Avgas II-

[Normy]

-I'm conducting an experiment with my '85 S2 5 speed. About 8 years ago, I put 10 gallons of 100LL aviation fuel in my 928 to see what would happen. "100LL" is 100 octane in aviation-speak with low lead content. There is still some lead, since there are plenty of old aircraft piston engines in the air with soft valve seats. This stuff is colored with a special blue dye that becomes clear if it is mixed with any other fuel, since aircraft engines need octane. It is different stuff- it really doesn't smell like gasoline, and when it burns, the exhaust smells different too; it has more of a plastic smell.

There are quite a few differences between 100LL and regular gasoline. The engines in light aircraft are very different from their road-going cousins. For example, the typical Piper Warrior or Cessna 172 is powered by what is known as an "O-320", or a horizontally opposed four cylinder engine. This four cylinder is air cooled and has a pushrod valve train, meaning that it is very similar to the type 4 engine in a 914. What is different is that while the 914 had 1.7, 1.8, or 2.0 liters of displacement, the O-320 has 320 cubic inches, or about 5.2 liters. Yet it only develops about 160 hp. The reason for this strange engine is simple: the crankshaft is attached to a propellor, and the prop cannot handle much RPM. 2800 is the redline on one of these engines, and if you want to make 160 hp at that low of a speed, you need lots of cubic inches and a lot of cylinder pressure. Since cylinder pressure can cause high temperatures, especially when the cyclic rate is slow....high octane is needed. What's more, aircraft engines are basically operated at high power settings for extended periods of time. You don't "floor" your Porsche in order to get to cruising altitude, but aircraft engines do. These can see wide-open throttle for several minutes while they climb to altitude, and internal temperatures and pressures can be enormous. Thus, 5.2 liters is needed to produce the same power that 2.0 liters worth of car engine normally would accomplish.

Getting back to the subject [damn, I can be long-winded!], back around 2002 I put 100LL in my 928 to see what would happen. The car ran fine for a day or two, but it seemed to slowly start to have driveability issues. These were minor- it started to run kind of rich, and the idle would hunt a little bit at stoplights, along with black smoke. After a week of driving, during which I used up most of the 100LL, I pulled the plugs and found them fouled.

That was then, this is now. I have, after a TON of trial and error, finally managed to get this car dialed in. It doesn't run rich any more [I found a bad MAF connector], and via some screwing around, I managed to get the rising-rate fuel pressure regulator dialed in so that the idle mixture is fairly lean [15-16:1], while the full throttle ratio is a nearly perfect 12:1. I'm using Bosch spark plugs that are WAY hot: WR9DP, or something like that. There is no hesitation any more, just plenty of wheel spin. In fact, the car has a huge problem hooking up now!

However, one of the best things I have ever done to this car is to install Porken's EZF'r ignition chip. The difference on this car was night and day- at part throttle, such as driving around town, the car seems to have so much more low RPM torque that I can't believe it is the same engine. That chip must give a LOT of advance. So much so that if I stop at a stop sign in a neighborhood, and leave it in 2nd gear, as I pull away, I hear about a second of spark knock, which of course is my own fault for lugging the engine. It is an easy trade- I'll take the around-town torque any day!

So my low fuel light came on today, and I decided to try an experiment. I drove home instead of to the Chevron station, parked the Porsche, and drove my Aerostar minivan out to the local airport. I took two 5 gallon containers with me, and had the local fixed-base operator [FBO] fill them up with 100LL. $4.42 per gallon means that I'm $44.20 poorer tonight, but I want to see what happens with the new setup. 100LL is 100 octane in aviation circles, but it works out to about 104 octane in automotive fuel. I'm going to drive the crap out of the car tomorrow, and then park it for a week [I have to go to Brazil for Fedex; back in Florida on the 13th], then drive it some more. When the fuel is spent, I'll pull the plugs and see what happens.

The long and short: Last time I did this, I basically illustrated why too much octane was...well, too much. I'm interested to see what will happen with the new chip, plugs, and fuel pressure regulator. It occurs to me that 100LL avgas might be a hot tip for the boostards.

N!

