L98 Piston question
Race Director
Joined: Sep 2003
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From: Database Error Indiana
The stock 400 rods are 5.585 if I recall correctly. If you use 350 pistons the stock wrist pin location lets the piston end up where it needs to be. I did it in 1988, before they knew how to make these kits in China.
Race Director
Joined: Sep 2000
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From: The Top of Utah
Originally Posted by rodj
Enlighten me
3.750 stroker pistons run about .125 different lower CH to accomodate the extra stroke.
Allowing .025 for avg deck height that would put the stock piston .100 out of the bore unless you change rods?
3.750 stroker pistons run about .125 different lower CH to accomodate the extra stroke.
Allowing .025 for avg deck height that would put the stock piston .100 out of the bore unless you change rods?
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Race Director
Joined: Sep 2003
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From: Database Error Indiana
Yes, change the rods. You are over thinking the situation, with deck clearances and all, and avoiding the obvious. The stock 350 pistons and the stock 400 pistons have the same compression height. When Chevy added the stroke, besides changing the bore from 4.00 to 4.125", They changed the rod length rather than the compression height of the pistons. All familiar Gen I and Gen II SBCs use a 5.7" rod, except for the 400, which uses a 5.565" rod. [5.7" - 5.565" = 1.35"], or 1/2 of the [3.75" - 3.48" = ] 2.70" difference in the strokes. 350 pistons (+.030"), in a 350 block, plus 400 rods, plus 400 crank (w/mains turned to 2.45") = a 383. All the familiar Gen I and Gen II SBCs have a block, center of mains to top of the block (deck), blueprint dimension of 9.025". Take 1/2 of the 383/400 stroke of 3.75" or 1.875" add the 400 rod length (5.565") and the 350/400 piston compression height of 1.561", and you get, [1.875 + 5.565 + 1.561 = ] 9.001". Mix that combination of parts into a 9.025" block and you'll get deck clearance of .024".
I am CFI-EFI, and I approve of this message.
RACE ON!!!
I am CFI-EFI, and I approve of this message.
RACE ON!!!
I knew that did not sound right when I posted the 400 rod length. It just would not come to me when I posted. Thanks for posting the correct number, CFI-EFI.
I just realised that 1988 was a freakin long time ago. I have a right to forget after 20 years.
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
CFI-EFI, I am familiar with the SBC maths.
I was refering to the poster's comment;
"I may have to re-think boring my 85, the cylinders are ok and the pistons looked good maybe I will build a 380 instead of a 383"
which implies he thought he could do a crank swap only,retaining his original rods.
I was refering to the poster's comment;
"I may have to re-think boring my 85, the cylinders are ok and the pistons looked good maybe I will build a 380 instead of a 383"
which implies he thought he could do a crank swap only,retaining his original rods.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by rodj
CFI-EFI, I am familiar with the SBC maths.
I was refering to the poster's comment;
"I may have to re-think boring my 85, the cylinders are ok and the pistons looked good maybe I will build a 380 instead of a 383"
which implies he thought he could do a crank swap only,retaining his original rods.
I was refering to the poster's comment;
"I may have to re-think boring my 85, the cylinders are ok and the pistons looked good maybe I will build a 380 instead of a 383"
which implies he thought he could do a crank swap only,retaining his original rods.
RACE ON!!!
