I have a 1983 Shovelhead Big Bore. The cylinders are 3-5/8", 0.30 over. The book says that I have a 4.25" stroke stock. The previous owner told me that it has a stroker kit. I'm assuming 1/4" but I'll check after I get the jugs back on. I'm calculating 97.6 CI (96.8 without the 030) stock and 103.3 CI stroked. Am I getting this right? That seems a little bigger than I expected.

 

Stock the stroke was 4 1/4 the bore was 3 1/2 (3.4975) = 81.6 cu in
4 1/4 stroke x 3 5/8 bore = 88 cu in
4 3/4 stroke x 3 5/8 bore = 97.8
If you look in the the timing hole there will be a S&S number if there are S&S wheels in there
Eastcoast Jim

 

Thanks, Jim but I must be missing something.

I get:
3.4975 bore / 4.25" stroke = 93.4 CID
3.625 bore / 4.25" stroke = 96.8 CID
3.625 bore / 4.75" stroke = 108.2 CID

My numbers are quite different. Can someone explain why it's not just a simple cylindrical volume calculation?

 

just sums I think...

[(bore/2)x(bore/2)x3.14] x [stroke] ...area of piston, I think you did circumference

x 2 cylinders

 

Check Gordon's post - you probably did some bad math
Pi X r2 X stroke X 2 cylinders

a 74 " motor is 3 7/16 bore x 4" stroke
a factory 80" shovel is 3 1/2 bore x4 1/4 stroke
add 3 5/8 bore cyl = 88 "
Did you check the timing hole for S&S wheels? - Eastcoast Jim

 

I'll just leave this here....
http://performancetrends.com/Calcula...splacement.php

 

A handy chart - Eastcoast Jim

 

Here's a few less keystrokes


bore x bore x stroke x .7854 = (single cyl disp)

x 2 cylinders

 

lol ...I couldn't find how to post up a superscript 2 to mean squared and Pi is easier to remember but yea, gets to the same place

 

This is a little embarrassing. I was just using a geometric calculator in AutoCAD instead of actually doing math. The numbers looked reasonable so I didn't notice that I was looking at surface area of a cylinder instead of the volume. That's what I get for being lazy.

Now I get:
3-5/8" bore +0.030 / 4.25" stroke = 89.18 CID (87.73 without the 030 over)

If it's 1/4" stroker:
94.43 CID

If it's 1/2" stroker:
99.68 CID

Thanks for helping me figure out that I'm not as smart as I thought I was.