[RKDinOKC]

Lead will stop up cats if you have them. There is a local station here in OKC that has a 101 pump for hot rod cars and bikes. I used it on my hopped up 951 so I could confidently run 16psi of boost. I don't see any reason to run it in my normally aspirated 928 though.

[76FJ55]

The lead will most likely plate out on your O2 sensor as well ruening it, therefore effecting closed loop opperation too.

100LL containd 2 g/gal of TE (tetraethyl lead)
unleaded auto 0.1-0.001 g/gal TE
leaded auto fuel (pre '86) 1 g/gal TE

So even with the LL (low lead) conotation associated the 100LL it still has twice the amount of lead as regular leaded fuel produced before 1986.

[Normy]

Originally Posted by 76FJ55

The lead will most likely plate out on your O2 sensor as well ruening it, therefore effecting closed loop opperation too.

100LL containd 2 g/gal of TE (tetraethyl lead)
unleaded auto 0.1-0.001 g/gal TE
leaded auto fuel (pre '86) 1 g/gal TE

So even with the LL (low lead) conotation associated the 100LL it still has twice the amount of lead as regular leaded fuel produced before 1986.

My car has no catalytic converters [right now], and the LH computer doesn't use an O2 sensor. My PLX air/fuel ratio meter does use an O2 sensor, but so far it appears to functioning correctly.

Well, I drove the car for about 100 miles over a period of days, mostly in the city, and burned off the avgas. Conclusion: Absolutely nothing. The car ran fine and powerfully during the few days I used this stuff with no plug fouling, but also no perceivable increase in power.

Points:

1. Excess octane probably doesn't help much on 10.4: 1 compression and natural aspiration.

2. Bosch platinum plugs in heat range "9" do not foul out on avgas, but nor is there any spark knock, even in Florida heat.

Someone with a 951, a 911 TT, or one of the boosted 928's ought to try this and see what the results are. I suspect that on a boosted engine along with a true knock-sensing ignition that this stuff would make a big difference.

N

[morriss]

The aviation fuel might work better for the old hot rods that ran on leaded gasoline. When I lived in San Antonio my father would go to a station next to the airport and put a full tank of aviation fuel in the '60 vette once a month. I don't remember it making much of a difference though; he did it more for the lead than anything else. The old Chevy fuel injections MUST have it.

[Normy]

Originally Posted by morriss

The aviation fuel might work better for the old hot rods that ran on leaded gasoline. When I lived in San Antonio my father would go to a station next to the airport and put a full tank of aviation fuel in the '60 vette once a month. I don't remember it making much of a difference though; he did it more for the lead than anything else. The old Chevy fuel injections MUST have it.

This fuel, this 100LL, or "blue" fuel, has a low level of tetraethyl lead. I don't think it will be produced much longer, since the aviation cylinders that have been manufactured in the 1970's that require a bit of TEL are now dwindling, and there is no reason that newer cylinders need the cushioning of the lead, since they probably have the hardened valve seats. I guess you never know, there may be some cylinder heads produced in the future.

N

[RKDinOKC]

I was able to make more power with 100 octane in my 944 Turbo not because 100 octane makes more power, but because I could run higher boost without pre-detonation. Higher boost makes more power not higher octane. Higher boost without higher octane makes the same more power as higher boost without higher octane, but only for a short time until internal bits break from pre-detonation then it makes quite a bit less power

[Normy]

Originally Posted by RKDinOKC

I was able to make more power with 100 octane in my 944 Turbo not because 100 octane makes more power, but because I could run higher boost without pre-detonation. Higher boost makes more power not higher octane. Higher boost without higher octane makes the same more power as higher boost without higher octane, but only for a short time until internal bits break from pre-detonation then it makes quite a bit less power

Yeah-

Also, if you have a knock-senor ignition, then you can make a bit more hp due to the fact that the knock sensors don't hear as much detonation/pre-ignition, and as such don't retard the ignition quite as much. That means more gas gets burned, more air gets heated to a higher temperature, and more force is applied to the piston.

I don't have a knock sensor ignition, I have EZF. But I do have wild cams and high compression, and I was interested to see how an engine like this that is now dialed in would behave on this fuel. I tried it about 8 years ago, and it fouled my plugs. Now that I have the car running right....it did nothing. I bet a 951 or a boosted 928 could really cause some serious trouble running on this stuff however!

