Most Compression To Run With Boost?

[oakeydoke]

I have a motor out of an old mustang bout 7years old been sitting up have now put the motor in a 92gt. Motor has about 30000 miles on it it has been bored to a 306 has the b303, windsor jr. heads, 1.72s, and gt40 intake with 70mm tb also long tubes and 24lb injectors. I cant remember the compression ratio of the car I must be getting old. My question is what would be the point at which you would not run a supercharger? Also did a compression test did not take all the plugs out but on the 1,3, and 5 cylinders it was 120 and the engine was not real warm either thanks in advance!!

 

[oakeydoke]

bump

 

[89MustangGX]

You can run a blower on a wide range of compression, the trick is all going to be in the tune. Find your compression ratio and go from there.

 

[vert]

Optimal comp. for boost would be from 8 - 9 to 1. I have seen some run with compression at 9.5 to 1. The lower the comp the more efficent the supercharger/blower will be.

 

[BaXTeR3221]

i dont think i'd run anymore than 9.5 to 1

 

[big_tiger15]

I read in a car mag that bumping the compression up doesn't help as much as people think. They did a test and got 4 hp for every .5 point they raised the CR. The test were all N/A dyno runs. I assume you get a bigger boost than 4 hp when you have higher CR and boost.
Keep in mind that they only went up to 11.5 to 1 and it was a lightly modded Chevy 350. Need to look and the final CR not static CR.

 

[89MustangGX]

This is an extreme example, but May 2005 MM&FF 5.4 supercharged race engine:

Going from 8:1-12:1 compression -

N/A - Gained 65hp / 44 lb-ft

Supercharged - Gained 225hp / 138 lb-ft

They also talk about a general 4% rule for estimating increase in power per 1 compression point.

Again, this is an extreme example -- but a good one to show you what compression can do.

 

[Sicarius428]

9:1 is as high as you realiably want to go with forced induction.
Kevin