race fuel?

[FiremanKay]

Dont crush me, just asking, is it worth it? Thanks

[grayracer513]

That depends. People use race fuels for one or both of two different reasons: Higher octane (not all race gas is higher octane), and more power. The first and most important thing to learn about that is that these two things have absolutely no relationship to each other.

Higher octane in and of itself will gain you nothing if you don't need it, and if you don't ping on pump premium, you don't need it.

Most racing fuels will produce a bit more power than pump gas, some as much as 1.5~2 hp, but you have to rejet richer to take advantage of that quite often, so you can't just switch back and forth that easily. The extra power costs extra money on an ongoing basis, instead of just once when you have a mod done. Not worth it to me.

[davidl9999]

Nutshell:

If you race and need that extra edge, I'd use it.

Long version:

If you want to have more power, use race fuel and jet your carb for it (richer) like grayracer513 said. Fuels like U4.2 add an oxidizer in the fuel, so you need a richer a/f ratio to get the bike to burn the fuel properly.

Not all pump gas is the same either. Stay away from gas with ethanol added to raise octane. Since ethanol makes less heat than gas, you'll make less power, even with premium. Just doing this can give you an advantage against other riders who don't know any better.

Also, the 100 octane street fuel is OK - as long as it's straight gas and not some ethanol mix, but may burn too slowly for your engine, so the "push" happens too far down the cylinder in the power stroke to do any good.

IMO, use the lowest octane gas that doesn't cause your bike to ping or lose power at high revs. That should be somewhere between 87 and 93 "pump" octane. I put a huge post on this last year sometime; maybe in the husky forum. I'll link it if I can find it.

[CaptainKnobby]

The only reason I run cam 2 is because it burns cleaner. I have used pump gas in a 05 yz250 and rebuilt the top end and found it had a lot of carbon built up on the piston.

After the new top end I used cam 2 and when it was time to put new rings in I noticed there were no carbon on the piston like before running pump gas.

Now that I have a 06 450f yami I just use cam 2.

[motomanmike26]

No.

Unless your bike aboslutely has to be run on it, then i wouldn't use it. Doesn't really make a difference except the money left over in your wallet when your done buying 5 gallons.

For my 250f, i have to use it. Its up in the mid 45hps an it runs on MR1 which is 135 bucks for 5 gals. Lets just say i never ride the bike, only race it an practice on my 450s.

For my 450s, i just run pump in it with NO ethonal. I think my bike performes better without any ethonal, an i also think that i get ride longer with a tank of reg 93 without any ethonal. I ride them a lot more too.

I used to have a stage 3 125, that bike was nuts. I had to run it on turbo blue(cheap - 7 or 9 dollars a gallon back then can't remember exctly). It was so modded out if i ran pump gas it would ruin the piston which happened once, so i ran turbo blue mixed 32:1 an it was fine.

Anyways, if your bike NEEDS to be run on race gas, then yes use it. If not, don't use it. Just a waste of money in my opinion.

[grayracer513]

Also, the 100 octane street fuel is OK ...but may burn too slowly for your engine, so the "push" happens too far down the cylinder in the power stroke to do any good.

Most of what you posted was correct, but this is another misunderstanding of octane. Octane number does not relate to the energy level or burn rate of the fuel, so what you have written here is false. Higher octane fuels do not burn slower.

Octane is ONLY a measure of the fuel's resistance to detonation, and that is all. Some certain fuels that are slower burning, or whatever else, may also be higher or lower octane, but those are two separate and unrelated attributes.

You may enjoy reading this:

http://www.faqs.org/faqs/autos/gasoline-faq/part3/

[KJ790]

Most racing fuels will produce a bit more power than pump gas, some as much as 1.5~2 hp, but you have to rejet richer to take advantage of that quite often, so you can't just switch back and forth that easily.

I wouldn't say most race fuels. This is only true of oxygenated race fuels, which very few are since many racing bodies prohibit the use of oxygenated fuel. Most race fuels will offer no power advantage at all. VP U4.2 is one of the few oxygenated fuels on the market right now, and is one of the only fuels that will offer power gains, but it is not very high octane.

