Aviation "Racing" fuel dangers to the engine?

[Mike E.]

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

Duke Williams did a seminar at last years convention. Here is the PowerPoint, it goes into some very deep detail about fuel on page 10. It backs up pretty much what Joe is saying above.

http://www.metroli.org/pdf/2012%20Nationals%20tuningseminar.pdf

[Don H.]

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

I have been running 100LL av-gas for over 25 years in my F.I. cars and it works great. The fuel bowl is perfectly clean (after years) and it starts "reasonably" well when very hot (90 degrees plus), try that with pump gas!!! Of course when I am on the road I have to run pump gas. Also JD recommends it, enough said! Don H.

[Joe C.]

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

Duke Williams did a seminar at last years convention. Here is the PowerPoint, it goes into some very deep detail about fuel on page 10. It backs up pretty much what Joe is saying above.

http://www.metroli.org/pdf/2012 Nati...ingseminar.pdf

Mike,

"Quench", or the volume left between the flat part of the piston crown and the flat part of the head (i.e.: outside of the combustion chamber) is a very important factor in determining detonation resistance. Vintage engines built during the 50's and 60's had wide variations in quench compared to modern engines, on the order of .020" or more. The nominal quench was specified at .050" (nominal piston to deck clearance) plus .018" (compressed steel head gasket thickness), or .068". Keep in mind that the piston to deck clearance could have varied by as much as about .020" within one engine and between engines, which yields quench anywhere between .058" and .078" . The tighter the quench, the less the tendency to detonate, and conservative minimum "safe" quench (before piston to head contact occurs) is about .040". Factors such as piston material, piston to bore clearance, connecting rod strength and modulus of elasticity and maximum RPM affect minimum safe quench.

If an engine is very carefully designed and built, safe quench has been achieved at as low as .025"! Obviously, an engine whose quench is .025" will have less tendency to detonate than one whose quench is .068", all else being equal. The engine that was mentioned in post #15, above, was designed and built with quench of .032" (plus/minus .0005"), as well as with special cooling capability and very low intake manifold temperature.

[Paul H.]

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

My old Vettes run fine on 93 unleaded premium with 10% ethanol. 61 383 stroker 10.25:1, 65 327/350 11:1, 68 427/390 10.25:1. No additives. I run these cars year round about 2,500 miles each and I drive them like they were meant to be driven. No pinging and the spark plugs burn alot nicer than they used to on leaded gas back in the day.

[Michael W.]

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

the spark plugs burn alot nicer than they used to on leaded gas back in the day.

Yes, another advantage of unleaded.

[Ken A.]

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

Finally, a breath of truthful air.

This is one of those topics that galvanizes people in opposite directions, and no amount of reasoned argument will make a lick of difference. In any case, here are some facts:

1. If you have reasonably quiet exhaust, and you can't hear detonation (considering you have average hearing acuity), then any inaudible detonation, if present, will absolutely do no harm, whatsoever, to your pistons and/or rings.
2. If you want to make absolutely sure that the engine is not severely detonating in a situation where the exhaust is very loud, then a chassis dyno will tell the tale. Advancing the spark timing to the point of power drop-off (indicative of detonation), and then retarding until power increases will yield optimal engine performance.
3. If an engine "runs fine" in no way indicates that it's running optimally.
4. All engines are built with varying tolerances and thus varying SCR, and although they will all "run fine" with the same tune, they will all respond differently to tailored tuning.
5. The engine builder whom you mention should go back to fixing vacuum cleaners. Steer clear of him.

[Michael H.]

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

Tell us what's wrong with the way your car runs and someone here can help you fix it. It should run perfectly on straight 91, ethanol mix or not.

What about the guys that have the boil issue with E10? And poor/erratic idle. (yeah, I know... you don't have that problem up there)

[Michael W.]

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

What about the guys that have the boil issue with E10? And poor/erratic idle. (yeah, I know... you don't have that problem up there)

Move out of the swamp to a less hostile environment?

Percolation/vapour lock has been traced to use of fuel having a low RVP. Apparently, the major contributor to low RVP in today's given fuel is butane and not everybody's favourite whipping boy, ethanol. Although a real problem for some owners in the Gulf states, it's not universal. Why do some guys in your area not have a problem and some do? My injuneering anal retentive obsessive compulsive background would guide me towards understanding and determining root cause and not apply bandaids.

As you've said no problem up here. Pretty much a non-issue for most of the continent. We fret more over the cost of tungsten vs. steel studs for our snow tires.

[Michael H.]

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

Move out of the swamp to a less hostile environment? Why do some guys in your area not have a problem and some do? My injuneering anal retentive obsessive compulsive background would guide me towards understanding and determining root cause and not apply bandaids.

Maybe the problem is in my imagination. Or maybe it's because I'm kinda new at all this car stuff. I'll try a few cans of fuel additive.

[Michael W.]

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

Maybe the problem is in my imagination. Or maybe it's because I'm kinda new at all this car stuff. I'll try a few cans of fuel additive.

Nowhere did I deny (here or elsewhere) that you have a problem, quite the contrary as clearly contained in the paragraph that you've edited out. The difficulty is isolating the cause and finding an appropriate fix. I don't think said fix is in a can of additive.

[Kurt G.]