Anyway...

N

[Griffinroydonal]

I have run Shell AV blue in my car and the only difference I saw was in my Billfold. Av blue 100 octane is $4.60 a gallon and premium is $3.00 a gallon. I had the fuel truck fill up the 87s4 after he gassed up the plane. The driver warned me about running avblue in the car but filled it up anyway. The car ran fine and I think it got better gas milage but for the money I will stick with mid-grade pump gas.

[Fabio421]

Your car shouldn't see any performance difference if it isn't tuned for the higher octane. Otherwise, it's just wasted money. Higher octane could be beneficial if you had knock or if you advanced the timing to take advantage of the added octane. Boosted cars could also see an advantage since the timing could be more safely advanced. Instead of Avgas why not just use Toluene? It's already in gasoline and is 114 octane. It's also mor eredily available to the average hobbyist as it's sold in paint stores.

TOLUENE - Some Basic Questions.



Q: Will my car benefit from octane boosting?

A: Consumer organizations have effectively emphasized the larger markups that oil companies charge for high octane gasoline, implying that for most vehicles higher octane fuel is a complete waste of money. It has been quite a long time since the consumer alert was issued. Since then engine technology has evolved greatly, while people's perceptions generally have not.

Modern vehicles now use computerized engine management systems that can react to engine knock and retard ignition timing if low octane fuel is being used. Consequently cars are now being manufactured with very high compression ratios that appear to give good fuel economy and at the same time good performance. This combination does assume that fuel of adequate octane is being used.


Q: Why bother to boost octane at all since my engine can run just fine on lower octane fuel?

A: For a high compression engine to run on low octane fuel, the engine management system will need to retard the ignition timing to prevent preignition or pinging. Retarding the ignition timing means that the firing of the spark plug is delayed until a later moment in the compression stroke. It does not take much to see that a later onset of combustion means that the combustion is less complete, which in turn mean less power and poorer fuel economy. It is possible that the casual driver will still come out ahead in terms of saving money by using low octane fuel, but the retarded ignition advance also means a rougher running engine and a much duller throttle response. Thus octane boosting is not necessarily of interest to all motorists but rather the enthusiasts.

For turbocharged or supercharged engines, insufficient octane will also lead the engine management system to curtail the amount of boost which in turn defeats the purpose of these engines.


Q: How did you discover using toluene?

A: Someone came across a web page that described various DIY home brew octane booster formulas. One of which used toluene as its main ingredient. As a Formula 1 racing fan of many years, I recalled that toluene was used extensively in the turbo era in the 1980s by all the Formula 1 teams. The 1.5 liter turbocharged engines ran as much as 5 bars of boost (73 psi) in qualifying and 4 bars (59 psi) in the actual race. Power output exceeded 1500bhp, which translates into 1000bhp/liter, an astronomical figure.

A motorsports journalist, Ian Bamsey, was able to obtain Honda's cooperation for his book "McLaren Honda Turbo, a Technical Appraisal". The book documents the key role that the toluene fuel played in allowing these tiny engines to run so much turbo boost without detonation. The term "rocket fuel" originated from the Formula 1 fraternity as an affectionate nickname to describe its devastating potency. Thus I concluded that I should focus my research on using toluene for my octane boosting project.

Individuals with good long term memory will recall that when unleaded gasoline was first introduced, only low octane grades were available. While it is not entirely clear that high octane super unleaded gas came about as a result of the advances in fuel technology in Formula 1, there is every reason to suspect that this is indeed the case, since many of the major oil companies were involved in the escalating race to develop increasingly potent racing fuel during this era.


Q: Why do you think toluene is better than other types of octane boosters?

A: Several reasons:

Mindful of the evil reputation of octane boosters in general, toluene is a very safe choice because it is one of the main octane boosters used by oil companies in producing ordinary gasoline of all grades. Thus if toluene is indeed harmful to your engine as feared, your engine would have disintegrated long, long ago since ordinary pump gasoline can contain as much as 50% aromatic hydrocarbons.

