Good idea, bad? Raising the compression up a whole bunch? How much to take off before things go bad...etc etc etc...
List of precautions, things I need to do. Help me out.
i also want to shave my cyl head...i wouldn't raise the compression more then 10.5:1 but don't know how much to shave to get from 9:1 to 10.5:1
How much would have to be shaved off the head to pick up a half point of compression? Maybe .020"? That's removing A LOT of metal. I'm familiar with the claims here but I remain skeptical.
Why are you skeptical? And what are the claims?
I only shave my head in the summer. :mrgreen:
Since bore X stroke is 2.913" x 2.228, displacement = 29.7 cubic in, and compression ratio (CR) is 9:1, total volume is displacement plus combustion chamber (CC), so:
Displacement + CC
---------------------- = 9 ==> D + CC = 9 CC
CC
D = 9CC - CC = 8 CC ==> D / 8 = CC = 29.7 / 8
pi stroke2 x depth
CC = 3.7125 cubic in, but CC = ----------------------
4
4 CC
so depth (d) = ------------ = 0.557 in
pi stroke2
Now if CR = 10.5 to 1 and skipping all that
CC = 29.7 / 9.5 = 3.126 cubic in
d = (4 x 3.126) / (pi stroke2) = 0.469
so finally reduction (R) = 0.557 - 0.469 = 0.088 in
Theoretically you need to grind 0.088 in, 11/128 = 0.086 in, but of course, I dont know about valve groves clearances or gaskets thicknesses.
/\---Saved me the math! I was just getting started too.
Hmmm, i wonder what kind of power increase it would be?
I think valve clearances would be alright. Id stick to the same gasket thinckness I ahve now. I think I might try it.
Thanks for the Math again!
Quote from: Rich500Thanks for the Math again!
You're welcome, just let us know how it works...
QuoteTheoretically you need to grind 0.088 in, 11/128 = 0.086 in, but of course, I dont know about valve groves clearances or gaskets thicknesses.
Man, what are you grinding? The top of the cylinder? Remember, you're grinding off a hemispherical chamber with a 3 or 4mm squish band. If all that is factored into that equation, you're good. You're good anyway.
I suppose the next question is how much does the extra point and a half CR multiply the force? There must be an explosion formula in the text books, right?
.088 is alot to MILL off the head. Don't forget, if you mill the head at all, you will have to get slotted cam sprockets to get the cam timing right after you mill.
Quote from: GisserMan, what are you grinding? The top of the cylinder?
My engine will remain stock, I just made some figures for Rich, considering the combustion chamber a cylinder... and, I should say MILL instead of GRIND, sorry...
Quote from: GisserRemember, you're grinding off a hemispherical chamber with a 3 or 4mm squish band. If all that is factored into that equation, you're good. You're good anyway.
I guess the chamber isn't a perfect hemisphere, for what I remember from Clymers manual, but will check. Compression ratios have to do with geometrics. And 0.088 is 2.24 mm. On the other hand I can't tell if is actually possible to get 10.5:1 compression ratio with the actual head.
Quote from: GisserI suppose the next question is how much does the extra point and a half CR multiply the force? There must be an explosion formula in the text books, right?
Again, theoretically, should calculate the termodynamical efect of heating the air in the MILLED chamber with the value of energy for the fuel, but that would take some more time and the figures could be very offset due to heat loses, pressure loses, non-burnt fuel, etc. However assuming same conditions for both original and MILLED chamber the figures would give us an idea of how much more power could we expect.
Quote from: reknelbDon't forget, if you mill the head at all, you will have to get slotted cam sprockets to get the cam timing right after you mill.
Yes, as timing has to do with engine's geometry too, something sould be done to fix the 0.088 in gap between the cranck and the camshafts.
I've had a head milled 0.020", but the power increase is negligible.
80 thou is a lot. I suspect you will run into piston and/or valve clearance issues. And you would definitley need to re-time the cams. 20 thou doesn't make much difference to the cam timing, and the cam chain tensioner can take up the slack without a problem.
You'd probably be better to remove material from the cylinders, rather than the head. Less change in the combustion chamber shape.
High compression pistons are a better way to go.
If you get over 10:1, you will have to run high octane fuel, which has less power than the low octane stuff and costs more. 11:1+ on an air cooled engine and you are into race gas at $4 Can. a liter...
Quote from: KevinCI've had a head milled 0.020", but the power increase is negligible.
what is your compresion at right now?
The last couple of engines I was racing were 11.5:1 with high compression pistons, running on race gas.
The 0.020" planed head was probably only at 9.25:1 or something - never calculated it.
is there pistons we can buy to raise compresion but to run it on unleaded gas?
i think JE makes pistons for the GS but that's all i know
JE can make pistons for your situation. But you will have to buy a minimum of 4 and it will cost about $800.00 :o
Maybe you could use JBWELD to make a bigger dome on the stock pistons :lol: :lol:
dont laugh, i've seen is used to reshape valve ports
I've used it on intake ports. But it wouldn't take the heat of the combustion chamber or exhaust port. :mrgreen:
For a second I thought you were serious!
Can higher compresion pistons be bought at a cheaper price then $800.00.
Quote from: BriggsFor a second I thought you were serious!
Can higher compresion pistons be bought at a cheaper price then $800.00.
I'm not sure if anybody sells less than 4 at a time. Maybe you can split a set with someone. :dunno:
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: BlueknytQuote4 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 :roll:
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