Question about compression vs boost
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From: Colorado Springs
Question about compression vs boost So with my stock bottom end, with a stock 10:1 compression ratio I'm guessing I can only run 5-7Lbs of boost safely. My question is, if I went lower compression by changing pistons or bigger CC heads how much more effective would this be than runninig a higher compression and lower boost? Say I lowered compression to 8 or 9:1 so I could runs a lot more boost, how much more HP would this make than running say 12 or 12:1.
is there a chart somewhere or something that shows anything like that?
Thanks
is there a chart somewhere or something that shows anything like that?
Thanks
Last edited by 80superbu; Jan 16, 2006 at 11:08 PM.
somebody posted a chart of max boost at a certain CR but i dont know how accurate that is.....its better to have lower compression and run more boost because you dont lose that much hp from dropping the compression.Shoot for between 8.5:1-9:1 and run more boost.youll make alot more power that way.
Staging Lane
Joined: May 2005
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Originally Posted by ddnspider
its better to have lower compression and run more boost because you dont lose that much hp from dropping the compression.
Staging Lane
Joined: May 2005
Posts: 80
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From: michigan
I was in the same situation as you last year. Built a nasty sbc motor and felt the blower calling my name.. After spending top doller building a top line n/a motor i needed to tare everything apart a built it over for forced induction... In my case i just swaped out my pistons to get the compression ratio down to 7.9.1, Reinforced the block and got some cometec head gaskets... Everthing worked out great.
A turbo typically needs a lower compression ratio than a centrifical supercharger. A positive displacement supercharger such as a roots style, also likes a lower compression ratio. With your LS1 turbo'd G Body, I would drop the compression ratio down to approx 8.0/1, and use good rods and pistons. That Malibu is going to fly!!! Bob
I agree...You have to consider for every point of compression it's somewhere around 3-4% increase in power just from compression but for every lb of boost it's like 7%...Those are rough estimates and you have to take in account that there are many other factors but the math is something like that...
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Verdad Gallardo just looking for personal experience when changing from a stock cr with low boost to a low cr with high boost. i have been thinking about this lately and would like to seesome personal experiances.
kevin
kevin
As far as my MPG I went from a stock block and a turbo and usually would see about 200-250 to the tank, after the rebuild and 8.7:1 CR I have not seen anything better than 180 miles to the tank. has anyone else had this happen? I know the cam makes a difference but I went with a lingenfelter GT-7 cam which really is not all that aggresive
If you start getting too low a CR, the car loses that 'snappy' feel.
IMO, I would say that starts to happen around 8.8:1 - 8.5:1.
For a daily driver, I would go 9.0:1. You'll put a lot of miles on there when you are not boosting, and it does help mileage.
A properly sized intercooler will help a lot and give you more options, like staying at 10:1 and running 7#. I'm at 9.6 and running 7.5# through a big FMIC, but I'm a centri blower. Premium pump gas and no ping. I think I could go to 9#.
If you are going to run the track a lot, maybe lower.
Great project!
Jim
IMO, I would say that starts to happen around 8.8:1 - 8.5:1.
For a daily driver, I would go 9.0:1. You'll put a lot of miles on there when you are not boosting, and it does help mileage.
A properly sized intercooler will help a lot and give you more options, like staying at 10:1 and running 7#. I'm at 9.6 and running 7.5# through a big FMIC, but I'm a centri blower. Premium pump gas and no ping. I think I could go to 9#.
If you are going to run the track a lot, maybe lower.
Great project!
Jim
unfortunatley i have no room in an s-10 with a v8 swap to put a fmic. it is hard enough to mak the turbo fit. i am split between 10:1 and 5-9 psi or 8.3:1 and 15-20 psi. it will definately get a meth kit though.
