91-98-avgas

[kiwi cowboy]

Ok you guys before anyone says look in search i have but my question is for my bike.
86 gsxr400 in pre 89 i have been running it on 98 but have just aquired some avgas.It seems to run ok down the drive [only just put it in ].
The manual says 85-95 octain or higher and unleaded or low lead recomended.
From whot i understand avgas is low lead now is this true?
So question: will it run ok on pure avgas or a mix without detrimental effects on the motor?.
Question 2: does avgas run richer or leaner than petrol?
Cheers for any advice im a noobe to racing and want as much performance without risking blowing the motor up through lack of knowledge so am here to ask the experts.

[Pussy]

Avgas definitely ISN'T low lead. It has higher levels of TEL (tetra ethyl lead) than the old leaded road gas used to have

[Flip]

It will run ok, the lead might fowl the plugs, but your motor wasn't really designed to run on leaded race gas. Avgas or race gas is actually high in lead. You might consider cutting it back 50% with pump gas.
It needs the same ammount of air as the other petrols but might burn a bit better because the lead promotes combustion after the spark has started. The only down side is Avgas is a narrow cut fuel and needs a really good hot spark to get the fuel to ignite, it can miss and backfire a bit in std motors.

[Peter Smith]

From my understanding the different octane rating have different burning speeds, so in some cases if you run a high octane AVgas you can actual loose power unless you alter the spark timing.
E.g. I was dynoing my 851 duke (back in the 90's) and was trying different chips for the fuel injection, runing on the old 96 super it had 96 RWHP. I drained the tank, put in some AVgas, ran the bike for a few minutes then back on the dyno and only got 94RWHP.
If your running stock ignition etc I'd stick with the 98 pump gas.
I'm running a GSXR1100 in pre'89s on BP 98 ultimate.

[Jantar]

Ok you guys before anyone says look in search i have but my question is for my bike.
86 gsxr400 in pre 89 i have been running it on 98 but have just aquired some avgas.It seems to run ok down the drive [only just put it in ].
The manual says 85-95 octain or higher and unleaded or low lead recomended.
From whot i understand avgas is low lead now is this true?
So question: will it run ok on pure avgas or a mix without detrimental effects on the motor?.
Question 2: does avgas run richer or leaner than petrol?
Cheers for any advice im a noobe to racing and want as much performance without risking blowing the motor up through lack of knowledge so am here to ask the experts.

Avgas is a higher octane, so is capable of delivering more oomph from each drop. But Avgas is designed to run in large capacity low reving engines. (eg a Lycoming engine runs best at 2400 rpm.) So avgas is unlikely to give you any real boost at other than low RPM.

As a real life example the Rotax 912 aircraft engine runs at 5500 RPM and the recommended fuel is 96 mogas. When run on this fuel the service interval is 100 hrs. It can run on avgas, but the service interval drops to 50 hrs.

[Pussy]

The "octane" figure is it's resistance to detonation (anti knock value)
I've had access to avgas for the last 18 years.... and wont touch the shit to run in my road vehicles

[CHOPPA]

The "octane" figure is it's resistance to detonation (anti knock value)
I've had access to avgas for the last 18 years.... and wont touch the shit to run in my road vehicles

Its good for turbo vehicles running high boost....

It makes your bike run cleaner but ive never noticed performance. Dont think your supposed to run it though, someone had me up about running it at a club day at puke cause my exhaust was white

[wharfy]

MY understanding is that the octane rating is simply a measure of the resistance to "knock" that a particular blend of fuel has. The higher the rating the more difficult it is to get it to burn. "Knock" is more likely in high compression engines and many "race" engines fall into this category and require fuel with a higher octane rating. I don't believe that higher octane fuel by itself will provide any performance benefit.

My $1.78c a litre worth

[Pussy]

MY understanding is that the octane rating is simply a measure of the resistance to "knock" that a particular blend of fuel has. The higher the rating the more difficult it is to get it to burn. "Knock" is more likely in high compression engines and many "race" engines fall into this category and require fuel with a higher octane rating. I don't believe that higher octane fuel by itself will provide any performance benefit.

