
The key is, that you can move that relationship with a multiple keyway timing set, and advance/retard it to wherever *you* choose. So, just because the cam company put a certain amount of advance/retard into it, it doesn't mean that you have to run it like that.
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While we are on camshafts, frankly I have never understood this (taken from another site & much proliferated);
"There is a very easy way to tell if the camshaft has been advanced by the cam company when the cam was machined. Look at the cam timing card and compare the lobe separation angle (LSA) with the intake centerline number. If the numbers are the same, then the camshaft has not been advanced.
When we look at the cam card, the intake centerline is listed at 107 degrees while the LSA is listed at 112 degrees. The numbers tell us the intake centerline has been advanced five degrees from 112 to 107 degrees after top dead center (ATDC)."
Never got this. Maybe I'm just stupid or missing the obvious.
Not stupid, it is hard to visualize
(http://tildentechnologies.com/Cams/images/twolobes.gif)
If you look at the picture we used in a different thread, when a cam is neither advanced or retarded, when compared to TDC (which centerlines are measured against) the cam is installed with each centerline equidistant from crank position at TDC.
If you advance it or retard it, compared to TDC, the LSA stays the same (ground into the cam) but the distance from TDC changes for both lobes, the cam can be viewed as "leaning" one way or another using the picture.
I wish there were drawings that showed them in a different order. Cam events will happen in this order, maybe this makes more sense (or confuses more LOL)
1 - Exhaust reaches max lift at exhaust centerline
2 - Piston reaches TDC
3 - Intake reaches max lift at intake centerline
- The distance in degrees between 1 and 3 = LSA
- If a cam is installed without advance or retard, those centerlines are equal distance from #2. ECL=ICL=LSA
- If an intake lobe has a centerline less than LSA, the whole cam was rocked toward TDC (advanced) and that also moves the ECL, opposite is true too
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66Fairlane,
Andy ,
Using the drawing above you can see the lobes are separated. That is of course the LSA and the lobes are ground to a specific "fixed" spacing. The only way that can be changed ( very slightly and not always) is to "regrind" the lobes. What can and does change is the "positioning" of the cam to the crank. I hesitate to use the common "timing" term as guys somehow think that is related to ignition timing which is totally independent. Cam timing numbers ( on the cam card) are calculated in a very simple way. I will use an easy example.
Cam duration at .050 is 260 ( on both) and lobe separation is ground to 110.
Intake opening is determined by taking half of the duration ( 130) and subtracting the LSA ( 110) so the intake opening on the card would be 20 BTDC.
Intake closing is determined by adding the intake opening number ( 20) to 180 ( to get to the opposite side of the lobe) and subtracting that from the total duration at .050 leaves the intake closing number of 60. 20+180+60 = 260 , the total duration. The "events" can change but the numbers always add up.
"I" calculate the exhaust numbers in the opposite way by getting the exhaust closing ( smaller number) first and then the exhaust opening number ( larger).
Cam advance can be tricky. In the above example advancing it 4*s would change the intake numbers to I.O. 24 and I.C. to 56. The exhaust is calculated as if it were retarded ( using my method) and those new numbers would be E.O. 64 and E.C. 16 . This is because of the "ICL" change from 110 to 106 and the "ECL" change to 114 ( 106+114=220 Divided by 2=s 110 the ground in lsa.
I hope that simplifies it a bit and removes some of the "mystery" out of camshafts.
Randy
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Hi Ross & Randy
Just been able to get back to this. Thanks for the explanation. Got it now.
Where I was going wrong was my understanding of the term 'straight up'. I did not realise it meant ICL & ECL being equi-distance from TDC. I always just thought it meant installed as per cam card recommendation. Thus I could not work out how you could grind advance in. Makes sense now.
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Hi Ross & Randy
Just been able to get back to this. Thanks for the explanation. Got it now.
Where I was going wrong was my understanding of the term 'straight up'. I did not realise it meant ICL & ECL being equi-distance from TDC. I always just thought it meant installed as per cam card recommendation. Thus I could not work out how you could grind advance in. Makes sense now.
You and about 99% of the rest of the engine building community.
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Hi Ross & Randy
Just been able to get back to this. Thanks for the explanation. Got it now.
Where I was going wrong was my understanding of the term 'straight up'. I did not realise it meant ICL & ECL being equi-distance from TDC. I always just thought it meant installed as per cam card recommendation. Thus I could not work out how you could grind advance in. Makes sense now.
You and about 99% of the rest of the engine building community.
Hahahaha whatever dude.
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I've wondered for awhile about the old factory cams, some of which Holman Moody still sells. All are dual pattern and must have been derived by extensive engine dyno or track testing by Ford or Holman Moody.
Specs in link:
http://www.holmanmoody.com/cams.html
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Hi Ross & Randy
Just been able to get back to this. Thanks for the explanation. Got it now.
Where I was going wrong was my understanding of the term 'straight up'. I did not realise it meant ICL & ECL being equi-distance from TDC. I always just thought it meant installed as per cam card recommendation. Thus I could not work out how you could grind advance in. Makes sense now.
You and about 99% of the rest of the engine building community.
FWIW, these guys get it......don't know who they are, but they get it.
http://www.camcraftcams.com/degreeing-a-cam/
"A cam ground with a 108 lobe separation and advanced 4 degrees will have a intake centerline of 104 and exhaust centerline of 112. Advancing it another 2 degrees will result in a 102 intake centerline and a 114 exhaust centerline. Adding the intake and exhaust centerlines together and dividing by 2 will give you the lobe separation. The same cam installed straight up (with no advance) will have a 108 intake centerline and a 108 exhaust centerline.
Note that straight up refers to lack of advance. It does not mean, “ We lined the timing marks up and installed the gears”. When I ask where the cam is installed and get “straight up” for an answer then I know the cam was probably not degreed in properly."
I checked Lunati's website...................they get it too.................
And from Jay Allen (Camshaft Innovations)......
"Straight up is when the cams intake centerline and exhaust centerline are the same. Hence, the intake centerline is also the same as the camshafts LSA as well. This can occur at any position on the crank gear. The camshaft does not rotate on its own. The position of the crank gear becomes irrelevant. "
Jay gets it.
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Decide right from the get go if gas mileage is important? Of so stay close to stock.
Of not, have fun, but don't get the biggest one possible.