How low would you go with CR
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Lowest I would go is 8.5:1. The lower you go, the less responsive the motor will be off boost. It won't feel as crisp. Granted you can run more boost, but that's not always the best. More boost equates into more possibility of the heads floating or other valvetrain problems. I say for a street car anywhere from 8.5:1 to 9:1 is ideal for forced induction. On these big V8 cars I would say 9:1, thats what I'm shooting for when I complete my TT setup. Plenty of boost with enough compression for the car to be responsive and crisp off of boost.
If im running a Turbo i would go 8.1 C/R and 8.5 C/R with a Supercharger. The reason is because turbos make all their peak boost in the mid range so if u want to run 18psi on pump gas u will see it all around 4000-4500rpm hence the lower C/R, while a SC can run the same 18psi on pump gas with 8.5 C/R because the SC setup will see full boost at the last few rpms. Im shooting for 8.5 C/R with my setup running between 16-18psi on pump gas plus alky injection for safety.
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9.5:1? WHY! That's limiting how much boost you can run on pump gas so bad, and for what? For 10 horsepower more off boost? So that you can have more throttle response for pulling away from that stoplight, but to sacrifice 100+ RWHP when you're making boost and want to go fast? Honestly, that makes no sense. I would rather have more power for *** kicking rather than more power for pulling into the drive through.
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Teching In
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Originally Posted by eviltwins
9.5:1? WHY! That's limiting how much boost you can run on pump gas so bad, and for what? For 10 horsepower more off boost? So that you can have more throttle response for pulling away from that stoplight, but to sacrifice 100+ RWHP when you're making boost and want to go fast? Honestly, that makes no sense. I would rather have more power for *** kicking rather than more power for pulling into the drive through.
Besides ... that extra 100+ rwhp is worthless on the street. 600hp vs. 700hp on the street? It doesn't matter, you'll probably smoke anything but a slick on a prepped surface. Personally, I'd rather pump some octane, play with timing on the FAST, and use that extra bit of compression and timing at the strip.
To each thier own. I'm simply pointing out one aspect of 'street-strip' by highlighting the word 'street'. If you don't have 50+ timeslips in your glovebox as the car sits right now, give consideration to how 'strip' you want it to be.
Worst case, if you can't make a decision, half the difference and to 8.5:1.
The best argument for lower compression is the extra margin you have for detonation.
If you drop a point of compression you will need to make another pound of boost to make the same power. But 700rwhp at 8:1 is safer than 700rwhp at 9:1.
My current engine is 8:1 or so, maybe 8.2:1... Right in there.
The best argument for lower compression is the extra margin you have for detonation.
If you drop a point of compression you will need to make another pound of boost to make the same power. But 700rwhp at 8:1 is safer than 700rwhp at 9:1.
My current engine is 8:1 or so, maybe 8.2:1... Right in there.
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Well right now i am thinkiong of 8:5.1 with a T-Trim 355 and AFR heads and a 608/624 224/236 on a 116 X lobes .....Iwant to make as much power as i can on pump gas SAFE....this year i will not have any kind of air cooling....
Would 8:5.1 with about 14lbs work.....
As far as driving the car every day as long as i have more power then stock down low i don't think it will be a big deal...
Would 8:5.1 with about 14lbs work.....
As far as driving the car every day as long as i have more power then stock down low i don't think it will be a big deal...
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the more static compression you are willing to run the more efficient the engine will be when off the boost. so unless you are going for a max effort street car then stay at 9-9.5. run alky to keep things under control
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Originally Posted by TTExpreSS
the more static compression you are willing to run the more efficient the engine will be when off the boost. so unless you are going for a max effort street car then stay at 9-9.5. run alky to keep things under control
no, cant say that i have. but when you lower the static compression you loose efficency... maybe I'm being too **** about it but I really, really, really like having 28mpg on the highway so I want the most static compression I can "afford". Sure I could loose a few mpg points and not worry about it but talk about having the best of both worlds... mega horsepower and mega mileage is too cool in my book. A little alky to control it is a small worry. 
I'm starting to think about building a shortblock for more boost. you think 8:1 will still get decent mileage? I only care cause I put 200-1k miles a week on the beast.
I'm starting to think about building a shortblock for more boost. you think 8:1 will still get decent mileage? I only care cause I put 200-1k miles a week on the beast.
If you want to be **** then don't reccomend alky.
All my research from before said that a drop of a full point of compression would result in a total power decrease of 3%.
So if I went from 10:1 to 8:1, I maybe have dropped 6%. I bet an 8:1 348ci LS1 + T400 combo like mine dynos 350rwhp on a dynojet. So I am gaining 400rwhp from 19-21psi.
IMO go lower. The folks who advocate higher compression are trying to serve two masters, NA and FI. If you want full FI you will go 8.25:1 and will never second guess the decision.
All my research from before said that a drop of a full point of compression would result in a total power decrease of 3%.
So if I went from 10:1 to 8:1, I maybe have dropped 6%. I bet an 8:1 348ci LS1 + T400 combo like mine dynos 350rwhp on a dynojet. So I am gaining 400rwhp from 19-21psi.
IMO go lower. The folks who advocate higher compression are trying to serve two masters, NA and FI. If you want full FI you will go 8.25:1 and will never second guess the decision.
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Originally Posted by Pro Stock John
If you want to be **** then don't reccomend alky.
All my research from before said that a drop of a full point of compression would result in a total power decrease of 3%.
So if I went from 10:1 to 8:1, I maybe have dropped 6%. I bet an 8:1 348ci LS1 + T400 combo like mine dynos 350rwhp on a dynojet. So I am gaining 400rwhp from 19-21psi.
IMO go lower. The folks who advocate higher compression are trying to serve two masters, NA and FI. If you want full FI you will go 8.25:1 and will never second guess the decision.
All my research from before said that a drop of a full point of compression would result in a total power decrease of 3%.
So if I went from 10:1 to 8:1, I maybe have dropped 6%. I bet an 8:1 348ci LS1 + T400 combo like mine dynos 350rwhp on a dynojet. So I am gaining 400rwhp from 19-21psi.
IMO go lower. The folks who advocate higher compression are trying to serve two masters, NA and FI. If you want full FI you will go 8.25:1 and will never second guess the decision.
PSJ, You think 14lbs and no cooling is a NO NO...What would be a safe level of boost....until i can put the inter/after cooler on....
Is there some good info on low CR , where did you find all your research ..
Is it true the lower the CR the more timing and boost you can run..with out the fear of knock....