Toluene is a pure hydrocarbon (C7H8). i.e. it contains only hydrogen and carbon atoms. It belongs to a particular category of hydrocarbons called aromatic hydrocarbons. Complete combustion of toluene yields CO2 and H2O. This fact ensures that the entire emission control system such as the catalyst and oxygen sensor of your car is unaffected. There are no metallic compounds (lead, magnesium etc), no nitro compounds and no oxygen atoms in toluene. It is made up of exactly the same ingredients as ordinary gasoline. In fact it is one of the main ingredients of gasoline.

Toluene has a RON octane rating of 121 and a MON rating of 107, leading to a (R+M)/2 rating of 114. (R+M)/2 is how ordinary fuels are rated in the US. Note that toluene has a sensitivity rating of 121-107=14. This compares favorably with alcohols which have sensitivities in the 20-30 range. The more sensitive a fuel is the more its performance degrades under load. Toluene's low sensitivity means that it is an excellent fuel for a heavily loaded engine.

Toluene is denser than ordinary gasoline (0.87 g/mL vs. 0.72-0.74) and contains more energy per unit volume. Thus combustion of toluene leads to more energy being liberated and thus more power generated. This is in contrast to oxygenated octane boosters like ethanol or MTBE which contain less energy per unit volume compared to gasoline. The higher heating value of toluene also means that the exhaust gases contain more kinetic energy, which in turn means that there is more energy to drive turbocharger vanes. In practical terms this is experienced as a faster onset of turbo boost.

Chevron's published composition of 100 octane aviation fuel shows that toluene comprises up to 14% alone and is the predominant aromatic hydrocarbon. Unfortunately composition specifications for automotive gasoline is harder to pin down due to constantly changing requirements.

Chevron's web site also describes the problems of ethanol being used in gasoline.

MTBE was heavily touted as a clean additive several years ago, and became a key ingredient in reformulated gasoline that is sold in California. But recently new studies arose that showed that MTBE was far more toxic than previously imagined. Organizations such as oxybusters have formed around the country to eliminate the use of MTBE in gasoline and several states, including California have passed new laws to eventually outlaw MTBE.


Q: Why not simply use racing gasoline or aviation fuel?

A1: Most types of aviation fuel have very high lead content, which would rule out cars equipped with catalytic converters. Most piston engined aircraft burn leaded fuel. Also aviation fuel has a very different hydrocarbon mix to optimize volatility properties at high altitude.

A2: Racing gasoline could be a much more convenient way to run high octane fuel compared to having to constantly mix in toluene with each fill up. There are, however a few caveats:


You don't know for sure if you are really getting what is being advertised. You should find out if the fuel inspectors verify the actual octane of the racing gasoline in addition to ordinary gasoline. If you paid $3/gallon and only got 94 or 95 octane instead of 100 octane you may conclude erroneously that your car does not benefit from octane boosting.

You don't know what octane boosters are used in the racing gasoline. The worst case scenario is buying leaded racing gasoline without knowing it. Unleaded racing gasoline may still contain damaging octane boosters like MMT or methanol. A very high alcohol content will lead to fuel line erosion, accelerated fuel pump wear, very poor fuel economy and possibly lower performance, as alcohols have a less impressive MON rating than aromatics.

It takes smaller quantities of toluene to achieve the same octane boost compared to 100 octane racing gas. I have not seen unleaded racing gas for sale that exceeds the octane rating of toluene.

Since toluene is not officially sold as a fuel, gas taxes do not apply. Also racing gasoline tend to have higher markups being of interest to the performance minded enthusiast and thus is very likely to be more expensive to buy and use long term than toluene, which is typically used in more mundane applications like paint thinner.

[JhwShark]

Fabio...
GREAT READ!

Thanks,
Jon

[mitsy]

you guys are so lucky 3.00dollars a gallon in the uk its 5.00pounds plus which is about 8.00 dollars ish im moving and bringing my shark with me

[Griffinroydonal]

You would be very welcome in the states and if you bring the shark it is easy to make friends. Every time you stop for gas or park it someone will want to talk to you about it.

[harborman]

Originally Posted by Griffinroydonal

You would be very welcome in the states and if you bring the shark it is easy to make friends. Every time you stop for gas or park it someone will want to talk to you about it.

