Sleepnfast
New member
Hey guys . Putting together a trail ported "02 700 SRX . The aplication will be primarily aggressive trail . Just wondering what guys are using for a final compression . Using premium pump gas (92 mostly around here ) Also are the numbers guys throw out for compression measured numbers (CC the heads ) Or just assuming Yamaha's advertised chamber volumes are accurate .? Maybe sleds are built with better quality control than cars but I know its not rare for a set of automotive heads to vary by more than 10% in chamber volume from one set to another . Which makes 10:1 on car "A" quite a bit different than 10:1 on car "B" .
Thanks guys
Thanks guys
YAMMIEGOD3:16
Active member
i just did my 02. i used my stock motor / heads as baseline. first squish, than compression, than cc. now you have everything apart so you can,t do that so start by getting heads cc before you do anything else. 3:16 (yammie tony)
Sleepnfast
New member
I have all my #'s from stock now , so that parts no problem Tony . And the equip to cc the heads etc etc ..So I if my stock configuration had no det problems ,what would ypu say I could safely ( or on the fast side of safely ) add ? .2 ?? .4??
YAMMIEGOD3:16
Active member
years past, what i saw was 160 or under psi/ compression was premium gas safe. roughly high 40,s squish. so if ya had 130 psi stock and healthy, a flat cut roughly .18 would raise compression to around 150. that really seems to be the magic number here. for me anyways. again and other will post everything has to be checked. 3:16 (yammie tony)
jabber800
New member
Sleepnfast. If you are in Ontario, pump premium is 91 octane. You can get away with a compression ratio in the mid 12/1 range. High 12's will put you in a very scary range with fuel quality differences at the pumps.
Determining the final compression involves knowing the porting specs. Compression ratio is more important for your needs anyways.
Pm me and we can go over your numbers.
Determining the final compression involves knowing the porting specs. Compression ratio is more important for your needs anyways.
Pm me and we can go over your numbers.
I think you mean 91 octane in canada, thats your guys premium........
adding compression is "ok" to do as long as you understand what your doing, the amount of cranking compression is a mere 1 factor to the 4 part equation, your squish angle and your MSV is more important! I can have 165lbs of compression and be just fine with 93 octane fuel, it all depends on the angles in the head and your MSV! Could I get away with 91 octane fuel and DCS....NO....
2 points in octane doesnt sound like alot but its a pretty far distance between 91 and 93 octane. Alot of 02 srx owners have complaints with the dcs on stock sleds, and the most simplistic answer and fix is add more octane, so if you have the light coming on when its stock adding more compression will make the light come on even sooner!
In a 02 srx with DCS your not going to be able to do very much with only 91 octane fuel unless you disable the dcs. In a trail port application,it depends on how the cylinder is modified, it should have the exh port widened not raised so it wont lower the compression as fast/drasticly as raising it, so you need less head work on a typical trail port job,especially on a 02 srx with dcs.
If your just flat cutting the heads and not redoing the squishband and anglesand also the radius on the edges your just gonna make more heat at a faster rate so youll end up with detonation quicker.
The 2000-02 srx are set up with less head volume and a tighter squish clearance then the 98-99 are so if your running the 8dn10 heads youd need to first check the volume of them and then check the volume of your heads on the cylinders with pistons at TDC, see what you have there. Sometimes your better off milling the cylinder bases then cutting the heads, it all comes down to your port job and how it was done, typically the cylinders have anywhere from .010-.012" deck clearance!
yamaha uses a corrected compression figure, thats differnt then your example of a 10:1 car as a typical 2 stroke is more then that, you can run 12.6-12.8:1 on pumpgas no problem but again this all comes down to the set up of the heads and the way the exh. port is done on the port job.
My examples on "pumpgas" is with 93 octane so with less octane your gonna have to be more conservative....quite a bit more. Also the quality of the gas isnt what it used to be, so with adding compression, play it safe and stay very close to stock with that or your going to get a visit from mr. squeeky I can assure you.
adding compression is "ok" to do as long as you understand what your doing, the amount of cranking compression is a mere 1 factor to the 4 part equation, your squish angle and your MSV is more important! I can have 165lbs of compression and be just fine with 93 octane fuel, it all depends on the angles in the head and your MSV! Could I get away with 91 octane fuel and DCS....NO....
2 points in octane doesnt sound like alot but its a pretty far distance between 91 and 93 octane. Alot of 02 srx owners have complaints with the dcs on stock sleds, and the most simplistic answer and fix is add more octane, so if you have the light coming on when its stock adding more compression will make the light come on even sooner!
In a 02 srx with DCS your not going to be able to do very much with only 91 octane fuel unless you disable the dcs. In a trail port application,it depends on how the cylinder is modified, it should have the exh port widened not raised so it wont lower the compression as fast/drasticly as raising it, so you need less head work on a typical trail port job,especially on a 02 srx with dcs.
If your just flat cutting the heads and not redoing the squishband and anglesand also the radius on the edges your just gonna make more heat at a faster rate so youll end up with detonation quicker.
The 2000-02 srx are set up with less head volume and a tighter squish clearance then the 98-99 are so if your running the 8dn10 heads youd need to first check the volume of them and then check the volume of your heads on the cylinders with pistons at TDC, see what you have there. Sometimes your better off milling the cylinder bases then cutting the heads, it all comes down to your port job and how it was done, typically the cylinders have anywhere from .010-.012" deck clearance!
yamaha uses a corrected compression figure, thats differnt then your example of a 10:1 car as a typical 2 stroke is more then that, you can run 12.6-12.8:1 on pumpgas no problem but again this all comes down to the set up of the heads and the way the exh. port is done on the port job.
My examples on "pumpgas" is with 93 octane so with less octane your gonna have to be more conservative....quite a bit more. Also the quality of the gas isnt what it used to be, so with adding compression, play it safe and stay very close to stock with that or your going to get a visit from mr. squeeky I can assure you.
Sleepnfast
New member
Ya soory guys 91 ,
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Sleepnfast
New member
I live very close to Mich border so 93 is close by . The only time my det light comes on is when I get caught short on fuel and am forced to buy low test as thats all that is available . Thanks again those were the types of ansers I was looking for . I have lots of experience with automotive go fast tricks but am fairly new to the two stroke stuff . So far the only thing the two have in common is suck ,squeeze ,bang ,blow .
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