E38 ECU, S/D operating system, forced induction. Barometeric updates?

[Blown353]

Hopefully this is a simple question... I did some searching and while it answered part of my question, it didn't answer all of it.

I'm getting ready to build a twin PT-61/76 turbo LS2 for my Chevelle as I just broke 1 piston in my Procharged / FAST EFI Gen 1 SBC. (Lightweight pistons with too-thin ring lands aren't a good match for 15 psi of boost... 5 years is all they'll last. LOL!) The new LS2 should be good for around 900hp and I was planning on running it MAFless with a Speed Density setup.

Anyways, I'm trying to decide on an ECU for the new LS2. I'm torn between a couple of aftermarket choices (Big Stuff 3, etc.) or using a factory E38 ECU and a speed density EFI Live setup.

I live in California, and while I live at 17' above sea level I can drive to 9000' altitude in 2.5 hours. My non-barometric/altitude compensated older FAST box right now can't deal with this and as such I have to load a new VE map when altitude changes significantly to deal with AFR changes going beyond the limits of WB02 correction limits in the ECU. It's a major annoyance to pull over at about the 4000' mark and pull out the laptop to adjust the VE table up or down.

My question is this: when running a factory ECU with an EFI Live Speed Density operating system and the engine is forced induction (meaning WOT MAP/Baro updates will not accurately reflect the barometric pressure), how does the ECU compensate & update for altitude changes? I really want something that will compensate properly for altitude changes in real time without having to pull out the laptop and load a new tune or adjust the current one.

The Big Stuff 3 and Pantera 882X ECU's for example both use separate MAP sensors for real time barometric monitoring and updating, but I haven't found a satisfactory answer of how the factory E38 ECU with a Speed Density OS will handle it in a forced induction application.

Thanks in advance...

[ScarabEpic22]

Hey man, sounds like a sweet setup for sure! I might download the latest EFILive software and run the update program so you can check out the latest E38 ECM calibrations. Theres a sample E38 tune file in the download that you can look at as well and play around with it. You cant however adjust the VE table without a V2 plugged in to get access to the VVE table. E38s can run SD from the factory by simply unplugging the MAF and turning the CEL light for the MAF off. Lots of guys run FI this way, havent heard too much complaining so far.

[Blown353]

I have access to a copy of EFI Live / V2 (a friend bought it for his Duramax but I do the tuning for him.)

I have looked through the E38 example files but I'm still unsure how the computer handles altitude & barometric changes while driving when the car is forced induction and thus can't do a MAP-reset of the barometric parameter at WOT-- since manifold pressure at WOT in a forced induction engine will not even be close to ambient conditions.

I just don't want to go down this road only to find that whenever I make a substantial altitude change while driving the ECM can't cope or I have to key off/key on to get it to update.

Having to key off/key on to reset the baro is far easier than having to pull out the laptop and retune at the side of the road like I have to do now with my old FAST, but I would prefer not to have to key cycle either!

[ScarabEpic22]

OK, Im no expert by any means but Im pretty sure it calculates the airflow based on g/cyl and you need to set the VE table based on logged data. As you increase in altitude the g/cyl value to decrease even though you are boosting and that should keep fueling in line. That said, I would trust someone who has done big hp E38s with varying altitudes more than myself as Ive never touched an E38, Im just looking and applying the random bits of knowledge I have.

Cant wait to see this beast up and running, having to reflash at 4000ft sounds horrible.

[WeathermanShawn]

I am not boosted, but I do a lot of mountain driving.

Even with a PCM program that compensates for altitude changes (Barometer), how about when you hit an inversion and the temperature/pressure fails to change in the same linear manner? Same phenomena that pilots encounter routinely. You can get some rapid air density changes in a short period of time.

Just a thought. Your car's 'barometer' is pretty basic..MAP & vacuum.

[GMPX]

Given the code behind the E38 and E67 was written with boosted engines in mind I think it would handle things correctly, however, I know you are looking for more than a 'I think' answer. That I can't give.

Cheers,
Ross