[70GS455]

From D. Elgin, contradicts UDH's comments:

Let us now take the four valve timing events and put them in order of importance. The LEAST important is the exhaust valve opening. It could open anywhere from 50 degrees to 90 degrees BBDC. If it opens late, close to the bottom, you will take advantage of the expansion, or power, stroke and it will be easier to pass a smog test, but you will pay for it with pumping losses by not having enough time to let the cylinder blow-down. You must let the residual gas start out of the exhaust valve early enough so that the piston will not have to work so hard to push it out. Opening the exhaust valve earlier will give the engine a longer blow-down period which will reduce pumping losses. But, if you are only interested in low speed operation, say up to 4000 RPM, you can open the exhaust valve later.

[Chris_69_SS]

Well, I better take out my UD 288/296..... Car ran too fast for my liking anyways!

[UDHarold]

Well, I've sold more cams than Dmitri has, and my cams have won more races than Dmitri's have......
Of course, we compete in different fields. Dmitri makes mostly sport car cams, for straight 4's, etc. Of course, the few times I have made cams for straight 4s, they won the 24 Hours of Daytona--Dmitri's haven't, they won Comp Elim at Indy with Doug Kjone--Dmitri's haven't, my cams have won the Daytona Dash series---Dmitri's cams haven't, etc. This is just a little of my 4-cyl stuff.
I don't want to get into a "who said what" fight. I have posted on this board a number of times that I view exhaust opening and intake opening to be of equal importance, with the exhaust opening obviously happening first, then in 3rd place is intake closing, which Dmitri has in 1st place, and then I think exhaust closing has the least effect of all.
Perhaps sometimes at PRI or somewhere similar he and I can debate this.

UDHarold

[Stikman33]

Harold, i love how you reply to these things. These are the facts, and thats it, lol. Awesome.

[Chris_69_SS]

Originally Posted by UDHarold

Well, I've sold more cams than Dmitri has, and my cams have won more races than Dmitri's have......
Of course, we compete in different fields. Dmitri makes mostly sport car cams, for straight 4's, etc. Of course, the few times I have made cams for straight 4s, they won the 24 Hours of Daytona--Dmitri's haven't, they won Comp Elim at Indy with Doug Kjone--Dmitri's haven't, my cams have won the Daytona Dash series---Dmitri's cams haven't, etc. This is just a little of my 4-cyl stuff.
I don't want to get into a "who said what" fight. I have posted on this board a number of times that I view exhaust opening and intake opening to be of equal importance, with the exhaust opening obviously happening first, then in 3rd place is intake closing, which Dmitri has in 1st place, and then I think exhaust closing has the least effect of all.
Perhaps sometimes at PRI or somewhere similar he and I can debate this.

UDHarold

Ah man, just when I get the cam out! Now I gotta slide it back in!!! DOH!

[cam-copier]

Didnt Demas cam win Daytona in the 4 car with Ernie Irvan driving?

[engineguy]

Harold,

I think it would be an excellent idea for you and Dmitri to have a debate (or discussion) about cam design philosophy at the PRI show or some other similar venue!

[UDHarold]

Isn't it funny that there is not a lot of debate about the various philosophies of cam design? Most cam companies are very quiet, except in the vaguest(sp?) of ways.
Cam companies that have automatic spec card printing and who also claim to have unsymmetrical cams print their data as symmetrical cams. Debates would be fun, but I don't think many companies would want to debate. They would all claim that to debate would be to reveal too many secrets---LOL!!

Here is a little thought for the most important vs. the least important valve opening/closing events.
If you can get to a dyno, get yourself 2 cams, with the same intake and exhaust profiles, but a 2° difference in LSA, say 110 vs 112, or 106 vs 108. The only difference is really the valve opening and closing timings.
Dyno both cams with the intake installed to the IDENTICAL intake CenterLine. The intake opening point and the intake closing point is identical in both dyno tests.
Why does the dyno show 2 different power curves? Both cams had the IDENTICAL opening and closing points on the intake. They only differed on the exhaust opening and closing points, and yet they produced different power curves.
Notice, I didn't say one was better than the other, only different. Each of them is best for some application, and that's why you talk to your cam grinder.
I know why they produce different power curves, and what effects the opening and closing points have on the power curve.
I still put the intake closing point as the 3rd most important in the cycle, beating out only the exhaust closing point.