[davidl9999]

Most of what you posted was correct, but this is another misunderstanding of octane. Octane number does not relate to the energy level or burn rate of the fuel, so what you have written here is false. Higher octane fuels do not burn slower.

Octane is ONLY a measure of the fuel's resistance to detonation, and that is all. Some certain fuels that are slower burning, or whatever else, may also be higher or lower octane, but those are two separate and unrelated attributes.

You may enjoy reading this:

http://www.faqs.org/faqs/autos/gasoline-faq/part3/

Heheh, that's what happens when I post "the nutshell version" of a complex thing. That's absolutely correct - The octane rating relates to the fuel's resistance to detonation (it also *can* make it harder to ignite depending on how it's formulated, but that'll just open another can of worms...)

It's been my experience that higher octane fuels because of their formulation have a flame front that travels more slowly than lower octane fuels. This behavior will, in fact, cause the highest cylinder pressure to occur further into the power stroke than a fuel with a faster flame front speed (that is generally of lower octane). If the piston gets far enough down the cylinder before the peak cylinder pressure happens, less energy is converted to torque on the crank, and the engine will make less power. The same will happen if the fuel burns too quickly and the piston hasn't travelled far enough to create a sufficient crank angle for work to be efficiently transmitted from the piston to the crank. Thus, the "area under the curve" (the integral of the energy released in the cylinder when the fuel burns) is meaningless if the work isn't done at the proper time in the power stroke.

The important thing here that wasn't said before is that fuels, whether it be pump gas, avgas (don't use this for dirt bikes...), or race fuels are formulated for specific purposes and they all have different ignition, total energy, and burn characteristics.

And the nutshell answer, restated: Switching from one fuel to another is unlikely to provide any performance gain without rejetting for the different fuel chemistry.

Fwiw, here's that link to the post I wrote back in '07:

https://www.thumpertalk.com/forum/showthread.php?p=4970253#post4970253

Hope that helps clear any of this up. ?

[FiremanKay]

cool, thanks guys. Lot of great minds on here. So what have I learned? save my money! got it

[davidl9999]

cool, thanks guys. Lot of great minds on here. So what have I learned? save my money! got it

Hehe, but would you have listened if the answer given was that simple??? ?

This question always turns into a debate.?

[642MX]

This question always turns into a debate.?

Just like oils, tires, and truck brands. ?

[FiremanKay]

Hehe, but would you have listened if the answer given was that simple????

Yea I think I would have, I dont have tons of money and I already was unsure about it. I do a good job about listening from those that have been there done that. You dont ask the old timers "why" in the department, you just listen and learn. I try to apply this as often as I can. Plus most of that was way over my head:bonk: ?

[oeder8140j]

I guess this would be the place to ask this but what is the highest compression you can run on 93 octane

[mcdrz]

Not as simple as just "compression ratio". You must factor other issues into the mix such as combustion chamber design, ignition, piston design, ports, etc.

Nobody mentioned the 3rd reason for using race fuel...jetting consistency. Some states like ours, the only thing that can be had, even pump premium 92, has 10% ethanol content by law (year around) ? .

And #4 lead content in some race fuels which is another argument in and of itself regarding modern 4 strokes and valve trains.

In general not worth the cost...unless motor mods require it.

[grayracer513]

I wouldn't say most race fuels. This is only true of oxygenated race fuels, ...

Not quite accurate. You are correct that oxygenated race fuels produce more power than pump gas partly by adding chemical oxygen to the combustion reaction. However, most reasonably good racing fuels have a higher energy content that most pump fuels simply by virtue of the fact that a larger percentage of their ingredients will contribute energy, rather than serving to reduce emissions or whatever, and doing nothing more than diluting the product. This is one of the differences between U4 and pump gas, much of which is heavily oxygenated. Pump gas uses junk oxygenators such as ethanol, which do provide oxygen, but contribute little or no energy of their own. In contrast, the oxygenating agents in U4 add to the total energy content.

