Discussion in 'Yamaha' started by DLStryker, Apr 16, 2017.
My new to me Banshee has 175psi kicking pressure. What octane do I need for this?
You might get by with 93, but listen closely for pinging, and check the plugs for signs of aluminum specs after a hard run, maybe a few times after too.
If either is present you should get by with a 50/50 mix of 93 and race fuel.
165psi has been known to get by with 93.
185+ is pushing full race fuel
Your 175 is kinda in that grey area
who built the motor? Cool head?
You need to measure compression ratio, not just cranking/kicking compression. You get cranking comp from a PSI gauge. You get compression ratio by measuring parts/clearance/tolerance in the motor. Cylinder volume and trapped head volume are others numbers you'll need.
If it was my bike, grab a cool head and throw on 18-19* domes.
Have a read here. http://www.2strokeheads.com/tech2.htm
Kicking pressure has more to do with octane requirement than calculated compression ratio.
You can run regular fuel in a 12:1 motor if you raise the exhaust port enough to get 140psi compression.
Even compression is not a totally reliable guide to octane need.
A well designed chamber can run much higher pressure without detonation than the stock Blaster chamber.
I was always told different. Compression readings can be flukey. Numbers don't lie. Figure out the dementions and see what they come out to.
But that's what forums are for. Good point.
The motor was built by Dune Trash Racing out of Wichita, KS. It has a Pro Design cool head.
What size CC domes are on it?
21 and 22 CC domes are the biggest you can get away with on pump gas.
You'll be around 19, a mix of 50/50 race/gas
Dune trash has always put out awesome motors. Kip (I think was his name) was the man at one point and time. Only problem, that was 10+ years ago. How's it run?
Don't know the CCs. Don't have time to take off the head right now. I have 8 units! Replacing my third chain getting ready for summer this weekend.
I have a two things to my advantage. I have VP fuel just 10 minutes up the highway from me. I can buy 1 gallon or a 55 gallon drum. Plus I have a great paying job. VP fuel C12, 108 octane, $11.50 a gallon... $100 a weekend... doesn't slow me down one bit. It wasn't always that way! But, I am financially comfortable today.
You are so right at "Kip"!! He helped me with a "light switch" big bore YZ125 I had a few years ago. Powerband was in the 10K+ region and violent!! He didn't build it. Not really even ridable for MX. We would take it in an open field and rip it! When it hit the pipe, it was crazy! Fun stuff!
I say "new to me". Kip, if I understand correctly, went to the aircraft industry. In Wichita, it is possible for an hourly, skilled laborer, to pull $85K a year.... overtime etc. Pocket change for me, but very enticing for some. I bought the bike.. maybe 7 years ago.. cannot remember. We ripped it one day and it has been in storage since. I met a tall, blonde, bi-sexual and 5 years of my life... well.. didn't include riding. And yes, I have pics. I have just in the last few weeks brought this unit out of the mothballs!!
Wow, tall blonde bi-sexual. Not my tastes, but so happy for you!
BTW, took off the stator cover. Stator plate is clocked forward. Original plate... dremeled so as to rotate froward. Guessing straight VP C12 is the best idea for fuel??
I'd say so. Make sure timing is +4 and have 19cc domes on.
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