It runs faster on low octane fuel?

[Truckedup]

The key to this is what does tel do other than raise the octane rating of the fuel? What does it cause to happen during the combustion process?
I know what it does to cylinder head temperature in an aircooled engine. I also know what white gas did in a lawn mower engine when I was at age 7, there is no anti detonate in that.

Lead limits the source of detonation, spontanous combustion of end gases occuring at the same time as normal combustion ,...That's what I have told many times from different reptuable sources , what does it do for air cooled engine head temperatures..? I use leaded C-12 in my vintage aircooled race bikes...but I never used any other fuel so I have no opinion...

[Ozonkiller]

Zx14 Kawasaki... Saw higher trap speeds in the quarter, higher hp on the dyno 87 vs 91

[plovett]

oops

[JodyB]

On my own all motor honda drag car. Was perfectly safe to make max hp on 93 with maxed ignition timing. Switched to 110 leaded fuel in anticipation of hitting it with nitrous. Required 3 more degrees of ignition timing to make the same hp on the dyno on the motor.

[JCR]

Great explanation. I've been suspect of the "lower octane burns faster" claim, but it seemed reasonable, and I have heard some pretty reputable engine builders regurgitate it. Goes to show that being an expert in one area doesn't mean much in a different area.

That is why they are an "engine builder" and not a "fuels chemist" that requires a PhD. in Chemistry.

[GRTfast]

Great explanation. I've been suspect of the "lower octane burns faster" claim, but it seemed reasonable, and I have heard some pretty reputable engine builders regurgitate it. Goes to show that being an expert in one area doesn't mean much in a different area.

That is why they are an "engine builder" and not a "fuels chemist" that requires a PhD. in Chemistry.

yep!!

[Truckedup]

How does it limit detonation? With no lead cylinder head temp goes through the roof, and helps eat exhaust valve seats, with lead cylinder head temps lower and low temp helps prevent the micro welding and etching of exhaust seats. Water injection also is an antidetonate and it cools the combustion gases as well.

I said how lead it limits detonation. Vintage Triumphs for example are not bothered much by valve seat issues from no lead fuel.Cylinder head temperatures are not generally an issue in vintage road racing.But with these old turds anything more than 9-1 compression is not suitable for pump gas unless factory squish/quench is reduced...I used leaded C12 because it's easy to find around here for "reasonable" racing fuel prices.

[David Redszus]

The speed of a fuel's flame propagation is affected by it's chemical structure. So, it could be possible that a lower octane fuel could make more power.

Not very likely. Fuel composition has very little effect on laminar flame speed for most commonly used fuels.
A/F ratio has a larger effect on laminar flame speed. But the most important factors are temperature and turbulence.

[David Redszus]

The key to this is what does tel do other than raise the octane rating of the fuel? What does it cause to happen during the combustion process?
I know what it does to cylinder head temperature in an aircooled engine. I also know what white gas did in a lawn mower engine when I was at age 7, there is no anti detonate in that.

Lead limits the source of detonation, spontanous combustion of end gases occuring at the same time as normal combustion ,...That's what I have told many times from different reptuable sources , what does it do for air cooled engine head temperatures..? I use leaded C-12 in my vintage aircooled race bikes...but I never used any other fuel so I have no opinion...

The presence of lead in a fuel serves to slow the rate of heat transfer from the wrinkled flame front to the unburned gas volume.

The flame front, being propelled by turbulence, moves at the same speed, but the reduced heat transfer allows more time for the flame front to combust the end gases before they autoignite.

This process occurs not just with lead but with other selected fuel components as well.

Octane buys you more time for the end gases to burn at a normal rate instead of detonating simultaneously.

Large bore, slow running, high inlet temperature or high compression temperature, low velocity engines are most susceptible to detonation. By reducing bore size, increasing rpm, increasing combustion turbulence and reducing chamber temperature, detonation can be reduced or avoided.

