Aviation "Racing" fuel dangers to the engine?

[William F.]

Re: Aviation "Racing" fuel dangers to the engine?

Duke, "Few small erosions in piston tops" from what you call "mild transient detonation" that you disregard doesn't sound good. What do you think is happening to the rings and cylinder walls? Do you think the GM engineers who warned about setting timing by ear since inaudible detonation might occur and significantly increase ring and cylinder wall wear were all DA's??

[Gene M.]

Re: Aviation "Racing" fuel dangers to the engine?

Didn't really want to get involved with this subject but here is how I handle it at the Shows and on the phones when customers say bad stuff about 100LL.
AT the fleas I just smile and nod my head and listen to the negative comments. I am not one to argue. Then when the customer walks away I completely ignore his/her comments about 100LL.
When my 63, the LWC (little white car) was judged at Marlborough and went thru the ops one judge said JD just what are burning in that thing?. Smells sweet. You know the answer.
Biggest reason I use it in everything I own that has a spark plug is it can set for an eon and never gum up. Once you start cutting it with crap gas though that really takes away from the effects of 100LL.
Anyhow I didn't read all your posts and typically don't.
You old guys remember Sunoco 260. Our Corvettes loved that stuff. My Dad only used Amoco White gas as he called it. No lead in it. That's all he would use in the old days. Later as back to work. CC is in 18 or 19 days. Whew!!!!

John,
I like your method of handling a conversation that could otherwise have negative results.

[Michael H.]

Re: Aviation "Racing" fuel dangers to the engine?

Duke, "Few small erosions in piston tops" from what you call "mild transient detonation" that you disregard doesn't sound good. What do you think is happening to the rings and cylinder walls? Do you think the GM engineers who warned about setting timing by ear since inaudible detonation might occur and significantly increase ring and cylinder wall wear were all DA's??

That oughta' get a several hundred word reply.

By the way, I agree with you.

[Michael W.]

Re: Aviation "Racing" fuel dangers to the engine?

Duke, "Few small erosions in piston tops" from what you call "mild transient detonation" that you disregard doesn't sound good. What do you think is happening to the rings and cylinder walls? Do you think the GM engineers who warned about setting timing by ear since inaudible detonation might occur and significantly increase ring and cylinder wall wear were all DA's??

From what I have learned and as Duke has already mentioned above, that generic warning from GM was broadcast across all vehicles lines. It falls into the same category as the valve seat vs. leaded gas issue- a big problem for heavily loaded vehicles being operated at large throttle openings for extended periods of time but of no concern for Corvettes. Given the decades of (mis)use these cars have been subjected to, has anyone actually seen such damage?

[Bob J.]

Re: Aviation "Racing" fuel dangers to the engine?

From what I have learned and as Duke has already mentioned above, that generic warning from GM was broadcast across all vehicles lines. It falls into the same category as the valve seat vs. leaded gas issue- a big problem for heavily loaded vehicles being operated at large throttle openings for extended periods of time but of no concern for Corvettes. Given the decades of (mis)use these cars have been subjected to, has anyone actually seen such damage?

Doubt many here do their own engine work so your poll isn't going to represent much.

[Michael W.]

Re: Aviation "Racing" fuel dangers to the engine?

Doubt many here do their own engine work so your poll isn't going to represent much.

If that's true, then all the 'sky is falling' predictions shouldn't carry much weight either.

[Duke W.]

Re: Aviation "Racing" fuel dangers to the engine?

Duke, "Few small erosions in piston tops" from what you call "mild transient detonation" that you disregard doesn't sound good. What do you think is happening to the rings and cylinder walls? Do you think the GM engineers who warned about setting timing by ear since inaudible detonation might occur and significantly increase ring and cylinder wall wear were all DA's??

On those disassembled engines where I observed some minor pits on the piston crowns that I attributed to detonation, I saw no other damage. Piston crowns, at high sustained load, run near the temperature where most aluminum alloys lose significant strength, so they are usually the first to show any evidence of detonation. The same applies to exhaust valves, so they are usually the next victim, but they often fail suddenly when a chunk of material separates.

All my cars are set up on the ragged edge of detonation. They have much better low end torque and get better fuel economy than the OE configuration. Mercedes recommends "premium fuel" for my 1988 190E 2.6 five-speed, but I run regular even with a more aggressive spark advance map. I only drive it in the November to June time frame when temperatures are cool, so that's how I can get away with it. If I drove it in the summer I'd have to use higher octane.