Also, remember the car draws attention from our police! I thought one cop was going to spring his neck as I drove by the other day. He was going the other way but he sure looked!!! Been happening a lot here!

[Normy]

Originally Posted by Fabio421

Your car shouldn't see any performance difference if it isn't tuned for the higher octane. Otherwise, it's just wasted money. Higher octane could be beneficial if you had knock or if you advanced the timing to take advantage of the added octane. Boosted cars could also see an advantage since the timing could be more safely advanced. Instead of Avgas why not just use Toluene? It's already in gasoline and is 114 octane. It's also mor eredily available to the average hobbyist as it's sold in paint stores.

TOLUENE - Some Basic Questions.



Q: Will my car benefit from octane boosting?

A: Consumer organizations have effectively emphasized the larger markups that oil companies charge for high octane gasoline, implying that for most vehicles higher octane fuel is a complete waste of money. It has been quite a long time since the consumer alert was issued. Since then engine technology has evolved greatly, while people's perceptions generally have not.

Modern vehicles now use computerized engine management systems that can react to engine knock and retard ignition timing if low octane fuel is being used. Consequently cars are now being manufactured with very high compression ratios that appear to give good fuel economy and at the same time good performance. This combination does assume that fuel of adequate octane is being used.


Q: Why bother to boost octane at all since my engine can run just fine on lower octane fuel?

A: For a high compression engine to run on low octane fuel, the engine management system will need to retard the ignition timing to prevent preignition or pinging. Retarding the ignition timing means that the firing of the spark plug is delayed until a later moment in the compression stroke. It does not take much to see that a later onset of combustion means that the combustion is less complete, which in turn mean less power and poorer fuel economy. It is possible that the casual driver will still come out ahead in terms of saving money by using low octane fuel, but the retarded ignition advance also means a rougher running engine and a much duller throttle response. Thus octane boosting is not necessarily of interest to all motorists but rather the enthusiasts.

For turbocharged or supercharged engines, insufficient octane will also lead the engine management system to curtail the amount of boost which in turn defeats the purpose of these engines.


Q: How did you discover using toluene?

A: Someone came across a web page that described various DIY home brew octane booster formulas. One of which used toluene as its main ingredient. As a Formula 1 racing fan of many years, I recalled that toluene was used extensively in the turbo era in the 1980s by all the Formula 1 teams. The 1.5 liter turbocharged engines ran as much as 5 bars of boost (73 psi) in qualifying and 4 bars (59 psi) in the actual race. Power output exceeded 1500bhp, which translates into 1000bhp/liter, an astronomical figure.

A motorsports journalist, Ian Bamsey, was able to obtain Honda's cooperation for his book "McLaren Honda Turbo, a Technical Appraisal". The book documents the key role that the toluene fuel played in allowing these tiny engines to run so much turbo boost without detonation. The term "rocket fuel" originated from the Formula 1 fraternity as an affectionate nickname to describe its devastating potency. Thus I concluded that I should focus my research on using toluene for my octane boosting project.

Individuals with good long term memory will recall that when unleaded gasoline was first introduced, only low octane grades were available. While it is not entirely clear that high octane super unleaded gas came about as a result of the advances in fuel technology in Formula 1, there is every reason to suspect that this is indeed the case, since many of the major oil companies were involved in the escalating race to develop increasingly potent racing fuel during this era.


Q: Why do you think toluene is better than other types of octane boosters?

A: Several reasons:

Mindful of the evil reputation of octane boosters in general, toluene is a very safe choice because it is one of the main octane boosters used by oil companies in producing ordinary gasoline of all grades. Thus if toluene is indeed harmful to your engine as feared, your engine would have disintegrated long, long ago since ordinary pump gasoline can contain as much as 50% aromatic hydrocarbons.

Toluene is a pure hydrocarbon (C7H8). i.e. it contains only hydrogen and carbon atoms. It belongs to a particular category of hydrocarbons called aromatic hydrocarbons. Complete combustion of toluene yields CO2 and H2O. This fact ensures that the entire emission control system such as the catalyst and oxygen sensor of your car is unaffected. There are no metallic compounds (lead, magnesium etc), no nitro compounds and no oxygen atoms in toluene. It is made up of exactly the same ingredients as ordinary gasoline. In fact it is one of the main ingredients of gasoline.

