Lean Cruise with E78?

[joecar]

LC does not save that much fuel (you're already not using much fuel at light load)... but even at light load, running lean will elevate combustion chamber temperature (which is not good for many reasons; remember, EPA/CARB likes the engine to run hot, but they don't like it from being lean).

( NOx might not seem like much, but if you've ever seen pictures of Los Angeles buried in brown fog in the late 1960's (I've also seen Sydney like this in the 1970's) then you know that NOx reacts with sunlight to make brown fog. )

( either way, LC is not really necessary, you're not saving much, and your engine does not really like LC )

[496Stingray]

Joecar, thanks for the educated reply.
I agree with you. After logging the AFR in Logworks-3 for 3 days (200 miles) my cruise mix is running 14.7-15 as it is which is lean enough. With careful tuning of my cam angles and and spark tuning (about a 1000 miles and 30 files worth of changes during that time with careful logging, plotting the data out etc) I have managed to bring the truck up from 13.5 to 19-20 mpg (all freeway) as long as I remain under 75Mph. In Texas we have speed limits set at 75-80 on the most of the freeways surrounding my area so my hopes were to achieve 17-19 @ 80Mph. Not going to happen pushing a 7,000 3/4 Extended cab, long bed into the wind at those speeds. It will hold 15.5-16 though and not downshift at the slightest grade anymore which is nice. I have severe Ashthma and pollution is the reason, (lower level Ozone etc.) so even with my Hot Rods I have kept cats in place on all of them. The dyno tests dont lie and if the cats are properly sized for the engine they dont cost much if any notable power loss on a daily driver. Also worth noting is the load on the engine pushing this monster at 80-85Mph wouldnt allow me to lean out the mixture safely anyhow.

I can say that tuning the higher end of the engine has resulted in some impressive gains. The L96 likes more cam retard at the higher end then GM put into the stock tables. It also enjoys quite a bit more spark. I plotted the MAF g/sec and have increased that number by 54 g/sec over stock from 4400-6000 RPM. Havent put it on a dyno yet but more air = more power. Being and HD GM was understandibly conservative with the tune to keep it in one piece.

Thanks for the thoughtful reply and education, the support from the EFI team is awesome!

- Rob
rob@mangierisrodandcustom.com

[joecar]

Hi Rob,

... With careful tuning of my cam angles and and spark tuning...

This is the key to economy and performance ^

... I have managed to bring the truck up from 13.5 to 19-20 mpg (all freeway) as long as I remain under 75Mph. In Texas we have speed limits set at 75-80 on the most of the freeways surrounding my area so my hopes were to achieve 17-19 @ 80Mph. Not going to happen pushing a 7,000 3/4 Extended cab, long bed into the wind at those speeds. It will hold 15.5-16 though and not downshift at the slightest grade anymore which is nice....

That is a very nice increase in mpg, good job ^
Yes, unfortunately as speed increases (above 50-60 mph) vehicle aerodynamics becomes significant (especially trucks).
This is the other key ^ (tuning the transmission to work intelligently with the engine (especially when engine has much torque), good deal

...I have severe Ashthma and pollution is the reason, (lower level Ozone etc.) so even with my Hot Rods I have kept cats in place on all of them. The dyno tests dont lie and if the cats are properly sized for the engine they dont cost much if any notable power loss on a daily driver. Also worth noting is the load on the engine pushing this monster at 80-85Mph wouldnt allow me to lean out the mixture safely anyhow...

Yes, we must make sure to maintain our health ^ (so we can continue playing with cars ) Yes, true, a modern cat of the right size will not impede flow (same as the MAF).

I can say that tuning the higher end of the engine has resulted in some impressive gains. The L96 likes more cam retard at the higher end then GM put into the stock tables. It also enjoys quite a bit more spark. I plotted the MAF g/sec and have increased that number by 54 g/sec over stock from 4400-6000 RPM. Havent put it on a dyno yet but more air = more power. Being and HD GM was understandibly conservative with the tune to keep it in one piece.

Thanks for the thoughtful reply and education, the support from the EFI team is awesome!

Yes, for many reasons, GM leave leave a lot on the table (not just to protect the drivetrain, but to make HP match the pricing levels... e.g. $Corvette > $Cadillac > $Firebird/Camaro > $Monte Carlo, and I'm sure various truck models fit in there also), and sometimes because the calibration engineer only went up to 4000 rpm...

Yes, I like people to learn how thing really work (and how to apply technology simply and effectively; I'm an engineer), thanks for the kind words.

[496Stingray]

This is the other key ^ [/COLOR](tuning the transmission to work intelligently with the engine (especially when engine has much torque), good deal

Very true I neglected to mention the major tuning changes I made to the T-43 6L90 shift schedules. Shifts were extremely late in stock trim. Say you applied enough throttle to hit 2200 RPM accelerating the trans would shift closer to 2700 allowing about 500 RPM without power before the shift would command. Created a really annoying driving experience that would make you "lift to shift" or just plant your foot into it out of aggrivation. Granted this was less prevalent when the truck has 2000-3000 lbs in the bed or towing a small car/hauler etc. My logic is Ill switch schedules to the Tow-Haul mode and leave the normal mode setup for running empty, normal street, day to day or spirited shifts when I want them.

Yes, I like people to learn how thing really work (and how to apply technology simply and effectively; I'm an engineer), thanks for the kind words.

I am an EE but manage network/security sales engineers by day and the car business is my side business/passion. Since I am learning this E78 and the torque based ECM in general I felt it wise to make incremental and documented changes and allow time to properly observe the outcomes. I began with the trans changes before ever touching the engine portion. Then began the engine incrementally, and as needed made some very minute adjustments to the shift schedule to match the power curve. I now have seamless acceleration with quicker and more firm shifts, the torque curve is improved down low substaintially as I focused heavily in the 1500-2500 range where most daily driving actually occurs.
Thanks again I really do appreciate the assistance/feedback.

[GMPX]

Funny thing, GMH went to great lengths to get better highway economy on the late model GenIV's, AFM, turning off charging to conserve alternator load on the engine (which sometimes results in a flat battery, but that is another story), so why then do the climate control engineers insist on leaving the A/C clutch engaged the whole time even when it is not cooling? Seems like one of those George W moments (left hand not knowing what the right hand is doing).

[496Stingray]

Agreed on that part. My C6 vette runs ac by default for everything then the truck decides to not allow engagement of the AC when the ambient outside temp is below 40F. So I get useless defrost in winters. Some move the sensor behind the radiator to trick it, I rigged a voltage regulator circuit to it to fool the ECM/BCM when needed with the push of a button hidden in the glovebox. Stupid design. Below freezing...ok debatable sense most moisture should be frozen out of the atmosphere but add in wet clothing,shoes, mats and the heater on and you want mixed mode dried warm air.

[joecar]

...

I am an EE but manage network/security sales engineers by day and the car business is my side business/passion.

...

I'm an EE; during my career I have slowly shifted from hardware to firmware to embedded software, and now I do linux kernel/driver programming (more specifically, device driver for Fibre Channel cards).

Yes, car stuff is my hobby (since I was 5)

[joecar]

... so why then do the climate control engineers insist on leaving the A/C clutch engaged the whole time even when it is not cooling? Seems like one of those George W moments (left hand not knowing what the right hand is doing).

Yes, this is very irritating... the vehicle exists solely for the purpose of the AC being able to run continuously...