Guys just had a question that as to deal with cutting heads and or raising cyl's with a base gasket that I am generally applying to all sleds. Im not planning anything for my SRX but would like to know some information.
What is the minimum squish amount for pump gas? I know there may be lots of different variables but I am wondering how this works.
What is the minimum squish amount for pump gas? I know there may be lots of different variables but I am wondering how this works.
mopar1rules
Active member
i think the msv (maximum squish velocity) has to play in it as well. if i remember right, mid 20's is for 92 pump gas and anything from like mid 30's is for race gas. msv readings from 28-32 would be for like a 50/50 mix of pump gas to race gas. i probably say around .050"-.065" is for pump gas. my banshee (i know its not a sled...but for example) runs on safely on 93 pump gas, with a squish of .050". i could go down to .045", but i'm going to leave it at .050" for a while. a guy can play with the angle of the squish band vs the tangent angle of the piston crown to the pistons crowns edge, to also get a different msv reading.
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does the srx stock suppose to run 93 octange? how is the best way to do the squish test? i was sold to take a piece of solder in the spark hole and tuen the piston to tdc and then pull it out and measure the thickness.
montynormand
Member
05vmax said:
Yes this is correct - BUT you need to measure close to the cylinder wall and not near the center of the head dome
mopar1rules
Active member
montynormand said:
not to mention, don't stick it in too far, where the solder sticks into on of the transfer ports and then when you cycle the piston over, it cuts the solder off and it falls down into the crankcase.
i pulled this stupid manuver on my banshee when i was checking the squish, 2 weeks ago. i ended up having to tear the top end back off to get the piece of solder out. 
it ended up in a oiling hole, that feeds one of the crank bearings. good thing i got it out.
mopar1rules said:not to mention, don't stick it in too far, where the solder sticks into on of the transfer ports and then when you cycle the piston over, it cuts the solder off and it falls down into the crankcase.
Thank you. I posted this in the SRX section cause but I guess it ok because it involves work already done to my SRX and Im glad you brough up the solder method.
I had mrviper port the motor on my SRX and when I measured the squish on a SRX motor he did for me about 4 years ago I remember recording what that measurement was with the solder. However, I DO NOT remember what the stock squish was and I know the heads were cut .011 to .012 to give it more compression and would be safe on pump gas for the minumum amount of squish while on pump gas.
What Im thinking about doing when I pick up my 440 exciter this winter is, adding a base gasket, measure the thickness of the base gasket and mill the heads that much PLUS whatever minimum squish I can take the heads down to to run pump gas. I might be missing a step or 2.
So what I want to do is see if I can add a base gasket and cut the heads the thickness of the base gasket plus whatever I can get off the squish for pump gas. What is the magic squish #
mopar1rules
Active member
for some reason, i keep thinking that the stock squish values are like in the .080" range.
Too many variables
Tom, you are banging your head against a wall. There are too many variables affecting compression to simply answer the question. Squish and compression can vary quite a bit depending on port timing, squish angle, head design etc etc. These things all affect what type of fuel you should be running. You could probably run pump gas with less than .050 of squish with a 13 degree head angle but if you still have the stock 11 degree head angle and less than .050 of squish you might have problems. This all, of course assumes that when you run "pump gas" you actually know what you are getting. Did you read the article "Hosed at the pump" that was on the Dynotech Reasearch website? Scarry!
Mopar..... .080 of squish? LOL!
Madmatt
Tom, you are banging your head against a wall. There are too many variables affecting compression to simply answer the question. Squish and compression can vary quite a bit depending on port timing, squish angle, head design etc etc. These things all affect what type of fuel you should be running. You could probably run pump gas with less than .050 of squish with a 13 degree head angle but if you still have the stock 11 degree head angle and less than .050 of squish you might have problems. This all, of course assumes that when you run "pump gas" you actually know what you are getting. Did you read the article "Hosed at the pump" that was on the Dynotech Reasearch website? Scarry!
Mopar..... .080 of squish? LOL!
Madmatt
Matt, Thanks for the reply. Yes, I am banging my head against the wall because I dont fully understand the different variables. ports, stroke ETC. Were you referring to my SRX when you mentioned the angle of degree? Mrviper ported my motor and cut the heads on the SRX so Im assuming its 13 degrees now? Not really concerned what it is. I just wanted to know if there there was a general rule-of-thumb to cut the heads when you add an additional base gasket or just cutting heads in general.
mopar1rules
Active member
Mopar..... .080 of squish? LOL!
