Supercharging and Compression ratio? - Team Camaro Tech
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post #1 of 7 (permalink) Old Oct 29th, 00, 09:18 AM Thread Starter
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69 Camaro 468.

How do you change compression ratio? If I decide to put in a centrifugal supercharger and I now have 10:5 compression. Will this cause for a whole new engine rebuild?

Thanks for the help!!!
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post #2 of 7 (permalink) Old Oct 29th, 00, 10:06 AM
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A centrifugal is pretty efficient compared to a 6-71 and generally wants closer to 9 to 1 compression. You will need to swap pistons or heads to get where you need to be. If you change pistons you might consider dropping the compression even more (nearer to 8-1) to allow more boost. You can run a centrifugal with 10-10.5 to 1 compression but you'll probably need an intercooler and very little boost; You are FAR ahead running low compression with high boost versus high compression and low boost.

Jody
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post #3 of 7 (permalink) Old Oct 29th, 00, 10:16 AM Thread Starter
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So how can you change compression just by changing the heads? Sorry I'm new at engine building and understanding compression ratios. Trying to gather some knowledge.

So, what is better high compression low boost or low compression high boost?

Thanks,
Chris
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post #4 of 7 (permalink) Old Oct 29th, 00, 10:29 AM
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to change the compression with just the heads you will have to get heads with a larger combustion chamber than what you have now. probably should go to 75cc or 76cc chambers for that.. depending on what size chambers you have now
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post #5 of 7 (permalink) Old Oct 29th, 00, 11:14 AM
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Depending on the chamber size of the heads you have now, you may or may not be able to get a large enough chamber to get the compression where you want it. If you change pistons ideally grab a piston specifically for blowers; forged, probably a little lower upper ring groove and a stronger top to deal with the added heat. Hypereutectics or cast can work in lower boost applications provided you don't have any detonation. Forged if you can afford it though.

Low compression with a higher boost will always make more power versus high compression and lower boost.

You also should pay attention to the camshaft. Wider lobe separation angles are beneficial to a blown motor as they will build boost faster, especially if it's a blower-specific cam. I swapped a hydraulic roller in my Pro-charged 406 from a Comp .640/[email protected] with 110 l.s. to a smaller .612/640 with 232/[email protected] with a 114 l.s. and picked up a bunch of mid-range power.

Jody
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post #6 of 7 (permalink) Old Nov 1st, 00, 09:15 AM
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I'm running a little over 9.5:1 with my carbureted Procharger set-up. I use the 9 PSI pulley and have no knock problems with 34 degrees of mechanical advance.

As others mentioned above, you will get more horsepower by using a lower compression ratio and blowing more air.

------------------
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See my website updated 9/01/00 at:

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post #7 of 7 (permalink) Old Nov 1st, 00, 12:07 PM
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I e-mailed you an Excel spread sheet to help calculate static compression ratio. It is very complete and works well. If anyone else wants a copy, please e-mail me.
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