sbf 302/342 stroker build need help please???

DirtyII

New Member
Nov 15, 2010
10
1
1
ok so I have a fresh standard bore 302 with a 3.400 stroker crank. now i know with a 5.400 rod length it will make a 342 stroker with standard bore..my question is would it still be a 342 or what would the cid be using the 5.090 rod i already have instead of going and buying 5.400 rods and also would i have any issues using these rods with this crank versus the 5.400's ???
 
  • Sponsors (?)


ok so I have a fresh standard bore 302 with a 3.400 stroker crank. now i know with a 5.400 rod length it will make a 342 stroker with standard bore..my question is would it still be a 342 or what would the cid be using the 5.090 rod i already have instead of going and buying 5.400 rods and also would i have any issues using these rods with this crank versus the 5.400's ???
pretty sure you will need pistons and rods for this to work properly. The stroker crank will split the difference of the stroke. So say you have a 5.400 crank and a 5.200 crank. .200 difference between the two, the piston will go .100 higher and .100 lower in the cylinder to pick up the extra .200 stroke. So your stock pistons will need to be replaced with ones that the wrist pin is higher in the piston. Otherwise you will most likely have interference with your heads. If you don't use longer rods the piston will come farther down in the cylinder. I don't know if this will cause an issue. This is the way I understand how a stroker works. Someone please correct me if I am wrong.
 
You have to match the rod length and piston to the stroke. If the rods are too short you will have no compression and the pistons will hit the crank at the bottom of the stroke. If the rods are too long, they will extend out of the cylinder at the top.

There are some variations in rod length for each given stroke, but the piston compression height (where the wrist pin hole is, vertically) has to match to get the piston top to the proper deck clearance, ie, the top of the cylinder bore.

The top of the piston should be about .002-005 in down in the cylinder at tdc. That is a good planning figure, the actual dist should be calculated and checked by the machine shop for your combo.
 
You have to match the rod length and piston to the stroke. If the rods are too short you will have no compression and the pistons will hit the crank at the bottom of the stroke. If the rods are too long, they will extend out of the cylinder at the top.

There are some variations in rod length for each given stroke, but the piston compression height (where the wrist pin hole is, vertically) has to match to get the piston top to the proper deck clearance, ie, the top of the cylinder bore.

The top of the piston should be about .002-005 in down in the cylinder at tdc. That is a good planning figure, the actual dist should be calculated and checked by the machine shop for your combo.

Correct :)

FWIW the deck height on a 302 is a nominal 8.203"
So take rod length + 1/2 of the stroke + Compression Height of the piston = deck height of assembly

So typical 3.4 stroke combos (5.4 + 1.7 + 1.09 =8.19) (5.315 + 1.7 + 1.175 = 8.19)
 
Something else worth mentioning is that rod length has nothing to do with displacement. Displacement = (pi * (BORE/2)^2) * STROKE * (number of cylinders)

So, an engine with a 4" bore, 3.4" stroke, and 8 cylinders is 341.805 cubic inches.