Madmatt[/QUOTE]
that's just a number that kept coming to mind. i might be thinking of something else then. what is the stock squish for his '02 srx. i know the '98 and '99 srx's had larger cc domes....correct? so the stock squish for a '00-'02 srx is what....070 or what?
Madmatt[/QUOTE]
that's just a number that kept coming to mind. i might be thinking of something else then. what is the stock squish for his '02 srx. i know the '98 and '99 srx's had larger cc domes....correct? so the stock squish for a '00-'02 srx is what....070 or what?
I think the 00-02 is 6 cc's tighter
I may just try and experiment with that old 440 thing. We'll see I am going to measure the stock squish first though.
I may just try and experiment with that old 440 thing. We'll see I am going to measure the stock squish first though.
mopar1rules
Active member
madmatt, that's where the .080" came from....my banshee. its got a .080" squish...that's what i was thinking of. aren't the srx's like .065" stock?
tomseal, i THINK the '98-'99 srx heads are 26cc and the '00-'02 heads are 24cc. not 100% sure, but pretty sure.
tomseal, i THINK the '98-'99 srx heads are 26cc and the '00-'02 heads are 24cc. not 100% sure, but pretty sure.
Hummmm
Tom....I don't know what Don did to your heads....ask him.
Mopar.....that sees like an awful lot of squish on your banshee. I don't know what an SRX was stock.
Madmatt
Tom....I don't know what Don did to your heads....ask him.
Mopar.....that sees like an awful lot of squish on your banshee. I don't know what an SRX was stock.
Madmatt
mopar1rules
Active member
Madmatt said:
yeah, its .080" stock. i just got done cutting .030" off and now i'm at .050" squish. i think i going to take another .005" off to get me @ .045". then i should be ok
i guess yamaha built in a lot of room for people to play w/the head.....seeing as it has .080" squish in stock form.
.080 is what my 98' srx is right now, so i guess the heads must be stock. good to know.
when you took .030 off your head what were you intending to do? Did you also add a base gasket? I belive Don took between .011 and 012 flat cut on the heads. I guess I will start by checking the stock squish in that old 440 and go from there. The question is, by adding that base gasket and changing the port timing be beneficial or not. I dont quite know why the 98-99 SRX's could be done with this cheap and simple mod and maybe not so much on the 00-02
I am pretty sure the 00-02 SRX heads are 6cc's tighter than 98-99
I am pretty sure the 00-02 SRX heads are 6cc's tighter than 98-99
mopar1rules
Active member
05vmax said:
see madmatt......080" wasn't out of the question...LOL
mopar1rules
Active member
tomseal6 said:
tomseal, are you asking me about the .030" head cut? the .030" head cut was done on my banshee (atv). are you also talking about adding a base gasket to your '02 srx or the old 440? i'm pretty sure adding the base gasket should help the motor make more "peak" power. the power band should get a little narrower, but the motor will pull more ponies up on top.
mopar1rules said:
The 440. I already had mrviper trailport my srx motor so I am leaving it alone. i was planning on doing a rebuild on the 440 so now I just need to find out how much I can cut the heads After I add the base gasket.
Im pretty happy with my SRX. Only 1 small issue to work out and its that darn DCS light coming at wide open even with some really FAT jets. Im 99.9% for certain that I have a fix for it though.
Base gasket
Tom....the extra base gasket raises the port timing. It's also known as a "poor mans port job". The reason why it works on the 98 and 99 and not the later SRX's is because the port timing is already higher from the factory on the later models (00 and up). It should be safe to assume that if you are adding a base gasket you would be able to cut at least that much off the head just to get the squish back to where it was before you added the gasket. Makes sense, right? Add it to the bottom & take it off the top. Maybe you can even take a little more off......but you should ask Don what to shoot for.....I am definately not an engine builder.
Madmatt
Tom....the extra base gasket raises the port timing. It's also known as a "poor mans port job". The reason why it works on the 98 and 99 and not the later SRX's is because the port timing is already higher from the factory on the later models (00 and up). It should be safe to assume that if you are adding a base gasket you would be able to cut at least that much off the head just to get the squish back to where it was before you added the gasket. Makes sense, right? Add it to the bottom & take it off the top. Maybe you can even take a little more off......but you should ask Don what to shoot for.....I am definately not an engine builder.
Madmatt