100vll

[Jim T.]

www.faa.gov/aircraft/safety/alerts/SAIB/.

[Paul J.]

Re: 100vll

Thanks for the info, Jim. That's helpful, but it really should'nt matter to us. We want non-ethanol fuel with a 100 octane rating. The lead does'nt really matter.

Paul

[Michael W.]

Re: 100vll

Probably 99% of Corvettes run just fine on 91-93 octane gas, ethanol or not.

[Domenic T.]

Re: 100vll

Jim,
Thanks for the info.

I never thought I would be using a steady diet of av gas in my cars and auto fuel in my airplanes.

With auto gas my vette ran fine but not GREAT.

I would never lower the compression on a vintage vette just to use auto fuel so I have to de-tune to run on auto fuel.

Most if not all of the guys that say we don't need av-gas in out cars probably never tried it.

They are right we don't need av-gas unless we want the old car to run like it was designed to run.

A lot of first experiance vette drivers did it with 91/93 pump gas and have never had the blast of the past using the right octane the engine was designed for.

Some one here needs to dyno with av-gas vs pump gas, with the engine tuned for each, or get 1/4 mile time differences.

I don't want to stir the hornets nest up by saying this BUT with pump gas my tires would not break loose easily.

With a 50/50 blend of av-gas it was smoke city. I know there was a HP boost with av-gas.

If you have not tried it tin a high compression engine then your coments really don't stand.


DOM

[Michael W.]

Re: 100vll

A lot of first experiance vette drivers did it with 91/93 pump gas and have never had the blast of the past using the right octane the engine was designed for.

Dom,

The vast majority of Corvettes were designed for 91-93AKI octane. In the 'good old days' before gas was rated by (RON+MON)/2 to get the AKI index it was labeled and sold under the RON rating only. Today's 93 octane is identical in octane to good old 98 from the 60s. The rating system changed, not the octane levels.

Yes, I've tried all the different fuels including 'racin' gas' and it made no difference.

[Domenic T.]

Re: 100vll

Michael,
You didn't mention av-gas.

Sorry but 98 octane didn't cut it then if you wanted real performance, Sunoco gave us the edge at that time.

98 octane worked in my dads car with 10:1 compression but not all that good in the 11.5:1 cars.

We only get 91 here in CA and when they had 92 it pinged in my car unless I retarded the spark advance.

You can use all the 93 you want, my compression is in the 11's and those octane levels just don't cut it.

Now the engines with 9 & 10:1 might find no less than todays 93 octane good to use but here we only get 91 and it only works in the smog engines with dish pistons that came out in late 1971.

When they reduced the octane in our gas chevy engines lowered their compression with dish pistons and bigger combustion chambers to reduce the pinging.

DOM

[Michael W.]

Re: 100vll

That's why I didn't say 'all'. As has been thrashed to death here many times, the vast majority run at full potential with 93 octane.

The market for those that truly 'need' higher than that is extremely small. It's just unfortunate that the myth of octane = HP won't go away, pretty much the same as 'leaded gas' being a good thing.

[Domenic T.]

Re: 100vll

Michael,
I am mainly refering to the older vettes 1971 and down that were offered with high compression,

That covers a whole bunch of cars.

If you have a low compression vette you can burn any thing and not see much difference.

When I worked as a chevy mechanic in 1971 I had a new car in my stall that needed a head.

When I saw the dish pistons in it that were only in truck engines, I called the service manager and showed him. I said look, this car has a truck engine.

He looked at me and said "get used to it, thats where its going, no more racing for chevrolet".

If your vette is newer than 1971 then you wont experiance pinging when tuned properly.

DOM

[Michael W.]

Re: 100vll

Michael,
I am mainly refering to the older vettes 1971 and down that were offered with high compression,

Me too. 71 and up low compression Corvettes run just fine on 87 octane. 93 is a waste.

[G A.]

Re: 100vll

It's just unfortunate that the myth of octane = HP won't go away, pretty much the same as 'leaded gas' being a good thing.

