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Old 12-25-2004, 02:13 AM
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421 small block chevys

Any of you guys have any experience in what it takes to get a 3.875 stroke crank into a 400 block?? I do know some room has to be made, but exactly how much?? What about rod length; I believe a 6" rod will work. Does the combo require a specialized oil pan?? Any feedback is greatly appreciated!!

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Old 12-25-2004, 06:46 PM
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Unless you have a crank that is specifically forged or cast for that application, it will require offset grinding the crank to get that stroke, which will require non- stock rods, as your rod bearing size will be smaller in diameter than the stock units.
Oil pan clearance shouldnt be a problem, but you could run into having to notch the lower ends of your cylinders to clear the rods, as has to be done with a 302 Ford with the 332 and 347 stroker kits.
Using a 6 inch rod may be difficult as due to the short deck height of the block, 8.5", your wrist pin will be necessarily a lot closer to the deck of the piston, and With a 6" rod, that would only leave you half an inch clearance between the deck of the piston and the center of the wrist pin. This would leave you only .100"between the top of the wrist pin and the deck of the piston. Your compression rings would be going around the ends of your wrist pin. You wouldnt be able to get a seal with it.
Even with a 5.7" rod, you would only have ..404" between the top of the wrist pin and the top of the piston, so you would be right back in the same situation with the compression rings.
Neither setup would allow your compression rings to seal.

Unless you have a crank that is specifically forged or cast for that application, it will require offset grinding the crank to get that stroke, which will require non- stock rods, as your rod bearing size will be smaller in diameter than the stock units.
Oil pan clearance shouldnt be a problem, but you could run into having to notch the lower ends of your cylinders to clear the rods, as has to be done with a 302 Ford with the 332 and 347 stroker kits.
Using a 6 inch rod may be difficult as due to the short deck height of the block,9",leaving you a compression height of 1.0625" your wrist pin will be necessarily a lot closer to the deck of the piston, and With a 6" rod, that would only leave you only .600" distance between the deck of the piston and the top of the wrist pin. Your compression rings would be going around the ends of your wrist pin. You wouldnt be able to get a seal with it.
Even with a 5.7" rod, you would only have a compression height of 1.3625". The biggest thing is going to be finding pistons for that compression height. You may have to run a rod as short or shorter than the stock 5.565".

Last edited by Max Keith; 12-25-2004 at 06:46 PM.
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