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prager
11-15-2006, 09:41 AM
Hello all, I have a kind of general supercharger question..Does compression ratio play a factor in the setup? I know when you use a blower you want to keep below the 9 or 9.5:1 range is the same true with a supercharger? Is 10:1 too high? Thanks!

South Bend, Indiana

JDP
11-15-2006, 11:36 AM
You could run it that high but even with super premium and the stock R2 compression you can't run full factory advance with pinging.

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Dick Steinkamp
11-15-2006, 11:53 AM
I've always used the words "blower" and "supercharger" interchangable, and called a turbo charger a "turbo", but I guess "blower" can mean both supercharger or turbocharger...they do essentially the same thing.

10:1 is probably the top end of the compression ratio for a NON BLOWN STREET ENGINE (unless you are dealing with today's computer controlled and sensor equiped engines). Even at 10:1 with a non blown engine you will have trouble finding gas that will enable you to run a decent total ignition advance. With a blower, you will have to fuel up at airports :).

It also depends upon how much boost you run with either the turbo or supercharger. With a lot of boost (15 pounds or so), static compression ratios are generally in the 7.5-8.5 range (even with race only motors). With less boost, you can run CR's higher.


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1956 Hawk
11-15-2006, 12:08 PM
There are several different factors here. Boost, cam timing, fuel octane, and design of the supercharger all figure into what compression ratio you can run. Combustion chamber shape, rod length and other things are also a factor, but harder to change. Here is a chart that gives a general idea of what boost you can run with different compression ratios:
http://www.procharger.com/mm/image/modelsboost.gif
I am running about 5lbs of boost on my 9.5:1 R2 on 91 octane gas with stock timing.
David

prager
11-15-2006, 12:19 PM
Thanks for the advice gents!

Still working to restore my 62 Lark in South Bend, Indiana