The thing you have to remember is that it is a good thing to run the engine
as rich as possible without costing you a full lap of fuel window. It makes
no sense whatsoever to have a lean mixture in the car unless you can get an
additional FULL LAP out of the bag of fuel.
Le Mans is 8 miles or so a lap, you need to lean the hell out of it to pick
up a complete lap and extend the fuel window. If the refueling window is
the same, the only downside to running fat is the small amount of extra time
the refueling rig is attached. Most times, fuel isn't the speed limiting
event in the stop. Tires, Brakes, drivers all seem to take longer.
Just a few thoughts on tactics.....
Scott Correa
>From: Stefanv@aol.com
>Reply-To: Stefanv@aol.com
>To: <jac73@daimlerchrysler.com>, <autox@autox.team.net>
>Subject: Re: Audi Does it Again.
>Date: Mon, 18 Jun 2001 13:40:14 EDT
>
>Thanks for the additional information.
>
>I already understood why it happens but did not know that the endurance
>guys purposely run that "comfortably rich" setup. Though once you said
>that, it "clicked" as to why they'd do that.
>
>Oh, and to reply to another's comment... yes, it is admittedly cool to
>watch.
>
>-STEFAN
>
>
>In a message dated Mon, 18 Jun 2001 1:13:20 PM Eastern Daylight Time,
>jac73@daimlerchrysler.com writes:
>
><< On Mon, 18 Jun 2001 10:13:37 EDT, Stefanv@aol.com said:
><SNIP>
> >As I understand it.
>
>To add to your understanding: The flames out the exhaust were only on
>"overrun", or closed-throttle conditions. In an endurance race, it's
>customary to set the fuel mixture into the "comfortably rich" zone, a bit
>richer than the best fuel/air ratio for peak power production, in order to
>assist the longevity of the engine for 6, 10, 12, or 24 hours. This is
>particularly true for turbocharged engines (like the Audis, Cadillacs,
>Bentleys), but is also done on normally-aspirated engines (I've seen
>overrun flames from the Corvettes and Vipers, for example).
>
>The reason for "comfortably rich" as opposed to stoiciometric or even
>slightly lean in an endurance racing engine is simple: lean means higher
>combustion temperatures, and a far greater potential for Bad Things to
>happen to pistons (like holes getting torched in the piston crowns).
>Running a little rich will actually cool the burn slightly, and having more
>fuel than oxygen means there's some leftover fuel -- very little under
>load, but there's a bit more on an overrun condition where the throttle
>closes and there's a wee bit of lag between that action and the injection
>system reducing the fuel shot. That extra bit of fuel passes through the
>cylinders, the turbocharger (if equipped) and lights off in the exhaust --
>or right at the exit of the exhaust where there's more oxygen available.
>You won't see the flames out the exhaust under load, except in Hollywood
>movies.
>
>Yes, it uses a wee bit more fuel than running stoic or lean, but it's also
>cheap insurance that the engine will be running in a fit state at the end
>of the race (because, of course, you have to be running at the end to be
>classified as a finisher...).
>
>I watched an awful lot of SpeedVision this weekend...
>
>Jim "Yeah, I'm an engineer" Crider
>autojim@att.net
>
>
>
>
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