Short story and a question

Years ago we installed high compression pistons on a BMW R90S.  We used dabs of clay on the the pistons, bolted the heads on and cranked it through several cycles and then pulled it apart to make sure the valves weren't hitting the pistons.  The clearance seemed OK so we put it together and went for a run.  

After a little break-in, we ran it against an identical stock bike (mine) and there wasn't any difference accelerating until we got to about 125 when my bike stopped pulling. The test bike kept going and slowly walked away from me.  

Based on this experience, I've always thought that raising the compression without other work such as cams etc. would only give results (if lucky) at the top-end. Is this wrong?

When we slowed, there was a ticking sound. We found that the valves HAD hit the pistons once it ran up to readline. Yuk.

OS

My understanding was that high compression was better for the low and midrange and sometimes detrimenal to the top end because high domed pistons interfere with combustion and require earlier ignition.  In your case I'd say empirical knowledge trumps the general theory.

Quote from: Bob BroussardI'm not sure if anybody sells less than 4 at a time. Maybe you can split a set with someone. :dunno:

I have (1) 79mm high compression piston and looking for a second.

will these JE pistons work good on a lightly moded GS like mine? i didn't do any internal work yet...for now 150 and 40 jets, k&n pod filter, GSXR can....

does anyone here want's to buy these JE pistons with me....they seem like a good upgrade so buying 4 doesn't make sense if you're only gonna use 2

i have one 79mm piston too, looking for some rings for stock or 1mm over pistons, trade?

Quote4 doesn't make sense if you're only gonna use 2

Build a backup engine? or at least a backup top end

Quote from: Blueknyti have one 79mm piston too, looking for some rings for stock or 1mm over pistons, trade?

A trade would work...I have (2) stock pistons and (2) 1mm over pistons. The 75mm pistons are currently installed and don't have a need for the stock pistons except I was keeping them as a back up.

Can you send me a pic of the 79mm piston to see if ours are the same?

yeah, i need to clean it up alittle, i say 79mm but it has 78.95mm engraved on it.  there is a W inside an oval cast into wrist pin boss on the bottom.  i will see if i cant get it cleaned at work and get a pick tomorrow.

i have cylenders and 1mm over pistons waiting for rings,  i have stock pistons but i havent had the 450 cyl bored out yet. the guy i made the deal with screwed me over.  so i need the 1mm over size the most.


i think ifound a source for total seal rings but have to mic the lands on the pistons for correct sizing. but looks like it would be a purchase of a set for 4 pistons.

Quote from: Blueknyt

Quote4 doesn't make sense if you're only gonna use 2

Build a backup engine? or at least a backup top end

that would work too but i can't spend $800 on pistons for now...maybe i'll buy them later when i have money to burn  

Quote from: Blueknytlooking for some rings for stock or 1mm over pistons, trade?

I have a (1) brand new 1 mm over piston and ring set, still in the Suzuki packaging....

ok, cleaned it up abit, top and crown lookok, looks like he was running highlift cam and looks like he milled one valve relief, just touched it with cutter, not deep at all, however looks like some galling on the skirt, below the oil ring groove.   this is on the Back side of the piston.  got a cheepy digi camera and trying to take pics now.

Quote
I have a (1) brand new 1 mm over piston and ring set, still in the Suzuki packaging....

how much are you lookin to get for em shoot me a pm/email trying to build couple motors.

i just found this page....this guy did a dyno run with some little mods and then shaved this cyl head 15 000ths and advanced the timing and got about 8 HP to the rear wheel

not bad eh?

http://home.pacbell.net/ryanmero/dyno.htm