Guess the tunnel port horsepower!

[My427stang]

I don't know how overscavenging would show up on the dyno data, but I think that one issue with your suggested approach is that more lift may not generate much more flow.  I don't have the flow numbers, but I'll bet that at .660" lift the flow on that exhaust port is flatlining, and adding lift won't generate much more.  The only potential benefit would be if the ramps were steeper and you got to the lift where flow maxes out more quickly, but then there is the issue of street reliability with the spring rates required for a faster ramp. 

Your question really begs for a back to back dyno test with different cams, to test the theory behind a long exhaust duration and overscavenging port.  So many FE questions, so little time...

I agree, unfortunately not a cheap or quick test.  My thought is that the exhaust valves would pass max flow twice if you run a lot of lift, and an exhaust port doesn't suffer fuel separation, so let it run up where it's ugly LOL.

Add that the exhaust is a much lighter valve than the intake side, you may be able to run a significantly more radical exhaust lobe, which would allow a little more intake lobe for a given overlap.

Man, I could retire from the USAF in <3 years and start doing some of this...

I can't wait until I don't have to move every 3-4 years again.  Any acreage for sale near you? 

[hotrodfeguy]

Off by 7 on the single 4 woot !!!

[Chad D]

How would over-scavenging show up on a dyno?

Overscavenging should show up lean on an O2 sensor, the fuel that makes it into the exhaust is unburned...

[jayb]

How would over-scavenging show up on a dyno?

Overscavenging should show up lean on an O2 sensor, the fuel that makes it into the exhaust is unburned...

Hmmmm, that's interesting.  If that were true then if you jetted up to correct the "lean" condition, you'd be dumping even more unburned fuel in the exhaust, and instead of going richer with more jet, the O2 sensor would show leaner.  I've never seen that, but then I don't know that I've ever had an engine that was overscavenged on the dyno.  That would be a weird situation, adding jet and seeing increasing A/F numbers...

[Chad D]

How would over-scavenging show up on a dyno?

Overscavenging should show up lean on an O2 sensor, the fuel that makes it into the exhaust is unburned...

Hmmmm, that's interesting.  If that were true then if you jetted up to correct the "lean" condition, you'd be dumping even more unburned fuel in the exhaust, and instead of going richer with more jet, the O2 sensor would show leaner.  I've never seen that, but then I don't know that I've ever had an engine that was overscavenged on the dyno.  That would be a weird situation, adding jet and seeing increasing A/F numbers...

VE% should show up considerably higher as well.  Saw it happen on a sprint car engine.  Very counterintuitive.

[CaptCobrajet]

How would over-scavenging show up on a dyno?

Flattening out on top and showing rich maybe?

Certainly no criticism on the motor, Blair does great stuff, but I have been considering how more lift/less duration on the exhaust side would work out.

My thought is, for these big ones, keep a constant overlap value (in my case for drivability) but instead of big exhaust duration, add intake duration for power but make a shorter, taller exhaust lobe that flows enough but shuts the door early.

Although I haven't figured out a way to calculate what the motor might want, it seems to me that especially with a very good header design, adding exhaust duration could  eventually overscavenge.   

The second phase to that is, if it is overscavenging and a quick and tall exhaust lobe will fix it, may as well get a little more intake lobe to make some additional top end power.

I noticed Kaase was doing it on his EMC Hemi motors, which are known to overscavenge with too much exhaust duration, but how would we see it on a dyno to know if a wedge was emptying the chambers?

