Grizz tim you're contradicting yourself totally. First you say aj is right(which he is) and then you say you had a car that made more hp at lower octane. He just said that no hp increases were noticed throughout octane levels, except the nascar race engine which made MORE HP with HIGHER octane. You claim your race engine made more hp at lower octane. Not trying to be argumentative, just your post makes no sense to me.

Oh well, its full of 89, a happy compromise. So much for posting, i'm going out riding!!!!! seeeeeeeeeeeeeeeya!

 

PrairieTwin, if you look under the seat and read more carefully, you'll see it says 91 min RON, research octane number, not the antiknock index we commonly see, 87, 89, 93. The antiknock number you see on the pumps is derived from this formula, using motor octane, and research octane numbers. Hope this helps you understand prairietwin. (RON+MON)/2 = antiknock index -87,89,93

 

Well, this is kindof half true. You don't "gain" horsepower with higher octane, but on those engines designed to run a higher compression ratio, they need a higher octane to fire when designed. If you have a lower octane rating, the flashpoint is lowered, pre-detonation occurs, and you get a HORSEPOWER LOSS.

AND REMEMBER, those "numbers" on pumps are NOT true octane ratings....

....and I'm back quiet.....

 

Thanks Lightman.

 

So what my buddy told me is true. NOT my bad. I'll keep running 87 in it and take the money I save on fuel and give it to Bearman for the CDI[img]i/expressions/face-icon-small-happy.gif[/img].

AJ650, you rate right up there with Alltoys and Nyroc! Glad to have guys like you on here to share their knowledge.

Good post guys. Thanks for the info.

 

MastrBlastr: thanks, I try to help where I can.

Chucky: You are right, engines designed in a way that require the higher octane will lose power without it. I didn't really delve into it as the discussion was about running higher octane than needed in a given engine, specifically our little v-twins. My biggest concern is keeping people from spending money they don't have to on higher octane our bikes don't need. There are definately motors out there that require the higher flashpoint of higher octane fuel. I would bet that with the mods Alltoys and Bearman have made to their bikes pre-detonation could be a problem.

 

Well my take is the engine runs nearly 10 to 1 compression. The cylinder and sleeves are fairly cheap (Aluminum alloy with ferrous sleeve) Higher octane will run a bit cooler no?

Any of you getting overheating problems running cheap gas?

The cheapest thing you can put in a motor is the highest quality gas and oil, eh?
I have been running cheap gas- same I use in the lawnmower, weedwacker chainsaw etc (without the oil...)
I'm going to run a few tanks of 92 & up to see whats the diff.
I have been getting some backfires..well, not backfire but hiccups thru the carbs at low throttle.

CWG

 

The owners manual plainly states to run 87 octane. I talks about this on pages 46 and 47 if anyone cares to look. The antiknock index is what you are looking for. Its the same in the manual as it is on the pumps.

I have always ran 87 in my P650 without any trouble. I have recently switched to 91 since I installed the degree key. Next time I buy gas Im going back to the 87 to see what happens. I tried a test last year when I did the spring test. My brother in law wanted me to try some 100 octane race gas. So, we drain mine as much as possible, put the race fuel in and low and behold we get slower times than we did with 87 octane.

 

the ONLY thing I notice when running 91 vs the normal 87 is how fast I use that tank..I dont get nearly the mileage out of 91 as I do 87..go figure..and it runs just fine with 87

 

in tech school we were taught that an engine runs best on its engineered octane and will loose power on any other.no damage from running higher just a slight loss of power. Higher octane fuels actually have fewer btu's and therefore less power.the power gain from running higher octane is mostly from being able to run higher compression..the power gained is more than the loss fromrunning fuel with fewer btu's.