splpete Posted June 18, 2004 Report Share Posted June 18, 2004 Ok ya'll I am almost done with the Shee mods and I am at the moment waiting on my A-Arms till I finish the suspension off but heres some Q's I installed a Noss head with 20cc domes, my compression jumped to 150. After that I put on my new stator and went +4. I have not checked comp. lately but my question is, might I have to run a higer octane fuel than 93? I have read that if your not over 160 then high octane is a waste but also that with an advance in timing I am fearing detonation. Is there a "rule of thumb" as far as this topic goes or is it all individual? I am really curious cause with all the time, effort and cash I pumped into my Shee I dont wanna fudge something up. Scott Quote Link to comment Share on other sites More sharing options...
Meat Posted June 19, 2004 Report Share Posted June 19, 2004 Scott good question. Do you have any porting work done ? 160psi is the "rule of thumb" for stock ported banshee's like you said, but the true way to determine your "race or pump" gas question is to calculate your compression ratio and try to factor in the variables like ignition timing and even what brand of pipes your running. I beleive that pipes that allow higher revs like CPI pipes for example would increase your chances of detonation. And your correct to be concerned with your +4 timing effecting what gas octane you can use. Let me just say that every engine reacts differently to engine mods..... with that said.... my Banshee currently runs at 165psi(20cc domes) Vito's powerpistons(raised domes) and +4 igniton timing. Last year my Banshee ran 24 cc domes and had 130psi, same PowerPistons and only +2 advance. I ran Sunoco Ultra 94 last year without any detonation so this year when I bumped my compression to 165 and went to +4 timing I had the same concerns as your having right now. I was ready to bite the bullet and shell out the big bucks for race or AV gas, but I decided to try the Ultra 94 before I switched to hi comp\dollar race gas. Im glad I tried the 94 pump gas because its running fine and I haven't experienced ANY detonation at 165psi\+4. My engine was over 3 years old at this point and I decided to try the 94 octane because..... If I experienced any damaging detonation, I wouldnt be too upset because my top end is getting old and tired anyways. I am glad to be able to keep running 94 octane. If your using an adjustable timing plate you could set it back a few degrees to "feel the water" so to speak. I had a respected builder tell me that +2 puts out nearly as much hp as +4 does, without as much heat buildup\detonation threat. I ran +2 timing for the past 3 years. Remember what I said about every engine reacts a little differntly to mods... so take my "compression\timing\pumpgas" example with a grain of salt. Keep her jetted on the fat side if you decide to try your 93 octane with your mods, richer jetting would help it run cooler and lessen the chance of detonation. Dial in your jetting later, testing for detionation. And if you here it pinging.... it should only detonate at high rpms, so get off the gas right away and let the rpms fall, then keep the engine cool by cruisin' around off the main jet. Keep that gas flowin' to your jugs because it cools the internals. Keep airflowing over the radiator to, just dont putt putt around. Once you have stopped the detonation(hopefully soon enough before any piston damage occurs) turn off the engine and fill er up with some VP race gas. hope i made some sense.... good luck with it Quote Link to comment Share on other sites More sharing options...
J..J. Posted June 19, 2004 Report Share Posted June 19, 2004 Smokin reply there Meat! I had a respected builder tell me that +2 puts out nearly as much hp as +4 does, without as much heat buildup\detonation threat. I ran +2 timing for the past 3 years. That sounds interesting, maybe I should back mine off a bit... splpete, apologies for hitting on your post without offering any advice. Quote Link to comment Share on other sites More sharing options...
sredish Posted June 19, 2004 Report Share Posted June 19, 2004 (edited) It's not gonna hurt anything to run some 50/50 wth 93 octane. I probably would with 160 and +4. Technically, you should hear it "pinging" or pre-detonating a little, but sometimes it takes a trained ear. Edited June 19, 2004 by sredish Quote Link to comment Share on other sites More sharing options...
geaux 4 it Posted June 19, 2004 Report Share Posted June 19, 2004 What is the percent of the oxygenation on the sunoco 94?We run 165-170 compression with 8 degrees of timing on pump 93,and had no proplems with detonation.The bikes been running for 2-3 years on it. Quote Link to comment Share on other sites More sharing options...
geaux 4 it Posted June 19, 2004 Report Share Posted June 19, 2004 A 2 stroke doesn't sound like a 4 stroke when they detonates it sounds like a chain skippping on a sprocket.It's a little faster detonating than a 4 stroke.That's what I notice in the past when I seen them do it. Quote Link to comment Share on other sites More sharing options...
splpete Posted June 20, 2004 Author Report Share Posted June 20, 2004 Thanks for the info Meat It looks like I am just gonna take it easy and get down to some testing, thats the only way for me to find out what Shee wants, needs. Thanks again. Scott Quote Link to comment Share on other sites More sharing options...
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