Opel CIH Engine Cam Specs

[tekenaar]

Here's a listing of Opel CIH engine cam specs, including some aftermarket grinds.

[jeff denton]

Hey, thanks Otto, that's cool. I cruised thru that and now wonder where to get a Schrick cam. I'd try that one in a heartbeat!

[RallyBob]

Originally Posted by jeff denton Hey, thanks Otto, that's cool. I cruised thru that and now wonder where to get a Schrick cam. I'd try that one in a heartbeat!

Jeff, I don't know how your track feels about cam profiles, but there's a particular cam I used to use for restricted circle track racing (usually limited by valve lift of .430" or less).

It's a .405" lift, 250 @ .050" duration cam, which I had ground to 106 degree lobe separation. If ever there was a way to wake up a 'stock' Opel engine, this is it! Cam Techniques in Florida used to grind this one for me.

Bob

[Betta Carotene]

what would be "stock" bob?

[jeff denton]

Thanks Bob. I'll write that one down. I'm gonna have at least a new head for next year. Rules say basically "run any cam" but stock valves, springs, etc. so I am limited to the .430 lift, correct? I still want to be totally legal, I think we can kick butt without cheating... My vast improvements already this year are all about spring rate and driver education, I am sure.

[Betta Carotene]

jeff my cam is within spring bind of the stock valves. .435 lift 230 @.050 110 deg lobe sep

[Hiro]

Bob,
I have a question about cam index:
Opel data say that most of the stock cams are retarded 1-9°,
But when I measure these cams,
I always find that the crossover point occurs some degrees before TDC, not after TDC,
So this would correspond to some degrees of advance, not retard.
Am I mixed up with my measurements,
Or is this some kind of discrepancy coming from how Opel defines "retardation"?
Cheers,
Hiro.

[jeff denton]

My buddy's cam for his 460 Ford came with instructions I had never seen before, they were looking at crankshaft degrees at which point the valves were "swapping", in other words, when the exhaust starts closing as the intake opens. Was Greek to me! Is this a method of degreeing a cam that you are doing, Hiro?
Somehow it was ingrained into my head long ago that a street car that wants off idle torque to really get moving should be advanced a bit, two degrees normally. A car that is gonna run near redline for fifteen minutes at a time should have its cam slightly retarded, up to four degrees.
There's gonna be a lot more to it than that, though, to get max performance, other factors come into play like exhaust efficiency, intake flow, and that's not to mention compression ratio and the science of octane and ignition timing!
There is just so much to it all that I have to respect a guy with a really hot car, be it on the street, drag strip, or oval track. Plus I know all too well that power is wasted by burning rubber. Getting it to the ground is a whole new subject! Making it go around a left hand turn so hard it hurts where the seat belts ride is an absolutely exhilarating form of contact sports... It takes me hours to get over the thrill of going twenty five laps in bloodthirsty traffic. Yeah. I'm hooked.
Betta, I think .430 lift is max with stock valve springs/spring seats. I must admit I have never even checked for coil bind, some engine builder I am, huh? I was only relying on the info that my cam at .430 would be OK with stock everything else... I think if the springs bind up, something should break, probably keepers or retainers or rocker arms.

[Hiro]

Originally Posted by jeff denton My buddy's cam for his 460 Ford came with instructions I had never seen before, they were looking at crankshaft degrees at which point the valves were "swapping", in other words, when the exhaust starts closing as the intake opens. Was Greek to me! Is this a method of degreeing a cam that you are doing, Hiro?

Yes it's how defines the crossover point: same lift value for both inlet and exhaust valves.
In my measurements, most camshafts show this crossover point to occur before TDC.
(I will try to post a pic)
OK the graph below shows various cam I measured,
The blue dot on the x axis is TDC,
The red dots are the crossover points for each camshaft.
HTH,
Hiro

[RallyBob]

Originally Posted by Hiro Bob, I have a question about cam index: Opel data say that most of the stock cams are retarded 1-9°, But when I measure these cams, I always find that the crossover point occurs some degrees before TDC, not after TDC, So this would correspond to some degrees of advance, not retard. Am I mixed up with my measurements, Or is this some kind of discrepancy coming from how Opel defines "retardation"? Cheers, Hiro.

I have no idea why you are getting different results. Especially if the head has been shaved. I have checked a few of them myself, and my camshaft grinder has checked them on his 'Cam Doctor' with similar results. Are you using any alternate parts in the engine that would affect this maybe?

[greensmurf20]

jeff, i'm running that .435 lift cam that allen has too. few thousand street miles on it, altho hard miles and nothings broke, just a rocker nut is starting to back off and needs replacing, as it always did that with stock cam anyways.