We were dealing with a 60% flow ratio exhaust to intake.  In my world, the lobes I used are "endurance" lobes.  This thing should make alot of laps and some street miles with no trouble.  I would have approached it differently if we had brazed the floors in the exhaust, and/or had a real aggressive camshaft.  I was using the split duration, tight centers, and the header/collector to crutch the 60% exhaust problem.  My gut tells me that it would be hard to overscavenge this combo.  If it had 75-80% exhaust ports, you would have seen a much different camshaft.  I also had pump gas on my mind.  The cam being pretty mild on the intake side, I tightened the centers to take some of the bite away from the DCR, which was fairly high for static of 11.3.  I know the DCR calculators don't address the separation, but more overlap will reduce the tendency to detonate at lower rpm.  Many factors led me to make the cam like this, and it did okay.  R&D with no budget constraints could no doubt produce better results, but I had no 500" road race TP data to draw from, so this was square one.......

[My427stang]

We were dealing with a 60% flow ratio exhaust to intake.  In my world, the lobes I used are "endurance" lobes.  This thing should make alot of laps and some street miles with no trouble.  I would have approached it differently if we had brazed the floors in the exhaust, and/or had a real aggressive camshaft.  I was using the split duration, tight centers, and the header/collector to crutch the 60% exhaust problem.  My gut tells me that it would be hard to overscavenge this combo.  If it had 75-80% exhaust ports, you would have seen a much different camshaft.  I also had pump gas on my mind.  The cam being pretty mild on the intake side, I tightened the centers to take some of the bite away from the DCR, which was fairly high for static of 11.3.  I know the DCR calculators don't address the separation, but more overlap will reduce the tendency to detonate at lower rpm.  Many factors led me to make the cam like this, and it did okay.  R&D with no budget constraints could no doubt produce better results, but I had no 500" road race TP data to draw from, so this was square one.......

Got it, and certainly don't think I am critiquing. If it looks that way I apologize. It's an awesome build that did everything right. 

I just brought it up because there is a lot of information out there on intake lobe selection, but exhaust tends to be more of a black art, although your discussion of using the headers to work the port shows you surely get it.

What I have been trying to wrap my head around is a way to increase intake duration while keeping the torque curve as flat as possible.

My theory is a very early and large intake lobe for these strokers, but to keep from excessive overlap, I want to find a fast way to empty the chamber with a faster exhaust lobe.

Ford actually did it in some of their motors, like the J code 302.  The issue I m running into is without dyno testing, its all a WAG, add to it there is very little exhaust lobe discussion, I am no engineer, but it seems like without a requirement to keep anything in suspension, overspeeding an exhaust port is less critical, so we may as well get into the lift area for max flow as soon as we can

What I can't figure out is how to time that lobe, because ultimately, the opening of that lobe will determine how big I can experiment with an intake lobe.

I know it sounds backwards, and I truly understand standard cam design, but I really want to estimate then prove or disprove an experiment.

For example.  (These numbers came out of my a$$ before I finished my first coffee BTW)

Cam 1 - standard kind of cam Intake 290/250/.650 lift, exhaust 294/254/.660 lift, 110 centers on 106 ICL

Intake closing point is at 71 ABDC, overlap is 72 degrees adv, at .050 overlap is 32 degrees

Cam 2 - Intake 300/258/.650 lift, exhaust 292/254/.690 lift, 112 centers on 101 ICL

Intake closing point and overlap is the same, but looking for lift to evacuate the cylinder not duration.

While I was coming up with an example, I think what I am finding is to do what I want, I  need to spread the centers and run a very early lobe to keep comparable numbers.  In addition, to make a significant increase in lift, I may not have a streetable lobe on the exhaust side (as you pointed out)

Moreover, I am not sure that my end result between those two cams I put up as examples would make that much difference anyway LOL

Opinions?

[CaptCobrajet]

What you are talking about is what I call "exhaust blowdown".   Putting a steep ramp on the opening side of the exhaust, running a fast rocker, and then a slow closing side to kill some valve speed on the closing side generated by the fast rocker arm.  I never had any luck with running the intake way ahead in anything FE.  The further apart the lobes are, the later I like to open the intake valve.  Wide centers on a street stroker would need low compression to avoid detonation, in my opinion.  Also, heavy street cars will pull better with tighter centers.  I do try to get all of the blowdown I can when the exhaust valve opens, and then let the header pull it through a slow closing side.  Some of this kind of theory is unfortuneately only proven through extensive testing...........which requires huge amounts of time and money, or seeing trends over time.  I have to go with the trends over time, because for some reason I never seem to have huge amounts of time.....or money, LOL.

