Offset Ground Crank Strokers
- Thread starter dirigo
- Start date
Howdy Dirigo:
Offset grinding on the crank throws can only increase stroke double the amount of undersize bearings used. For example offset grinding a journal using a .020" undersize bearing will increase stroke by .040". A 200 stroke would increase from 3.126" to 3.166".
The gain in stroke, displacement and compression comes using stock parts and standard machining processes. It does require a top notch machinist and quality equipment.
An advantage to offset grinding is a decrease in deck height, in this case, by .020". A decrease in deck height improves quench effect and improve combustion efficiency.
I'll runn the numbers on the calculator and get back to you with the actual increase in displacement.
Adios, David
Offset grinding on the crank throws can only increase stroke double the amount of undersize bearings used. For example offset grinding a journal using a .020" undersize bearing will increase stroke by .040". A 200 stroke would increase from 3.126" to 3.166".
The gain in stroke, displacement and compression comes using stock parts and standard machining processes. It does require a top notch machinist and quality equipment.
An advantage to offset grinding is a decrease in deck height, in this case, by .020". A decrease in deck height improves quench effect and improve combustion efficiency.
I'll runn the numbers on the calculator and get back to you with the actual increase in displacement.
Adios, David
David & Will, they make a .040 under rod bearing where you can increase the stroke & bring the piston closer to the deck still using stock rods & pistons, that is what David is refering to.
Will, i think you are thinking a honda or mitsubishi rod with a smaller big end where you can grind the crank to match the dimensions of the rod. The problem which rod can you use on a 200 to gain say a .125" in stroke & still clear the camshaft. On the 250 you use an import rod for possibly a .250" gain in stroke. Am i close on that assumption?? Bill
Will, i think you are thinking a honda or mitsubishi rod with a smaller big end where you can grind the crank to match the dimensions of the rod. The problem which rod can you use on a 200 to gain say a .125" in stroke & still clear the camshaft. On the 250 you use an import rod for possibly a .250" gain in stroke. Am i close on that assumption?? Bill
Howdy Back:
I ran some numbers on the calculator. Offset grinding the crank throws .020" for a stroke increase of .040", increasing the stroke to 3.95" yields and increase in displacement of 2"- from 250 to 252. CR increases by 1/0 to 8.2:1.
On a 250 with it's huge deck height offset grinding the crank is a good part of a solution to move toward a zero deck height. Offset grinding along with using a 255 V8 piston at .085" taller than a stock 250 would reduce the deck height by .125"! That would be a more important step toward efficiency then an increase in displacement.
I should have asked earlier, What is your goal?
Adios, David
I ran some numbers on the calculator. Offset grinding the crank throws .020" for a stroke increase of .040", increasing the stroke to 3.95" yields and increase in displacement of 2"- from 250 to 252. CR increases by 1/0 to 8.2:1.
On a 250 with it's huge deck height offset grinding the crank is a good part of a solution to move toward a zero deck height. Offset grinding along with using a 255 V8 piston at .085" taller than a stock 250 would reduce the deck height by .125"! That would be a more important step toward efficiency then an increase in displacement.
I should have asked earlier, What is your goal?
Adios, David
Offset grinding to .020 under will only increase the stroke .020. This is assuming a perfect standard crankpin to start with. Think of where the center of the crankpin is stock and when offset ground. The center only moves one half of the undersize. You then get .010 increase at the top of the stroke and the other .010 increase at the bottom of the stroke. This works better on engines with large crankpins such as 460 fords so that with the use of rods with smaller big ends and of an appropriate length larger stroke increases can be achieved.
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