As an aside, you are also correct that the U4 fuels have a generally lower octane number, simply because they don't need to be any higher. But don't miss the point that U4 is 95 Motor octane, not a 95 US pump AKI. That's about 98-100 at the gas pump.

It's been my experience that *some* higher octane fuels because of their formulation have a flame front that travels more slowly than lower octane fuels.

If the word "some" is inserted into this statement, as I have done here, it becomes more accurate. There are a number of ways to increase octane, and some do have side effects that can cause unwanted behaviors in fuel. Tetraethyl lead and toluene, for example do not retard the burn speed of the overall fuel mix (toluene, in fact, is an accelerant), while ethanol plainly does. Only very low grade fuels behave like this, and the interesting thing about it is that the slower burn speed also occurs in high compression engines that do need the octane, reducing their power potential as well.

Octane, in and of itself, is not directly related to the problem, however.

cool, thanks guys. Lot of great minds on here. So what have I learned? save my money! got it

I think you got the point. If you are in a situation where 1~2 hp will really make the difference in your winning or loosing, it may be worth it. Otherwise, it isn't.

[davidl9999]

Gray...

I don't mind debating a subject, but dude, were really on the same page here. The whole point of my initial post, which still seems to "need" correction from the freaking' ivory tower to be "more accurate", was to be reasonably brief and get the point across without writing a freakin' book about the subject. It was adequate for that from the beginning. How about just letting it go... ?

[grayracer513]

Taking things personally and getting yourself in a knot isn't going to help much.

The reason absolute clarity and unambiguity is necessary in this matter is because the issue is so poorly understood by most people. That isn't your fault, but rather, an outgrowth of over half a century of mis-marketing high octane fuels.

Apart from that, the particular point you raised with which I took issue, specifically the inference that "high octane fuels burn more slowly", is categorically false. It is true that some do, and it is true that some do as a result of the approach taken to increasing the octane, but it is also true that most don't, and in fact, some low octane fuels burn more slowly than do some others. So the point is still that the two attributes actually have nothing to do with one another, and a higher octane number does not indicate a slower burn speed.

[davidl9999]

Taking things personally and getting yourself in a knot isn't going to help much.

The reason absolute clarity and unambiguity is necessary in this matter is because the issue is so poorly understood by most people. That isn't your fault, but rather, an outgrowth of over half a century of mis-marketing high octane fuels.

Apart from that, the particular point you raised with which I took issue, specifically the inference that "high octane fuels burn more slowly", is categorically false. It is true that some do, and it is true that some do as a result of the approach taken to increasing the octane, but it is also true that most don't, and in fact, some low octane fuels burn more slowly than do some others. So the point is still that the two attributes actually have nothing to do with one another, and a higher octane number does not indicate a slower burn speed.

You're totally right that every fuel has it's own characteristics and that octane has nothing directly to do with burn rate. In fact that's in the post I wrote in 2007 and included in this thread. It's beyond me why there's still a problem.

It's not personal. It's simply that this is a forum, you're a moderator, and you're picking the crap out of people's posts - not only mine - after you already picked through them. It's more annoying than anything because going back to readdress stuff that wasn't enough of an issue the first time around just feels like a waste of time. Do you want people posting because they want to be helpful, or do you want people to write categorically concise responses that can be held up to your close personal scrutiny for omission, error, and addendum - which gets beyond not fun after a while? I think that keeping people interested in posting is key here.

-Dave

[642MX]

I guess this would be the place to ask this but what is the highest compression you can run on 93 octane

Most guys can get by with 93 octane with a 13.5:1 piston. I used race gas when I ran a 13.5:1 because of a little pinging in hot temps (I probably could've used 93 without issues), but I didn't. I'm back to 12.5:1, but with a larger displacement... its smoother, more broad, and its happy on 93 octane.

[TIG88]

Most guys can get by with 93 octane with a 13.5:1 piston. I used race gas when I ran a 13.5:1 because of a little pinging in hot temps (I probably could've used 93 without issues), but I didn't. I'm back to 12.5:1, but with a larger displacement... its smoother, more broad, and its happy on 93 octane.

Sorry to hijack the thread, but was the 13.5 a big change?