I have no plans to sell any of my cars, and I'm not worried about damaging them due to occasional light, transient detonation.

BTW, I don't set timing "by ear". I always use a dial-back timing light and set total WOT spark advance at where I believe the engine will achieve maximum output across the rev range. That would be nominally 38 degrees total centrifugal plus initial for a small block, then get it all in as soon as possible with available centrifugal springs. Then I do "detonation testing" as described earlier by John Seely.

John's original "11:1" 375 HP FI engine did not exhibit any audible detonation on California 91 PON fuel with 38-39 degrees total WOT spark advance despite how hard I tried to induce it, but the centrifugal curve had been slowed relative to OE, so one of John's action items it to dig up a set of OE springs and run detonation tests again.

There is more information on the subject in my San Diego presentation. You should read it.

Duke

[Joe C.]

Re: Aviation "Racing" fuel dangers to the engine?

On those disassembled engines where I observed some minor pits on the piston crowns that I attributed to detonation, I saw no other damage. Piston crowns, at high sustained load, run near the temperature where most aluminum alloys lose significant strength, so they are usually the first to show any evidence of detonation. The same applies to exhaust valves, so they are usually the next victim, but they often fail suddenly when a chunk of material separates.

All my cars are set up on the ragged edge of detonation. They have much better low end torque and get better fuel economy than the OE configuration. Mercedes recommends "premium fuel" for my 1988 190E 2.6 five-speed, but I run regular even with a more aggressive spark advance map. I only drive it in the November to June time frame when temperatures are cool, so that's how I can get away with it. If I drove it in the summer I'd have to use higher octane.

I have no plans to sell any of my cars, and I'm not worried about damaging them due to occasional light, transient detonation.

BTW, I don't set timing "by ear". I always use a dial-back timing light and set total WOT spark advance at where I believe the engine will achieve maximum output across the rev range. That would be nominally 38 degrees total centrifugal plus initial for a small block, then get it all in as soon as possible with available centrifugal springs. Then I do "detonation testing" as described earlier by John Seely.

John's original "11:1" 375 HP FI engine did not exhibit any audible detonation on California 91 PON fuel with 38-39 degrees total WOT spark advance despite how hard I tried to induce it, but the centrifugal curve had been slowed relative to OE, so one of John's action items it to dig up a set of OE springs and run detonation tests again.

There is more information on the subject in my San Diego presentation. You should read it.

Duke

You should clarify this by inserting a colon between the words "degrees" and "total", lest most here will tell their "mechanic" to set their distributors with too much spark advance.

[Domenic T.]

Re: Aviation "Racing" fuel dangers to the engine?

Well I would like to clarify a sentence in my original post as I didn't proof read it.

Sorry but I made it sound like pump gas made my engine quit while it was running but it didn't.

After running low on my mixture of av gas and pump gas, then filling my tank with pump gas and turning off the engine, is when the engine would diesel and blow back thru the carb.

I have to depend on pump gas in my drivers and that's that, but in the past I used water injection and it did the trick. Unfortunatly we can't do that on our beauties.

I will confess that on my drivers I set the timing to whatever fuel I am burning and when I feel like a kid, I mix avgas and treat myself to some tire burning

I am old school and a stock freak so I still believe in keeping the compression the way it was as that is as important to me (engine design) as the rest of the car.
Please don't misunderstand me, I am not saying that it is a MUST to use certain fuels as I respect ALL that is being said. I only do it (mix av gas) when I want to treat myself as times have changed and we don't always get our way or what we want.

DOM

[William F.]

Re: Aviation "Racing" fuel dangers to the engine?

Like I said, the warning about setting timing by ear was in a CORVETTE news, not in a truck, etc. tech bulletin. All this setting timing on ragged edge of detonation may be good if you're drag racing and going to rebuild the engine frequently, but I suspect factory specs are going to give the best balance of performance and longevity on our cars we don't want to blow up for sake of a few extra hp. And remember, timing specs were back when we had 100 octane premium. Why did we need the octane(forget about the lead) then if some say we don't need it now even if our engines are up to snuff, especially the 11:1 compression ones? Again, were the GM/Corvette engineers just DA's? Don't think so.

[Joe L.]

Re: Aviation "Racing" fuel dangers to the engine?

