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Old 06-30-2010, 06:35 PM
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Quote:
Originally Posted by Newbie3191
well i know it is a 70's model motor i will get the casting number though but how do you know what size crank you have i mean are there numbers or something i can find. and i already have the pistons i guess all i would need is the crank and connecting rods. would i have to get my block worked on too? and what size cam would you use my cam has the number cmc 1539. thanks for the input i will look into it
Well if you want to use a 3.75" stroke crank you will need different pistons. You will need to add up your stack to get your deck height. This is an important measurement when you start to change stroke, rods, and pistons. The SBC has a deck height of 9.025". This means from the center of the crank to the top of the deck surface is 9.025".
Ill show you how to add up your "stack". This consists of your piston pin height + your rod length + half your stroke.

Now we need to see what we know. The crank stroke is 3.75" You need to divide this in half because stroke is from TDC to BDC and we are measuring from the center of the crank to TDC. This will give us a measurement of 1.875". Now add the rod length which for this build a 5.700" rod will be fine. So now the measurement is 7.575".

Now the only missing measurement is the piston. We know we want to end up at 9.025" so just subtract 7.575" from 9.025" and you will get 1.45". So we just found out that the piston pin height should be 1.45". BUT SBC engines are not the best cast blocks and can vary corner to corner and block to block so i would aim closer to a deck height of 9.000"-9.015". Like I said go to summitracing.com go to the engine section and select roating assemblies and then go through and choose chevrolet, 350, gen I, and then 3.75" stroke, 5.7" rod and you will figure it out.

Hope this wasnt too confusing im not the best at explaining things. Oh yeah the block will need a little notching done to it to clear the crank. Or take it to your machinist he will know what to do

If i were you it seems that you are new to this and i would just to a freshen up on your 357ci and do a vortec head swap and a cam swap. LEarn slowly and dont rush it. You will be able to get 350-400hp with a decent cam.
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