ok, who can help solve this.

tried it on a few web calculators and it didn't work.

if I have a 103 as a result of a 4.38 stroke and 3.875 bore

and I replace the flywheel with a 4.625 stroke (4 5/8)

difference is .24 in stroke.

whats my new displacement.

Can I add a .25 thick cylinder base gasket to raise my cylinders to avoid changing my valve to piston clearance while keeping my compression intact?

 

109 CI.

0.7854(Bore sq) x Stroke x 2 = Cubic Inches

No you cannot add a .25 spacer to the bottom of the jugs. How would you fit the intake? Or exhaust?

 

Even if you were able to add the spacer, it would only need to be .125" thick because 1/2 the increase in stroke would be at TDC and the other 1/2 at BDC.

 

The additional volume (displacement) per cylinder is found using the formula for the volume of a cylinder = "pi" times R squared times H, where

"pi" = 3.1416 (approximate)
R = 1.9375"
H = 0.24"

That calculates to 2.83 cubic inches per cylinder = 5.66 cu inches total

To check the calculation, original R is bore / 2 = 1.94 so::
3.1416 x (1.94)(1.94) x 4.38 = 51.8 cu inches per cylinder = 103.6 cu inches

(Note that the measurements and the value of pi are "rounded off" to the calculation is only approximate)

 

yes...I initially thought that as well.

 

good question. all the intakes I seen have an open bolt hole on one end and a close one on the other. and if the spacer only needs to be .125, maybe this would not be impossible.

 

I got a 109 also.............

 

Why not just buy a set of pistons for it instead of trying to add base spacers, longer pushrods, and a new intake? Would be cheaper and less hassle. And either way you slice it, the compression ratio changed because the cylinder volume is different.

 

If it was OK to do that, that would be the way it is usually done, which it is not! There are a lot of competent engine builders out there who do it the 'normal' way and that seems good enough for me! When I stroked my Evo my builder used shorter pistons.

 

Thanks, thinking out loud here, I can play with the head gasket to tweak the compression back to where it should be.....the longer push rods are OK, thought of that....don't think I need new pistons, have some new cast and new forged...new intake , I think that any changes to intake surface mating spacing as a result of raising the jugs can be compensated for by adding gaskets between existing intake and existing jugs. i'm mainly after keeping my valve to piston clearance within limits after the new flywheel is installed. Raising the jugs should do that....there's plenty of cylinder wall available...certainly .125 to .25. don't need a whole lot and raising the jugs is easier in my mind than cutting the valve grooves on the pistion surface deeper. I could cut into the forged ones...but don't think there's enough meat on cast ones to go that route.