High compression vs timing
I have a 418 with 11.5 CR, 215 TFS heads, 234/242/.600/.610 117+2 cam. I use 94 octane and the most timing it will tolerate is 22* above 4400 rpm @WOT. I have 2 heat range colder than stock spark plugs and a 160* stat. My intake valve closes at 52* ABC.
If you had a cam with an earlier intake closing, then the DCR would increase and would require less spark advance. And if you had higher engine temps, that would also require less spark timing.
Russ Kemp
If you had a cam with an earlier intake closing, then the DCR would increase and would require less spark advance. And if you had higher engine temps, that would also require less spark timing.
Russ Kemp
Last edited by Russ K; Feb 27, 2014 at 10:12 PM. Reason: Had the wrong intake duration spec
I have a 418 with 11.5 CR, 215 TFS heads, 243/242/.600/.610 117+2 cam. I use 94 octane and the most timing it will tolerate is 22* above 4400 rpm @WOT. I have 2 heat range colder than stock spark plugs and a 160* stat. My intake valve closes at 52* ABC.
If you had a cam with an earlier intake closing, then the DCR would increase and would require less spark advance. And if you had higher engine temps, that would also require less spark timing.
Russ Kemp
If you had a cam with an earlier intake closing, then the DCR would increase and would require less spark advance. And if you had higher engine temps, that would also require less spark timing.
Russ Kemp
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My 402 I ran 12:1 with 91 octane. Its all in the timing and tuning.
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From: North Carolina
I believe that the OP is asking for "theoretical" differences in power between a high-compression motor having to run "shortened" timing to avoid detonation vs. a lower compression motor than could run greater ignition advance, up to the limits of 93 Octane fuel.
Any thoughts on this ?
Any thoughts on this ?
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I believe that the OP is asking for "theoretical" differences in power between a high-compression motor having to run "shortened" timing to avoid detonation vs. a lower compression motor than could run greater ignition advance, up to the limits of 93 Octane fuel.
Any thoughts on this ?
Any thoughts on this ?
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From: North Carolina
Yes, but what happens at the opposite ends of that spectrum . . .
Lower compression with greater spark advance vs. higher compression with less spark advance . . .
Say, a 9.5 SCR motor with a lot of advance vs. a 12.5 SCR motor backed off ... Assuming that 11:1 was "ideal", hypothetically.
Which would make more power, with all else being equal, including the camshaft?
Say, a 9.5 SCR motor with a lot of advance vs. a 12.5 SCR motor backed off ... Assuming that 11:1 was "ideal", hypothetically.
Which would make more power, with all else being equal, including the camshaft?
Which would make more power, with all else being equal, including the camshaft?
If more and more timing meant more and more power, than I guess that would be different. But that's not always the case, a certain cam and heads will only take so much timing to be efficient. At that point, the even though the low compression engine can handle more timing, it's done making more power.
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Between then I would imagine the 12.5 motor would make significantly more power. There's only so much timing you can efficiently put in a motor, so just throwing insane amounts of timing at a low comp motor does not mean it will keep making power.
If more and more timing meant more and more power, than I guess that would be different. But that's not always the case, a certain cam and heads will only take so much timing to be efficient. At that point, the even though the low compression engine can handle more timing, it's done making more power.
If more and more timing meant more and more power, than I guess that would be different. But that's not always the case, a certain cam and heads will only take so much timing to be efficient. At that point, the even though the low compression engine can handle more timing, it's done making more power.
Doesn't seem to be the problem here but I know a lot of oldschool guys believed timing advance was power. Realistically in a perfect world the plugs could fire at TDC and only begin burning the fuel and building pressure after the piston changed direction and headed back down the bore. Building pressure before TDC is wasted energy BUT it is a compromise that has to be made because the flame takes time to travel and build pressure.
So I would agree with compression within reason.
So I would agree with compression within reason.
Building pressure before TDC is wasted energy
Point is, unless you build instant pressure, there will always be wasted power. That's why timing is not always a determining factor of power, but compression is (as long as it doesn't predetonate).
No not arguing, just stating that it's a fact of life with this type of stuff. All of which means that the ICE is limited in how timing affects its power production, thus the idea of a low compression motor with lots of timing does not sound as good as a high compression motor with less timing.