Ideal boosted a/f ratio and timing

[parish8]

in the LS world it seem like everyone was comfortable in the 11.6-11.8 range.

in the LT world I see some people still at 11.6-11.8 and others that are going all the way up to 12.6-12.8. A guy I know that tunes a couple of cars a day is telling me 12.6-12.8 is what he recommends.

does anyone have any info on this?

on the dyno does it make more power richer or leaner?

how about with low boost levels like below 7psi?

how about on e85, we would have to talk lambda not actual a/f ratio but you know what I am asking?

now on to timing. in the LS world I was always happy to keep my timing around 15deg max and get all the power I wanted with more boost. we tried a little more timing a few times and had issues but the motors always liked more boost. how about the LT motors? what kind of wot timing should we be looking at?

[gmtech16450yz]

I couldn't tell you about the LT engines, but with the Direct Injected/boosted LNF's we all ran .88-.89 Lambda even up at 30psi boost. There's got to be hundreds of thousands of combined miles on high hp LNF's running that lean without issues. There are stock situations where these DI engines are running at 1.0 Lambda even at WOT.

The guys that are running port fuel injected ratios like 11.6 or 11.8 in Direct Injected engines don't know what they're doing. Simple as that.

[Higgs Boson]

not to mention trying to push the DI system to 11.x is just going to max it out super early. The stock LT4 runs 12.5 or so, there is no reason to richen it up from there.

[HNK]

So running 12.8-13.0 should be fine with the LT4?

[Ben Charles]

I've had great luck with around .84 lambda on boost and .88 on NA combos

[HNK]

Did you try leaner or just decided to stay at .84?

[gmtech16450yz]

The OP also mentioned E85. So obviously the reason you run richer in boosted situations is to control knock and exhaust temps. But has anyone done any REAL testing with EGT probes installed running leaner mixtures on boosted E85 engines? IN THEORY, you're using a fuel that is inherently cooler and you're using somewhere around 25% more of it. That's not even talking about the anti-knock differences, just the liquid cooling effect and the additional amount of the fuel going through the engine.

Why then would you not be able to get away with running an E85 boosted (or not boosted even) engine leaner than the equivalent gas setup? Again, in theory alone it would seem like you would have the same amount of fuel cooling effect by running an E85 air fuel ratio ~25% leaner than gas if there's ~25% more of the fuel going through the engine? Add in the higher octane and the cooling properties and my question is this... Why aren't we all running WAY leaner on E85, boosted or not?

[Area47]

The OP also mentioned E85. So obviously the reason you run richer in boosted situations is to control knock and exhaust temps. But has anyone done any REAL testing with EGT probes installed running leaner mixtures on boosted E85 engines? IN THEORY, you're using a fuel that is inherently cooler and you're using somewhere around 25% more of it. That's not even talking about the anti-knock differences, just the liquid cooling effect and the additional amount of the fuel going through the engine.

Why then would you not be able to get away with running an E85 boosted (or not boosted even) engine leaner than the equivalent gas setup? Again, in theory alone it would seem like you would have the same amount of fuel cooling effect by running an E85 air fuel ratio ~25% leaner than gas if there's ~25% more of the fuel going through the engine? Add in the higher octane and the cooling properties and my question is this... Why aren't we all running WAY leaner on E85, boosted or not?

Depends on the set up. Some engines don't like it and will make more power/torque at a richer afr/lambda, than leaner. Laws of diminishing returns.

[parish8]

The OP also mentioned E85. So obviously the reason you run richer in boosted situations is to control knock and exhaust temps. But has anyone done any REAL testing with EGT probes installed running leaner mixtures on boosted E85 engines? IN THEORY, you're using a fuel that is inherently cooler and you're using somewhere around 25% more of it. That's not even talking about the anti-knock differences, just the liquid cooling effect and the additional amount of the fuel going through the engine.

Why then would you not be able to get away with running an E85 boosted (or not boosted even) engine leaner than the equivalent gas setup? Again, in theory alone it would seem like you would have the same amount of fuel cooling effect by running an E85 air fuel ratio ~25% leaner than gas if there's ~25% more of the fuel going through the engine? Add in the higher octane and the cooling properties and my question is this... Why aren't we all running WAY leaner on E85, boosted or not?

I can't answer your question but the lt4 tune does have the pe filled out for gas and alcohol. They are very close to the same numbers for both fuels.

[parish8]

You guys have convinced me to go with .84 lambda at my current boost level. Once I add port injection and turn up the boost I will run it richer.

[Ben Charles]

That's what I would do

Port injection is easy to add too, don't let these big shops on the corvetteforun tell you otherwise

[gmtech16450yz]

I can't answer your question but the lt4 tune does have the pe filled out for gas and alcohol. They are very close to the same numbers for both fuels.

Good point. Most of the stock tunes I've looked at have the alcohol table leaner than the gas, but that's in vehicles that aren't flex fuel capable anyway so I think they just throw the 1.149 EQ in that table for kicks.

This one is interesting though, this is a stock '15 Z06 file. So should we be leaning out the E85 in the middle and rich on the low and high ends? Hmmm. I'm just wondering if this is one of those things that's "what everyone has done" and nobody has REALLY looked into the chemistry and physics behind it? Just like the OP mentioned, there are "tuners" that are still running DI engines at port injection fuel mixtures. Just because it's "the norm" doesn't mean it's right.

[parish8]

That's what I would do

Port injection is easy to add too, don't let these big shops on the corvetteforun tell you otherwise

I am not the least bit afraid of it and getting an aftermarket ECM on board will offer lots of great features like boost control, egt, nitrous, aux fuel pump control... it is just kind of expensive. It is funny how the shops make it out to be a big deal.