UDHarold

[cam-copier]

I agree with a lot of what your saying.
Dema had an advantage by grinding a lot of twin cam engines and then
seeing the results on the dyno. He has had a dyno in his building for 25 years or more. The interesting part about a twin cam engine is the lobe seperation angle
or centerlines are not set in stone, meaning they can be changed from 108 to 110 or whatever you want. Domestic v8 style cams are stuck on the seperation angle ground into the cam.
I agree the exhaust valve closing is the least important.
I do believe the intake closing and exhaust opening are the most important.
Intake opening comes in 3rd.

[UDHarold]

Cam-Copier,

Exhaust opening and Intake opening are of equal importance. These 2 points tie for 1st place. Intake closing is 3rd, and exhaust closing is 4th. I have maintained this for about 25 years, and I design my cams using this theory.
Other people have other theories.......

UDHarold

[Bob West]

We know who Harold is,,,does the cam-copier care to identify hisself?

[zwede]

Very interesting thread. I was always under the impression (delusion???) that intake closing point determined DCR and therefore was critical in determining how much static compression could be run on pump gas.

So my question is: Does the order of importance change for different applications? Is the intake closing still in 3rd place when the application is street performance on pump gas?

/Markus

[UDHarold]

zwede,

Because the intake closing point is only JUST that, different duration intake lobes on different ICLs and LSAs may all have the IDENTICAL intake closing point, but greatly different amounts of fuel/air to compress, and different cylinder pressures, and actually very different dynamic compression ratios, as measured by cylinder pressure. In fact, think of an unblown engine and a blown engine with the identical intake closing point. You would think that maybe they would have different ACTUAL dynamic compression ratios? I think of the dynamic compression ratio as the amount of air/fuel trapped in the cylinder at intake valve closing, and then compressed. This is the same thing that Pat Kelley is saying, only he is looking at the capacity of the cylinder as a static number. I view the amount of air/fuel in the cylinder as influenced mainly by the cam, and its' dynamics(Pun unintended).
Exhaust opening and intake opening govern how much air/fuel is going to enter the cylinder. Intake closing determines how much you trapped in the cylinder. I maintain that, using my cam design methodology, inertia ram is still filling the cylinder when the intake closes, and no charge is back-flowing into the intake runner.
Other companies have other theories......

UDHarold

[cam-copier]

I think intake closing point is also an rpm governing event. The later you close the valve the greater the RPM potential the engine has.

I agree with Markus's idea on pump gas and dcr. I think the compression ratio should be one of the last parameter chosen when building an engine. With a predicted VE %, and a a known intake closing point the compression ratio can then be set.

Who I am... I worked for Elgin for about 14 years, the last 10 as the manager. I now have my own company and like Elgins I primaraly do foreign car camshafts. Hopefully my posts do not look like an argument, I am only stating my opinion like anyone else on the board.
I am very interested in your ideas on intake valve opening.
FWIW, I do not completely agree with the Elgin quote in 70GS455's first post. I like many others have my own ideas.

I also have a ton of respect for Harold and his accomplishments. Back in 1985 a freind of mine, Will Pennington had a 355 cu in 64 Nova with a U/D .626/.626 roller cam. The car on 26x8 slicks ran 11.2 @121 on motor and 10.30 @ 130 on nos. That was super fast for 1985 and especially on a small tire.

[novadude]

Great discussion, guys!

Because the intake closing point is only JUST that, different duration intake lobes on different ICLs and LSAs may all have the IDENTICAL intake closing point, but greatly different amounts of fuel/air to compress, and different cylinder pressures, and actually very different dynamic compression ratios, as measured by cylinder pressure.

BTW... you guys that get hung up on static DCR need to read this and REALLY think about it. Don't get me wrong... it's a good tool, BUT....

You think a 406 engine with a 1.72 valve 283 power pack head will have the same dynamic dcr as the same exact engine with a good flowing AFR head (keeping cam and ICL the same). I'll bet you can run more C.R. on the resricted motor without running into detonation, as the actual cylinder filling is less.