Av fuel in 701

[tmc9046]

Thought I would try 100 octain AV fuel mixed half and half with pump gas in my stock 701.Bad idea it ran like chit!!Had way less top end and no bottom end.Why is this I would think if anything it should help it.Got home and put straight 93 octain in it and it ran great again. :bad3:

 

[hobbs]

compression ratio

Octane is a fuel's ability to resist detonation and/or preignition
It comes down to your compression. If don't have a really high compression head the extra(RON) Research Octane Numbers do you no good. Not saying that your ski is, but a lower-performance engine will not generally perform better with high-octane fuel, since the compression ratio is fixed by the engine design. At high RPMs, there is very little time (real time - not crank rotation) for fuel to release its energy. Peak cylinder pressure should occur around 20° ATDC. If the fuel is still burning after this, it is not contributing to peak cylinder pressure (lower top end).Unless you have a heavily modded machine with ultra small domes, leave the high octane stuff alone. I still run 93 pump with an 849 stroker at 190 psi. The burn and wash on the piston head tells you your machine is set up properly and mine are looking normal. If you don't have one, pick up an aftermarket head, it's the best bang for buck upgrade for any ski.

 

[Matt_E]

Unfortunately, pouring avgas into your tank doesn't make your ski/truck/car run like an airplane.

 

[Kennay]

Art lied to me

 

[Zippy_VIP]

Just had this conversation yesterday with a good friend who races sitdowns.. Isnt there something that has to do with an "additive" that is used because of the elevation and gravity pull with planes that sometimes putting ava gas into certain motors causes huge losses? Rather using race gas that isnt cut with ty ethanol is better used??

 

[OCD Solutions]

According to previous threads on this topic, AV has a slower flame front so it actually doesn't burn as hot, less Btu's = less power. Also, the Octane rating is calculated differently and if the same calculation method is applied as road fuels, it really only equals mid grade pump gas.

I burned it for years but only because I got it by the drum for free. I never really noticed a power difference from pump to AV but I always mixed it 50/50 with premium.

 

[Algonquin]

Engine design is what I am specializing my education on so I might be able to shed a little light on this since it comes up often.

The higher the octane rating the less specific energy the fuel has. So your 87 octane has more energy than 93.

Basic Engine power output is increased by raising compression, rpms, and timing. Each will raise combustion chamber heat. This increase can cause detonation. Detonation is the only reason to use a higher octane fuel. Run the lowest grade fuel you can without detonation. Of course many of us don't want to find this out the hard way.

Higher octane fuel burns slower. You want peak cylinder pressure at 14.7 degrees ATDC. Assume your engine was designed from factory for 87 RON. When you put in 100 RON you are pushing peak cylinder pressure back and wasting power.

I don't know much about AV fuel but from a little research its octane rating (MON) is actually higher than RON. So if you're running 100 AV gas, its closer to 110 RON.

 

[hobbs]

lead

Correct me if i'm wrong but doesn't av gas contain lead or is that just race fuel?

 

[OCD Solutions]

AV fuel is 100LL (Low Lead)

It also says right on all my barrels that lead is a marine polutant and is not to be used in marine applications. :biggrin:

 

[OCD Solutions]

I don't know much about AV fuel but from a little research its octane rating (MON) is actually higher than RON. So if you're running 100 AV gas, its closer to 110 RON.

See, I was told that it was the other way around. I stand corrected?

 

[lvfreestyle]

Av gas

Group K did a report on fuels, look it up in there archives. Good info. AV gas has less power than regular gas. BTW less octane is more power as long as it's not detonating your engine to piesces

 

[vitaly]

Engine design is what I am specializing my education on so I might be able to shed a little light on this since it comes up often.

OK, we are all attention... :scratchchin:

So your 87 octane has more energy than 93.

Sorry, but you fail right there. :sad2:

Higher octane fuel burns slower.

It does not mean it has less energy.


I hope you are not putting the 87 in your dad's Porsche and retard the ignition to get "more energy".