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Old 04-28-2008, 01:00 PM
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? on a 377 sbc

i have a good running 400 sbc and im looking to destroke it and make it a 377. i have the main bearing spacers and a std. scat crank. i talked to the local engine builder and he told me that with a 350 crank in a 400 block, the stroke would be much shorter and i would lose a bunch of compression and i would need to get longer rods. does any one know if i would be able to run a 377 by just installing the main bearing spacers and crank in a 400 with the stock rods?

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Old 04-28-2008, 02:10 PM
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Let's go through the math not only for you, but for others who may be reading this.

All small block Chevies use the same block deck height, 9.025". That's the measurement from the centerline of the main bearing bore to the block deck where the heads bolt on. They also all use a piston deck height of about 0.025", meaning the "stack" of parts used measures 9.000" and the piston is down in the bore 0.025" with the piston at TDC.

All small block Chevies use the same rod length (5.700") except the 400, which uses 5.565". That dimension is measured from the centerline of the big end to the centerline of the pin end of the rod.

When swapping parts, you have to add up the "stack" to achieve 9.000". That's 1/2 the crank stroke, total rod length and piston compression height (the measurement from the centerline of the wrist pin to the crown of the piston). 305's, 350's and 400's all use the same 1.560" compression height on the pistons, although they are all three different bore sizes.

So, let's say you were going to use a 3.48" stroke 350 crank in a 400 block and used a 5.700" rod instead of the stock 5.565" rod. The "stack" would compute thusly:
1/2 the stroke would be 1.74". Rod length would be 5.700" Piston compression height with a stock 400 piston would be 1.560". Adding these together, we get 9.000".

So the answer is, use a stock 400 piston, 5.700" rods from a 350 and the 350 crank. Bingo!!!

Note to other readers who are unfamiliar with the de-stroke concept:
The 400 crank main bearing diameter is 2.650". The 350 crank main bearing diameter is 2.450", so in order to have the 350 crank work in the 400 block, you must use special thicker main bearings. These are called spacer bearings. The outside diameter of the bearings fits the 400 main bearing bore in the block and the inside diameter fits the 350 crank main bearing diameter.

Last edited by techinspector1; 04-28-2008 at 02:54 PM.
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Old 04-28-2008, 02:16 PM
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377 Rods

You can't run the 400 rods with the 350 crank because they're too short.The 400 rods are 5.565" and the 350s rods are 5.7" so the piston deck height is too short.So you'll need the 5.7 rods.Check with Speedomotive they sell a lot of stroker kits for the sbc,and will have the parts you'll need to finish your stroker motor.
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