srx head cutting

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ottawaair

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does anyone have a general guideline as to cutting heads. I am running about 118 psi comp. now. For example, would milling .010 off head gain me 5psi or more like 25 psi?? Just looking for approx. figures from somebody that hea done this. Or maybe some comp. #'s from race heads if you know the cc's of your heads.
 
A .010" head cut off the mating surface will show an APPROX 10 psi cranking compression and nets just under 1 cc reduction in the cyl head volume. This will result in just over a 12:1 uncorrected compression ratio, this is getting to the limit of what should be run on premium pump gas.
Before you cut the head you have to check your squish clearance, you will be reducing the squish by .010" as well. The tightest Squish I would recommend for a trail motor Yamaha tripple is .055".[I run approx .058"]
When I do my heads I cut the surface area and the squish to achieve my desired compresssion ratio, while maintaining a 'SAFE' squish clearance.
JMO
 
that is what I wanted to know- thank you. I knew to check my squish before doing anything, but also didn't know the limits of that. How do YOU check your squish. I also thought about 145psi was the limit on premium. maybe asking for trouble. I would like to see about 130 - 135 psi as long as the squish is within spec. Thank you for that info.
 
Shave 25 thou from heads & add 2 base gaskets & really wake it up.
cheap-o porting job!!!!
 
ottawaair said:
that is what I wanted to know- thank you. I knew to check my squish before doing anything, but also didn't know the limits of that. How do YOU check your squish. I also thought about 145psi was the limit on premium. maybe asking for trouble. I would like to see about 130 - 135 psi as long as the squish is within spec. Thank you for that info.
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Cranking compressions readings are variable dependant on gauge accuracy, compression ratios, exhaust port heights, temp, oil, altitude ect. Remember, the "Math" of the engine has to be right. You could have a cranking compression of 125lbs yet have a compression ratio that requires 110 octane race fuel! I have two comp gauges that vary approx 10 psi, and my VMAX4 Mod sled only cranks out about 145 PSI, needs 110+ octane and turns at 10,200RPM.
 
TURK, how come you only cut the heads .025", when having a total of 3 base gaskets? on the '98-'99 heads, i thought i remember you being able to shave off .010" safely and the the additional .020" would be for the 2 additional base gaskets? so, don't we want to be shaving .030" instead of .025"? or are you being conservative, due to the crappier gas now a days?
 
are you guys measuring new or used gaskets. If they're used, that's better, to know the compressed thickness. I am going to check the squish this week & go from there. I am not building a race motor or anything, I just like to see compression a little more than 118psi. I also just went through this motor, top to bottom, the cyl's. have 4000 miles but i did new rings, so should be good there. I used a Winderosa gasket kit, maybe the base gasket was thicker, I did not compare the two.
 
ottawaair said:
Does anybody happen to have a Winderosa top end gasket kit they could measure the thickness of the base gasket????
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The Yamaha base gasket is a metal "shim" style gasket.I have not used anything but Yamaha gaskets...If the Winderosa base gasket is anything but a metal gasket...I would suggest you order in the Yamaha base gasket!
 
yea, i think it was more like a regular gasket, not the metal shim type. I think I will start there, probably leave it for now. Good project for this summer.
 
800vmax4 said:
More then .025" off the mating surface only is a lot, more then that might start to eat into the edge of the squish band...JMO
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oh, i know i would need to recut the squish band, to get back the proper squish clearance. i was asking about how much turk likes to take off, cause the more you take off, obviously the tighter the head is going to become. i was wondering if he had the cc volumes and such, w/.025" off and like .030" off.
 
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