8.9:1 too low?
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From: Dublin, CA
8.9:1 too low? I did a www.rosspistons.com compression ratio calculation:
Bore: 3.905"
Stroke: 3.622"
Head: 71cc
Gasket: .040" (Cometic)
Deck height: .010" (Diamond dished forged)
Dish: -8.6cc
Cylinders: 8
Results -- 347.03 CID -- 8.95:1 CR
I also have a 114 LSA cam.
Am I building a dog?
Bore: 3.905"
Stroke: 3.622"
Head: 71cc
Gasket: .040" (Cometic)
Deck height: .010" (Diamond dished forged)
Dish: -8.6cc
Cylinders: 8
Results -- 347.03 CID -- 8.95:1 CR
I also have a 114 LSA cam.
Am I building a dog?
Re: 8.9:1 too low? All depends on how much boost you plan to put to it, and what converter your gonna use.
Also depends on how big the cam actually is.
I'm at 8.7:1, fairly big cam for a 348, and a 6 speed. Off boost, and below 3500 it's a tad doggy. But it starts to come up on the cam by 4000, and the boost is right behind it. Then it don't matter
With a reasonable stall, you'll probably never notice it. But you should be able to lean on it pretty hard and still use pump gas.
Also depends on how big the cam actually is.
I'm at 8.7:1, fairly big cam for a 348, and a 6 speed. Off boost, and below 3500 it's a tad doggy. But it starts to come up on the cam by 4000, and the boost is right behind it. Then it don't matter
With a reasonable stall, you'll probably never notice it. But you should be able to lean on it pretty hard and still use pump gas.
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Re: 8.9:1 too low? Yep I tihnk if you had a ~3200 stall converter you wouldn't even notice it 
With good heads and a decent cam you would probably see around 300-320RWHP NA at 8.9:1.
Dont forget if you want to raise the comp slightly you could do a light mill of the heads to get you to wherever you want compression wise. I think 8.9:1 with 12-15#'s intercooled would work great on pump gas and a good tune
Cheers,
Chris
With good heads and a decent cam you would probably see around 300-320RWHP NA at 8.9:1.
Dont forget if you want to raise the comp slightly you could do a light mill of the heads to get you to wherever you want compression wise. I think 8.9:1 with 12-15#'s intercooled would work great on pump gas and a good tune
Cheers,
Chris
Re: 8.9:1 too low? I have mine set at 8.9:1.
i do notice it a little bit compared to the 10.5:1 but its not that bad, just doesnt jump as much as the 10.5 when you it the throttle but isnt that bad. also gas milage decreased some, now i get about 20mpg compared to the 25 i used to get stock, but you have to make some sacrifices when you make 500hp, i dont think its to bad for 500+
i do notice it a little bit compared to the 10.5:1 but its not that bad, just doesnt jump as much as the 10.5 when you it the throttle but isnt that bad. also gas milage decreased some, now i get about 20mpg compared to the 25 i used to get stock, but you have to make some sacrifices when you make 500hp, i dont think its to bad for 500+
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From: Dublin, CA
Re: 8.9:1 too low? Thanks guys, I was a bit concerned. On corvetteforum the common word is not to go below 9.3:1. Odd because ATI recommends 8.5:1-9:1.
With 8lbs + FMIC and stock everything else, I was putting out 522rwhp.
Besides the forged bottom end, the other major parts are A&A Stage 2 CNC heads and Thunder racing cam (224/227 .563/.569 114 LSA). It would certainly suck if it didn't run as well.
With 8lbs + FMIC and stock everything else, I was putting out 522rwhp.
Besides the forged bottom end, the other major parts are A&A Stage 2 CNC heads and Thunder racing cam (224/227 .563/.569 114 LSA). It would certainly suck if it didn't run as well.
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Re: 8.9:1 too low? You wont run as well at 8#'s. You would need to pulley up. If yolu are concerned go to 9.2:1 but I wouldnt go any higher than that if you are looking for 600RWHP or more.
