What is good compression for 600 Twin?

moss

moss

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I just did a cold compression test on my sled and buddies. Can't warm mine up yet, as I am waiting for a bolt and new exhaust gasket, and I have the exhaust completely off.

When I tested cold, I had roughly 122-125 on both sides. My buddies 94 Vmax was right around the same cold.

Is this decent numbers? I will test again when warm and expect those numbers to rise, but just wanted to know if its around right or if its low?
 
SamuelJackson said:
I think you can lower head. 600 twin is consevative as stock. Example exciter sx got 150psi.

I am running mine with 170psi, what is at the limit with normal fuel.
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Yah I have been thinking of doing the head gasket mod, but I was testing more to see if my Rings where ok, I think with those numbers Cold I am ok for rings. Both sides had pretty much identical numbers.

With the head gasket mod, do you have to run higher Octane fuel, or will 87 Octane be fine? Thats one of the reasons I've held off, gas is $$$ Enough, and my Sled isn't great on gas as it is, so I don't want to do something that will make it even more costly to ride.
 
I run premium gas in mine with the thin hg. I'm not saying that I haven't had a couple of gallons of regular in there to get me to the next station but I usually run premium.
 
120's is pretty good stock. i was only getting 130 on my sxr 700 with a shaved head and gasket mod. as for using 87 on the head gasket mod i wouldnt. a few extra bucks at fill u is always cheaper then a rebuild after a burn down. i have always run 92+ no mater what i have for mods. also PSI isnt the way to check on how much u can bring the head down. u have to actually measure the clearance of the squish zone. u can detonate at 120 as easily as u can at 170 if ur squish is too small for the fuel. and if u dont know what the squish is its the area on the out side of ur combustion dome. .050inch is the minimum clearance u need on 92+ with the stock angle of squish. detonation occurs when the gas in the squish ignites from pressure befor the rest ignites from the plug when the 2 flame fronts hit they make the "knock" and the point at which they hit gets super heated and burs some of the piston away. thats why if ur running to low of an octane u burn a hole in the piston.

long story short a combination of psi, squish, rpm and bunch of other factors determine what octane u should run not just one or the other.

not to say that say that SamuelJackson is wrong for 170 being the limit for his sled but the motors are different. if i ran 170 on my old sled i would have blown it up on pump.
 
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