Help! Experienced Accel Gen 6 tuners.
 

Just got my twin turbo 355 Chevelle. But I am at high altitude (5500 ft.) and I need to tune it. I can plug it into the laptop, run the program... But I know nothing about tuning. Is there anyone that is reputable that might get on the phone with me and tune this thing over the phone, off my laptop? Or even just dial into my laptop directly and tune it?

I haven't dealt with a Gen 6, but at 5500 feet you will probably need to richen the entire map about 30-35% and also add a several of degrees of timing in all the cruise areas to make up for lost combustion efficiency. It will probably want a bit more timing under boost.

I know it seems counter-intuitive to richen the map as the car is now at a higher altitude; common sense and carb experience says that as altitude goes up air density decreases and thus the mixture gets richer and you need to lean it out.

However, with an ECU that doesn't have barometric pressure compensation such as your Gen 6, the prevailing "standard" pressure at startup will drop from ~100 kPa at sea level (where the car was) to probably about 80-85 kPa at 5500'; this moves the tune into a lighter load and thus leaner area of the tune than it would be at sea level so the car will be lean all the time.

I am going to attempt this. You're not the first to tell me about richening it up. It still is hard to get that thru my thick skull, doesn't seem to make sense. But I trust you're experience, so that's what I'm going to try and do. Thanks!:D

you are correct, it seems opposite of what your brain would tell you. But it is true, at least with the aftermarket speed density systems like Accel, BigStuff 3, FAST, etc.

I had to pull over on the way to Hot August Nights with the Chevelle and richen the entire fuel map 30%. It was dead lean at about 5000 ft altitude. After I richened the map I also allowed minus and plus 25% of fuel adding/subtracting through the computer, and the same high altitude tune ran perfect down at sea level. That is how a local tuner gets them to run at altitude and sea level. By the way, mine is Bigstuff 3 with altitude compensation, but it won't work at higher elevations, maybe good to 2500-3000' feet at best.

Jody

Ecu 882= Baro + Map
 

My EMS, ECU-882C-x, has the MAP AND BAROmetric sensors (two seperate) mounted onto the circuit board.
"BOTH 100% FULL TIME"
The "quest" from the coast to Lake Tahoe (9000') is quite common for, boats, buggies, and cars.

What was found:

The fuel pressure regulator's "baro" reference point determined the correction slope direction.

When the regulator was referenced to manifold pressure,
the slope direction would allow for LESS of the "fuel multiplier" object.

When the regulator was referenced to atmosphere (air),
the slope direction would allow for MORE of the "fuel multipier" object.

Lance

Where are you located? I know a guy who has tuned a few supercharged gen 6 setups.

Agreed Lance, I've made this observation as well. How the FPR is referenced does play into the necessary fueling corrections. I neglected to ask or mention the effects of FPR reference point in my old post.

I just find it rather sad that most of the "mainstream" boxes (including my older FAST) have no barometric compensation capability... because real world cars seldom drive at a steady altitude all the time and how a feature this critical to "jump in and go" capability could have been overlooked or omitted is a HUGE oversight!

In a relatively "flat" state like Missouri the lack of barometric compensation is not a huge problem, but in my case I can go from sea level to 9000' over a 2.5 hour drive and it can be a real issue!

Now you are talking in foreign languages:lol: I did find a tuner for the Gen VI. It is a temporary fix. But I also do have quite a range of altitudes with what I do. So I'm putting in a new FAST system in 2 weeks! It looks like this may be the start of what I thought was NOT going to be a project car. But this website doesn't help. I keep finding things I want to "spruce up" or just flat out change!

sell your computer and enjoy your car...... :thumbsup: if not you will end up doing a complete frame-off "spruce up" in no time at all... LOL

Don't bother with the new FAST XFI if you're looking for a step up when it comes to better performance over changing altitudes... because the XFI doesn't have true real time barometric compensation feature either and it still won't run right for your particular application if you drive the car to another altitude without a power cycle! The XFI firmware pseudo-comps for altitude with a "load indexed" speed-density strategy in their new firmware. The problem is it uses the main MAP sensor and thus can only update the barometric parameters during key-on startup and WOT-- which works OK with naturally aspirated setups as it can read the WOT MAP value every time you floor it and use that for the new barometric value but with your turbos the feature is rather ineffective to say the least because at WOT it doesn't see the true prevailing barometric conditions. Thus, for your forced induction application to have it refresh the barometric value requires you to shut the car off and then restart so it can read the key-off MAP value to get the barometric conditions. It's better than no correction at all like your Gen VI but still a pain in the butt as you have to pull over, shut the car off, and then restart it.

If you drive the car over a wide range of altitudes then forget the FAST XFI, Accel Gen VII, and the other boxes that get most of the advertising time; none of them treat this condition properly!

I've never used one of Lance's 882C boxes but I do like the specs & capabilities and I'm considering upgrading my ECU to one of his; Lance uses a separate MAP sensor to get the barometric conditions (i.e. altitude) so it can comp for weather/altitude changes in real time without a key-off reset.

Bigstuff 3 also uses a separate map sensor for altitude compensation, at additional cost. It doesn't work............. :( If I had a do-over, I'd use a GM computer and tune it through HP Tuners of Efi Live if altitude compensation was a big factor.

Jody

That pisses me off. If it were me I'd be bitching at Meaney like there was no tomorrow to either get it working or to get a refund for the non-functional add-on! You paid extra for it! :mad:

I hear you on using an OEM ECU, but for this application an aftermarket ECU is just easier-- provided it's the right aftermarket ECU! That's why I know he'll be disappointed in the XFI-- it will not solve his current problem given the forced induction application.

Speed density and altitude compensation can work and the problem has been solved; look at all the old GM speed density EFI stuff from the 80's and early 90's. Granted GM had the advantage of time and money for each engine package, but they did real time barometric updates via one MAP sensor by reading the manifold pressure at specific RPM & TPS settings and then comparing the actual MAP values at that RPM/TPS to a table of "ideal" MAP values at that same RPM/TPS and using the difference between the two for the barometric compensation. That's a lot tougher to do when you're not an OEM and not tuning an ECU for one engine you're going to build millions of, but the principal is the same and can be easily accomplished in the aftermarket with a secondary MAP sensor. Given the wide variety of engines that an aftermarket ECU may be used with a secondary MAP sensor is the most logical choice.

If I stick with my Gen 1 SBC stuff I'm certainly going to upgrade to a more capable ECU such as Lance's 882C, but if I make the jump to LSX I'm going with a factory ECU and EFI Live.

This has become way more interesting than I ever thought it would be. I love learning this stuff. I somewhat mis-spoke though. I get typing faster than I can think.
My immediate reason to upgrade ECU's (to FAST, maybe now) is to be able to retard the timing under boost. Mine's not even doing that now. That's #1 priority. Altitude stuff is just another part of it. I don't really travel from hi to low or vice versa, but it would be nice to not have to screw with it. I will continue my research and check out Lance's. Jody, you know anything about these? Maybe I just need a boosted LS7:unibrow:

I do not have any personal experience with Lance's stuff, but he seems like a sharp guy. The altitude comp isn't a huge deal for me, at least not enough to swap ecu's. I have my high altitude map, only takes 30 seconds or so to swap it if need be. Would be nice if it actually worked though.

Jody