[jayb]

I try not to overthink this stuff too much, because there are way too many variables coming into play that can affect the results.  But Ross's second cam selection, where he went with a wider lobe separation and advanced the ICL, is exactly what I've been doing on my SOHC motors for the last few years.  I've been running 114 or 116 for the LSA, and advancing the intake lobe as far as possible until piston to valve clearance becomes an issue.  On my engines this is usually around 106 or 108.

I've been thinking about another series of dyno tests, the Great Cam and Head Comparo LOL!  There's a lot of projects in the way first, but it would be interesting to chase down theories like this with some real back to back dyno testing.

[CaptCobrajet]

The wider separation will work better than the tight centers when the exhaust flow is really good.  In the case of your cammer, I think you are right to use wider centers.  The 108 is about as far as I would move it forward with a 114 sep.  That said, some engines might like to go further advanced.......I just never start any further than that.  I would assume that one of the cams is going to retard quite a bit in a cammer from chain stretch, so maybe that one should go forward a little more and the other one back a little?  Maybe when I grow up I will get a cammer!  I always wanted one, but have never taken the plunge.  I think all consenting adults should own at least one cammer!

[fetorino]

All the focus on exhaust duration and cam profiles nobody noticed the top secret road race oiling system.  It worked really slick on the dyno.

[machoneman]

Cool! Was surprised to see at first a billet pan but that would be really hard to duplicate in sheetmetal. Your design, Jay's, someone else? How about another pic showing the pickup port side? 

[fetorino]

Cool! Was surprised to see at first a billet pan but that would be really hard to duplicate in sheetmetal. Your design, Jay's, someone else? How about another pic showing the pickup port side?

I wish I came up with that design.  It is Bill Daileys brainchild.  He makes some great stuff for some very competitive teams in several series.

http://www.daileyengineering.com/dailey_engineering_home.htm

When we fired up my motor on the Dyno Sat morning some questions about the oiling system remained.  I called Bill's shop and he answered the phone and all my questions.  As we were hanging up he said "I'll be here a couple more hours so don't hesitate to call if you need something"

When choosing parts nothing beats a vendor/manufacturer who will support what they sell.  Bill is proud of his stuff and has a bit of an ego about his stuff being the best.  But when the rubber meets the road he is exactly the kind of guy you want to deal with and will take the time to ensure you understand his design, how it works and how to set it up.  His system worked flawlessly in addition to being super compact hanging down only 1.8" from the pan rail on the block.

[fetorino]

I decided witht he cost of race gas the raged edge dynamic/static compression for pump gas and what I'd read about E85 that I'd give it a try.  So Blair took my engine back to the dyno. The set up remains the same but with a single Holley 4150 on top calibrated for E85.

Anyone have a guess how it did?

Here are the specifications:

- 496", 4.375" stroke, 4.255 bore
-  11.3:1 static compression, CP pistons
-  Stock tunnel ports ported by Blair, 375 cfm on the intake, 225 on the exhaust, 2.25/1.75 valves
-  Bullet roller cam, .660 lift, 258/270 @ .050", 107 LSA, ICL=105
- Dyno headers, stepped, 1 7/8"/2"/2 1/8", merge collectors
- Intake manifold  is a 1X4 single plane modified for a Dominator carb.  Running a tricked out 4150 carb for E85
- Dailey 4 stage Dry sump oiling system

This engine is designed for a road racing application in my '69 Torino.  Peak horsepower and Torque guesses please this time we didn't run the 2x4 since I didn't want to pony up for a pair of E85 carbs. lol

[machoneman]

SWAG: 675 hp, 590 lbs/ft.