Mike, a question comes to mind spurred by this statement. What, if you or someone else happens to know, is the "octane" rating of Nitro-Methane, as used in Top Fuel/Funny Car's? I know (i think )that a higher octane rating means longer carbon chains, less chance for detonation and thus the opportunity for more timing advance. To me that equals horsepower. Yes???

I recall only that methane is one carbon atom with 4 hydrogen atoms 'sharing' their electrons (hydrogen being EXTREMELY combustible in the presence of O2) but can't remember anything about the 'nitro' part (I believe the nitro supplies the O2??).
Anyway I'd like to learn about the octane rating of this fuel.

Dan

[Michael W.]

Re: 100vll

This is what I've learned from people that I believe know their stuff. Nitromethane normally is not rated on the octane scale but if a number was to be assigned in would be in the area of 75 or so. Surprise! Nitro has very little resistance to detonation and is said to 'explode' rather than 'burn' like gasoline. Conversely, the very evil ethanol that causing the sky to fall has an octane rating of 100 AKI yet far less energy per volume than pure gas. An octane number therefore has no connection to how much energy a fuel contains.

I am more versed in the art of causing methane to burn, my buds on VH always make sure they're sitting up wind for that very reason.

There is truth that higher octane can allow greater spark advance or 'lead' by reducing potential detonation, but all engines reach a point where additional advance would be counterproductive. In the case of excessive advance, the combustion gas pressure would attempt to push the piston downwards before it has completed it's upward travel, essentially turning the engine backwards.

Small block Chevs are known to offer peak HP at no more than 36-38* advance under low vacuum (wide open throttle) conditions. BBCs like a little less from what I have learned. Duke can confirm or correct the above as required.

What this boils down to- if an engine can be operated at full throttle w/out detonation and 36-38* of advance, higher octane or greater advance is of no benefit.

Hope this helps, except for the methane blue flame story.

[John H.]

Re: 100vll

Dan -

The key advantage of nitromethane is its oxygen content. It actually burns slower than gasoline, which is why nitro cars run 50*-60* of advance; "lighting the fire" has to start earlier. That was the case when I ran my AA/FD in 1961-62, and it's still true today (they run a LOT more boost today, and a MUCH higher percentage of nitro vs. methanol and benzene, and MUCH higher cylinder pressures).

[G A.]

Re: 100vll

Mike & John,
Thanks for enlightening me. In my case, I tend to learn better by taking an extreme example and I believe this worked again.
WOW am I surprised by the "octane" rating. The knee-jerk reaction is to think nitro would be 150+ rated octane. And with the slow burn + O2 that nitro provides, John, the big picture does make sense. Slow burn = efficiency. Burning everything = more power. So I think I can finally see why octane does not = horsepower.

Dan

[Domenic T.]

Re: 100vll

Dan -

The key advantage of nitromethane is its oxygen content. It actually burns slower than gasoline, which is why nitro cars run 50*-60* of advance; "lighting the fire" has to start earlier. That was the case when I ran my AA/FD in 1961-62, and it's still true today (they run a LOT more boost today, and a MUCH higher percentage of nitro vs. methanol and benzene, and MUCH higher cylinder pressures).

John,
Glad you pointed out the burn time and the reason to start the burn earlier by advancing the timing.

I learned that regular (in the old days) burns faster the premium and thats why the timing was less.

Also the WWII guys said they burned the valves in jeeps when they ran them hard and used av-gas.

One WWII mechanic said it was because the high octane fuel was still burning as it was going past the open exhaust valve and that it didn't completely burn using the timing for lower octane fuel.

Made sence to me.


DOM

[Michael W.]

Re: 100vll

Unfortunately Dom, that's more myth and misunderstanding. All gasoline burns more or less at the same speed and any variation is independent of the octane rating. There's 'fast burning' premium and 'slow burning' regular and vice versa.

The octane rating of a fuel represents resistance to detonation and nothing more.

To be clear, what John said is true- different types of fuels burn at different speeds.