Why no more lean burn??

[RustyLugNut]

Originally Posted by towndrunk

We are running lean burn in first gen Chevy Volts with good results, but does require a custom tune and open loop.

We run leanest (~20:1) at 1400 rpm (idle speed) and normal AFR above 2200 rpm. Running lean requires a lot more cam advance and a lot more spark due to the loss of power and slower burning mixture when lean. You also don't want to run lean with a cold engine, which created a lot of hurdles, but I think we handled it quite well. With the addition of a alcohol sensor ($45 in parts), the mixture is accurate with either premium fuel or ethanol blends of E30 (due to higher octane) to E85. Since the first gen Volt is high compression, we decided to stick with premium fuel to take advantage of it. Our tune is highly optimized even with E85.

It may not sound so impressive running max lean at 1400, but we're able to maintain 1400 rpm at highway speeds of up to 59 mph for an extended period of time.

More info on HPTuner's forum. forum.hptuners.com/showthread.php?63020-First-Gen-Volt-Tune-(Volterado)

. . . can you summarize the gains, if any, of your lean burn tuning?

Thanks,

[towndrunk]

Sorry, I can't tell you an exact number since I traded the vehicle last December. But I was getting 42 mpg @ 70 mph before adding lean burn.

Again, the gains from lean burn were at lower rpm, due to the higher load the Volt has due to the motor generator. So minimal gains at 70+, but substantially better at 55-ish.

[twj347]

Originally Posted by towndrunk

We are running lean burn in first gen Chevy Volts with good results, but does require a custom tune and open loop.

We run leanest (~20:1) at 1400 rpm (idle speed) and normal AFR above 2200 rpm. Running lean requires a lot more cam advance and a lot more spark due to the loss of power and slower burning mixture when lean. You also don't want to run lean with a cold engine, which created a lot of hurdles, but I think we handled it quite well. With the addition of a alcohol sensor ($45 in parts), the mixture is accurate with either premium fuel or ethanol blends of E30 (due to higher octane) to E85. Since the first gen Volt is high compression, we decided to stick with premium fuel to take advantage of it. Our tune is highly optimized even with E85.

It may not sound so impressive running max lean at 1400, but we're able to maintain 1400 rpm at highway speeds of up to 59 mph for an extended period of time.

More info on HPTuner's forum. forum.hptuners.com/showthread.php?63020-First-Gen-Volt-Tune-(Volterado)

I'm interested in how you changed the cam timing for your lean burn tune. I'm running a lean burn tune on my Subaru WRX (up to 17.5:1 with up to 7.5 degrees ignition advance.) with some success, which I posted about here.

I haven't changed cam timing at all as I'm not really sure how it affects the tune. Is it recommended to advance both intake and exhaust timing in tandem or adjust valve overlap as well? My DIT engine is knock limited even at highway cruising loads, so tuning cam timing may be tricky, as it will affect knock, and therefore ignition timing.

[towndrunk]

We used commercial tuning software, HPTuners, about $500. The Volt engine is VVT so it's just a matter of tweaking the cam timing. We used a 2017 Buick Encore turbo for a base tune and kept the exhaust cam around .5° and increased the intake cam a couple deg where we were going more lean. Then we had to add a LOT more spark. It was a gradual thing, go a little lean, and when the engine wouldn't stay at that rpm, adjust cam and spark to make a little more power.

There's no way to do it without a custom tune. You're not going to do it by tweaking sensors.

In theory, the HPT licenses used cost about $100, so if you had access to the software, you wouldn't have to spend the full $500. You get 10 licenses with the HPT package.

[towndrunk]

The first gen Volt is knock happy. Stock runs a lot of spark to get good mileage. We found out the hard way that reducing KR reduced mileage. We were over a year into tuning before we figured out to embrace knock.

[rmay635703]

Originally Posted by towndrunk

Sorry, I can't tell you an exact number since I traded the vehicle last December. But I was getting 42 mpg @ 70 mph before adding lean burn.

Again, the gains from lean burn were at lower rpm, due to the higher load the Volt has due to the motor generator. So minimal gains at 70+, but substantially better at 55-ish.

So is the project over?

What did you trade into?

[towndrunk]

Originally Posted by rmay635703

So is the project over?

What did you trade into?

Newer Volt. (see my sig.)

First gen is on hold since no-one has found anything to update. When we're able to read the tune from second gen Volt, the Volterado tune may change, but I can't imagine any major changes. Right now Volterado is stock Volt above around 3000 rpm, although below is modified 2017 Buick Encore. Other areas are one or the other, depending on what we liked better. Probably parts of second gen Volt might be incorporated into the tune, but again, I can't imagine the end result being much different from what we currently have.

One thing that has never worked properly is the electronic thermostat.
Higher temps yield better mileage. Second gen runs about 209F, yet, unless it's a hot day, first gen tends to run a lot cooler, well under 200, despite changes to the thermostat settings. Even Encore thermostat settings run cold on first gen Volts. Maybe we need the grill shutter to achieve that. Still, that will be one of the things to try.

So it's on hold, unless someone finds something to update and most of the current group consists of enthusiasts, not tuners.

[towndrunk]

Originally Posted by RustyLugNut

. . . can you summarize the gains, if any, of your lean burn tuning?

Thanks,

I reviewed some old logs and it appears the gains are about 3 to 5 mpg at 60 to 65 mph, depending on rpm. In other words, about 8 mpg at 1400-1600 and about 3 mpg at 1800 rpm. At 2000 rpm, little to no improvement. I think we could get by with a little less cam/spark at 1400 rpm since that tuning was done at 10°F, but no-one has tested that theory.

I'm sure gains would be much higher with a vehicle that doesn't have such a high load on it.

[RustyLugNut]

Originally Posted by towndrunk

I reviewed some old logs and it appears the gains are about 3 to 5 mpg at 60 to 65 mph, depending on rpm. In other words, about 8 mpg at 1400-1600 and about 3 mpg at 1800 rpm. At 2000 rpm, little to no improvement. I think we could get by with a little less cam/spark at 1400 rpm since that tuning was done at 10°F, but no-one has tested that theory.

I'm sure gains would be much higher with a vehicle that doesn't have such a high load on it.

Interesting and useful information.

Lean-burn is poorly understood by the lay and your work supports much of what has been only postulated on this forum. Thanks again.

[hayden55]

Pretty cool to see. I always wondered why a lot more people don't modify the tunes like how the performance guys do. Would love to see some more development on the 2nd gen volt.