squish ?????

T

tunme

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i am planning to do a head mod,but you guys keep talking about the "squish"
so could some explain.thanks
 

squish is the area in the combustion chamber were the piston and head virtualy touch, this cause lots of turbulance and make the efffective combustion chamber smaller.

all this causes better combustion.
fine tuning the shape ad size of the squish area determines how much better

if the squish area has too big a gap, its not as effective.
if its too small, the piston will hit the head (not good) conecting rods do acualy strech a miniscule amount.
 
squish notes..

good post srx600guy, the squish band is the area in which most people dont take the time to set up correctly and this is where you will have problems. If your going to do a head mod on a sled, you need to know what the stock squish is set at. This can be done in a easy fashion of simply using a bit of lead solder (.080" or larger)bent into a 90 degree "L", its important to have the solder touch the sides of the bore and you can feel the smooth side when inserted thru the sparkplug hole. You want to check the squish at the left and right side of the cylinder, this prevents the piston from rocking back and forth on the wrist pin and will give you a false reading, just stay on top of the wrist pin and youll be fine. Each engine can be differnt, there is machine work tolerances when engines are built, so the reading you get from 1 will not mean its the same in the others, deck clearance,head relief , piston top will all play a role in the reading. In most Yamaha sled cases, you will want a good .052-.055" to be considered safe pump gas range. The 2000-02 srx usually have .060-.063" stock, the 98-99 srx were a bit wider. So what you want to do is take your stock reading and subtract the safe range from it, this will give you the correct amount to mill off the head. You can mill significantly more then that,**BUT**, you will have to machine the squishband angle and "rechamber the head" to do so, its not something the average guy is going to do, and really isnt neccessary unless its a special built purpose engine, like ice drags, grass,etc. The stock squishabnd is 14 degrees, and by changing to a steeper angle like 17-19degrees, you can run more compression with out having detonation, the reason is this, the stock angle is very flat and by milling the head , it sits even closer to the piston at TDC then before, the mixture becomes trapped in the squishband at TDC, when the plug fires, it will only burn the mixture in the center, and the trapped mixture out in the band becomes stagnent and builds heat, it then fires from heat(like a diesel), this is the detonation, and it makes little indents in the edges of the piston, like a small pick hammer pounding on it. By changing the angle to a steeper one, it helps to force the mixture to the center of the haed and promote better flame travel on the top of the piston crown. This enables you to run higher compression without the risk of detonation, but again, this is not just a quick easy flat mill of the head, and not really much gain for the "trail sled", was just tryin to give you a idea of why and where.
 
Is the angle measured from the chamber mounting surface, or the piston mating surface?

Who can I send my chamber inserts to to cut them? I'm sure I could have my buddy do them at the machine shop he works at, but if that's not possible I'd like to have someone who knows what they are doing cut them.

I wonder if I could use my 20 cc chambers and recut them for the larger squish and still get away with it?
 
"could I run the 20cc inserts if machined"?? Ya probally could yamablu, but I would cut them to 17 at the start then taper to 19 finish. This will take a tad of the compression away from the 20cc inserts, and be a good thing in your case. Squishband is the semi flat part inside the bore of the cylinder, its easy to see with a head upside down.
 
Yeah I know where the squish band in the chamber is, my question on the squish band pertains to the 0 degree referrence. Do I want 17 degrees from the flat mounting surface of the chamber, or a 17 degree difference from the angle of the piston to the squish band. I'm thinking it's from the mounting surface, but I could be wrong.
 
thanks guys,mrviper700 great details thanks so for my normal trail riding and
occasional friendly drags a set of "megapower" heads (22cc)from maxxperformance would be a good upgrade.
 
I don't no where you will find 22cc chambers on megapowers cause their not out their, either 23.7 or 19cc is all that maxx perf makes. And my megapowers were no where close in compression to what Gary[maxx perf] said they should be, so if you buy megapowers good luck. With machining they are great but you need someone to do that, and it all costs more when it shouldn't[I think more chambers should be available].
 