My $1.78c a litre worth

You're quite correct.
Avgas is a crude fuel designed for crude engines.
An Avco Lycoming IO 720(horizontally opposed 720 cubic inch 8 cylinder) is only pulling 400hp at 2650rpm (redline)
Continental IO 520 (horizontally opposed 520 cubic inch 6 cylinder), 300hp at 2850rpm(which is relatively high speed for an aircraft engine).
Avgas burns slower to prevent detonation.
It's loaded with lead

[mossy1200]

General rule is higher the octaine the longer the flash period of ignition.
91 will have intense short burn
av gas will have less intense cooler longer burn
98 will be half way between.
The longer burn is great for higher compression motors that have advanced timing but 100av gas not great blending would be better.Generally about 2degrees advanced from stock.Originally designed for slower rev motors to give extended combustion at lower temp so on you high rev motor combustion could still be occuring at bottom of piston stroke causing wasted power.
My post classic has fixed timing with no advance options and dyno has indicated my horses decline after 95 octaine getting lower and lower.av gas was less powerfull than 91octaine.
If you have adjustable timing plate then you could start to play around with fuels and mixtures etc.
Would suggest you trial the av gas and take 91 in tin to blend it down if you notice loss of power in straights or hesitance coming onto throttle.

Trial and error or dyno runs.Your call.I think your 25year old bike will repond best to 95/96

[Mark Pav]

Just verifying that avgas IS NOT low lead. It is higher in lead content than the old 96 pump gas that is no longer available. There is an advantage to avgas that no one has mentioned. Because you cannot get out and push if an aircraft engine stops because the fuel has water in it, it must be guaranteed not to have water in it. If you get it from a certified supply source at an airfield you can be reasonably sure that it has been stored in good conditions. Likewise it is more likely to be of consistent quality than pump gas stored in the local "dodgy brothers "gas station. In an ideal world all the above is true but YMMV...... I found some old dyno figures to prove the case for NOT using avgas. These were on my old 1989 FZR1000W modified engine. On a Dynojet 150 acceleration dynamometer the figures were 155 bhp on avgas, 156 bhp on 95 octane, and 160.5 bhp on 91 octane pump gas. Bearing in mind that at the time I did not have the facility to easily alter ignition timing to suit the fuel, I was doing the reverse, I was adjusting the fuel to suit the ignition timing !!! Yes avgas has a higher anti knock value for sure. If your problem is related to fuel knock and you have no other way of addressing it, it might solve your problem. Unless you raise the compression ratio to exploit the anti knock advantage that avgas offers, you will see less power , not more.

[marty]

I used to run my old school W351 powered ski boat exlusively on Avgas. It never really saw much more than 3000rpm, and had the timing sorted (we were apprentice aircraft engineers at the time), so I had no issues with it. My turbo Skyline however, burned exhaust valves out with monotonous frequency.......

Even the 110-130LL avgas now has high lead level - I wouldn't run a high revving 400 gixxer engine on it unless you absolutley knew what you were doing.

[GSVR]

Ok you guys before anyone says look in search i have but my question is for my bike.
86 gsxr400 in pre 89 i have been running it on 98 but have just aquired some avgas.It seems to run ok down the drive [only just put it in ].
The manual says 85-95 octain or higher and unleaded or low lead recomended.
From whot i understand avgas is low lead now is this true?
So question: will it run ok on pure avgas or a mix without detrimental effects on the motor?.
Question 2: does avgas run richer or leaner than petrol?
Cheers for any advice im a noobe to racing and want as much performance without risking blowing the motor up through lack of knowledge so am here to ask the experts.

Avgas can be useful as an additive if you have pinking problems. Blending 91 and avgas seems to work well starting at 50/50. I've also heard alot of conflicting views on percentages and how it effects detonation. A blend of 91 and avgas should make more power than 98 alone.

If moneys no option you could also run ELF race fuel but I'm not sure about the legallity of the stuff with MTBE in it.

Now I will brace myself for someone to attack this post!

[roogazza]

The Bandit when stock (with pipe and jetting) at 9.5 to 1 comp was at its best on 91.
But after a few tins on compression I now run 95/98. There is a noticable difference giving it 98. Gaz.

[kiwi cowboy]

Avgas can be useful as an additive if you have pinking problems. Blending 91 and avgas seems to work well starting at 50/50. I've also heard alot of conflicting views on percentages and how it effects detonation. A blend of 91 and avgas should make more power than 98 alone.

If moneys no option you could also run ELF race fuel but I'm not sure about the legallity of the stuff with MTBE in it.

Now I will brace myself for someone to attack this post!

not sure on the ELF as dont know the octain rating but might play with a 50-50 blend and see how it goes