Sometimes, tuners will use excess fuel to cool the chamber, which often then requires additional ignition timing. But if leaner (not lean) conditions are encountered, the advanced ignition timing becomes a very destructive factor.

[HiPer Express]

Formula 1 teams use lowest octane rating allowed by rules, which is 95, european ron/mon I think. Because it makes most power.

[cjperformance]

Formula 1 teams use lowest octane rating allowed by rules, which is 95, european ron/mon I think. Because it makes most power.

Yes I had heard some years back that F1 had a 'minimun' octane rule , due the the very high rpm they were looking for the fastest burning fuel they were allowed. That said I have no idea what their fuel choices were or composition of said fuels so its not really conclusive!

[David Redszus]

Formula 1 teams use lowest octane rating allowed by rules, which is 95, european ron/mon I think. Because it makes most power.

Yes I had heard some years back that F1 had a 'minimun' octane rule , due the the very high rpm they were looking for the fastest burning fuel they were allowed. That said I have no idea what their fuel choices were or composition of said fuels so its not really conclusive!

Formula One rules, including fuel rules, are always changing. A few years ago, I had access to the fuel rules but they are probably different now.

Formula One allows only those components that are found in ordinary pump fuel. But they may be blended in a wide variety of ways, resulting in the possibility of many fuel blends.

Consider that pump fuels may contain over 450 different components, that gives the fuel chemist a lot to play with. The rules do limit the maximum and minimum amount of each component category by carbon number.They do allow oxygenates but not lead compounds.

The fuels are tailored to the needs of a specific engine; not in pursuit of a "silver bullet" performance fuel.

But the FIA does allow an escape clause. A team may use experimental fuel compounds if the intent is to test fuels for potential commercial use.

Ultimately, a team and their technical sponsor oil company, can make almost any fuel they wish as long as they can justify their reasons. But once a sample fuel is submitted, they are not allowed to make changes.

It still comes down to "run whatcha brung" but keep the tech inspectors in the loop.

[cjperformance]

Formula 1 teams use lowest octane rating allowed by rules, which is 95, european ron/mon I think. Because it makes most power.

Yes I had heard some years back that F1 had a 'minimun' octane rule , due the the very high rpm they were looking for the fastest burning fuel they were allowed. That said I have no idea what their fuel choices were or composition of said fuels so its not really conclusive!

Formula One rules, including fuel rules, are always changing. A few years ago, I had access to the fuel rules but they are probably different now.

Formula One allows only those components that are found in ordinary pump fuel. But they may be blended in a wide variety of ways, resulting in the possibility of many fuel blends.

Consider that pump fuels may contain over 450 different components, that gives the fuel chemist a lot to play with. The rules do limit the maximum and minimum amount of each component category by carbon number.They do allow oxygenates but not lead compounds.

The fuels are tailored to the needs of a specific engine; not in pursuit of a "silver bullet" performance fuel.

But the FIA does allow an escape clause. A team may use experimental fuel compounds if the intent is to test fuels for potential commercial use.

Ultimately, a team and their technical sponsor oil company, can make almost any fuel they wish as long as they can justify their reasons. But once a sample fuel is submitted, they are not allowed to make changes.

It still comes down to "run whatcha brung" but keep the tech inspectors in the loop.

Interesting thankyou David.

[peejay]

Formula 1 teams use lowest octane rating allowed by rules, which is 95, european ron/mon I think. Because it makes most power.

Because of the horrible chamber shape dictated by the massively oversquare layout, and the high RPM used, they are power limited by flame propagation speed.

Solution: Run in a state of controlled detonation instead of combustion. No more flame speed limitation.

[Roundybout]

We keep a good amount of pump fuel on hand for mowers, dirt bikes, generator ect. and it sometimes doesn't get used up for 3-6 months. Never had an issue in the summer with starting, running or any fuel related issues. Only use ethanol free fuel so that might have some bearing on it. I have noticed when we get to the winter months and the winter blend kicks in up here in NH whatever stored over winter and used come summer time they run like crap. Hard starting and crappy throttle response.