MrViper, what kind of squish are you running with the 17* squish angle? I don't know how to calculate that. to be honest the squish angles are still abit advanced for me, I'm just using them to calculate the time for the flamefront to reach the cylinder wall.
 
its all in the set up

Depends junior, if you have decent gas available, I set them up all the time at .045-.050" trail engines, now on race engines, I have gone down to .018"-.030" before. just depends on what your gonna do with it and how long your gonna run it wfo! You wont want a super tight one for 1/4 mile asphalt, 2000 ft speed runs, its like a engine brake at a long distance, but ,they sure do rip in 500ft grass.

*****these specs are with rechambered heads, re cutting the squishband angles**************If your just flat cutting the heads or taking out headgasket layers, stay at .052-.055" squish for pump gas*************
 
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mrviper or any one else that would like to comment.
In your earlier response you indicated a .052-.055 in. squish band would be safe for most Yamaha sleds. Based on information from this site I recently removed 2 of 3 head gaskets from my 02 Viper resulting in .043-.045 squish band. Do I need to be concerned about detonation using 93 octane?

Additionally, does anyone have any dyno numbers with respect to head gasket mods? I would guess maybe a couple of HP and improved (quicker) response.
 
nyviper, if your squish is measured properly at .043 then you are plenty tight. Is it a stock head or not and what mods, but I wouldn't want to run that low, .050 minimum if your a trail rider.
 
nyviper

right, .052"-.055" squish for trail engines using a flat head cut method, the only way you should deviate from this is by changing the squish angle, and its not really something you be gaining alot for a trail engine. I would install 1 more layer back in the viper, it already has more compression in 2 of the cylinders then a srx, stay as close to .052-.055" as possible for trail ,and if your a tad over so be it, its the safe side to be on.
 
mr. viper and GS30 thanks for the response.
My engine is a stock 02 with the exception of the head gasket mod.
In regards to the accuracy of measurement, I did it almost identically as mrviper described above. In fact, I did it twice and generated the same numbers both times.

Has anyone else out there actually measured viper squish after removing two gaskets and if so are your numbers similar to mine? If they are, and it's agreed that .043-.045 in. is too tight, maybe this information should be posted in the tech section.
 
mrviper700 said:
Depends junior, if you have decent gas available, I set them up all the time at .045-.050" trail engines, now on race engines, I have gone down to .018"-.030" before. just depends on what your gonna do with it and how long your gonna run it wfo! You wont want a super tight one for 1/4 mile asphalt, 2000 ft speed runs, its like a engine brake at a long distance, but ,they sure do rip in 500ft grass.

*****these specs are with rechambered heads, re cutting the squishband angles**************If your just flat cutting the heads or taking out headgasket layers, stay at .052-.055" squish for pump gas*************
Click to expand...

that's awesome, thanks man, I appreciate the info. :rockon:
 
Two layer's pulled on my 02 Viper. Squish is .055" mag and center, .065" PTO.

Pulling one layer .005" will reduce chamber volume by .475 cc's. Pulling 2 layers .015" reduce's chamber volume by 1.42cc's.
As you can see, stock squish specs would be plenty safe for almost any fuel!

mrviper700, do you do head mods? I've been thinking about have PTO chamber sized the same as the center and mag, for mountain riding and drag race use.
 
that seems tight, i believe mine measured .058 on the mag and center and .052 on the pto. this is from my bad memory though. i can check my book.

i ran it this way for a 1 1/2 year on super and sled screamed. would show 115 on all conditions and on great going 122. never a plug or piston untill the god da#$%@$#%@$#%@$#^%@$^@$%@!#$% pipes i put on the thing ,


but im not bitter
 
viper head mod

mtnviper, the head mod on a viper lowers the compression on the other 2 cylinders to match the already lower compression of the pto. Maybe I misunderstood you, but I think you thought it was the other way around??

easiest way I know of to make all 3 high compression is with aftermarket heads or srx heads set up for the viper, then you get into a aftermarket water rail expense too.
 
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