More compression for a 408
#229717
02/19/09 01:17 PM
02/19/09 01:17 PM
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Joined: Dec 2006
Posts: 1,178
Indy
FlyFish
OP
super stock
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OP
super stock
Joined: Dec 2006
Posts: 1,178
Indy
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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.
67 Barracuda street car, 408, e85, 1.38 60', 6.44 @105.9 in the 1/8 mile, 10.19 @130.5 in the 1/4...so far....
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Re: More compression for a 408
[Re: FlyFish]
#229719
02/19/09 07:27 PM
02/19/09 07:27 PM
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Joined: Sep 2004
Posts: 2,091
oberlin, Ohio
Rapid340
top fuel
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top fuel
Joined: Sep 2004
Posts: 2,091
oberlin, Ohio
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My opinion is: you could run a 50% mix if you have a decent quench height and keep the tune-up reasonable.
Things that would go in your favor:
1) cool air intake
2) thermal coating valves and/or piston crown.
If you do all these you may be able to run pump 93.
1971 Factory Appearing Duster 340 11.000 @ 122 mph
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Re: More compression for a 408
[Re: runya]
#229721
02/19/09 08:14 PM
02/19/09 08:14 PM
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Joined: Dec 2006
Posts: 1,178
Indy
FlyFish
OP
super stock
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OP
super stock
Joined: Dec 2006
Posts: 1,178
Indy
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Yea, the cam is a little small for the compression. I picked the cam last fall when I thought I was rebuilding my 360 with the stock crank. Would it not be much of a gain for the headache (and expensive race gas)? Is 10.5 :1 compression enough for larger cams in the future?
67 Barracuda street car, 408, e85, 1.38 60', 6.44 @105.9 in the 1/8 mile, 10.19 @130.5 in the 1/4...so far....
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Re: More compression for a 408
[Re: FlyFish]
#229722
02/19/09 08:24 PM
02/19/09 08:24 PM
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Joined: Jan 2003
Posts: 549
Bristol, Va
fasteddie
mopar
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mopar
Joined: Jan 2003
Posts: 549
Bristol, Va
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I would go for the highest compression I could get with flat top pistons. Domes would shroud parts of the chamber requiring more ignition advance, in turn requiring more octane to keep out of detonation.
2003 Bristol Dragway Sportsman Champion
2016 Bristol Dragway Power Hour Champion
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Re: More compression for a 408
[Re: FlyFish]
#229725
02/20/09 11:01 AM
02/20/09 11:01 AM
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Joined: Oct 2004
Posts: 8,165
Left Coast
BobR
master
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master
Joined: Oct 2004
Posts: 8,165
Left Coast
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Quote:
Yea, the cam is a little small for the compression. I picked the cam last fall when I thought I was rebuilding my 360 with the stock crank. Would it not be much of a gain for the headache (and expensive race gas)? Is 10.5 :1 compression enough for larger cams in the future?
The extra 1.5 points of compression will result in about 40+ HP. This isn't just peak HP, though, this is everywhere in the power band. I never had much problem with spending a few more bucks on racing gas since A. you only use about 5 gallons per race and B. I usually had a BUNCH of money in my motor so what's another few bucks for good gas? Don't take this wrong but if spending money on racing gas is a concern maybe you shouldn't be doing this. My street only 416 Challenger has 11.75-1 compression and I mixed it 50/50.
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Re: More compression for a 408
[Re: runya]
#229726
02/20/09 05:27 PM
02/20/09 05:27 PM
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Joined: Aug 2004
Posts: 3,333
MARYLAND
69Cuda340S
master
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master
Joined: Aug 2004
Posts: 3,333
MARYLAND
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Quote:
Maybe OU812 will chime in, he spece'd mine and the selection was a sweet match to my combo. 
He spec'ed a hydraulic roller for my engine and I am real happy with the power output.
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Re: More compression for a 408
[Re: BobR]
#229727
02/20/09 05:45 PM
02/20/09 05:45 PM
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Joined: Jan 2003
Posts: 11,711
Portage,michigan
B3422W5
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 11,711
Portage,michigan
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Quote:
Quote:
Yea, the cam is a little small for the compression. I picked the cam last fall when I thought I was rebuilding my 360 with the stock crank. Would it not be much of a gain for the headache (and expensive race gas)? Is 10.5 :1 compression enough for larger cams in the future?
The extra 1.5 points of compression will result in about 40+ HP. This isn't just peak HP, though, this is everywhere in the power band. I never had much problem with spending a few more bucks on racing gas since A. you only use about 5 gallons per race and B. I usually had a BUNCH of money in my motor so what's another few bucks for good gas? Don't take this wrong but if spending money on racing gas is a concern maybe you shouldn't be doing this. My street only 416 Challenger has 11.75-1 compression and I mixed it 50/50.
I agree 100%..compression will make notable difference going from 10.5 to 12 in power, and who cares about gas, if you race it 90% of the time anyhow
69 Dart GTS A4 Silver All steel, flat factory hood, 3360race weight
418 BPE factory replacement headed stroker, 565 lift solid cam
Best so far, 10.40 @127 1/4
1.41 best 60 foot
6.60 at 103.90 1/8
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