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.020 overbore : Approx hp/tq gains on 4.6

Old 11-03-2006, 03:55 PM
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Armydad
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Default .020 overbore : Approx hp/tq gains on 4.6

Hi all,

Does any one know what the approximate hp and torque gains are with a .020 overbore. Also does the increased surface area of the piston head effect comp ratio or is that just a function of the combustion chm.


Thanks
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Old 11-03-2006, 04:00 PM
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2000GT4.6
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Default RE: .020 overbore : Approx hp/tq gains on 4.6

A .20 will add virtually nothing to your 2v car, espcially with stock heads/cams/intake. Even most of the stroker kits do not add alot of power on built cars.
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Old 11-03-2006, 04:19 PM
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Default RE: .020 overbore : Approx hp/tq gains on 4.6

Well actually I will be having ported SVO heads a Crower blower cam and probably the FRPP s/c. Also headers full exhaust, CAI, TB, I probably should have mentioned all that, sorry.
ORIGINAL: 2000GT4.6

A .20 will add virtually nothing to your 2v car, espcially with stock heads/cams/intake. Even most of the stroker kits do not add alot of power on built cars.
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Old 11-03-2006, 08:16 PM
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JD1969
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Default RE: .020 overbore : Approx hp/tq gains on 4.6

You don't bore an engine for added HP. Boring is done to true the cylinder walls and provide a good seal for the rings.
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Old 11-03-2006, 09:11 PM
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hotrod7687
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Default RE: .020 overbore : Approx hp/tq gains on 4.6


ORIGINAL: JD1969

You don't bore an engine for added HP. Boring is done to true the cylinder walls and provide a good seal for the rings.
+1

You might get a 1-2 hp gain if your lucky. You buy the pistons with the compression ratio you want, they will already have the overbore factored in.
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Old 11-03-2006, 10:24 PM
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Default RE: .020 overbore : Approx hp/tq gains on 4.6

How Does this motor differ from any other? A bigger bore means more power! It Might not be huge number but it does give some. My Experience is with my 71 notch w/ a 302 that was bored and stroked to 357! 500Hp w/ dual quad carb's a beast, to say the least... And about a dozen hand built Chevy 350's.... A few were strokers.. Why doesn't it add power in a modular?

Mike
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Old 11-03-2006, 10:24 PM
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Default RE: .020 overbore : Approx hp/tq gains on 4.6


ORIGINAL: JD1969

You don't bore an engine for added HP. Boring is done to true the cylinder walls and provide a good seal for the rings.
[sm=exactly.gif]

.020 overbore is just a clean up...only adds like 2 cubic inches.
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Old 11-04-2006, 12:10 AM
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Default RE: .020 overbore : Approx hp/tq gains on 4.6


ORIGINAL: JD1969

You don't bore an engine for added HP. Boring is done to true the cylinder walls and provide a good seal for the rings.
thanks for the response, I agree that perhaps.020 is more of a trueing of the cylider walls, but why then would someone need to go bigger? To increase displacement and make more power. if you need to overbore .040-.060 just to true the walls, you should look for a new block.
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Old 11-04-2006, 12:19 AM
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Default RE: .020 overbore : Approx hp/tq gains on 4.6

ORIGINAL: JD1969

You don't bore an engine for added HP. Boring is done to true the cylinder walls and provide a good seal for the rings.
Why do you think guys take 350s and stroke them to 383s? More power! More potential! You don't bore out a 350 30 over and put a 400 block crank and pistons in it to seal rings. Don't know where you got your information from.
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Old 11-04-2006, 01:05 AM
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droptoppony
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Default RE: .020 overbore : Approx hp/tq gains on 4.6


ORIGINAL: Armydad


ORIGINAL: JD1969

You don't bore an engine for added HP. Boring is done to true the cylinder walls and provide a good seal for the rings.
thanks for the response, I agree that perhaps.020 is more of a trueing of the cylider walls, but why then would someone need to go bigger? To increase displacement and make more power. if you need to overbore .040-.060 just to true the walls, you should look for a new block.
some will do a .020 over on an engine rebuild then if they make a change take it out to .030 over...modular blocks shouldn't be taken out much more then that thus the reason for resleeving them when going with a big bore. Now a big bore will add some power.
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