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Old 03-21-2007, 04:19 PM
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destoked 350 turbo

one of the guys i work with told me he read in a magazine that you can destroke a 350 to a 305 and it knocks the compression down to like 7 to 1 or something like that and revs realy high and is perfect for a turbo because of the compression. has anyone ever heard of this and is it possible. if so id like to try this.

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Old 03-21-2007, 04:34 PM
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Your friend is FULL of BULLFEATHERS ...

A 350 and a 305 share the same stroke on the crankshaft ( 3.48 ) . The 305 has smaller cylinder bore.
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Old 03-21-2007, 05:00 PM
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***ditto Deuce***

The 305 and the 35O share the same stroke of 3.48 inches. If you used a 327 crank in a 350 block you would get a 327 because the 350 and 327 share the same bore of 4 inches, if you used a 307 crank in a 350 block you would once again get a 327 b/c a 307 and 327 share the same stroke of 3.25 inches. The only production crank I know of that you can stick in a 350 to get numbers of around 305 is the 283 crank with a stroke of 3 inches, even then that would only leave you with a basic production 302 small block chevy (4 inch bore/3 inch stroke) which is in fact 3 cubic inches less than what your friend said you could get by de-stroking a 350.

The only possible way to get exactly 305 cubic inches of displacement out of a 350 block with a 4 inch bore is with a custom made crank with a stroke of 3.034 inches.


Last edited by kuhn-77; 03-21-2007 at 05:06 PM.
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Old 03-21-2007, 05:20 PM
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^^^yes, but then it would be a big bore 305 with a short stroke and it probably would rev pretty high...power characteristics would probably be pretty similar to a 302 I would imagine...so yeah, you'd have 305 cubes, but it wouldn't be the same as the 305 produced by chevy
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Old 03-21-2007, 05:56 PM
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stroke will not effect engine compression, rod length will ( changes deck height )
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Old 03-21-2007, 06:15 PM
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Quote:
Originally Posted by matt167
stroke will not effect engine compression, rod length will ( changes deck height )
Actually that isn't correct either. Compression ratio is dictated by volume of the combustion chamber when piston is at BDC divided by volume of the combustion chamber when pistion is at TDC.

Lessened stroke if all other factors stay the same will decrease both displacement and compression.
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Old 03-21-2007, 06:48 PM
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my buddy said he read this article in a popular hot rodding magazine and it was chevys anniversary of the 350 and it was just a theory that no one has tried but they said it was solid. in the magazine it says destroke a 350 and make the compression racio in the 7s and it almost eqauls to a 305 or something and it revs high and can handle alot of boost. i didnt get to read it and he was confused by it so neither of us are sure.
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Old 03-21-2007, 07:03 PM
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Quote:
Originally Posted by matt167
stroke will not effect engine compression, rod length will ( changes deck height )

There's a reason you dont put 327 heads on a 383 stroker with flat tops unless you want ungodly compression

That half an inch difference in stroke between a 327 and a 383 bumps up your compression ratio quite a lot
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Old 03-21-2007, 07:42 PM
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it says use longer rods and that makes the compression drop to the sevens so it will handle insane boost and not blow. i think it would be bad *** if it could be built and if it would work.
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Old 03-21-2007, 07:53 PM
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For an engine to be able to handle "insane" boost levels then it goes beyond just lowering the compression. Probably most importantly, the engine engine has to be built to be able to handle the kinds of force that much power would create. This means using a forged crankshaft, forged pistons, aftermarket connecting rods, a cam ground for a turbocharged engine and many other factors...

As stated before the 350 and 305 have the same stroke so you can't destroke a 350 to a 305 as they were configured from the factory. While short stroke engines are generally perceived as high RPM screamers you also have to remember that the quality of your valvetrain plays a critical role. A hydraulic flat tappet camshaft generally isn't the best choice for turning 7,500 rpm... Again, the quality of the rotating/reciprocating assembly would be a factor here too...

Otherwise, you can build just about whatever you want just as long as your patience and your wallet will allow it.
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Old 03-21-2007, 08:20 PM
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Quote:
Originally Posted by Blazin72
Otherwise, you can build just about whatever you want just as long as your patience and your wallet will allow it.
Your talking about A LOT more money than a big block with equal power at a way lower RPM and the valve train life would be less of an issue. And also you would have computers on your car for turbo timers and other things it needs.....computers.....ewwww
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Old 03-22-2007, 05:29 PM
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Quote:
Originally Posted by Koolaid
Actually that isn't correct either. Compression ratio is dictated by volume of the combustion chamber when piston is at BDC divided by volume of the combustion chamber when pistion is at TDC.

Lessened stroke if all other factors stay the same will decrease both displacement and compression.
right you are, but only if the deck height is changed by changing rod length. which changes the deck height.
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Old 03-22-2007, 06:27 PM
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(partial quote from matt167's last post)
"but only if the deck height is changed"
.
This is incorrect!
A change in STROKE alone will cause a change in compression ratio.
Pick any of the widely available compression ratio calculators and try it.
I did, using:
4.00" bore
64CC combustion chambers
10.00CC piston top volume
0.00" deck height
0.039" head gasket thickness
..
With a 3.48": stroke the comp ratio is: 9.7:1
With a 3.75": stroke the comp ratio is: 10.4:1
JA
BTW: Here's the calculator I used
http://www.bgsoflex.com/cr.html

Last edited by johnnya; 03-22-2007 at 06:47 PM.
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Old 03-22-2007, 08:51 PM
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4.020 bore x 3.00 stroke = 304.6 ci and a 4.030 bore x 3.00 stroke = 306.1
the first of the 2 could be considered a 305
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Old 03-23-2007, 12:02 AM
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A 0.020"-over 350 block with a 3" crank and flat-top pistons with 6 cc's of valve relief, zero deck and a 0.039" gasket with 8 cc's and 76 cc heads would end up at 7.93:1 static compression ratio.
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