ATT report

[Joey D]

After owning the ATT for some time and putting some miles on it I have found a downside to it. Lack of boost at 45-50 mph. I am up in NH and there is a lot of rolling hills where your speed is around 45 and the lack of boost requires more throttle input which results in the truck wanting to shift in and out of OD.
On the highway or towing or even around town it's great but this area is it's downside

 

[Michaeljp86]

So you would be better off with the stock turbo?

 

[Big T]

I shift into 3rd when driving the 5,600' vertical climb to Big Bear Lake.

 

[Slim Shady]

What rpm are you running at that speed? What kind of final gear ratio do you have. Manual transmission,automatic.? This is good information, I run a manual so I keep the truck between 1500 and 2400 most of the time. These are the things to document, this helps determine the area that needs improvement.

I think that the tune may be able to be tweaked to minimize all the shifting, by holding the gears longer on more throttle input at lower rpm. But i might be wrong. I love this stuff, document the particulars. Maybe we can start a thread for the anomalies that people find and then I can see if an improvement in the tune or the turbo will cover the problem. Thanks for the input.

Dennis

 

[Joey D]

RPM's hit 2000 in 3rd then it drops to OD at 45mph dropping the rpm's to 1500-1600. Now to maintain 45-50 on small rollling hills you need to press down on the throttle more than with the GM 8 it had stock and I think the conputer see's throttle position and just downshifts to 3rd.
My truck is an auto with 4.56 gears and 37in tires. Final drive is almost identical to stock, 4.10 gears 30 in tires

 

[Crankme69]

What exhaust & air cleaner are you running? OEM tune?

 

[Joey D]

I have a 4in exhaust and stock air cleaner setup and a heath ecm reflash thats about 2 years old now.

 

[great white]

...I think that the tune may be able to be tweaked to minimize all the shifting, by holding the gears longer on more throttle input at lower rpm. But i might be wrong...

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.....

 

[Michaeljp86]

I have a OBDI cable hits a laptop, I never got into the ecm stuff like I wanted to. But from what Im told if you know what your doing you can do about anything with the obd1 computers.

 

[buddy]

Some shorter tires would help

OBD1 guys have similar options and one thing I like to do is modify downshift and kickdown throttle percentages so it holds gears a little longer with throttle. Just increasing the fuel curve helps this too, since you might get more fuel before reaching that stock downshift/kickdown percentage. But I will say 1500-1600rpm is not a great place to be with this powertrain. You would probably be happier and more efficient if you cruised around 1800rpm, so the TCC can actualy hold its lockup above its stall speed. And the engine produces more torque there.

So a set of 35" tires would probably help you run more efficient and keep you in the engines power band where it can operate most efficiently and less lugging where you have to use more fuel to maintain less RPM. The taller and heavier the tires the more power its robbing. You might need the clearance though, so its good you have the 4.56 gears. The GM8 certainly holds more boost easily which can help throttle response when that low in RPMs. Unless you also cruise a lot at more than 65mph, then I highly recommend getting your 45-50mph RPMs up a couple hundred.

 

[Turbine Doc]

I have a 4in exhaust and stock air cleaner setup and a heath ecm reflash thats about 2 years old now.

Hey Joey,

That program needs some tweaking for your vehicle now, I climbed the same hills mountains you are in now last summer when going to school in Schenectady and driving the NE with my ATT & Heath program tweaked for the ATT without issues.

Your tall tires have a lot of rolling resistance, plus the program Bill had 2 years ago was tailored for GM-8

Bill & I tweaked 4 combinations last summer to get smoke more passerby friendly when I was in NY before going with final tune I have now I got this past spring.

You should give him a call & ask about a tune similar to what he has in mine now, also the TCC lockup mod in there now vs tune 2 years ago that did not have TCC lock is well worth the reflash tweak cost,

 

[Joey D]

Some shorter tires would help

I need the tires though

 

[Joey D]

Hey Joey,

That program needs some tweaking for your vehicle now, I climbed the same hills mountains you are in now last summer when going to school in Schenectady and driving the NE with my ATT & Heath program tweaked for the ATT without issues.

Your tall tires have a lot of rolling resistance, plus the program Bill had 2 years ago was tailored for GM-8

Bill & I tweaked 4 combinations last summer to get smoke more passerby friendly when I was in NY before going with final tune I have now I got this past spring.

You should give him a call & ask about a tune similar to what he has in mine now, also the TCC lockup mod in there now vs tune 2 years ago that did not have TCC lock is well worth the reflash tweak cost,

I will call him this week and see what he has for me.

