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Discussion Starter #1
I've got a few questions that I think will be answered pretty quickly.....

When you guys do boost launces in 4hi what is the safest range to stay in.....no more than 10psi? or what?

Second question....does it not matter what speed you go while in 4wd hi as long as you are going in a straight line or what? pretty much what I am asking is if it is ok to race somebody while in 4hi and take the truck up to about 80 or 90 mph?
 

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It wont really matter how fast your going as long as your not turing. All the front drivetrain is spinning alll the time anyways, its just not locked.

I would be scared to launch over 10-12 lbs of boost myself unless you have billit shafts!
 

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10-15psi is all you can get out of your truck at stand still anyway, stock front ends will handle about 110mph in 4x4, if you are even getting close to the 100mph club in the 1/4 you are doing great and probibly will not be running stock parts any way. :peelout
 

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Discussion Starter #4
10-15psi is all you can get out of your truck at stand still anyway, stock front ends will handle about 110mph in 4x4, if you are even getting close to the 100mph club in the 1/4 you are doing great and probibly will not be running stock parts any way. :peelout
well i just wanted to know because whenever I race somebody on the street I usually just do it in 2wd and I was curious about how much boost is too much boost when it comes launching these new trucks in 4wd...i don't take the truck to the drag strip that is why I wanted to know what speeds i could "safely" take the truck up to while in 4hi.

thanks for the responses
 

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I've a question that maybe is answered if I read between the lines on this but let's just clarify.

This really displays my ignorance of auto trannies. I consider that a good thing...been a stick driver most of my life including the only 2 turbos I have put much time on (1981 RX-7 and 2005 WRX).

How do you achieve max launch performance from an automatic turbo? If it was a stick you'd bring the RPM up to achieve boost pressure and rely on slipping the clutch on launch. With an auto how do I bring up the boost before rolling? Stand on the brake and the gas at the same time? Neutral drop? Either of these would seem to be tough on parts.

And yet with modern trannies they are achieving better 0-60 times with an auto than a stick...how do they get the boost?
 

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How do you achieve max launch performance from an automatic turbo? If it was a stick you'd bring the RPM up to achieve boost pressure and rely on slipping the clutch on launch.
One foot on the brake, one on the throttle. This is one of the reasons the autos are faster than the manuals...a diesel won't make much boost unless it's loaded and it's difficult to load a manual...then there's the whole ordeal of a VERY short rev band...:w:
 

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One foot on the brake, one on the throttle. This is one of the reasons the autos are faster than the manuals...a diesel won't make much boost unless it's loaded and it's difficult to load a manual...then there's the whole ordeal of a VERY short rev band...:w:
Fast answer. Thank you. How many RPM? This sounds like the poor old TC would be getting cooked pretty good during this.

Of course this is all academic since I would *NEVER* engage in street racing or any other activity requiring a max performance launch.
 

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Fast answer. Thank you. How many RPM? This sounds like the poor old TC would be getting cooked pretty good during this.
Each truck will be different...the only way to tell is with a boost gauge :thumbsup

As for T/C getting "cooked"...not really. It will heat the tranny fluid up in a hurry, though...
 

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1st you have to disable the torque management. Throttle and brake together will build boost, the torque convertor will also play a part in how much boost. My convertor is loose, I can build plenty.



Dodge | Commins | Forum
 

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I've been to the track a few times, and the torque management limits the truck to 10psi for a boosted launch, anybody know how to disable it.
 

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I know, I was just giving you a hard time
 

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Nothing yet
 

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So, if we have those <imperfect> auto locking hubs and <virtually impossible not to get off the dealer lot>> electronic dash mounted 4WD knob, can we launch in 4Hi and immediately switch it off so that we are not running power through the case and axles or will the transfer case not switch under hard acceleration in the 6-8 seconds it takes to hit 60? Not that I would need to do this on public streets either of course.....
 

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Discussion Starter #18
So, if we have those <imperfect> auto locking hubs and <virtually impossible not to get off the dealer lot>> electronic dash mounted 4WD knob, can we launch in 4Hi and immediately switch it off so that we are not running power through the case and axles or will the transfer case not switch under hard acceleration in the 6-8 seconds it takes to hit 60? Not that I would need to do this on public streets either of course.....

Good question...i would like to know the answer to this also.

yeah you're right, who would ever think of racing on the street!?!?!? it is against the law... :w:
 

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I can tell you what I know from racing the truck, the 4 wheel drive light will go off, but it will not disengage under load. It will disengage once i let off of the throttle.
 

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I can tell you what I know from racing the truck, the 4 wheel drive light will go off, but it will not disengage under load. It will disengage once i let off of the throttle.
X2! tried it and same result, thought it was out but no.
 
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