which octane gas do you put?

[yjsjin]

Originally Posted by qubert

Using lower octane gas than rated can cause detonation (AKA Autoignition of fuel) what happens is that the temperature inside the cylinder will ignite the fuel mixture before the piston is ready, before the spark (Higher octane gasoline has a higher autoignition temp) This causes bad things for obvious reasons, and can often be heard as a pinging sound. Serious detonation will break your engine, again for obvious reasons -- 1 piston pushing left, one pushing right... something has to give.

All that being said, its not really a problem AFAIK to limp around on lower octane gas IF YOU GET STUCK. Don't romp on the throttle, or push it and you shouldn't have a problem.

thanks for the info!

[Enzo_Guy]

My manual calls for 89+ in m bike, but since it has domed pistons that brought the compression up, I only use 93+.

[Enzo_Guy]

Originally Posted by yjsjin

i just tried 85 cuz i know someone was using lower dan manufacture octane and he didnt have any prob he was doing that cuz hes bike was like more than 10 yr old the engine mustv been already fucked up anyways he didnt care.. lol

I would be really wary of 85, there's a good amount of ethanol in that. With your 12.8:1 ratio, I would ONLY use 93+. Anything can cause serious detonation at that high of a CR.

With V8 cars the generally accepted line between using 93 and 101+ is ~10.5:1, so think about how much higher than that you are (the difference being that the cylinder walls on a bike stay cooler and are less likely to detonate at higher CRs, but 12.8 is very high regardless).

[RayOSV]

Originally Posted by Enzo_Guy

I would be really wary of 85, there's a good amount of ethanol in that. With your 12.8:1 ratio, I would ONLY use 93+. Anything can cause serious detonation at that high of a CR.

With V8 cars the generally accepted line between using 93 and 101+ is ~10.5:1, so think about how much higher than that you are (the difference being that the cylinder walls on a bike stay cooler and are less likely to detonate at higher CRs, but 12.8 is very high regardless).

You can't compare bike CR to a car CR. ALL bikes have a CR higher than most cars - even those bikes that require only 87 octane gas.

[Tripped1]

Originally Posted by Enzo_Guy

I would be really wary of 85, there's a good amount of ethanol in that. With your 12.8:1 ratio, I would ONLY use 93+. Anything can cause serious detonation at that high of a CR.

With V8 cars the generally accepted line between using 93 and 101+ is ~10.5:1, so think about how much higher than that you are (the difference being that the cylinder walls on a bike stay cooler and are less likely to detonate at higher CRs, but 12.8 is very high regardless).

You know very little about valve timing do you.

[porky786]

Originally Posted by yjsjin

on my kawi manual it said put 90+ octane one time i tried regular gas 85 octane and it seemed like it was harder to start and had less power now im using 91 octane only

Why would you want to put ethanol related gas in you motor if you have a choice, good for the enviornment but it will carbon up a motor.

Ever 6 month I purchase 5 gal of leaded race fuel, a cup per tank every chance you get, it eats all carbon and provides upper cylinder lubrication.
even in a cat

[Lewd Ferrigno]

Well, I find this topic interesting. I usually put 91+ octane in my bike, but a famed engine tuner (think won AMA nationals) told me that midgrade works best in city riding. You're often not going fast enough for the bike to need that much cooling.

Indeed my built TL1000R ran better on midgrade. This was a bike with porting and increased compression as well.

[OldSchlPunk]

Originally Posted by Tripped1

You know very little about valve timing do you.

There are multiple things that I'm sure he's unaware of. Combustion chamber shape, bore, piston dome shape. It all works together (or all works against one another).

[Enzo_Guy]

Originally Posted by Tripped1

You know very little about valve timing do you.

I know with a high CR you have to get it right or you will have some detonation problems.

To be honest I am not well-versed in the ignition/valve timing aspect of high-performance motors, I have always dealt more the bottom ends. I understand the basics of how the cam timing, ignition timing, and crank cycle all need to be in sync for everything to work properly (especially with high-performance motors where there is much less margin for error), but I am not an expert by any means.

If you would like to explain how ignition and valve timing pertain to helping a high compression motor burn lower octane fuel, I (and likely a few other members reading this thread) would certainly like to learn about the subject.

[Lewd Ferrigno]

Originally Posted by OldSchlPunk

There are multiple things that I'm sure he's unaware of. Combustion chamber shape, bore, piston dome shape. It all works together (or all works against one another).

flame turbulence, speed? Stoichiometric mixture? Included angle?

Sorry, just mentioning things having to do with motorcycle combustion. Not even sure it's relevant, just showing off my e-Penis.

[mjfan12]

ninja 500's only call for regular 87 (lowest I've ever seen). Maybe in the rural areas they have 85 or something.

I just filled up with some Mobil 87 today.

I prefer Shell though but there wasn't one nearby.

[Enzo_Guy]

Originally Posted by OldSchlPunk

There are multiple things that I'm sure he's unaware of. Combustion chamber shape, bore, piston dome shape. It all works together (or all works against one another).

