I run a Jasper "355" and I am in the process of a head swap. I'm trying to calculate compression ratios, however I am getting 2 different bore & CID numbers from 2 different situations.

First, the fella at Jasper emailed me this:
"The block is bored 40 over and the crank is 10 under on both rods and mains. Stroke is 3.48". Using the corrective formula (bore x pi x stroke x 8) brings CID to 353.841. Since the normal dispacement increments is 5 per 30 thousandths, you would round the result up to 355"

When I do that out longhand, I get 353.35 (close enough). That also means I have a 4.040 cylinder bore. The calculator I am using to find CR tells me my CID is 356.88.
http://www.projectpontiac.com/ppsite...nt/view/16/30/

What am I missing here? Am I correct in my bore of 4.040 and stroke of 3.48? Please help me straighten this out so I can get accurate calculations.

Thanks...
Eric

 

355 is .030 over
357 is .040 over
With 3.48 stroke

 

This is why government-run lotteries are so successful - people haven't learned math in government-run schools.

The volume of a cylinder is the area of the base times the height. The area of the base is the radius squared times pi. The radius is one half of the diameter or bore. For a 4.040" bore, that's 2.02" squared times 3.14159. Stroke is the height, so times 3.48". Times 8 cylinders, 356.879 cubic inches, rounded to 357 cubic inches.

 

Gawd Bless It!! I'm glad I asked, a BOSS 357 sounds much cooler. Thanks for helping me out with that, the CR calculator makes much more sense now.

(although I do have to change my liscence plate now...)

 

Call it what you want, it's still a 350.

 

Send a PM to JT and see if he'll change your screen name here now

 

Ahh, ever the voice of reason. Your advice is usually spot on, but a sense of humor sometimes helps.

Good idea Sonix, I just did that. Hey, if they could use decimal points in screen names and plates, I'd be happy to be BOSS 356.879! I'm a Taurus, I gotta be precise!!

 

For the purpose of CR calculation, it's a 356.879. . .

Admittedly, if you don't accurately enter details such as dome cc, head gasket cc, deck height, and chamber cc, it isn't going to be the determining factor, anyway.

 

I know 5-7. I had the rest of the information at hand, it's the simplest of things like say, the displacement, that gives me the hardest time. Jeez...

 

This is why I made a spreadsheet to calculate all this for me. Much faster and far less of a chance of me screwing it up.