Toluene has a RON octane rating of 121 and a MON rating of 107, leading to a (R+M)/2 rating of 114. (R+M)/2 is how ordinary fuels are rated in the US. Note that toluene has a sensitivity rating of 121-107=14. This compares favorably with alcohols which have sensitivities in the 20-30 range. The more sensitive a fuel is the more its performance degrades under load. Toluene's low sensitivity means that it is an excellent fuel for a heavily loaded engine.

Toluene is denser than ordinary gasoline (0.87 g/mL vs. 0.72-0.74) and contains more energy per unit volume. Thus combustion of toluene leads to more energy being liberated and thus more power generated. This is in contrast to oxygenated octane boosters like ethanol or MTBE which contain less energy per unit volume compared to gasoline. The higher heating value of toluene also means that the exhaust gases contain more kinetic energy, which in turn means that there is more energy to drive turbocharger vanes. In practical terms this is experienced as a faster onset of turbo boost.

Chevron's published composition of 100 octane aviation fuel shows that toluene comprises up to 14% alone and is the predominant aromatic hydrocarbon. Unfortunately composition specifications for automotive gasoline is harder to pin down due to constantly changing requirements.

Chevron's web site also describes the problems of ethanol being used in gasoline.

MTBE was heavily touted as a clean additive several years ago, and became a key ingredient in reformulated gasoline that is sold in California. But recently new studies arose that showed that MTBE was far more toxic than previously imagined. Organizations such as oxybusters have formed around the country to eliminate the use of MTBE in gasoline and several states, including California have passed new laws to eventually outlaw MTBE.


Q: Why not simply use racing gasoline or aviation fuel?

A1: Most types of aviation fuel have very high lead content, which would rule out cars equipped with catalytic converters. Most piston engined aircraft burn leaded fuel. Also aviation fuel has a very different hydrocarbon mix to optimize volatility properties at high altitude.

A2: Racing gasoline could be a much more convenient way to run high octane fuel compared to having to constantly mix in toluene with each fill up. There are, however a few caveats:


You don't know for sure if you are really getting what is being advertised. You should find out if the fuel inspectors verify the actual octane of the racing gasoline in addition to ordinary gasoline. If you paid $3/gallon and only got 94 or 95 octane instead of 100 octane you may conclude erroneously that your car does not benefit from octane boosting.

It takes smaller quantities of toluene to achieve the same octane boost compared to 100 octane racing gas. I have not seen unleaded racing gas for sale that exceeds the octane rating of toluene.

Since toluene is not officially sold as a fuel, gas taxes do not apply. Also racing gasoline tend to have higher markups being of interest to the performance minded enthusiast and thus is very likely to be more expensive to buy and use long term than toluene, which is typically used in more mundane applications like paint thinner.

GREAT POST! Thank you, by the way!

With 10.4:1 compression, I have always been concerned about detonation with my non-knock sensor 928S2 in the United States. This car was sold in Austria, and the fuel in Europe is a point or two higher typically in octane. Though there's no boost on my 928, it isn't impossible to burn a piston without a blower. My high-school friend Matt Rogers raced a GSXR-750 for a few years at Grattan raceway up in Michigan and he eventually found small aluminum balls on the tops of his pistons when he pulled the bike motor apart. He had installed a Muzzy exhaust; apparently he didn't re-jet the carbs right and when he was racing he apparently overheated his pistons. With a helmet on and with that screaming exhaust and the wind noise he didn't hear the detonation. Well, my 928's exhaust can be heard in Palm Beach County [I live in Broward~], I have my stereo cranked up always, and I drive with the windows wide f*cking open. And I drive like a bat out of hell- I get 9-10 mpg with my 928 for a reason. There is nothing wrong with that engine- I just like the way that a big-block V8 such as this sounds when it winds out.

I wanted to see if there was any advantage to this stuff now that I finally seem to have my drivability issues surmounted. I found no advantage whatsoever. Well, I guess one advantage: My wallet weighs somewhat less, so I guess the car is faster afterall, due to the loss of weight~

N!