Quote from: dgyver on April 27, 2013, 07:24:15 PM
Go big or go home!

We are and unfortunately I had to.LOL

Awesome Ben!

You have to put pics are my attention can not be focused.. ... hint hint..

Do you have a part number and a photo of those pistons? My project is still sitting in boxes in my basement driving me nuts. I'm going to have to reshape the combustion pocket in the head and maybe machine down the pistons too in order to make my setup fit. Else I'll just abandon my current pistons and seek out something new...like what you're trying maybe?

No part number. I bought them used.

The cylinder was bored to fit a larger sleeve. The upper case had to be cleared to accept the larger sleeve. I had the sleeves honed properly to fit the pistons. Using Wiseco XG rings.   

Reprofile the pistons. That has to be done most of the time with these type of mods. I have yet to see a piston that does not have enough material.

The pistons we are using are 80mm(569cc). THEY ARE NOT IN THE PISTON LINE UP PICS.

74mm is stock size.








This is the clearanced case for the bored and sleeved cylinder block.




Here is the bored and sleeved cylinder block with the pistons set it.

Jumping to 78mm, assuming all other things are the same (some are not) but for the sake of comparison lets assume they are.

Stock 74mm bore with
56.6mm stroke
The compression is 9.0:1

With a 78mm bore @541cc
It brings it up to 10:1

With 80mm bore @ 569  it goes up to 10.4:1

http://www.cbperformance.com/v/enginecalc.html  Feel free to mess around with the calculations to see what you get if you change things.


If those pistons are have a larger volume than stock (I'm guessing they do quite a bit) then the compression ratio goes up even more.

The stock cylinder has 4mm of wall thickness.  Going to 78 leaves 2mm of wall left.  After that you would need sleeves installed.

The GR 650 sleeves can be installed with some milling work.  They start off at 77mm and have 4mm worth of material to go from there.

This is an example of GR 650 sleeves fitted to a GSX400 block with 78mm bore 1100 pistons.


Biggest you can go with the GR sleeves is 597 @ 82mm and that leaves 2mm left of wall thickness.

What about any big bore kits for the 2 valve GS1100's ?


Where did you get those sleeves from ?   How much flange was left on the top?

I bought them used.

I haven't cc'd everything but I think I will be at 11:1 CR when we are done.The copper head gasket is a little thicker than the GS unit so may bring that down a little.It will be a premium pump gas engine.MekanniX,what head gasket are you using and did you have to open the gasket up to fit the cylinder bore?

This is getting good! After rebuilding moped engines for a while- I have great respect for you all attempting this. I will be following in yer footsteps someday!!

I went with cometic fiber gasket. 0.043" @78mm

Quote from: MekaniX on April 29, 2013, 08:12:17 AM
I went with cometic fiber gasket. 0.043" @78mm

Thanks.