What octane to run??

[snakeman52646]

Ok I have a 98 Banshee:
milled head
bored .80 over
alien dmc exhaust
adjustable timing plate ( at +4 right now)
compression test at 200 psi each jug
reed spacers
Ok theiris a place I can get race fuel at they have 112 octane and 119 octane. Which would be the best to run to my set up? Also should I leave the timing where it is when i run the race fuel?
Thanks in advance.
Billie

[GPracer2500]

Are those ratings MON, RON, or R+M/2? There's more than one kind of octane rating. Specifically, which two fuels are we talking about here? Find out exactly what the fuels are. When matching a fuel to an engine there's more to consider than just octane rating.

For 200psi cranking it's a safe bet you'll be just fine with MON 112--even with +4 ignition advance (although I couldn't say how much advance is optimal for performance). However, there are so many variables that go into determining an engines required octane rating and so many different specific fuel blends that testing is really the only way to be absolutely sure a fuel is compatable with a particular engine. In other words, make your best estimation about your engine's octane requirement, pick a fuel, and go find conditions that favor detonation. Test and look for signs of deto. If you can't find any then you know that fuel is at or beyond the engines required octane rating for those test conditions.

If testing for deto is impractical or beyond your skill-set, then all you can really do is pick a fuel that you're pretty darn sure is going to be safe in your build. 200psi isn't all that extreme for a Banshee so it shouldn't be hard to settle on something that's sure to be safe.

[snakeman52646]

I will have to check on the ratings. Thanks for replying so quick. I tell you I have been doing searchs on the net a good part of the day and man my head is a spinning. I guess I am just scared and do not want to mess my motor up by running to less or to much of a octane. I am prob just trying to read to much into it and getting confused.LOL. Anyways thanks again for the quick response.
billie

[rooster300ex]

I'm running an 11:1 wiseco piston with 89-93 octane and have no detonation. At first I thought I needed to run 110, but acutally made it run worse. I know what ya mean about being scared that you might destroy your motor over simple octane choice. I would try that 112 octane that your have available, and like GPracer2500 said you have to put your engine in situations where detonation can occur, and determine if you need a higher octane rating.

[snakeman52646]

ok got the 112 octane running it with klotz. still pinging:confused:
Ran it for about 10 to 15 min. Sounds like a bb pinging around in my pipes. not real bad but noticable. Should I run it longer span to see if it persists? it seems to be running ok. Could it be my timing still? It's still at +4.
thanks,
Billie

[GPracer2500]

Get rid of the +4 and see what happens. Jetting matters too. If you're borderline lean then deto is more likely.

You can usually hear deto before it starts to noticably hurt performance but that doesn't make it ok to let the condition persist.

[snakeman52646]

ok thanks appreciate your help. I am going out now to set timing. I let ya know what happens.
thanks again,
Billie

[snakeman52646]

ok took the timing back to 0. still pings out of the right side pipe. Both plugs look about the same. A tannish color.:confused:
Billie

[snakeman52646]

does not seem to be running hot either. I have a temp gun and ridding pretty hard for awhile it reads around 150.
billie

[GPracer2500]

Are you sure what you're hearing is deto?

When do you hear it? What throttle opening? Under load? Not under load? When you hear it can you make it go away by unloading the engine? Did the timing change have any effect?

[snakeman52646]

It sounds like bbs or somthing pinging around in my pipe. Does it at idle. and the timing had no effect. also it's in my right side pipe only.
Billie

[400exrider707]

Originally posted by snakeman52646
It sounds like bbs or somthing pinging around in my pipe. Does it at idle. and the timing had no effect. also it's in my right side pipe only.
Billie

You should really only be hearing the detonation while the engine is under load ie in gear and on the gas. If you hear it at idle its probably not deto. Check to make sure your exhaust is tight and not leaking anywhere.

[snakeman52646]

ok will check it out . here in a few. and let ya know.
appreciate it.
billie

[snakeman52646]

ok the exhaust looked snug and no leaks. It runs great top and bottom end. does not over heat. When its at idle it will sound fine then it will ping a couple times then sound fine. kinda like ping.....ping ping..........ping. Boy I hope that does not make me look like an idiot. Anyways you can put your hand on the pipe ( the fat part of it) and actually feel the pings almost like somthing is on the inside of the pipe tapping it. I have gone thru all the timing +5 down to 0, and also have 112 octane in it. If it was det wouldn't between the 2 have solved it?:confused:
Billie

[400exrider707]

Originally posted by snakeman52646
ok the exhaust looked snug and no leaks. It runs great top and bottom end. does not over heat. When its at idle it will sound fine then it will ping a couple times then sound fine. kinda like ping.....ping ping..........ping. Boy I hope that does not make me look like an idiot. Anyways you can put your hand on the pipe ( the fat part of it) and actually feel the pings almost like somthing is on the inside of the pipe tapping it. I have gone thru all the timing +5 down to 0, and also have 112 octane in it. If it was det wouldn't between the 2 have solved it?:confused:
Billie

If it was det you should be hearing it under load...and more than likely on both cylinders not one.

[snakeman52646]

ok thanks. appreciate your help.
thanks,
billie

[rooster300ex]

Thats how banshee's sound. You won't hear it in the pipe you will hear it in the jugs.