WNYViper
New member
Hey guys, I am looking for some figures. I have been keeping an eye out for an aftermarket head for my Viper for a while and found one on the for sale page in my price range, except it is a 14:1 CR head for 5000+ft elevation, and I am at about 900ft. I am pretty familiar with automotive engines, and realize in order to run pump gas they like to keep the CR down below 12.5:1, is this true for 2-stroke snowmobile engines, too? It is a Speedwerx head so it has o-rings to seal the cylinders, so I was thinking of taking my factory head gasket and using a layer or two to increase the chamber volume enough to bring the CR down to 12.5 or less, which I figure I need atleast .0236" (.6mm), would this work? Or... should I just bite the bullet and buy a set of replacement domes for a 12:1 setup (and throw the money I saved by buying a used head instead of a new one).
Any help is greatly appreciated. I did some searching and couldnt find much so I hope I am not overlooking the obvious and beating the horse to death.
Any help is greatly appreciated. I did some searching and couldnt find much so I hope I am not overlooking the obvious and beating the horse to death.
mopar1rules
Active member
you'll have to either bit the bullet and buy new 12:1 domes from speedwerx, or they could possibly machine your current 14:1 domes to the 12:1 specs for less? don't run the stock viper head gasket, as it won't seal to the speedwerx head and domes. the speedwerx head has grooves machined in it and is designed to run w/o-rings. you will love the head tho when done. it does make a difference.
i think 12:1 will be a bit high for 92 94 octane
mopar1rules
Active member
its not. i've used the head for 1 season w/no trouble what so ever. did a comp test and it said 125psi approx. i know a guy shouldn't get too caught up in comp readings, but the stock head pulled 120psi on my gauge and then w/speedwerx head and the same gauge, it would pull around 125psi. plenty safe for 92 octane.
WNYViper
New member
I talked to my local Yamaha dealer today and they said that i would probably have to bite the bullet too... they said if anything to try shimming the base gasket up to decrease CR but then he said that I didnt hear it from them, lol, so thats a 'no go, you'll blow'... guess i'll be ordering the 12:1 domes and try to sell off the 14:1 domes, hopefully there is a market for just the domes...
I really shouldnt visit my dealer all that much, lol, he also noted that he knows someone who will be selling a complete bender triple pipes kit pretty soon... oh boy... i like hp... lol... and this will be pipes, silencer, jets, clutch kit as a package deal... hmmm... i think i might mod the Viper out and try to find an SX or something for a bomber sled that gets decent mileage... lol
I really shouldnt visit my dealer all that much, lol, he also noted that he knows someone who will be selling a complete bender triple pipes kit pretty soon... oh boy... i like hp... lol... and this will be pipes, silencer, jets, clutch kit as a package deal... hmmm... i think i might mod the Viper out and try to find an SX or something for a bomber sled that gets decent mileage... lol
mopar1rules
Active member
did you contact speedwerx to see if they can machine your 14:1 domes into 12:1 domes?
well sounds a little high but at 125 psi if those cylinder are stock i'm pretty sure your not at 12:1
WNYViper
New member
Guess that answers that question. hmm... where was that site that I saw the replacement domes at... lol...
mopar1rules
Active member
i work in a machine shop, maybe the cnc lathe operator could bust some out for ya. i have a speedwerx head on my buddies viper, that i could replicate the dome on. that's what i got on the comp gauge....125. speedwerx calls it 12:1 domes i think. so does speedwerx not make the head or replacement o-rings and domes for it anymore?
WNYViper
New member
I just ordered the replacement domes from a store online, I hope they actually have them...
I got another email from the Speedwerx Tech Support...
I am just waiting on an email from the place that I bought the domes from that says that they dont have 3 of em, lol,
that would be my luck...
I greatly appreciate the offer to take them into your work, Mopar1rules, but the amount of time that someone would have to spend measuring the 12:1 domes and figuring how much needs to come off the 14:1 domes, then fixturing them, and cutting them would take a good portion of time. If Speedwerx thinks it would take them 5hrs I couldnt begin to guess what it would take someone who doesnt already know what needs to be done.
I got another email from the Speedwerx Tech Support...
I am just waiting on an email from the place that I bought the domes from that says that they dont have 3 of em, lol,
that would be my luck...I greatly appreciate the offer to take them into your work, Mopar1rules, but the amount of time that someone would have to spend measuring the 12:1 domes and figuring how much needs to come off the 14:1 domes, then fixturing them, and cutting them would take a good portion of time. If Speedwerx thinks it would take them 5hrs I couldnt begin to guess what it would take someone who doesnt already know what needs to be done.
Just simply open up the dome you have and set squish up on the engine, its not a big operation, any machine shop can do this.
measure your domes for the volume(cc's), by simply taking a peice of plexi glass with a small hole drilled in center of it. Take a large cc syringe if you dont have a liquid burrett, and with the dome placed upside down in the table vise via the sparkplug screwed into the hole, place a small smear of grease on dome edge to seal water from coming out, place plexi glass on dome and recored how much liquid it takes to fill dome up to surface of plexi glass. Stock viper has 21cc domes on center and mag and 24 cc dome in the pto cylinder for referance.
$375 to reset up domes, man thats insane price....lol, more like $100 for all 3 is realistic price
measure your domes for the volume(cc's), by simply taking a peice of plexi glass with a small hole drilled in center of it. Take a large cc syringe if you dont have a liquid burrett, and with the dome placed upside down in the table vise via the sparkplug screwed into the hole, place a small smear of grease on dome edge to seal water from coming out, place plexi glass on dome and recored how much liquid it takes to fill dome up to surface of plexi glass. Stock viper has 21cc domes on center and mag and 24 cc dome in the pto cylinder for referance.
$375 to reset up domes, man thats insane price....lol, more like $100 for all 3 is realistic price
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