Why high octane gas rather than octane boost ?
Thread Starter
Instructor
Joined: Aug 2004
Posts: 155
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From: SF Bay Area CA
Why high octane gas rather than octane boost ?
hi,
I understand that high octane has higher resistance to premature detonation on high comp-ratio engine, but I have been wondering why people uses expensive high octane gas rather than octane boost with 92 gas.
Is there anything which is harmful for engine or fuel system to use octane boost ?
I understand that high octane has higher resistance to premature detonation on high comp-ratio engine, but I have been wondering why people uses expensive high octane gas rather than octane boost with 92 gas.
Is there anything which is harmful for engine or fuel system to use octane boost ?
Drifting
Joined: Aug 2004
Posts: 1,883
Likes: 124
From: Lubbock TX
Octane basically determines a fuel's resistance to detonation. With gasoline, that's done by refining the impurities out. The more "pure" the gasoline, the more detonation resistant it is, so it has a higher octane rating. Additives make gasoline more detonation resistant by adding chemicals that impede or retard detonation. As I understand it, when you do the math, it's cheaper to run higher octane than by using additives anyway.
Thread Starter
Instructor
Joined: Aug 2004
Posts: 155
Likes: 0
From: SF Bay Area CA
But octane boost I can find at shop is $5 to $10 and advertises that you can put one bottle to 20 gallon of gas(I don't know how much octane it results in , though).
I'm sure that using 100 octane gas is probably more expensive than that. Am i wrong ?
I'm sure that using 100 octane gas is probably more expensive than that. Am i wrong ?
Drifting
Joined: Mar 2006
Posts: 1,526
Likes: 2
From: Oak Ridge NC
Octane boosters advertise that you will gain 3 points, 6 points or whatever...remember that a point is 1/10. An octane booster advertising a 6 point gain takes your from 92 to 92.6. Not worth the money.
I can buy 110 race gas (leaded) for $5 a gallon. You can find 100 unleaded octane in these parts for about $5 (last time I looked).
Thread Starter
Instructor
Joined: Aug 2004
Posts: 155
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From: SF Bay Area CA
Drifting
Joined: May 2006
Posts: 1,544
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From: Youngstown Ohio
Additives are unpredictable at best. If you have a $20k engine it's best to use quality products including fuel, with that said I have used additives at times as I run different plugs and fuel octane for street vs. raceing, and have added octane booster or very high octane fuel to raise a partial tank of 102 or 105 to 108-114
Check this site for more info:
http://www.sunocoinc.com/site/consum...ditionalfuels/
Check this site for more info:
http://www.sunocoinc.com/site/consum...ditionalfuels/
Racer
Joined: Mar 2005
Posts: 393
Likes: 3
From: Dallas, TX
all you need to do is find a small local airport and go fill up where the planes do. they sell 100octane low lead at the small airport near my house, it averages about a dollar more a gallon than premium at the regular pumps. Ive gotten some strange looks when I pull up to the pump where a Cessna normally fills up. I think its worth it, I dont absolutly have to run airplane fuel, I can run 93 pump gas without a problem but she like 100LL alot better.
-alex
-alex
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Burning Brakes
Joined: Oct 2006
Posts: 1,089
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From: Native Californian CALIFORNIA
Army
For you that have high compression engines ther airport is a must.
However, plenty of engines produce hp at lower cr's that allow for pump gas. Pump gas is the way to go
However, plenty of engines produce hp at lower cr's that allow for pump gas. Pump gas is the way to go
Safety Car
Joined: Oct 2000
Posts: 3,547
Likes: 12
From: Carbondale Pa.
I thought that A/V gas was an urban legend kinda deal, and wasnt really suited for use in cars, something about the formulation and different additives that is used in its production, is it taxed the same as gas at a regular station ? I remember my uncle having a Mercedes diesel years ago and using home heating oil for it untill his supplier found out that his home was heated by natural gas. Peace,,,Moosie 
Team Owner
Joined: Apr 1999
Posts: 21,953
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
all you need to do is find a small local airport and go fill up where the planes do. they sell 100octane low lead at the small airport near my house, it averages about a dollar more a gallon than premium at the regular pumps. Ive gotten some strange looks when I pull up to the pump where a Cessna normally fills up. I think its worth it, I dont absolutly have to run airplane fuel, I can run 93 pump gas without a problem but she like 100LL alot better.
-alex
-alex
It is not chemically the same as automotive fuel. It is made to run at over 10,000 feet in relatively low rpm motors with very high compression. One of the planes I fly gets max GPH vs speed at @ 1800 rpm. It's vapor point and flash point are all wrong for automotive use.
