Effect of increased compression?

[RizzoTheRat]

I've just discovered that the revised engine on later versions of my bike had a slightly different shaped crown on the piston, fitting the Mk2 pistons in a Mk1 engine should increase the compression from 9.2 to 10.5. Apart from a potential power gain what other effects would this have? Would the ignition timing need to change, would it not work too well on the standard cams (can't use Mk2 cams as the crank angle is different)? Second hand engines do come up on e-bay from time to time, I'm half tempted...

This is with carbs not injection assuming that also makes a difference.

[Boosted LS1]

You could get better fuel returns as well so long as you don't drive harder/faster.

[stevieturbo]

Thats a huge jump...ignition timing will definately need checked, and adjusted.

[toohuge]

As mentioned above, that is a huge jump. I would be tempted to change the head bolts to stronger alternatives just in case.

[RizzoTheRat]

I'll check the specs but as far as I'm aware the head bolts are torqued the same in the Mk2 as the Mk1. It's a pretty low stressed engine, only producing about 75bhp from an 850cc parallel twin. A lot of engine parts are interchangable, I believe the barrels and head are the same, the main difference was it want from a 360 degree crank to a 270 (hence wouldn't be able to Mk2 cams and CDI), and the increase in compression. I'll have to see if I can find what angle they both spark at, and check part numbers of the head bolts.

Any ideas how much hotter it would run due to the increased compression? I think the Mk2 has a larger radiator, but my Mk1 tends to run very cold anyway

[ssray]

I put a 12.5 piston in place of the std 9.5 to one piston in my xt600, It lifted the front wheel in 2nd(a bit) apart from that i left the ignition the same and checked the plug colour, probably a good idea to have it checked on a dyno.
i assume its a tdm850? it should`nt run much hotter, use water wetter to be sure.
Ray