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ATT reliability

WestVdiesel

WestVdiesel

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Location
Hedgesville WV
Hey everyone new to the site i have a 98 gmc 6.5 with 142,000 miles im now looking to do some upgrades i know theres alot of stuff already on the ATT but nothing that really gave me a direct anwser, i was looking into getting an ATT but the only thing thats holding me back is the fear of it blowing head gaskets popping heads and just creating too much over preassure all around what is everyones opinion of the turbo and is it safe to run on a stock 6.5 daily without it causing problems
 
Welcome to TTS!

The ATT helps deliver the same power as other alternatives and does it with significantly lower boost. So no need to beef-up the motor to handle more pressure.

Case in point is that when I got my new motor (with stock head gaskets), I asked about ARP studs and the recommendation was to use what came with the P-400 as the ATT's was not a concern.

Have seen some manage to get their ATT to ~20 psi, but I have a very hard time getting over 12. Even at the boost levels I get, it is plenty for towing and driving.
 
The ATT delivers less boost pressure, but, more air in the upper RPM range. The air is not as hot so less boost still means more oxygen. The turbo is loved because in the upper RPM range there is less back pressure on the exhaust side. So your engine is not working as hard to exhaust the exhaust past a restrictive GMx turbo. This means less cooling fan use when towing. Hot exhaust trapped in the engine due to a restriction will heat it up more.

I have put two turbo's on the dyno: the ATT at 14PSI and the HX40II at 23PSI. Boost numbers alone don't mean more power. The numbers were 7-16 HP and 20 FT LBS different with 10 PSI boost difference. Link.

As far as a daily driver and stock... From a stoplight and flooring it: The ATT turbo will not light up below 2000 RPM. Far as I am concerned another popular turbo I tested the HX40II won't light up below 2000 RPM as well. Regardless this is a completely different mindset and driving style. The GMx spools from the starter RPM and then chokes around 2200 RPM. The ATT is lighting up at 2000 RPM and will pull like a freight train all the way to redline.

Bottom line is you need to quit lugging your engine at low RPM with a bigger turbo. Stock is ok, but, you want a tune and 4" exhaust at the minimum. You may be mechanical injection so forget the tune...The tune should change shift points and eliminate turbo boost out of expected range codes.

Spool valves and High Stall Yank Converters really wake things up!
http://www.thetruckstop.us/forum/threads/let-the-insanity-begin-time-to-yank-it.43647/
 
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Thank you everyone for all the replies i think i will go with the ATT i already have a 4 in exauhst on the truck and plan on getting the kojo tune with the turbo and my fuel pump is electronic not the mechanical also what is everyones reccomondation as far as tunes go and everyones view towards the kojo tune
 
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I'm not a 6.5 guy, but from what I hear the ATT has been one of the best mods any 6.5 guy on here has made. Hard to argue with all the happy customers.
 
Kojo now offers att specific tunes that have been proven to make the turbo start building noost down to as low as 1400 with a stick shift.
 
Steady RPM with full load is different from a stoplight "dig". @THEFERMANATOR is noting you are doing say 45 MPH and roll into the throttle lightly. What is the lowest RPM you see boost? His point is the tune is able to light off the turbo at a lower RPM. This is very useful when you really don't have enough load to justify downshifting. (Tuners were getting this figured out when I sold my 1995 Spool Valve equipped DS4 years ago. The Spool valve clearly showed Dennis, the Fellow who makes the ATT, was retarding the timing to spool the ATT at a lower RPM. Kojo I do not know specifically what he does. This is just one tuner trick example being made available on our forgotten diesels. )

In the Appalachian Mountain area flat lands without grades don't apply so much as it would in the flat lands of say Kansas. (IMO it doesn't apply to me at all out here...) This is where the bigger ATT turbo with any sort of trailer or full load on the truck is good advice. Daily drivers without load is a different driving style, however, the reward is getting up the grade with full power in the upper RPM. I suggest you already know the falling over feeling your GMx turbo gives you in it's upper Asthma Attack RPM range. Link to article of mine.

My favorite example you are in high gear and roll into a 10% grade. Speed limit is 45 MPH on this exact grade I use for testing and the sports cars like Porsche, etc regularly provide a front door. Getting into the grade takes more fuel than high gear with the TCC locked will burn smoke free on the DB2 setup of mine. So I had the tuner shift the 4L80e earlier. It just starts to smoke some and any further speed reduction or adding throttle will downshift it.

Tune or not a big turbo is a change of driving style. IMO think "REV IT UP!" and you get a rewarding experience. Unlike a gas engine diesels can run at Max RPM and full load all day and not blow something up. Well, most days anyway and with some cooling system improvements depending on your model year.
 
Gearing, big tires, and heavy weight truck also can come into play. Hummers/ hmmwv for instance need most of the help above 35 mph- where every ATT and hx40 ive driven has done great.

As soon as leroy gets his kit done for the hummer guys, i expect a delay or backorder for a minute on ATT. After the 2nd hummer owner tells his story- the line will form.
 
Ive got 35 in tires and live in the moutains 95 degrees F and a 1 mile pull up a mountain and im at almost the 210 degree mark and it not all that steep either as WarWagon was saying i can feel it choke out on the hills even while running empty does anyone know how to find out what gears i would have in the rear
 
If it still has stock gears in it, you can look in the glove box at the rpo codes. Gt5 is 4.10, gt4 is 3.73, and gu6 is 3.42. 4.10 seems to be the most common for 8 lug trucks.
 
Sweet thats what im lookin for im just lookin to get a little more power out of my truck expecially so i can climb hills without going from 55 to 40 mph and being able to just step on it and go when i need to
 
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