ATT report

[Acesneights1]

You're not wrong.

As long as he's running a 4L80E, it's all "tweakable" in the program:

That's an OBDII list, I assume OBDI would be similar. The TCC behaviour is also programmable.

I don't work in OBDI so you'd have to get a hold of someone who does.

My PCM holds the trans in gear longer for less RPM drop on the upshift and better performance while loaded down with the trailer. TCC behaviour is also modified.

I'm still not at the level of what Bill puts into his PCM flashes, but I'm getting close.

Of course, being able to tweak the trans and knowing what to tweak are two very different things.....

His truck is a 98...Is he running an OBD1 tranny ?

 

[great white]

His truck is a 98...Is he running an OBD1 tranny ?

Dunno.

I've got sigs turned off (too much space use on an iphone) so I was just covering all the bases.....

 

[buddy]

The power from tires also comes from a torque perspective. You are guaranteed to lose low end torque/hp at the wheels due to the longer lever arm. The power at the end of the rubber is less and you cannot get them to accelerate as fast with the same given power input. For example you can spin a set of 30" tires from a stand still, but not a set of 35" tires. And thats not because the 35" tires grip better. It literally takes more power to turn them, and with the lower gearing, that helps make up for it.

His gearing is set up great, for driving 55mph-75mph. But if the majority if driven at 40-50mph then it would just be a good idea to leave it in 3rd gear whenever in a place with hills. Then you have the high speed in the right RPM power band and over the torque converter stall speed, and you have the same in 3rd gear at lower speeds, especially since TCC locks in 3rd. It might be running 2200rpm in 3rd, but thats fine, motor loves that speed just fine, and will prevent annoying shifts that cause it to unlock and jump to 3000rpm.

 

[Acesneights1]

Hmmm I need thicker skin ??
Back on point...If the tranny is hunting around at 45 mph why should that be the reason for a lack of boost ? I don't know what size tires my Dually came with factory but it had 245's on it and the speedo was off say...6 mph approx so I know the "bigger" tires had an effect on it. It did exactly what Buddy said and Joey describes about hunting around however at no time did I lose boost/power or have any smoke. I am not knocking your product but Joey's truck IS lifted and used for off road and maybe your product does not fit his needs. I had a long talk with Bill Heath about putting a 6.5 setup on my CUCV and that it was lifted and I use it off road and he actually suggested I may be happier with a GM4 as it would give me more low end response even though he personally believes the GM8 is the best turbo for our trucks. Now Joey's thread started with "ATT Report" not "my tranny is shifting weird". Alot of people are giving opinions on the effects of running bigger tires but I DO run bigger tires and I don't see them causing the issue he has. If I am reading this wrong, by all means correct me but it seems to me exactly as he worded it, his boost is dropping off to nothing when the tranny shifts 3-4. Now my old 93 had an NV4500 which has a pretty large gap between 3-4 . A bit too large actually to the point where it was a PIA in a 40 mph zone. But when I shift from 3-4 I get a little black smoke but my GM4 snapped back pretty quick. Most of the stuff I have seen about the ATT and read and asked people in PM's(no I will not reveal who) have said they have seen the most benefit towing and I am suggesting in an off road performance category, maybe it's not the best choice. Hopefully he will chime in soon and clarify.I would not run out and buy a Holset either although so far what I have seen it seems to give the best of both but I don't think the controller has been worked out yet.
I normally stay out of the ATT threads and just read but being someone who has built lifted trucks since the 74 Ford/429scj/Bigfoot days and built them when there were no "kits" I hate hearing how...It's the lift, or it's the tires. If the truck is done right the effect is minimal and I saw Joeys truck personally in my driveway. It's built right.

 

[Slim Shady]

Yeah deleted my post, thought better of it after I re read it. Need to get over people having differences of opinion with you. Those things are going to happen. Do you know what it does to a motor like ours, IDI high Compression 20:1 or better lugging it around at 1400 to 1500 rpm with 6 or eight pounds boost ?

Bottom ends go bad pretty quickly doing that. Rock crawler trucks don't even do that. So maybe we are having an appropriate discussion about tire size and gearing for a truck that is not a typical installation. If the turbo is not sufficient or I misrepresented the turbo in any matter I will buy it back. I put my money up when the talk is cheap, I have always said that customer satisfaction for me is number one.

Unless you are saying otherwise ?

 

[Acesneights1]

Nope, just want to see all aspects and for the record I have talked to people that were very happy with it. My interest is more in the off road performance area. That and I strongly dis agree on blaming his tire size.

 

[buddy]

I dont blame his tire size, I am blaming the rpm range the tire size and gearing put him in at the speed he is having problems. Combine low power RPM band and Tranny torque converter stall speed area, to more resistance from big tires and the whole thing easily explains the issue at hand before turbo issues.

The GM8 probably is a better choice for off road crawling, but I don't believe it to be the best turbo for the 6.5.

 

[Joey D]

I think the issue is the lack of boost at low throttle in this rpm range. The computer tells the truck to downshift while taking into account throttle position, boost pressure, speed. My final drive ratio is very close to how it came from the factory, 4.10 gears 29in tall tires. Yes the 37's offer more rolling resistance but it's not whats causing the issue.
This does not make the turbo a bad choice, if i was towing I would have pulled it into 3rd gear to keep it from hunting back and forth anyways.

 

[Acesneights1]

How would you rate it for off road use say crawling or Mudbog ?

 

[Joey D]

Crawling it's fine, at least to me. My crawling is in 4lo and going slow off idle and the 6.5 handles it no problem. Mud running is foot to the floor and the turbo is doing it's job.

 

[buddy]

The PCM really doesnt take boost into account for shifting. It is mainly throttle position, so it is as you originally mentioned, you have to put more pedal to get more power than you did with the GM8, which that pedal position versus the speed you are going, determines it has to shift. That can be tweaked easily to not downshift, but will cause a little more lugging.

Your drive ratio is actually more like 3.73s now if to compare to 4.10 with 29" tires. About 10% more gear with 25% more tire.

So if everything else was equal in load, then it should be rolling at a couple hundred less RPM than it used to at say 65mph. Thats a good thing in my book, except at 1500rpm cruising, because its sitting on the stall speed of the converter.

You are at the same RPMs as me with 3.42 gears and 30" tires, and yes I have the same issue with either turbo I use. I also get a little chuggle or chatter on minor drops in load, like a very minor dip in the road.

 

[Joey D]

The PCM really doesnt take boost into account for shifting. It is mainly throttle position, so it is as you originally mentioned, you have to put more pedal to get more power than you did with the GM8, which that pedal position versus the speed you are going, determines it has to shift. That can be tweaked easily to not downshift, but will cause a little more lugging.

Your drive ratio is actually more like 3.73s now if to compare to 4.10 with 29" tires. About 10% more gear with 25% more tire.

So if everything else was equal in load, then it should be rolling at a couple hundred less RPM than it used to at say 65mph. Thats a good thing in my book, except at 1500rpm cruising, because its sitting on the stall speed of the converter.

You are at the same RPMs as me with 3.42 gears and 30" tires, and yes I have the same issue with either turbo I use. I also get a little chuggle or chatter on minor drops in load, like a very minor dip in the road.

I just did the math and your right on the final drive. It was closer to stock when i ran the 35's.