More compression...Yes...No..????

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flyfish

flyfish

C8H18+N2O = :-D
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I’m getting ready to select the pistons for my 408 and I had a few questions. If I increased the compression from about 10.5:1 to 12:1 what would be the consequences?

Would there be much of a power gain?
Would a 50/50 pump/race gas work?
Would the car run hotter?

Just trying to get some opinions before I order the slugs.
The rest of the combo is as follows:
408, Air-gap intake, 750 dp
Comp solid roller, XE286R, 248/254 duration and .576/.582 lift
Eddy heads (might be able to get some light port work done $$$)
727, 8” PTC converter, 4.10 gears, 3250 lbs with driver
90% race with some street time.
 
You should still be able to run your current fuel mixture on 12:1 compression with closed-chamber aluminum heads. Power should go up with more torque across the RPM band (and better low-RPM street manners), and if anything the engine may run a little cooler due to higher combustion efficiency.
 
flyfish said:
If I increased the compression from about 10.5:1 to 12:1 what would be the consequences?
-You should get about 6% more power at every point on the curve, and the peak rpms will be reduced by about 500rpm.


Would there be much of a power gain?
-Yes. Honestly, 10.5:1 with that cam is low, I would have aimed more for a static of 11.25:1

Would a 50/50 pump/race gas work?
-with careful tuning, I'd think pump high test (93) would be fine. Remember the timing curve should be slower and the total lower on a 4" stroke with small chambers.

Would the car run hotter?
- not if your cooling system operated fine now.
Click to expand...

Some general changes.. i definately see a ton more power by going with a stage 2 port (bowl, gasket match, and pushrod pinch, plus if you didnt have them corrected, have a high quality valve job done as part of the porting. The intake is giving up power with the new compression... I'd go single plane M1 with an open spacer, and that carb right now is way too small. Look to a Holley HP950DP or Street Avenger 870VS. If you want more, while the heads are getting worked, enlarge the pushrod slot/hole, and fit 1.6 rockers to it.
 
I'm running 12.5:1 cr with aluminum heads. I'm nowhere near 50/50 mix. More like 20% 112 and 80 93 pump/hi-test. No signs of detonation.
 
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