Running an LS lean of peak at WOT?

[Grant]

I'm looking at an endurance racing class where I'm limited on power, and fuel consumption is important.

Could a ~16:1 AFR on 93 octane work? I know aircraft commonly cruise lean of peak, but this is at altitude where detonation is presumably less of a problem.

Thanks.

[1980RS]

I'm looking at an endurance racing class where I'm limited on power, and fuel consumption is important.

Could a ~16:1 AFR on 93 octane work? I know aircraft commonly cruise lean of peak, but this is at altitude where detonation is presumably less of a problem.

Thanks.

You can do it but I would certainly watch the EGT numbers for sure with a 16:1 A/F ratio.

[mag2555]

I don't think this can be discussed without having the dynamic compression as part of the conversation.

[Grant]

I don't think this can be discussed without having the dynamic compression as part of the conversation.

We'd only need 280whp, so I was thinking we'd run something like a stock L33. Trimming the throttle to produce the desired power.

[mag2555]

Why is running on the lean side such a priority for you?

[Grant]

Why is running on the lean side such a priority for you?

Fuel burn. Each pit stop costs us time.

[stealth]

Is water injection allowed?

[Grant]

Is water injection allowed?

Yes. Think that would be needed to prevent detonation?

[mag2555]

How many total miles or laps is the race that your thinking that a air to fuel ratio like that will shave off a pit stop or make for a shorter pit stop by not putting in as much fuel?

I would sooner be hunting down friction reduction moves that may be able to be done within the engine like a crank scraper or a 5 lb reduction in oil pressure, or drivetrain friction reduction moves!

[Grant]

The shortest race would be 7 hours, the longest could be 24.

We've got a dry sump pan with integrated scraper. Optimizing oiling and crankcase vacuum is a great idea but we can do that in addition to AFR adjustments.

[In-Tech]

Hello,
What endurance environment is this? Marine or off-road? What is the RPM band you seek to run lean? Leaner than stoich should actually reduce EGT because the combustion energy is decreased, however I think that will depend on load. I've done quite a bit of lean cruise(up to 17:1 AFR based on 14.7 stoich) LS based on the factory lean cruise GM AUS calibrations. You might be better off a little bit richer than stoich(~.92 Lambda) to improve the economy when under a higher load. I have one of these combinations planned to maximize fuel economy but I won't be on the dyno with it for at least a couple months.

[Grant]

The environment is road racing. RPMs would be kept modest since we're power-limited, so maybe 4-6000? I know it'll make less power LOP than a normal ROP AFR.

My current endurance racer has a 2.0L MZR engine and has, because of a failing fuel pump, run LOP (15.5 to 17:1) AFRs on 93 octane during an endurance race. We were far enough ahead that we didn't need to beat on it to win, but still saw high-90s kPa MAPs so were nearly WOT at times. Engine came out of that fine, though the ECU logging was not working so I don't know if it was seeing any knock and pulling timing.

I guess we'll just try it and see what happens!

[In-Tech]

Do you already have an ecu planned for this project? Are you interested in a cam change to help control the heat? 5th cycle(Otto) style might work very well for you and improve fuel efficiency too, unless you need "bang on" torque down really low in the rpm band.

[Circlotron]

Normally not the thing for a race engine, but a bit of EGR might be worth trying. That would enable wider throttle opening for a given torque output and consequently lower pumping losses. And EGR when running LOP would probably help keep EGTs in check too. Sorry for all the TLAs...

[In-Tech]

Shoot I can't remember which one exactly, Otto, Miller, Atkinson...a well designed variant of these will self egr with small amounts of vacuum(TB closure)too