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Old 11-10-2010, 08:11 AM
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Increase Comp new 396

I have a new biult 396 with 10hrs on it.
Mistake: CR is 8-1 I want 10.5-1 i used flat top pistons and did not do my math. >.120 deck clearance. I want to switch to AL heads and Have 10.5-1
Question: Can I switch pistons without tearing the whole engine down and rehoning????

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Old 11-10-2010, 08:22 AM
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Drop the pan, lift the motor Disconnect the rods, ect/,,,//
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Old 11-10-2010, 11:07 AM
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Should i lightly hone the cylinders??
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Old 11-10-2010, 11:29 AM
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A couple of thoughts.

The 10.5:1 target is a bit high for a pump gas engine (mine is a tick below 10.5:1 and I spent a lot of time and effort to work the issues related to detonation).

Depends on which heads you have, but changing heads to reduce chamber size could get you very close to where you want to be. I used domed pistons (-25cc) and quickly found that the variation in cast iron heads put me very close to too much compression.

Also don't just think of static compression, look at dynamic compression which accounts for static compression combined with cam specification and timing. There are some very good calculators to help with this on sites like KB or Comp cams, etc as well as links in the knowledge base of our forum. A good target for dynamic compresion is just below 9.5:1 for a pump gas engine.
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Old 11-10-2010, 02:39 PM
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i thought i was safe at 10.5 to 1 with Edy heads????? Thank you !
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Old 11-10-2010, 03:41 PM
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Yea, i think 10.5 is kinda high for pump gas. I'd stick with somewhere closer to 10:1, just to be safe.
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Old 11-10-2010, 04:31 PM
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Quote:
Originally Posted by starnest
A good target for dynamic compresion is just below 9.5:1 for a pump gas engine.
I don't know whose calculator you're using, but with the Keith Black calculator, 8.0:1 up to 8.3:1 is a realistic range of DYNAMIC COMPRESSION RATIO for pump gas. If you have access to a DynoSim, run the combination and look for BMEP of 190 or less for pump gas.
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Old 11-10-2010, 04:34 PM
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Quote:
Originally Posted by bigalow
I want to switch to AL heads
Whose heads and what chamber size? I have had a hassle trying to find decent forged 396 pistons lately.
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Old 11-11-2010, 05:47 AM
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Thank you TECHINSPECTOR1 I need some help here?
I want to run a bigger Roller Cam (running a Hyd 230 duration 485 lift aprox at @50 dnt have specs i front of me. Runs good but I WAANT TO GO FASTER )but I need 160PSI for the Roller Cam. I only have 135PSI now. I think i need to boost my CR to get the required PSI?

If i have to add a little race gas when I fill up its OK. Not a daily driver
I want to run a Race Demon , Roller Cam , 550 lift 250 in duration at @50 somewhere in there. i havent picked the cam yet. I need to figure my cyl PSI first right????

THANK YOU SIR for your help
Got to have 575 HP might have close to 500HP now
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