Using racing fuel

[Paul G]

Last Saturday I was talking with a guy who has a 67 Mustang with a 331 stroker. I have ridden in the car and it makes neck jerking power. He says that he sometimes tops off the tank with racing fuel, and it performs better. My question is, if the engine is tuned to run on 91 octane, will increasing the octane by adding racing fuel, make the engine more powerful? With modern cars an engine tuned for 87 will not perform better with a higher octane fuel.

[cdr]

it has been proven that putting higher oct than the engine needs makes less power

[440]

I've noticed a cleaner burn. My 77 truck will run on 91 and even 85, when you back off with a bit of RPM it carries on like a popcorn machine. When running 100 unleaded or 110 leaded it's as smooth as silk, and the lovely sweet smell of the 110 is pure bliss.

[oldschool]

it has been proven that putting higher oct than the engine needs makes less power

that is true....any more octane than needed is a waste of $$$$$$

[Chryco Psycho]

if the engine is de-tuned for pump gas then adding racing fuel & retuning will definatly make more power , if you can run full timing under full load with no pinging on pump gas adding race fuel will hurt power

[Challenger340]

it has been proven that putting higher oct than the engine needs makes less power

that is true....any more octane than needed is a waste of $$$$$$

YEP !

[440]

What's the explanation for crisper deceleration, I always thought it was unburnt fuel but remember Ron saying popping on decel is a lean condition. Longer burn time?

[cdr]

What's the explanation for crisper deceleration, I always thought it was unburnt fuel but remember Ron saying popping on decel is a lean condition. Longer burn time?

possible lean,or exhaust leaks

[440]

It has to be a lean condition, what is the remedy to cure it? And why does it go away with high octane fuel?

[Cooter]

ALOT of the "Racing fuel made more power in my daily driven, 8.5:1 engine" crap, is all in the users head. You "Think" it makes more power, therefore it does.


Actual dyno may show different story. only when the engine is Retuned, will it benefit from racing fuel. Sure, higher octane fuel will idle cleaner, idle better, burn cleaner, plug life exteneded, etc.

I've heard if cats are "modified" on late model injected cars, the higher octane fuel actually allows the engine PCM to allow more timing and such therefore, more power than if it was cutting timing out due to cheap fuel.

[Paul G]

ALOT of the "Racing fuel made more power in my daily driven, 8.5:1 engine" crap, is all in the users head. You "Think" it makes more power, therefore it does.


Actual dyno may show different story. only when the engine is Re-tuned, will it benefit from racing fuel. Sure, higher octane fuel will idle cleaner, idle better, burn cleaner, plug life extended, etc.

I've heard if cats are "modified" on late model injected cars, the higher octane fuel actually allows the engine PCM to allow more timing and such therefore, more power than if it was cutting timing out due to cheap fuel.

That is the way I understand it as well. A late model performance car that is tuned for 91 or 93 will run best on 91 or 93. It can run on a lower octane fuel just not with as much power. The PCM will take out timing to kill detonation, so it will run okay, just under powered. My truck is a prime example, 05 SRT10 Ram. It says to use 91 octane. I have tried 89 and it runs without issue. Just under powered to the point that I can actually feel the difference. A regular engine that is tuned for 87 will have all it's performance available with 87. Higher octane fuel will do nothing since the engine controller can not take advantage of it. This is how newer cars work, so I have read. I guess our older cars are still basically the same. Except it has to run the fuel it was built for.

I was just curious since I hear of so many guys "adding race fuel" to an older classic muscle car and thinking there cars perform better. I guess not.

So is it possible to take timing out of an older performance engine and run a lower octane, less expensive, fuel? I wonder what the overall advantage or disadvantage would be?   

[Challenger340]

This could get REALLY long, so gonna try and simplify for explanation...
Gasoline contains approximately 134,000BTU's(British Thermal Units) of heat energy per Imperial Gallon Liquid volume.....
Thats it, Thats All....
No matter if it's the highest priced C16 Leaded Racing Fuel,
or,
the CHEAPEST regular unleaded bought at discount Joe's ....
If it's a BENZENE ring hydrocarbon blended for automotive use..... it's "GASOLINE" and that is it's total Heat Energy POTENTIAL, when released during the Combustion process.

Now, the amount of that Energy that can "absorbed" and transferred into mechanical motion by the Engine, is of course a seperate matter, dependant upon many factors like Compression Ratio(Incipient Heat to Combustion), Volumetric Efficiency, Mechanical Advantages(Angularities)etc., etc., etc., ...all pretty much built in factors to Engine design according to the intended application.

But, when talking about fuels, and octane ratios therein, IMO, it is important to understand "what" a fuels Octane rating is, and what it does...
Gotta simplify to keep this short...
but basically, (no arguments wanted just for explanation here) "Octane" is a rating of a fuels ability to resist self-Ignition or detonation(different subject by itself) due to the HEAT of compression.

Higher Compression Ratios, designed to extract higher thermal efficiencies during combustion, require HIGHER Octane fuels that can resist self ignition from higher compression heat, and "wait" for a spark to ignite at the correct time to place maximum burn pressures at the " best" point for push on the Piston.
Lower Octane fuels, when used in HIGH Compression Engines, can NOT wait for the spark and self ignite from the higher compression heat, placing highest burn pressure at the incorrect time on the Piston, hence knock and less power.

There are also burn rates attached to many different Oxygenated fuels, but by now the "concept" should be clear ?

So back to the claim that High Octane Race Fuels make a "low compression" 4 stroke automotive engine, go faster tham it does on lower octane fuel that it 's compression ratio is compatible with.....
and we have tried this many times on the Dyno
I simply disagree.

We've tried C12, C14 & C16, with different tunes, and various timing/jettings, all the way up to 10.5:1, NADA, Zilch...DONUT, and usually lost power.
actually,
when we got really close to the detonation range for the Compression Ratio on Pump Fuels, we made noticeably MORE power !

No wars wanted, just my opinions.

[Ghoste]

That by far, was one of the best explanations I have ever read for octane.

[440]

Excellent explanation Challenger. Hmm, my question still remains but becomes more complex, lean pop or rich pop. Could the octane resist igniting in the exhaust or does the slower burn make up for a lean condition ?

[Cooter]

440, if it's popping out the exhaust upon decel, then you most likely have an exhaust leak. You'd be surprized at how little of a leak it takes to pop out the exhaust coming down from 5000 RPM...

[440]

On two completely new systems? I'm not ruling it out though.

Mostly cruising down hill off throttle say 45 mph or so, or backing off the throttle on the freeway. I don't really care if it pops or not, I kinda like it. Just curious as to why the popping goes away when race fuel is used.

[cdr]

On two completely new systems? I'm not ruling it out though.

Mostly cruising down hill off throttle say 45 mph or so, or backing off the throttle on the freeway. I don't really care if it pops or not, I kinda like it. Just curious as to why the popping goes away when race fuel is used.

if its carbureted back out the idle mix screws 1/2 turn,you can go more or less and test drive to see what works