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need some help guys. i plan on getting the escort in the 12's soon, but what is the idea compression ration on a turbo motor boosting at 15 to 18 psi? the pistons are custom and they will be sent off soon but i need to get your opinions if i can. as it is, stock CR is 9.6 to one and runs 9 psi. i get about 3 or 4 psi @ 2300 rpms and i expect it to spool faster with the pnp head. whats the best cr to go with, anyone?
 

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With pump gas I'd run 8.5 to 1 and tone the boost down to 10-12 to start.


If you want to run 15+ expect to put in 100 or better.
 

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Got Incon? said:
With pump gas I'd run 8.5 to 1 and tone the boost down to 10-12 to start.


If you want to run 15+ expect to put in 100 or better.
thanks man that means a lot to me, i ship to the mid east tommrow and my tour is 1 year :eek: ill go with custom ross 8.5 and have the shop tune it while im gone. ill post dyno numbers when i get back... wish me luck and god bless you all and support the usa and its troops!

Specalist Miles
650th trans (po)
wilmington nc
 

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I like 8:1 for a pump gas motor. I actually run a hair under that (~7.8:1).
 

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I'd agree for a race car,


For a street car, you don't want static cr to be too low, or you will have no power off the boost. You don't want to stay in the boost all the itme now do you :)
 

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Got Incon? said:
I'd agree for a race car,


For a street car, you don't want static cr to be too low, or you will have no power off the boost. You don't want to stay in the boost all the itme now do you :)
It's not as bad as you would expect. It's not as bad as I expected. I run 7.8:1 in my daily driver. Worse than that i do it at 6000ft. On the positive side I can run 18 psi with full timing on pump gas.
 

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Cool!

So this '78 setup with 8.3:1 compression is just ducky :joy:

Too bad they only put out 143HP :lol:
 

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Asking someone what compression ratio on a turbo motor is like asking a guy if he likes big boobs, small boobs, or medium boobs. Everyone likes something different.

Me? I like big boobs and low compression.
 

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I like big boobs and plenty of compressions !!!
Sorry !!!
 

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Got Incon? said:
I'd agree for a race car,


For a street car, you don't want static cr to be too low, or you will have no power off the boost. You don't want to stay in the boost all the itme now do you :)
Would going from something like 9:1 to 8:1 or a hair under 8:1 really make a huge difference in power? Wouldn't it only be like 20-30 horsepower? That seems like a fair trade off to be able to run more boost to me. :confused:
 

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1000HP said:
Would going from something like 9:1 to 8:1 or a hair under 8:1 really make a huge difference in power? Wouldn't it only be like 20-30 horsepower? That seems like a fair trade off to be able to run more boost to me. :confused:
The old rule of thumb is 4% loss in power for 1 point drop in compression. I started at 9:1 then went to 8.5:1 then down to 7.8:1. Unfortunately I don't have any track numbers for comparison but I really couldn't tell any SOTP difference. In my experience your choice of cam and intake is going to have a much greater effect on your low end throttle response than the CR.
 

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my 331 is going to be around 8.3-8.5:1
 

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I guess turboing my car later is out of the question then. It's going to be around 10:1 compression. C6OE, 289 heads, stock pistongs.
 
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