Instructor
Joined: Nov 2004
Posts: 162
Likes: 0
What about lead substitute (if you don't have a cat.)?
Wasn't it possible to have higher compression on the older leaded cars because the lead prevented detonation? Didn't the CRs fall because carmakers had to run on unleaded, and unleaded pump gas would detonate unless it had a much higher octane or lead?
I just had hardened valve seats installed, but I still have a 11:1 CR to deal with on my '70...
Wasn't it possible to have higher compression on the older leaded cars because the lead prevented detonation? Didn't the CRs fall because carmakers had to run on unleaded, and unleaded pump gas would detonate unless it had a much higher octane or lead?
I just had hardened valve seats installed, but I still have a 11:1 CR to deal with on my '70...
Tech Contributor
Joined: Aug 1999
Posts: 14,365
Likes: 6,345
From: At my Bar drinking and wrenching in Lafayette Colorado
all you need to do is find a small local airport and go fill up where the planes do. they sell 100octane low lead at the small airport near my house, it averages about a dollar more a gallon than premium at the regular pumps. Ive gotten some strange looks when I pull up to the pump where a Cessna normally fills up. I think its worth it, I dont absolutly have to run airplane fuel, I can run 93 pump gas without a problem but she like 100LL alot better.
-alex
-alex
Racer
Joined: Dec 1999
Posts: 269
Likes: 0
From: Berea, KY, USA
Oh I hate to disagree with Lars........but...
Lars is correct in that AVGas does not have road taxes paid and it is illegal to pump in your car for road use....most airports will pump into 5 gal cans.....
but...
AVGas 100LL has higher vapor pressure not lower. The higher pressure is so the gas will not cause vapor lock at higher altitudes....not good for the fan to stop when that is what is keeping you in the air....That being said the only disadvantage of higher vapor pressure is hard starting on colder days...the fuel will not vaporize as easily and cause a flood condition....wet the plugs.
Other that this problem...below 32F or so...AVGas is exactly what high octane motors need.....100LL is about 105 octane as measured the "old" way. Of course 100LL does contain lead...so it should not be used if you have "cats".
100LL contains NO alcahol or other additives that are harmful to your fuel system.
Dave62
and PS Lars...I very much respect your work and help on this forum...
Lars is correct in that AVGas does not have road taxes paid and it is illegal to pump in your car for road use....most airports will pump into 5 gal cans.....
but...
AVGas 100LL has higher vapor pressure not lower. The higher pressure is so the gas will not cause vapor lock at higher altitudes....not good for the fan to stop when that is what is keeping you in the air....That being said the only disadvantage of higher vapor pressure is hard starting on colder days...the fuel will not vaporize as easily and cause a flood condition....wet the plugs.
Other that this problem...below 32F or so...AVGas is exactly what high octane motors need.....100LL is about 105 octane as measured the "old" way. Of course 100LL does contain lead...so it should not be used if you have "cats".
100LL contains NO alcahol or other additives that are harmful to your fuel system.
Dave62
and PS Lars...I very much respect your work and help on this forum...
Instructor
Joined: Mar 2005
Posts: 182
Likes: 4
This is just an old wives tale about getting great power out of Av gas
It is not chemically the same as automotive fuel. It is made to run at over 10,000 feet in relatively low rpm motors with very high compression. One of the planes I fly gets max GPH vs speed at @ 1800 rpm. It's vapor point and flash point are all wrong for automotive use.
It is not chemically the same as automotive fuel. It is made to run at over 10,000 feet in relatively low rpm motors with very high compression. One of the planes I fly gets max GPH vs speed at @ 1800 rpm. It's vapor point and flash point are all wrong for automotive use.
Tech Contributor
Joined: Aug 1999
Posts: 14,365
Likes: 6,345
From: At my Bar drinking and wrenching in Lafayette Colorado
You have your high vapor pressure and low vapor pressure terms reversed. High vapor pressure is more prone to vapor lock - not the other way around. Avgas has lower vapor pressure than auto gas and is therefore harder to start in cold weather (you can check me on that - there's a pretty complete reference to this in FAA Advisory Circular AC65.9).
Lars
Lars
Last edited by lars; Dec 18, 2006 at 06:38 PM.
Racer
Joined: Dec 1999
Posts: 269
Likes: 0
From: Berea, KY, USA
Lars,
You know I should have known better than make that post...you are correct....its been too many years on this old brain.....and to think I used to make the test instrumentation to test Vapor Pressure!
...anyway we agree it is harder to start in cold wx.
You know I should have known better than make that post...you are correct....its been too many years on this old brain.....and to think I used to make the test instrumentation to test Vapor Pressure!
...anyway we agree it is harder to start in cold wx.
