GAS AND COMPRESSION DO'S AND DONT'S
- Thread starter rz350guy
- Start date
the thought is guys are saying they have all this compression race baja wot for miles and run a ton of compression, the thought is lets get some good solid info on air cooled motors and acurate nos. seems like alot of people blow up their blasters, why? well mainly wot down the road in 6th gear and ooops it just quit why?
The reason that people blow up there blasters going down the road wot is mainly because they don't have them properly tuned (jetted, good oil and properly maintained).
Say what you want about high comp and air cooled motors. All I know is that I've got 185 lbs of comp and have been running 110 octane for a year now with no issue's.
Also, the reason that I have my motors built is because I'm sponsored by the engine builder and he's been porting 2 stroke engines for over 20 years and knows what he's doing
Say what you want about high comp and air cooled motors. All I know is that I've got 185 lbs of comp and have been running 110 octane for a year now with no issue's.
Also, the reason that I have my motors built is because I'm sponsored by the engine builder and he's been porting 2 stroke engines for over 20 years and knows what he's doing
actually the reason most people blow up blasters
A. lack of proper assembly and maintenance (improper torque, not cleaning mating surfaces, gauging mating surfaces, pulled studs, airleaks and improper jetting)
B. while we are talking about jetting, very few bikes seize on the main jet.
most bikes seive when you lift. if your main jet i really too lean, your not going to make it 2 miles down the road screaming in 6th gear. what happens is that either the needle, needle jet, slide cutaway or pilot, or a combination are lean. your screaming along, piston crown temp is running 1250 or so. you blip the throttle either comming up to a turn, of trying to be nice to the motor, it suddenly goes lean as you let off, and airflow decreases. the 1250 degree piston spikes to 1400 and the piston melts.
A. lack of proper assembly and maintenance (improper torque, not cleaning mating surfaces, gauging mating surfaces, pulled studs, airleaks and improper jetting)
B. while we are talking about jetting, very few bikes seize on the main jet.
most bikes seive when you lift. if your main jet i really too lean, your not going to make it 2 miles down the road screaming in 6th gear. what happens is that either the needle, needle jet, slide cutaway or pilot, or a combination are lean. your screaming along, piston crown temp is running 1250 or so. you blip the throttle either comming up to a turn, of trying to be nice to the motor, it suddenly goes lean as you let off, and airflow decreases. the 1250 degree piston spikes to 1400 and the piston melts.
I would say jetting is usually the reason, that or an air leak...or just poor maintenance.
More than once, riding in the winter, friends have blown up their 2 strokes....in snow storms, ripping down main roads. We assumed it was jetting, every time.
More than once, riding in the winter, friends have blown up their 2 strokes....in snow storms, ripping down main roads. We assumed it was jetting, every time.
Interesting. I never knew that. Now that you say that....it was never me blowing up the motor, but I think the pistons went when we were slowing down....not while we were wide open doing 50+mph on 30mph roads in full blown snow storms.
So what you're saying is that it's a good thing to have the pilot and needle rich, along with the main jet?? I'm gonna go change my clip position and get a larger pilot!! I run rich enough on the main jet, I know. Not much you can do about the throttle cutaway....right?
why 110 when you have 185 lbs. comp I would think you could definately get by with 100 have you ever tried it and whose 110 is it, dont take this wrong we are gonna end up with a good discussion and after awhile all of us will have a much better understanding about fuel and compression, theres people that have 125 lbs. comp and use race gas.
ok, so i have 145 compression.. how much more can i shave my head to use 93 still if any? if i have it ported wont i lose compression? might be a little off topic..
There is no magic number for shaving the head, but if you want good advice I would ask someone like flotek.
they say .035" from stock.
i've been learning recently that there is definately no fixed compression ratio limit for a certain octane. there are sooo many factors that play into it such as spark timing, air/fuel ratio, how well your engine breathes, etc.
i've been learning recently that there is definately no fixed compression ratio limit for a certain octane. there are sooo many factors that play into it such as spark timing, air/fuel ratio, how well your engine breathes, etc.
Cranking compression, swept/trapped compression ratio, volumetric efficiency, timing advance, msv are all factors in what fuel octane to run. I've seen motors making 185 lbs of compression run all day on 100 octan, and I've also seen motors making 165 lbs of compression back out plugs with anything less than 110. Like said above, there are many factors to determine what fuel to run.
I have yet to see overheating issues with a properly tuned aircooled engine reguardless of the compression. Note that I said properly tuned.
I have yet to see overheating issues with a properly tuned aircooled engine reguardless of the compression. Note that I said properly tuned.
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I maybe off but I read a page with diagram of 2 strokes tuning, the guy was saying that 2 strokes comp. will vary on rpm because of scavanging efficancy. so if you got say 10:1 on idle you could go up to 18:1 when you hit the powerband on the motor, because of the efficancy the motor reaches can be over 100%. idk if that makes any sense to any of you, but it did to me.
thats why people are always looking for a better pipe. and why the top level pro's back in the 2stroke supercross days may hve had a pipe that said brand X but that definitly want the pipe brand X sold to the public. a REALLY good engine build can take the extra time to design the porting and using the same trusty slide rule, design the pipe
i believe blasters are blown up in the snow alot is because colder air is more dense, the best air you can get lays on top of snow, meaning its very dense and when you dont re-jet for all the cold air then it leans out the bike, thus getting hot and frying the rings/piston. and also the piston and cylender are made of diffrent metals so they expand and contract at diffrent temperatures, so when it gets hot because of lean conditions the piston may expand first, thus scoring /scraping cylinder walls ... just my thaughts on that i could be wrong
plugs back out because of to tight of squish? or to much comp. damn Trinity makes plug hold downs.
which is derived from? to tight of squish or comp. but usually cut heads with no concept of clearances
I agree, or heat. Detonation due to compression can be solved by increasing fuel octane, detonation due to heat can usually be solved by proper jetting, detonation due to tight squish clearance would require a thicker base or head gasket or proper machining of the head.
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