Someone Teach Me About Cams... Single Pattern vs Dual Pattern

[CaptCobrajet]

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.

[blykins]

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. 

[mbrunson427]

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.

[CaptCobrajet]

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.

[blykins]

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. 

[gt350hr]

     I found that high altitude engines respond well to increased intake duration because of the lesser air density.

[scott foxwell]

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.

[scott foxwell]

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.

[gt350hr]

 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

[fekbmax]

.

[My427stang]

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. 

[scott foxwell]

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.

[My427stang]

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. 

[scott foxwell]

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...

[andyf]

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.