Pre ignition in saws...

[Sparkysparks9]

Good mornin all... Have a quick question...

I used to mess with 2 stroke atv's regularly years ago...generally the banshee. I have seen guys on here with saws pushing +\- 220 psi. I was just thinking about pre-ignition. If I remember correctly, if the atv's were running much over 180 psi on pump gas, they could start to have problems with pre-ignition, burning holes in the Pistons. Mine was running around 185 psi, so I always at least did half av gas, and half premium.

I can't say that I have ever seen a saw with the same problems...anyone have any reasoning behind this?

 

[Marshy]

Subbed

 

[Marshy]

Maybe the octane your all using is enough. Mix up some low grade and see what happens.

 

[Nitroman]

The Banshee and most ATV 2-stroke had expansion chambers which would increase the dynamic compression considerably when running. Saws only have a muffler so there would be no supercharging as with expansion chamber.

 

[BGE541]

I use 87 as is

No oil?

 

[Sparkysparks9]

The Banshee and most ATV 2-stroke had expansion chambers which would increase the dynamic compression considerably when running. Saws only have a muffler so there would be no supercharging as with expansion chamber.

Never run one of the piped saws...what fuel do most of them run?

 

[jmssaws]

93 is what I use but I've run 87 with no issues and that's with saws over 235lb compression with a huge timing advance.

On 87 after a good hard cut my 066 likes to keep running after you shut it off but it's not detonating.

I've cn one saw out of a gillion I've had a part that was detonating and it was a bone stock ms 460, it had a few hundred little holes in the top of the piston.

 

[spencerpaving]

Short stroke and dwell is why....last year I had a pipe on my 084 with a 36"bar and made multiple cuts in a big oak and never had a problem with pre ign or det.

 

[jmssaws]

Bore size and plug location all play a role as well, av fuel robs power and is a waiste of money, It will noticeably take the snap out of a saw

 

[Blokhead]

Bore size and plug location all play a role as well, av fuel robs power and is a waiste of money, It will noticeably take the snap out of a saw

The engine in this bike dynoed 162hp at only 8300 rpm, and runs on 100% 100ll avgas. 100 is the octane, and LL is low lead. Its a twin cylinder 700cc stock bore, and stroke Polaris snowmobile motor. True 14:1 compression
It doesn't get any better than aviation fuel for quality, and consistency, plus it has no ethanol. The only reason it might run slightly less snappy is becasue the octane rating is higher than what's needed in a saw. Aviation fuel is rated differently that auto gas, but the general consensus is 100ll is about 105 octane.


Oh, I built the motor, and the pipes

 

[jmssaws]

Well said, a small bore saw looses power with 105 octane, I notice a loss in power with anything higher than 93.
Av is good fuel but completely unnecessary.

 

[spencerpaving]

Very nice

The engine in this bike dynoed 162hp at only 8300 rpm, and runs on 100% 100ll avgas. 100 is the octane, and LL is low lead. Its a twin cylinder 700cc stock bore, and stroke Polaris snowmobile motor. True 14:1 compression
It doesn't get any better than aviation fuel for quality, and consistency, plus it has no ethanol. The only reason it might run slightly less snappy is becasue the octane rating is higher than what's needed in a saw. Aviation fuel is rated differently that auto gas, but the general consensus is 100ll is about 105 octane.


Oh, I built the motor, and the pipes

Very nice! My race sled has a 1200 crankshaft motor on spray....every pass the spark plugs would come loose from deto and that was running vp import

 

[Cj genever]

162hp on dyno or was that the rating on the engine stock? You calculate the pipes on paper or with software? I calculated pipes for my v65, but never got to the build. Took an evening to do all the math on paper!

Nice build. Must be scary as hell in that chassis though!

 

[jmssaws]

I built a cr125 once on alcohol that made 85hp on the dyno, blipped the throttle in neutral while on the dyno and exploded the transmission, and I mean exploded!

 

[Blokhead]

Very nice

Very nice! My race sled has a 1200 crankshaft motor on spray....every pass the spark plugs would come loose from deto and that was running vp import

Thanks, I was always worried about detonation so that's why I dialed it in on the dyno. The operator used a simple piece of copper tubing attached on one end to his headphones (kinda like a stethoscope), and the other end is soldered into a lug that was bolted to the head. He listens for "clicks" while its running. 3-4 clicks in a row, and he shuts it down.

 

[spencerpaving]

Thanks, I was always worried about detonation so that's why I dialed it in on the dyno. The operator used a simple piece of copper tubing attached on one end to his headphones (kinda like a stethoscope), and the other end is soldered into a lug that was bolted to the head. He listens for "clicks" while its running. 3-4 clicks in a row, and he shuts it down.

Dynotech??? Jim czekala is the man!!

 

[Sparkysparks9]

My banshee was pushing 93 rwhp...it was a blast, but became a handful to ride consistently in the sand.

This photo was pretty outdated...but it's one of the last photos I can find...spent much more time riding, than snapping photos!! Lol


I always thought it was funny....other riders thought the AV or race gas gave them more power. Always asked how many psi they were running...most of the time they looked at me like I was speaking a different language. Others that knew and were below 180...I would always tell them they were burning up their pocket book for no reason. Do love the smell of race has in the morning, though

 

[Blokhead]

162hp on dyno or was that the rating on the engine stock? You calculate the pipes on paper or with software? I calculated pipes for my v65, but never got to the build. Took an evening to do all the math on paper!

Nice build. Must be scary as hell in that chassis though!

Thanks, Took it to Dynotech research in Batavia NY. Arguably the number 1 snowmobile dyno in the country.
I used TSR software (no longer sold), plus Mota. Its helps to be a sheet metal worker when laying out the cones.

I made everything on the bike, and yes that modified stock frame really does not inspire me with confidence. The pipes are kinda heavy, and stick way out to the side, so the bike is not perfectly balanced. I have to slide my ass to the left on the seat, or it will pull hard right when its up on the wheely bar.

 

[Blokhead]

Dynotech??? Jim czekala is the man!!

Yep, DynoTech Jim know his ****!!!!

 

[Blokhead]

My banshee was pushing 93 rwhp...it was a blast, but became a handful to ride consistently in the sand. View attachment 467772

This photo was pretty outdated...but it's one of the last photos I can find...spent much more time riding, than snapping photos!! Lol


I always thought it was funny....other riders thought the AV or race gas gave them more power. Always asked how many psi they were running...most of the time they looked at me like I was speaking a different language. Others that knew and were below 180...I would always tell them they were burning up their pocket book for no reason. Do love the smell of race has in the morning, though

Nice! My brother had a banshee. I had an RZ350 on spray! Always ran that on pump gas though. Wiseco's always had light 4 corner seizure marks.