Running an LS lean of peak at WOT?

[In-Tech]

Hopefully Mike can chime in with his thoughts. I am not in the cam business nor do I want to be, although I am not lean to the subject. I have my own stuff built for my own combo's and don't sell 100 cams a week. Besides that, people generally think you can take someone's numbers and have "your cam guy" do the same thing. Furthest from the truth EVER. Lobes @.050", whatever seat, and LSA/ICL, don't matter a fack between different manufacturer's.
Carry on

[BILL-C]

I am very familiar with what you are trying to do. My shop builds both sprint and endurance road race engines for both vintage and modern race cars. You are still in a race situation! You need to be looking for the best BSFC numbers you can achieve and 16-1 air is nowhere near that.

[Grant]

I am very familiar with what you are trying to do. My shop builds both sprint and endurance road race engines for both vintage and modern race cars. You are still in a race situation! You need to be looking for the best BSFC numbers you can achieve and 16-1 air is nowhere near that.

Thanks, so is LoP only useful at lower MAPs / higher altitudes? I'm not sure when piston aircraft tend to transition to it, but they're RoP during takeoff.

[FC-Pilot]

The piston aircraft I fly do not like being anywhere near max power while also being on the lean side. Now, when cruising at around 14,000’ it is a different story. While cruising up there, even “full throttle” is only 65% of max power, which is like being about half throttle at sea level. Still, often times when I am cruising up there I still have the throttles reduced while running on the lean side. I feel the comparison of a low compression and low RPM aircraft engine and an engine being used for a race is like comparing cantaloupe to cannonballs.

I like the comment about designing an engine build to minimize the BSFC numbers.

Paul

[Mike Laws]

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.

Carbureted or fuel-injected?

[stealth]

Is water injection allowed?

Yes. Think that would be needed to prevent detonation?

Absolutely.... I would certainly have a system piped in. Do some research... water is VERY effective...

[David Redszus]

Many times race engines that are reported as being lean, actually are not lean. Most often they
are very close to stoich or slightly rich where best power is produced. And then they knock.

When engine tuners use excess fuel enrichment to control knock, timing is often also
advanced to improve ignition. But, then when enrichment is reduced, we have excess ignition
timing which significantly contributes to knock.

An engine that is truly running lean will not knock. Lean burn engines have been around for many years.
But it won't make much power, either.

EGT is a very poor indicator of mixture or propensity to knock. High EGT and knock are inversely related.
A data logger that captures EGT, lambda, ignition timing, throttle, and rpm, shows the facts quite clearly.

To obtain improved fuel economy for endurance racing, we modify the fuel blend with the addition of
toluene and xylene. An enrichment index can be used for fuel comparison. Simply multiply the stoich
value by the specific gravity.

Race fuel stoich = 15.0 * SpG = .695 = 10.44.
Toluene stoich = 13.68 * SpG = .869 = 11.88.
An improvement in economy of 14%, if pure toluene could be used; it can't, a blend must be used.

[BLSTIC]

You say you're "limited on power"

Can you expand on that? Is it a dyno run on race day, a fuel flow limitation, a restrictor plate? How are you limited?

[Grant]

The piston aircraft I fly do not like being anywhere near max power while also being on the lean side. Now, when cruising at around 14,000’ it is a different story. While cruising up there, even “full throttle” is only 65% of max power, which is like being about half throttle at sea level. Still, often times when I am cruising up there I still have the throttles reduced while running on the lean side. I feel the comparison of a low compression and low RPM aircraft engine and an engine being used for a race is like comparing cantaloupe to cannonballs.

Thanks, this is the information I was hoping for. We may try it anyway just to see what happens, once knock detection is properly tuned. Maybe LOP + water injection could be an option, if LOP produces better BSFC.

You say you're "limited on power"

Can you expand on that? Is it a dyno run on race day, a fuel flow limitation, a restrictor plate? How are you limited?

Dynojet before the race, and on race day if you podium. They do not mandate how power is restricted, beyond penalties for flat power curves and the like. It's all similar to how NASA classes ST and TT cars.

To obtain improved fuel economy for endurance racing, we modify the fuel blend with the addition of
toluene and xylene. An enrichment index can be used for fuel comparison. Simply multiply the stoich
value by the specific gravity.

Race fuel stoich = 15.0 * SpG = .695 = 10.44.
Toluene stoich = 13.68 * SpG = .869 = 11.88.
An improvement in economy of 14%, if pure toluene could be used; it can't, a blend must be used.

Interesting, thanks!

Carbureted or fuel-injected?

Definitely EFI.

[Mike Laws]

The piston aircraft I fly do not like being anywhere near max power while also being on the lean side. Now, when cruising at around 14,000’ it is a different story. While cruising up there, even “full throttle” is only 65% of max power, which is like being about half throttle at sea level. Still, often times when I am cruising up there I still have the throttles reduced while running on the lean side. I feel the comparison of a low compression and low RPM aircraft engine and an engine being used for a race is like comparing cantaloupe to cannonballs.

Thanks, this is the information I was hoping for. We may try it anyway just to see what happens, once knock detection is properly tuned. Maybe LOP + water injection could be an option, if LOP produces better BSFC.

You say you're "limited on power"

Can you expand on that? Is it a dyno run on race day, a fuel flow limitation, a restrictor plate? How are you limited?

Dynojet before the race, and on race day if you podium. They do not mandate how power is restricted, beyond penalties for flat power curves and the like. It's all similar to how NASA classes ST and TT cars.

To obtain improved fuel economy for endurance racing, we modify the fuel blend with the addition of
toluene and xylene. An enrichment index can be used for fuel comparison. Simply multiply the stoich
value by the specific gravity.

Race fuel stoich = 15.0 * SpG = .695 = 10.44.
Toluene stoich = 13.68 * SpG = .869 = 11.88.
An improvement in economy of 14%, if pure toluene could be used; it can't, a blend must be used.

Interesting, thanks!

Carbureted or fuel-injected?

Definitely EFI.

Have much successful experience with similar endurance racing like this. All carbureted though. D. Redzsus is your guy for EFI. Best of luck...

[ClassAct]

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.

Carbureted or fuel-injected?

Hey Mike, I sent you a PM. Did you happen to see it?

[Mike Laws]

Hey Mike, I sent you a PM. Did you happen to see it?

No sir. I just checked and nothing there.

[ClassAct]

Hey Mike, I sent you a PM. Did you happen to see it?

No sir. I just checked and nothing there.

I sent you another PM. Let me know if that one came through.

Thanks Mike

[Grant]

Do you guys have any opinion on an L83 (5.3L gen V direct injected) vs. an L33 with a LY2 4.8L crank in it? I know the DI motor has big fuel efficiency advantages at part throttle, and can safely run higher compression. That suggests WOT BSFC is better. However it's 10% larger in displacement, so we'd have to throttle / VVT it down more to hit our power limit. On the other hand this means the car would be more fun when not class racing...

The L83 significantly more expensive to do since we don't have a bunch of gen V parts laying about.

I wonder if the LY2 crankshaft fits in a L83...

[dannobee]

I think Circlotron has the right idea. Use EGR to increase fuel mileage AND when on the dyno to kill some of the hp at WOT. Should be easily controlled by whatever ecm/pcm you're using. You could easily command it with the pcm parameters and by using a toggle switch. Fuel economy mode, egr on. Dyno testing, egr on (fully open egr valve). "passing mode," egr off. LS's had a few different egr systems and can be easily adapted to your needs. Forget leaning out the mixture, you'll hurt stuff in an endurance race.