Like I said, the warning about setting timing by ear was in a CORVETTE news, not in a truck, etc. tech bulletin. All this setting timing on ragged edge of detonation may be good if you're drag racing and going to rebuild the engine frequently, but I suspect factory specs are going to give the best balance of performance and longevity on our cars we don't want to blow up for sake of a few extra hp. And remember, timing specs were back when we had 100 octane premium. Why did we need the octane(forget about the lead) then if some say we don't need it now even if our engines are up to snuff, especially the 11:1 compression ones? Again, were the GM/Corvette engineers just DA's? Don't think so.

William------


The octane rating system used in the 60's for motor gasoline is different than the system that's been in use for at least the last 20 years. Most cars of the 60's era did not specify an octane rating for particular engines, instead just specifying "regular" or "premium". I don't know that all "premium" gasolines of the 60's were "100 octane" (by the rating system used during that period) because gasoline filling station pumps rarely, if ever, specified an octane rating.

Also, aviation gasoline is rated by an octane system not used today for motor gasoline.

[Duke W.]

Re: Aviation "Racing" fuel dangers to the engine?

Everything you said, Joe, was spelled out in more detail in my San Diego presentation, and I recall you were there.

I doubt if Ford bothered to download and study it. He'll take his cherished beliefs to the grave regardless of evidence to the contrary.

Duke

[Michael H.]

Re: Aviation "Racing" fuel dangers to the engine?

Like I said, the warning about setting timing by ear was in a CORVETTE news, not in a truck, etc. tech bulletin. All this setting timing on ragged edge of detonation may be good if you're drag racing and going to rebuild the engine frequently, but I suspect factory specs are going to give the best balance of performance and longevity on our cars we don't want to blow up for sake of a few extra hp. And remember, timing specs were back when we had 100 octane premium. Why did we need the octane(forget about the lead) then if some say we don't need it now even if our engines are up to snuff, especially the 11:1 compression ones? Again, were the GM/Corvette engineers just DA's? Don't think so.

I agree. If I do fiddle with the timing on the 66, I try to find that "ragged edge" and then drop it back about two/three degrees retarded from that point. I don't want to be on that edge. Too many things change from day to day to be on the edge. That's pointless for an old collector car.

I rebuilt that 11-1 425 HP back in about 1984, driven it all around the country and it still runs just as flawlessly as it did then. I want to keep it that way.

Max timing sounds like chatter from the hot rod discussion boards. Not a restoration site.

[Michael W.]

Re: Aviation "Racing" fuel dangers to the engine?

And this is where the primary myth stated- gasoline back then 'used to be 100', now all we can get is 93. People conveniently forget, or didn't know, that the rating system changed in the mid-70s.

I beleive most premium gas available in the '60s was approx. 97-98 RON octane which is equivalent to today's 93 PON or AKI..

William------


The octane rating system used in the 60's for motor gasoline is different than the system that's been in use for at least the last 20 years. Most cars of the 60's era did not specify an octane rating for particular engines, instead just specifying "regular" or "premium". I don't know that all "premium" gasolines of the 60's were "100 octane" (by the rating system used during that period) because gasoline filling station pumps rarely, if ever, specified an octane rating.

Also, aviation gasoline is rated by an octane system not used today for motor gasoline.

[Don H.]

Re: Aviation "Racing" fuel dangers to the engine?

Didn't really want to get involved with this subject but here is how I handle it at the Shows and on the phones when customers say bad stuff about 100LL.
AT the fleas I just smile and nod my head and listen to the negative comments. I am not one to argue. Then when the customer walks away I completely ignore his/her comments about 100LL.
When my 63, the LWC (little white car) was judged at Marlborough and went thru the ops one judge said JD just what are burning in that thing?. Smells sweet. You know the answer.
Biggest reason I use it in everything I own that has a spark plug is it can set for an eon and never gum up. Once you start cutting it with crap gas though that really takes away from the effects of 100LL.
Anyhow I didn't read all your posts and typically don't.
You old guys remember Sunoco 260. Our Corvettes loved that stuff. My Dad only used Amoco White gas as he called it. No lead in it. That's all he would use in the old days. Later as back to work. CC is in 18 or 19 days. Whew!!!!

I could not agree more with JD (the man). I just returned from a 200 mile trip (each way) to the Illinois Chapter meet and my 375 unit does not even idle on pump gas - runs perfect on AV gas. (I think I already said this earlier in this thread). Don H.