# Pistons, Cranks SBC

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by lukers, Sep 4, 2000.

1. ### lukersRegistered Member

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Hello All,
I have a math question about interchanging pistons and cranks and such. A stoker 383 uses 5.565 rods. Compression height is 1.561. Does this mean that the piston travels just a little bit higher. If I subtract the crank stroke of 3.75(400 crank) and 3.48 (350 crank) this = .270
Now I subtract the rod height 5.7 (350) and 5.565 (400) this = .135 The compression height remains the same in both applications. With that in mind it looks like I have added .135 to the stroke. .270 - .135 = .135 Is my math correct?

If this is and I do the same math using a 327 piston and a 5.565 rod in a 350 with the 350 crank, does this same math add .113 to the stroke? I really just want to know if I can use 5.565 rods and 327 pistons in a 350 block using a standard 350 crank? Hmmmmm

2. ### tRustyK5Big meanieStaff MemberSuper ModeratorGMOTM WinnerAuthor

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Well as far as I know the only thing that affects stroke is the crank. Different rod lengths can be used with the same crank and the stroke does'nt change. I don't know about the interchangability (definitely not a real word) of pistons. I know that the wrist pin location is what determines the maximum rod length. If the wrist pin is high on the piston you can use a longer rod.

Yes the 400 crank is .270 longer. They would use a shorter rod and a standard piston. You are increasing your stroke by .270, .135 above the crank centerline and .135 below the crank centerline. Thats the reason the rods used are .135 shorter, so the piston comes up to but not above the deck height. The bottom line is that at bottom dead center the piston will have travelled 3.75" down the bore. God I'm confusing myself

Rene
Rene

3. ### lukersRegistered Member

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You have cleared things up for me. I understand stroke much better now. Now I see that the real difference between the 327 piston and 350 piston is where they attach to the rod. Stroke difference need not be considered in my case because I am not changing my stroke if the crank stays the same (3.48).

So my math is just a difference in compression height and rod heights. The difference between the two CH's are 1.678(327) and 1.561 (350) = .117 So what this means to me is that this will push the piston .117 higher (out of the cylinder.)

So to solve the height I can adjust the rod. from 5.7 to 5.565 the difference of .135 thus putting the piston .018(.135 - .117) lower in the cylinder at tdc. And this much lower at the bottom of the stroke.

Is this making any sense yet?

Luke

4. ### Captkaos1/2 ton status

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What exactly are you..

What exactly are you trying to do? I am WAY confused on your question and description.

If you put 327 pistons on a 350 crank the piston will come out of the block .23" approx. (assuming zero deck height) If you use shorter (SBC 400) rods then in only sticks out .186". If you use 350 pistons on a 327 crank the opposite will be true. Pistons below the deck. IE LOW compression. Stroke of the motor never changes, just the rod/stroke ration. In a nutshell, it won't work.

Chris Lucas
http://www.captkaoscustoms.com

5. ### lukersRegistered Member

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Re: What exactly are you..

I wanted to see if I could just bore over .020 and use some (327)pistons and (400)rods I could have lined up. I wanted rods for a later stroker job.
Thanks for the feedback
Luke