 

[Acesneights1]

I need the tires though

I doubt they are affecting you much with 4.56s. I run 4.56s with 35's on a 135hp NA 6.2 and it pulls better than when it had stock tires as the motor was always screaming past it's torque range before.
I know, just throwin it out there.....
My 93 had 35's also with a 6.5 and a GM4...4.10's...It pulled fine...The only lag I got was from the wide range on the older NV4500.

 

[Slim Shady]

I doubt they are affecting you much with 4.56s. I run 4.56s with 35's on a 135hp NA 6.2 and it pulls better than when it had stock tires as the motor was always screaming past it's torque range before.
I know, just throwin it out there.....
My 93 had 35's also with a 6.5 and a GM4...4.10's...It pulled fine...The only lag I got was from the wide range on the older NV4500.

ACES I think that he has a problem with the shifting in and out of overdrive, just in case you didn't see the initial thread.

"I am up in NH and there is a lot of rolling hills where your speed is around 45 and the lack of boost requires more throttle input which results in the truck wanting to shift in and out of OD.
On the highway or towing or even around town it's great but this area is it's downside"

 

[buddy]

The tires affect power a lot, and he has 37" tires. From both requiring more torque to turn them, to putting you at lower RPM. The 4L80E torque converter is not happy at 1500rpm on hills, so OD sucks in this area with load even with the GM turbo. A manual tranny would not be as affected. I put taller wheels on to get my RPM down on the interstate, and yes that did help on the highway and interstate above 55mph. But it reduced my in town efficiency and below 55mph cruising. As well as losing low end power.

 

[Turbine Doc]

I doubt they are affecting you much with 4.56s. I run 4.56s with 35's on a 135hp NA 6.2 and it pulls better than when it had stock tires as the motor was always screaming past it's torque range before.
I know, just throwin it out there.....
My 93 had 35's also with a 6.5 and a GM4...4.10's...It pulled fine...The only lag I got was from the wide range on the older NV4500.

Kenny tires most definitely impact available power, so much in fact that on several dyno pulls I've been on guys bring smaller tires just to get dyno numbers up even with Strokes-Dmax-Cummins regardless of final drive ratio Ive seen guys swap tires.

What you are forgetting with his current flash is that it was not programmed for added on variables in his truck now so shift points if he feels the need to continue with the 37" tires need to be adjusted to take into consideration of new variables added to the mix.

 

[Pillow]

The 4L80E torque converter is not happy at 1500rpm on hills, so OD sucks in this area with load even with the GM turbo

I agree with Buddy on this issue. The 4L80E has a dead spot around 45 mph no matter what turbo is on it due to its shifting nature... Too early into OD at 45, it should be moved up to 50 IMO.

 

[Acesneights1]

I disagree. You guys gotta remember, I have seen Joeys truck personally.(I love his front axle swap, I so wanna do it.).It's easy to speculate what big tires do but Joeys truck is setup right and gear appropriately. Granted both my rigs had no computer(thank god for that) but as far as the tires taking away power , I have owned and built lifted trucks all my life(see my photo album) and the impact of bigger tires is minimal if the truck is setup right which in Joey's case it is. He has compensated with gearing. The truck may have some added drag with bigger tires, but it also loses drag by having a straight axle front diff with manual hubs. He doesn't have front axles spinning. IIRC he is running alum wheels vs the weight of steel factory. I don't think they are having as much impact as you guys think at all. See the 91 Jimmy in my Photo album. It had 3.42s with the stock tires and half ton junk diffs. I swapped out 8 lugs with 4.10s and 33's and the truck did not lose ANY mpg and drove better than it ever did. I do agree also with Buddy about the dead spot. My Dually had it and that truck was tuned by Heath. Bill tuned the ecm personally(I sent MY ecm to him) and it still had that spot where it was hunting around.

 

[Acesneights1]

ACES I think that he has a problem with the shifting in and out of overdrive, just in case you didn't see the initial thread.

"I am up in NH and there is a lot of rolling hills where your speed is around 45 and the lack of boost requires more throttle input which results in the truck wanting to shift in and out of OD.
On the highway or towing or even around town it's great but this area is it's downside"

REALLY ? Cause I read also lack of boost. Is that described some other way ??My Dually trans did the same thing and I didn't have a lack of boost with my GM8 just annoying that the tranny could not make up it's mind. Maybe he should look into that Holset VGT. It might better suit his needs.