Compression bump vs. more timing
Thread Starter
Tech Contributor
Joined: Mar 2003
Posts: 12,094
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From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
Compression bump vs. more timing
If a H/C set-up was to give you a dcr of 8.1:1 would you have more power in the end by running more timing or bumping the compression to 8.6-8.8:1 DCR? I know the car will run hotter somewhat. I see 178-183 as the norm so it isnt that bad.
I have dropped compression and can run up to 6 more degrees timing in some areas resulting in some good gains but I wonder if the higher dcr and close-to-stock timing curves would be more power/low end TQ.
One point in static compression usually yeilds 14hp and 20rwtq at peak and more TQ down low. Some say 1 degree of timing can be 2-3hp at peak.
Any input or experience with this?
I have dropped compression and can run up to 6 more degrees timing in some areas resulting in some good gains but I wonder if the higher dcr and close-to-stock timing curves would be more power/low end TQ.
One point in static compression usually yeilds 14hp and 20rwtq at peak and more TQ down low. Some say 1 degree of timing can be 2-3hp at peak.
Any input or experience with this?
Race Director
Joined: Jan 2000
Posts: 12,375
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From: Florida
Spin, it seems to me from all my reading on the subject that bumping compression is the better way to go, for several reasons: (1) compression gives you better torque across the range, whereas + timing moves Tq lower but at the expense of top-end power; (2) higher SCR means tighter quench, which means better knock control and more power (3) more timing for a given LSA makes the exh valve open earlier, which may become detrimental on a large-duration exhaust cam, and moves you further away from the upper 40s BBDC stock EVO which the motors seem to like.
That said, I have also been told that 112 ICL seems to work best on these motors, and you need -4 to -3 overlap to get good idle, resulting in most of the cams we look at being a 114+2 or so.
That said, I have also been told that 112 ICL seems to work best on these motors, and you need -4 to -3 overlap to get good idle, resulting in most of the cams we look at being a 114+2 or so.
Burning Brakes
Joined: Feb 2006
Posts: 903
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From: Miami FL
I on the other hand prefer timing. I had my head/cam setup at 11.75:1 SCR. I couldn't run any timing at peak tq. I had a max of 16* of timing at peak tq and could add back some timing towards redline. If I ran no cats I was able to squeeze a degree or so more out of it.
I had better results in the past setting things up in the very low 11's as far as CR goes and being able to sqeeze another 4-6* of timing into the car. When the weather gets ugly down here (90+ 85% humidity+) you notice how much more prone the car is to have a knock event. It is easier for me here in FL to pull some timing when the weather gets ugly. Pulling some compression during the summer season down here is a bit tough.
As far as dyno tuning timing usually gives me 2-3hp/5-6tq and then reaches a point where the hp and tq comes in 1hp/2tq ranges. I usually stop adding at that point.
On my H/C setup that I just tore down the car was seeing great results by adding timing but the car would have very bad KR events so I couldn't add any more timing.
Just my .02 cents on my own experiece.
Dougie
I had better results in the past setting things up in the very low 11's as far as CR goes and being able to sqeeze another 4-6* of timing into the car. When the weather gets ugly down here (90+ 85% humidity+) you notice how much more prone the car is to have a knock event. It is easier for me here in FL to pull some timing when the weather gets ugly. Pulling some compression during the summer season down here is a bit tough.
As far as dyno tuning timing usually gives me 2-3hp/5-6tq and then reaches a point where the hp and tq comes in 1hp/2tq ranges. I usually stop adding at that point.
On my H/C setup that I just tore down the car was seeing great results by adding timing but the car would have very bad KR events so I couldn't add any more timing.
Just my .02 cents on my own experiece.
Dougie
Thread Starter
Tech Contributor
Joined: Mar 2003
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From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
That was 2-3hp and 5-6tq per degree you saw during dyno time?
Thanks for relaying the info and I respect that it is the result of experience. You seem to be a big source of good info these days Doug. Your tinkering pays off for all of us.
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