aviation fuel and timing
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Joined: Sep 2014
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From: siler city nc
aviation fuel and timing so i was in my automotive class at the local college and my teacher used to do a lot of racing and he swears up and down if you run aviation fuel you can have some serious timing curves but what is the benefit to this why would you run extremely high octane fuel and advanced timing are the benefits worth it and what type of benefits will you get out of it?
You probably confused aviation fuel with alcohol or methanol, which top dragsters run.
But they also run insane amounts of boost and/or compression, so they need that type of fuel for proper safety.
On an N/A road motor with less than 11.1 compression that would not be the case, as you can usually run all the timing you ever need on pump gas. Now a high compression motor or one with lots of boost will gain power by advancing timing higher than pump gas can handle, but again those are full on drag motors professionals run...not street cars that you and I drive around.
Don't know of anyone driving around on the street with straight methanol/alcohol in their gas tank.
But they also run insane amounts of boost and/or compression, so they need that type of fuel for proper safety.
On an N/A road motor with less than 11.1 compression that would not be the case, as you can usually run all the timing you ever need on pump gas. Now a high compression motor or one with lots of boost will gain power by advancing timing higher than pump gas can handle, but again those are full on drag motors professionals run...not street cars that you and I drive around.
Don't know of anyone driving around on the street with straight methanol/alcohol in their gas tank.
Racers have been using aviation fuel for decades on stuff....
you will hear lots of older races talk about how they used to use Av-Gas
it tends to burn slower....not necessarily higher octane...this is usually due to the Lead content...and Lead helps prevent detonation....it does not stop spark being fired too far advanced and causing knock (yes...knock and detonation are two different things)
it also burns a little different because its designed with high altitudes in mind.
this should help some
http://en.wikipedia.org/wiki/Avgas
or...it could just confuse the hell out of you..LOL
you will hear lots of older races talk about how they used to use Av-Gas
it tends to burn slower....not necessarily higher octane...this is usually due to the Lead content...and Lead helps prevent detonation....it does not stop spark being fired too far advanced and causing knock (yes...knock and detonation are two different things)
it also burns a little different because its designed with high altitudes in mind.
this should help some
http://en.wikipedia.org/wiki/Avgas
or...it could just confuse the hell out of you..LOL
The first thing to understand is what timing does - what happens when you advance or retard timing.
The goal is for the flame front to advance from the plug to the main combustion chamber charge at exactly the right time. You want that nice explosion at just a few degrees after TDC. Too soon and you get detonation; too late and you lose power.
The flame front moves at a set speed - no more and no less. As rpm increases, the speed of the flame front does not increase. To keep the explosion happening at exactly the right time, you have to fire the plug sooner and sooner. For some complicated reasons, that works well up to about 3,000-3,500 rpms. Then there's there's no advantage to advancing it even more.
High octane fuel - especially leaded - actually burns slower; and that helps prevent detonation (pre-ignition). But that also means you MUST advance the timing more to make the same power. Because of the slower burn rate, high octane fuel may actually cost you power if your engine doesn't need it.
Some high octane fuels - like E-85 - actually burn faster. Those fuels need less timing, and can make more power than av gas.
The goal is for the flame front to advance from the plug to the main combustion chamber charge at exactly the right time. You want that nice explosion at just a few degrees after TDC. Too soon and you get detonation; too late and you lose power.
The flame front moves at a set speed - no more and no less. As rpm increases, the speed of the flame front does not increase. To keep the explosion happening at exactly the right time, you have to fire the plug sooner and sooner. For some complicated reasons, that works well up to about 3,000-3,500 rpms. Then there's there's no advantage to advancing it even more.
High octane fuel - especially leaded - actually burns slower; and that helps prevent detonation (pre-ignition). But that also means you MUST advance the timing more to make the same power. Because of the slower burn rate, high octane fuel may actually cost you power if your engine doesn't need it.
Some high octane fuels - like E-85 - actually burn faster. Those fuels need less timing, and can make more power than av gas.
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Joined: Aug 2004
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From: Auckland, Nth Is, New Zealand.
Avgas is now really an old school fuel, a leaded 100 octane 'if fresh' that we used because that's what was available then.
Way better off now using the modern fuels that don't foul plugs due to the lead etc.
Here in NZ I now use our local pump Gull 10% Bio Fuel, says 98 but has been tested at 100 octane.
Our rally & LS7 powered Super Tourer race car class also use it.
Way better off now using the modern fuels that don't foul plugs due to the lead etc.
Here in NZ I now use our local pump Gull 10% Bio Fuel, says 98 but has been tested at 100 octane.
Our rally & LS7 powered Super Tourer race car class also use it.
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Sounds like the guy is decades behind in his "knowledge" if he thinks more advance is the source of power. Advance is a compromise, ideally you could fire at tdc and not have any combustion pressure build while the piston is rising. As covered though the flame takes time to travel.