If I had 9 to 1 static c.r. and the cam was listed as good for 9 - 10.5 to 1, I could get a performance gain by advancing the cam timing thereby closing the int. valve earlier and raising the dynamic c.r.?
The cam in question is Isky 390164 for install in a stock 360 mopar with the new magnum heads and 4bbl intake, 600 holley vac. sec. and 340 exhaust manifolds.
Just wondering if I understand DCR in relation to cam selection.

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Advise should be taken as ongoing, that way, when you get to realizing what you are doing you can include yourself.

Yes, closing the intake valve sooner raises the dynamic compression ratio as it traps more mixture in the cylinder at low engine speeds.

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Joshua

My brother and I are building an engine apiece, his a 360 and mine the slant 6, the 360 combo listed there sounds like a potent steet combo although the large valves may use up the carb before he gets much high end, and in my reading I found that more DCR will be good at high end.

I really wanta try that cam.

A forum I read, a guy said he got 400+ ft. lbs. from an almost stock 360 and that cam

It really made sense to me to choose a torque cam and advance it, with the large valves it should flow well enough to decrease dwell at BDC, I would guess (without any measuring) that it would be safe at 3 to 4 deg. advance.

I got all the paper work with my slant 6 (bought it built) and they put a cam advance bushing in it, I'll have to measure it and see what its at, Doc said the DCR is wwway high for my static.

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Advise should be taken as ongoing, that way, when you get to realizing what you are doing you can include yourself.

You can't just arbitrarily pick a cam and then advance it. If you'd be willing to tell me more about the 360 and how it will be used I could most likely spec a cam that works even better than the Isky. I can't find anything on that Isky other than advertised duration and valve lift. Lame. Need the lobe centerline angle and the duration at .050".

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Joshua

I have gathered that I cannot assume specifications but I was thinking that if I had a good air flow that I could think about useing the compression to advantage on the higher end, I'm going to pursue the specs on that cam, seems its sort of a mystery and from what I'm learning, the slant six has some tall advantages on the torque side.

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Advise should be taken as ongoing, that way, when you get to realizing what you are doing you can include yourself.

The #1 most important valve event is intake closing. Early intake closing traps more mixture at low speeds and increases the dynamic compression ratio. Later intake closing trades good low speed cylinder filling for improved high speed cylinder filling. To a point. Moving the installed cam centerline changes the intake closing along with all the other valve events, but the intake closing is the most important to how the engine runs.

For every engine there is only one best intake-to-exhaust lobe centerline. Once you know that best centerline and choose the amount of overlap based on how the engine is to be used the duration is a given. If/when you split the duration on the intake and exhaust you adjust the duration as needed. Slants like a little more intake duration so we may take 2-3° off the exhaust valve duration and add it to the intake duration. The opposite is true of most production cylinder heads on Chrysler small blocks, but not all!

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Joshua

Ok I read about the overlap and how advanceing the cam generaly gives better low end, but you can understand what I was thinking with DCR too, Ill take a backseat till I come up with some measurements and ideas on what I want to get done, thankyou's.

_________________
Advise should be taken as ongoing, that way, when you get to realizing what you are doing you can include yourself.