Cheers,
Chris
Cheers,
Chris
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From: Chi-Town, IL
Re: 8.9:1 too low? My 6.0L 372c.i. 9:1 compression motor suprised me when I first drove it, it moves the car around pretty well for being a low compression motor...
I have a baby cam in it too, 214/218 .540/.550 114lsa...I'm going to see how the #'s are when its all said and done, then I might make a cam change if its not getting there w/the power, but so far the motor has been great to drive on the street, I've put close to 500 miles on it, and I'm still on the same NAPA belt w/the occasional throttle stab, also running around on 100 octane...
What would a 372 iron block motor put down on the rollers with 9:1 compression, that cam, and TEA S2 heads....??
I have a baby cam in it too, 214/218 .540/.550 114lsa...I'm going to see how the #'s are when its all said and done, then I might make a cam change if its not getting there w/the power, but so far the motor has been great to drive on the street, I've put close to 500 miles on it, and I'm still on the same NAPA belt w/the occasional throttle stab, also running around on 100 octane...
What would a 372 iron block motor put down on the rollers with 9:1 compression, that cam, and TEA S2 heads....??
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Re: 8.9:1 too low? 8.9:1 is fine.
No reason to run more compression, if you run more you need to scale back your timing or run higher octane (for comparative levels of boost).
No reason to run more compression, if you run more you need to scale back your timing or run higher octane (for comparative levels of boost).
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From: Fresno,CA
Re: 8.9:1 too low? I dont understand why you guys dont lower the compression to 8.7-8.5 and run more boost. You would loose a little bit out of the hole, not much though. But your top end would be much greater. Plus you could crank up the timing.
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Re: 8.9:1 too low? BIGBOS you would see around ~350-370RWHP I bet depending on a number of factors. BTW your cam is TINY.
I bet you have 50RWHP swapping out the cam to something agressive like a 230/244 114LSA cam with advance ground in
I bet you have 50RWHP swapping out the cam to something agressive like a 230/244 114LSA cam with advance ground in
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From: Germantown, MD
Re: 8.9:1 too low?
BIGBOS you would see around ~350-370RWHP I bet depending on a number of factors. BTW your cam is TINY.
I bet you have 50RWHP swapping out the cam to something agressive like a 230/244 114LSA cam with advance ground in
I bet you have 50RWHP swapping out the cam to something agressive like a 230/244 114LSA cam with advance ground in
Mike
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Re: 8.9:1 too low? It depends on where you want to shift. With a 114LSA cam and 230 intake duration you will have a power peak of approx 6400-6500rpm depending on a few factors.
Depending on where he wants to shift he might want to grind some advance in to lower the intake valve closing point and lower the peak.
Cheers,
Chris
Depending on where he wants to shift he might want to grind some advance in to lower the intake valve closing point and lower the peak.
Cheers,
Chris
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From: orlando, florida
Re: 8.9:1 too low? not to hijack the thread but just wondering how much boost you could run with say, 9:1 compression. and how much hp differance going from 10:1 comp. @ 8psi to 9:1 comp. @ 8psi. just curious how much comp. affects hp and tq.
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From: Dublin, CA
Re: 8.9:1 too low? With 8.9:1 I'm planning on 12psi, 15psi if I can get away with it. After all, my old 944Turbo ran 1bar (14.5psi) with a stock bottom end.
We'll see what changing the pulley from a 3.85" to a 3.5" does. This time I'm running a boost gauge.
We'll see what changing the pulley from a 3.85" to a 3.5" does. This time I'm running a boost gauge.
Thread Starter
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From: Dublin, CA
Re: 8.9:1 too low? Doh! I double-checked my numbers, Cometic gasket is .057" thick, not .040". That brings me down to 8.66:1 CR, and with a 114LSA cam. I may have to go for a larger crank pulley to get the boost up...
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From: Chi-Town, IL
Re: 8.9:1 too low? You will for sure need to go with a larger crank pulley to see that boost, I'm shooting for 12-13psi on my setup, I have a 7.85" crank pulley and a 3.3" blower pulley, both 8 rib...