[GTJIM]

Originally Posted by jeff denton Somehow it was ingrained into my head long ago that a street car that wants off idle torque to really get moving should be advanced a bit, two degrees normally. A car that is gonna run near redline for fifteen minutes at a time should have its cam slightly retarded, up to four degrees. There's gonna be a lot more to it than that, though, to get max performance, other factors come into play like exhaust efficiency, intake flow, and that's not to mention compression ratio and the science of octane and ignition timing! .......I must admit I have never even checked for coil bind, some engine builder I am, huh? I was only relying on the info that my cam at .430 would be OK with stock everything else... I think if the springs bind up, something should break, probably keepers or retainers or rocker arms.

The major influence on the rev range that a cam "works" in is the Intake closing point.
Advance the cam and the Intake closes earlier - dynamic compression ratio increases and reversion of the intake charge is decreased which increases the BMEP ("Brake Mean Effective Pressure") in the lower rev range. This translates directly into more torque at lower revs.
Retard the cam and the Intake closes later - dynamic compression ratio decreases and the reversion in the intake charge increases in the lower rev range but at a higher rev range the "ram charging" effect begins to work due to higher charge velocity - this moves the peak torque up the rev range.
The Intake closing point is so critical that the cam can be fine tuned by simply altering the valve clearance. Tighter retards the Intake closing - looser advances it.
Seems back to front but the Intake closing point is on the trailing flank of the cam lobe - advancing closes it earlier and visa versa.

The "split overlap" point that you are measuring, Hiro, has less effect, except as it is moved, advance or retard, the intake closing point moves with it.
Also, as the exhaust/Intake centreline is moved apart or together (can only be done when grinding the cam as it is the movement of the lobe centre lines with respect to each other!) the cam "overlap" is varied which increases or decreases the amount of exhaust gas dilution and/or Intake charge loss through the exhaust valve.

Cam Lift: The effect of cam lifts near coil bind has a life shortening effect on the springs well before coil bind is reaches due to heat build up in the springs as they are stressed more and more. Coil bind will destroy valve gear in short order but running near it will fatigue springs quite quickly. If you cannot get a 0.020" (0.5mm) feeler gauge between the centre coils of the valve spring at full lift then you are really stressing the valve springs past their design limits!

[N61WP]

Very nice explanation! Cam timing can be sooo confusing.

I'm going to cut and paste this to save for future reference.
Thanks Jim!

james

[Hiro]

Originally Posted by RallyBob I have no idea why you are getting different results. Especially if the head has been shaved. I have checked a few of them myself, and my camshaft grinder has checked them on his 'Cam Doctor' with similar results. Are you using any alternate parts in the engine that would affect this maybe?

Sorry, I did not explain how I do the measurements:
I follow the method described here:
camshaft measurement by OHF
This method only requires a head, dial indicator, cam sproket, one solid lifter, a degree wheel fitted to the sproket, and a hand-made plexiglass ruler.
I find this method easier to perform because you don't need the complete short bloc to read the degree wheel sticked to the crank pulley,
It's also independant from the head being milled or not.
The only additional thing to do is convert the sproket degrees into crank degrees to plot the data.
This plot is usefull for me to compare camshafts data and choose one fitting my requirements,
Then of course the proper timing setting has to be done on the assembled engine.
HTH,
Hiro

[Hiro]

Originally Posted by GTJIM The major influence on the rev range that a cam "works" in is the Intake closing point. Advance the cam and the Intake closes earlier - dynamic compression ratio increases and reversion of the intake charge is decreased which increases the BMEP ("Brake Mean Effective Pressure") in the lower rev range. This translates directly into more torque at lower revs. Retard the cam and the Intake closes later - dynamic compression ratio decreases and the reversion in the intake charge increases in the lower rev range but at a higher rev range the "ram charging" effect begins to work due to higher charge velocity - this moves the peak torque up the rev range. The Intake closing point is so critical that the cam can be fine tuned by simply altering the valve clearance. Tighter retards the Intake closing - looser advances it. Seems back to front but the Intake closing point is on the trailing flank of the cam lobe - advancing closes it earlier and visa versa. The "split overlap" point that you are measuring, Hiro, has less effect, except as it is moved, advance or retard, the intake closing point moves with it. Also, as the exhaust/Intake centreline is moved apart or together (can only be done when grinding the cam as it is the movement of the lobe centre lines with respect to each other!) the cam "overlap" is varied which increases or decreases the amount of exhaust gas dilution and/or Intake charge loss through the exhaust valve. Cam Lift: The effect of cam lifts near coil bind has a life shortening effect on the springs well before coil bind is reaches due to heat build up in the springs as they are stressed more and more. Coil bind will destroy valve gear in short order but running near it will fatigue springs quite quickly. If you cannot get a 0.020" (0.5mm) feeler gauge between the centre coils of the valve spring at full lift then you are really stressing the valve springs past their design limits!

Thanks for your input, Jim!
Playing with the valve lash is appealing too,
But it also changes valve lift and duration,
Which is not the case when you move the split point only,
It's why I prefer this way of tuning.
Of course by doing so I also shift the exhaust timing,
But it's impossible to change only one parameter with our CIH cams,
One of these days we will need some VANOS system like BMW's ;-)
Hiro