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

Hey guys. Hopefully this will help a little with the understanding of Avgas. The stuff you get now is labeled 100LL. Translated low lead, minimum octane 100. The lead content in today's Avgas is about a third of what it was pre 1980 something. Prior to then we used 80-87 octane in the little single engines and 100-130 octane in the larger 6+ cylinder engines. Due to refining limits from the EPA and a decreased demand in the 80-87 octane fuel they did away with it. The 100LL is a minimum 100 octane, blue in color and runs very dry, and hot. A petroleum engineer told me several years ago that is I mixed 5 gallons of regular 87 octane car gas with a gallon of 100LL I'd get about the same lead content car gas used to have and an octane of about 110.

[Duke W.]

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

Move out of the swamp to a less hostile environment?

Percolation/vapour lock has been traced to use of fuel having a low RVP. Apparently, the major contributor to low RVP in today's given fuel is butane and not everybody's favourite whipping boy, ethanol. Although a real problem for some owners in the Gulf states, it's not universal. Why do some guys in your area not have a problem and some do? My injuneering anal retentive obsessive compulsive background would guide me towards understanding and determining root cause and not apply bandaids.

As you've said no problem up here. Pretty much a non-issue for most of the continent. We fret more over the cost of tungsten vs. steel studs for our snow tires.

No, RVP is not the cause of vapor lock and hot soak flooding in vintage engines. RVP is an issue with evaporative emissions from modern vehicles, and it's measured at 100F. Nowadays new vehicles have such low exhaust HC emissions, it may be possible that the majority of HC emissions come from fuel supply vaporization, so we will probably continue to see lower RVPs in the future, and RVPs today are lower than they were in the fifties and sixties.

Modern engines are not suseptible to vapor lock and hot soak flooding issues that we see in vintage engilnes because beyond the fuel supply tank, the system is essentially sealed and operating pressure is at least 35 psig.

The culprit in vintage car vapor lock and hot soak flooding is the lower mid range boiling points - say from the 20-50 percent points of the distillation curve due to the presense of ethanol that has a boiling temperature of 170F.

Regarding octane requirement of vintage engines, owners need to understand the different octane measuring methods and which one they are dealing with and how to convert one to another. Then they need to do some testing.

First, the spark advance map should be tested to determine if it meets OE spec or is somethilng else. Pre-'71 engines should be tested with the highest octane commercially available fuel. If it doesn't detonate, let the tank get near empty then add a few gallons of the next lower octane and test for detonation. (Many high compression engines were rebuilt with lower compression beginning in the seventies, and most owners don't know what the true CR of their engine is.)

Carbureted 265s and 283s that have OE compression likely don't need the highest octane available fuel, and '71-up engines were designed to operate on unleaded regular gasoline (91 RON or 87 PON) and don't need higher octane unless they were rebuilt with higher compression.

Additional information and a step-by-step approach is at the link referenced in post #16. You can just do the octane test and leave everthing else alone, but your engine will perform better and use less fuel if you optimize the spark advance map first. If you can change spark plugs and adjust the dwell angle, you should be able to optimize the spark advance map and conduct fuel octane tests. It's not rocket science!

Whenever this question comes up there are about as many "opinions" as there are responses to the question. Anecdotal evidence indicates that most known never-rebuilt OE engines operate detonation-free on common commercially available fuel, and there is no need for race gas, avgas, or any snake-oil additives. There are exceptions, but what really counts is what octane fuel is required in YOUR specific engine to operate detonation-free in YOUR specific driving environment and YOUR specific driving style.

Once you have a rational/analytical approach to the "problem" - if one actually exists - then it's time to go out to the garage, get out the equipment and tools, and go to work.

Duke

[Michael W.]

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

No, RVP is not the cause of vapor lock and hoat soak flooding in vintage engines. RVP is an issue with evaporative emissions and it's measured at 100F. Nowadays new vehicles have such low exhaust HC emissions, it may be possible that the majority of HC emissions come from fuel supply vaporization, so we will probably continue to see lower RVPs in the future, and RVPs today are lower than they were in the fifties and sixties.

Modern engines are not suseptible to "vapor lock" issues that we see in vintage engilnes because beyond the fuel supply tank, the system is essentially sealed and operating pressure is at least 35 psig.

The culprit in vintage car vapor lock and hot soak flooding is the lower mid range boiling point - say from the 40-60 percent points of the distillation curve due to the presense of ethanol that has a boiling temperature of 170F.

Glad you chimed in. There was a discussion on 'that other board' regarding the association of RVP with percolation and vapour lock. It was this same discussion that first advanced the increased usage of butane as a possible culprit. What say you?

[Michael W.]

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

Hey guys. Hopefully this will help a little with the understanding of Avgas. The stuff you get now is labeled 100LL. Translated low lead, minimum octane 100. The lead content in today's Avgas is about a third of what it was pre 1980 something. Prior to then we used 80-87 octane in the little single engines and 100-130 octane in the larger 6+ cylinder engines. Due to refining limits from the EPA and a decreased demand in the 80-87 octane fuel they did away with it. The 100LL is a minimum 100 octane, blue in color and runs very dry, and hot. A petroleum engineer told me several years ago that is I mixed 5 gallons of regular 87 octane car gas with a gallon of 100LL I'd get about the same lead content car gas used to have and an octane of about 110.

Kurt- first off, no Corvette 'needs' lead in any amount. That's an olf myth that has proven to be just that, many times over.

Although some avgas is called '100LL' don't assume that this is 7 points higher than 93 octane automobile gas. Two different rating scales as Duke mentions.

Mixing 87AKI with 100LL avgas at a 5:1 ratio will most certainly not give a rating of 110AKI. A rough guess would be some where around 90ish.

[David K.]