I do know piston and head shapes a bit. Combustion chambers nowadays are mostly hemispherical from what I understand (I don't keep up with new engine design as much as I should, so I could be wrong there). I always did old cars (mostly small block Chevys and a few Pontiacs) so the I had to work with what I had, which was typically inferior combustion of the gas due to the chamber shape. When working with old GM blocks, they are all pretty much the same chamber design so the only things you watch for are chamber size vs piston dome/dish size and flow rates.

I know Trick Flow developed an 18-degree SBC head that is supposed to have superior chamber design over the typical 23-degree heads The idea behind it is that with a shallower valve angle they are able to run a 56cc chamber as opposed to the popular 72cc street/strip chamber. So let me see if I can sum up what allows this head to work at higher compression with out something pinging. The shallower valve angle and the more central positioning of the valves allow for more efficient burning of fuel. The old combustion chambers had an odd design that caused more fuel to burn on one side of the chamber than the other which meant uneven combustion and not being able to compress the fuel as much. The new design solved this problem by redesigning the entire head from ground up to allow for more efficient compression of the fuel, which leads to being able to run more compression. That's why newer cars with newer combustion chamber designs can run higher CRs than the cars I'm used to working with (Lexus comes to mind immediately, I remember a few of their vehicles ran such CRs as 11.5 and even 12.0, and when I worked there I would always stare wide-eyed when customers said they only put 87 in their car).

Anything below this has no real relevance to my point, it is merely me telling a bit of a story about some know-it-alls.

Other babbling about small block Chevy combustion chambers if anyone is interested:
Before the 18-degree heads, chambers under 70cc were reserved for guys with 305s, race-fuel burning track motors, and people with no sense. These people with no sense would buy the small-chamber heads and drop in large dish pistons to run pump gas, but they didn't realize that you can't get high-flow heads with a high-lift cam, then just lower the compression and try and drive it around under 2500RPM. I remember several times at car shows hearing the rich guys with more money than brains talking about how their SBC in their 1969 Camaro (which of course they paid to have done, they could never get their own hands dirty) was not running right. And every time I would go over and just peek at their car pretending to be just some kid (I was between 14 and 17 when this kind of stuff happened all the time) checking their car out. And lo and behold, as soon as I look under the hood of the car, there are some shiny new aluminum racing heads (usually the 64cc Dart Pro 1s). I would start a conversation asking some simple questions about their motor and then would move into asking head specs. The numbers they would name off proudly from the memorized brochure were usually terrible for street cars, but these guys assumed the high-performance Dart and Brodix heads had to be some of the best because they were expensive. I would then try to politely explain to them that I overheard them talking about how their car was not running right and I might be able to help them. They would smile with that, "Awww, this kid without a drivers license thinks he can help me, I hope he doesn't embarass himself," look. I would then try to explain to them that the huge intake runner (some as big as 230cc on a street only SBC!), the cam that had too much duration, the oversized carburetor, the combustion chamber that was too small, and the massively dished pistons they were using just in order to run racing heads on pump gas was not a friendly combination. I tried to explain to these guys that by knocking down the compression and trying to drive street RPMs with these motors is what was actually the problem, they were dumping WAY too much air and fuel into cylinders for the engine to keep up at lower speeds. I told these guys it was causing the engine to stall out because it had too much air and fuel coming in, but they just thought some kid (I also look kind of young, I'm a month from 19 and people still ask me if I am 16 yet) was shooting his mouth off and that the problem was the guy who put the motor together for them. EVERY one of those guys blamed the guy who built the engine, not once could it have ever been their choice of parts and the guy they paid just put it together knowing it was never going to work, but also knew it wasn't worth trying to explain to the guys why it wouldn't work because they would just take the motor somewhere else until someone agreed to build it.

Moral of this story: if you ever have a problem with your car/bike, sometimes the kid who doesn't have his license yet is the one with so much time on his hands (because he can't drive anywhere yet) that he has researched the subject since he could pronounce piston (that would not be me by the way, I don't know nearly as much as some of the guys here do).

[Royal Tiger]

My bike calls for 92 minimum. If I stop at WaWa or Sheetz, they top at 92. Sunoco & Shell have 93, as does BP and Hess.

I did notice all of them have a 10% Ethanol sign on the pump.

[p_mihai_ro]

Regarding Ethanol....

I noticed that Sunoco doesn't have the "10% ethanol included" labels on their pumps, and I also noticed that 89 gas they sell gives best mileage in my Civic. I know that as you go up in octane, the power of the gas gets decreased (because of the anti autoignition additives).

Anyway - on topic, I use 91 in my bike. Manual says 87 minimum.

[Royal Tiger]

The Sunoco I use 90% of the time for my bike and car has it. I know the northeast uses Ethanol longer/more then the rest of the US due to population density. I consider Maryland northeast. Maybe not.