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Compression ratio???

 
Old 01-25-2019, 04:40 AM
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Default Compression ratio???

Im planning to buy an LM7 based 347 short block and put Trickflow/Tooley fast as cast heads on it with 64cc chambers. I will use arp studs and gm mls gaskets. I have the choice of shelf pistons in -3.2cc or -11 cc. Im thinking the -3.2cc and depending on deck clearance would put me around 10.7 to 1 static. Fuel is e85 and cam will be either the jam cam or a custom cammotion grind. Boost level will be around 15 psi to start, but I want around 800 rwhp eventually so what ever boost it takes to get there.

Lets avoid telling me how you make more with $300 junk yard builds all day long and stick to the topic of compression ratio on this build. Boost will be from my current D1x procharger.

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Old 01-25-2019, 06:44 AM
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You never actually asked a question.
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Old 01-25-2019, 06:53 AM
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Originally Posted by JoeNova View Post
You never actually asked a question.
Sorry it was early...with the choice of -3.2cc or -11cc pistons and the other information about the combo which would you choose? Off the top of my head I think the difference was either 10.7ish to 1 or 9.8ish to one depending on the unknown deck clearance.
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Old 01-25-2019, 07:07 AM
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The aluminum 5.3 I'm swapping into my corvette at some point is ~11:1. I've ran 13:1 with boost and E85 on a 4 cylinder.
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Old 01-25-2019, 07:27 AM
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Originally Posted by JoeNova View Post
The aluminum 5.3 I'm swapping into my corvette at some point is ~11:1. I've ran 13:1 with boost and E85 on a 4 cylinder.
Ok that makes me feel better about the 10.7 to 1. My car is primarily a street toy with trips to the track. So with the small cubic inch centrifugal setup in a heavy street car the higher compression should help I was just afraid it would be too much.

As always appreciate your input.
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Old 01-26-2019, 09:22 AM
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We have a 377” running 26+ psi on pump E85. Its at 11:1 CR.

Good tuning and run it Hard!

Best of success with your build.
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Old 01-27-2019, 08:49 AM
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Im 10:1 with Jam Cam. Love my street toy. Many centri set ups here with 10.7 that have had great results. Jam Cam @ 6* overlap & E85, I would think you have a great set up. Its all in the the tune.
Take a look at Detoxx, Im pretty sure he runs a ProCharger with substantial boost @10.7.
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Old 01-28-2019, 03:30 PM
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We have a lot of customers in the 10.5:1 neighborhood on E85. Also, if I may, have a look at our CS 232/248 LS Supercharger Camshaft. It is a terrific performer in an aggressive setup:
http://www.cammotion.com/camshafts/c...r-centrifugal/
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Old 01-28-2019, 08:16 PM
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Originally Posted by NitrOmm View Post
Im 10:1 with Jam Cam. Love my street toy. Many centri set ups here with 10.7 that have had great results. Jam Cam @ 6* overlap & E85, I would think you have a great set up. Its all in the the tune.
Take a look at Detoxx, Im pretty sure he runs a ProCharger with substantial boost @10.7.
Yep 21psi, SBE LS3, 10.7:1 CR
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Old 01-29-2019, 01:18 AM
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I would absolutely go with the higher compression with a centrifugal and e85. The boost curve of a centrifugal lends itself to working well with higher compression compared to small turbos or positive displacement blowers.
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Old 01-29-2019, 04:01 AM
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Originally Posted by Detoxx03 View Post


Yep 21psi, SBE LS3, 10.7:1 CR
How much timing are you able to run?
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Old 01-29-2019, 09:37 AM
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Originally Posted by BCNUL8R View Post


How much timing are you able to run?
Mine is at 15 or 16. If I had forged internals Id bump it closer to the 20s if it likes it. Im
gonna bump the CR into the 11s also when I do it.
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