3 vs 4 cylinder

[dcb]

You need to try again <insert serious smiley here>.

I said in my hypotherical engines that "even though the stroke and displacement are identical", this implies that the total piston area is also identical. What has changed is the number of cylinders and the piston radius) to keep displacement (and total piston area) even. The single cylinder with the same displacement/stroke has roughly 1/3 less contact with the cylinder wall than the 2 cylinder.


The stroke is the same in both cases, the 1cyl has a piston radius of 1.414 and the 2cyl has a piston radius of 1. The total circumference (the part that rubs against the cylinder wall) is much larger in the 2 cylinder.

[guitarterry]

can anybody tell me what an offset grind using oversize bearings (easy to get) would give me in displacement loss.

[dcb]

Not when you respond like this when given good info:

Originally Posted by guitarterry

This is wrong, wrong, wrong

[metromizer]

Originally Posted by guitarterry

If u actually did offset grind and destroke and use a xfi cam with less lift. couldnt u just mill the head to boost the compression back up. actually if u maxed the compression that would help out even more. even easier would be mill the block. of course u would need to use oversize bearings

unfortunately simply milling the head won't do it... It's not just compression ratio you loose by destroking, you increase deck height. Put another way, all other things being equal, the piston would now sit unacceptably lower in the bore at top dead center. You must restore the deck height by A) using a piston with a taller compression height (wrist pin hole moved closer to the skirt, away from the crown) which is a new piston, or B) slightly longer con rods... maybe C) With some engines, you can mill off the top of the block and liners, but I am not sure you can get away with that on a 4 cylinder Suzuki. Give me bore and stroke numbers (83mm bore?) for the 4 cyl and I can tell you what the new stroke needs to be to get to l1, and how much 'too far' the piston is down into the bore.

either way, I was just pointing out it's doable, but sort of expensive and time consuming to figure out.

I know we are just talking, but I think I see a much easier engine swap to a 3 cylinder is in your future...

[metromizer]

Originally Posted by guitarterry

can anybody tell me what an offset grind using oversize bearings (easy to get) would give me in displacement loss.

You really want to go at it from the other angle...

bore and stroke numbers will give you displacement. rearrange the math such that you fix bore and 4 cylinders, and the answer spit out is new stroke.

You can't pratically get away with any adapter bearings or oversize... the ones available are in very small increments only suitable for repairing a damaged journal, not destroking.

Offset grinding a crank is accomplished a couple different ways:

prep and submerge arc weld the journals ,<build up>, grind, stress relieve, straighten, re-nitride the journals, balance, (I probably missed a step or two).

Many times you can find another rod that uses a smaller bearing journal size (Honda journal is real popular right now with race engine builders). Smaller enough that you can offset grind the crank without adding any new material.