I looked at a few places, and read that the stock compression for my '89 600 is 11.1-1. I have an extra engine sitting around was thinking about having the heads milled to bump the compression up to 12.1-1. Wondering how much more power I can get out of doing that?

Bdub

 

I think what you mean is to have the cylinders bored out to one size over, then use one size over pistons and rings.

That will increase the bore of the bore x stroke = bhp scenario.

How much you would gain really varies from bike to bike because of valves, timing etc.

Sorry can't be of more help, but I'd suggest you ask a local shop that does this sort of thing the cost vs. gain etc.

 

No, you're talking about upping the displacement. I'm saying bump up the compression of the bike. Shaving a few thousands off the heads will yield a higher compression/ more horsepower. Newer '03+ have 12.1-1 + compression. I know they have FI to help, but even older carbed muscle cars created horsepower with higher compression. This has to be a cheaper alternative to boring out the cylinders.

Brian

 

OIC,...

I've never done that. Have bored a cylinder once, but never fine honed an engine head and such.

Sorry 'bout that.

 

Correct me if I'm wrong, but wouldn't removing material from the combustion chamber lower the comression ratio?

Now if you put some pistons in the engine that had taller domes, that would raise your compression ratio, but you'd also run more risk of piston to valve contact.

 

If you merely remove material from the area above the piston head itself yes, you will lower the compression because you are creating a larger combustion chamber. If someone shaves the entire head surface, bringing the entire area above the piston closer to the top of the piston, it will raise the compression. Imagine installing the head with no gasket. The entire assembly is tighter to the piston head. Not even sure if these heads can be shaved, I have never seen the underside of one.

 

Sorry bd! I misread what you wrote. That would be an interesting expirament.