Competition Launch in 4-HI

[ob1kobi]

Seems like alot of you do it. How safe is it, and how much HP/Torque can the transfer case handle? Do you shift back into 2 wheel after the launch, or keep it in 4 wheel all the way? Thanks

 

[HillCountrykid]

I can't answer anything but the rated torque on the t-case. It's rated at 5555 lb/ft.



Brian

 

[Strick-9]

I have the light duty transfer case and I haven't broken it yet. I do 4wd launches about 3-5 times per month. I have however broken the snap ring on the back of the case. Combine the spline lock that occurs during a high torque usage with the rear suspension compression from hard acceleration and you have a huge force shoving the driveshaft into the T-case.



I don't leave the line nearly as hard as some people do though. My g-tech readings are about . 7g's on take off. That's building about 3-4 lbs of boost before leaving. I don't know how many g's people are pulling that leave at 15+ psi of boost spinning all 4 tires, but I'm sure it's much higher than mine.



I try to shift out of 4wd, but I get too excited when I'm racing and often forget.



I can't tell you how safe it is. I will break it eventually. I just haven't yet.



-Chris

 

[KatDiesel]

This isn't a easy question to answer.



Is it safe? So far yes, I haven't broken anything yet... . keyword being yet. Its kinda of a "use at your own risk" type of thing..... if you don't mind breaking it... then use it.



Yes I try to pop the level back to 2wd after it shifts into 2nd.



Up till now I have tried to launch at 10psi or less... ... gonna try 15psi now.

 

[Cummins Corvette]

Kat- I remember you saying that there was at least one time that you left the line with all 4 tires spinning. Tell me that was at 10 psi or less.

 

[KatDiesel]

Originally posted by CAnderson

Kat- I remember you saying that there was at least one time that you left the line with all 4 tires spinning. Tell me that was at 10 psi or less.

Ya that was with the KwikSpool..... and last November, I kept it under 10psi. With the B1 I am gonna try and step it up a notch or two and see how it reacts.

 

[Swayse]

So far so good

I launch in 4x4 all the time at the strip. Good for a 14. 265 at 92. 59. I launch in 2nd gear, with 3. 54 gears and 315x75x16 tires. I left it in 2wd when I dynoed 385hp and 899. 8 lbs.

 

[Snow man]

I think launching in 4x4 is relaitively safe with 300 or less hp,with an auto,over that and it could be costly. To those of us drag racing,it is worth the risk to get out of the hole,whether that be a broken output shaft,or grenaded T case. I think launch in 4x4 is better for the rear axle than launching,spinning in 2wd. If you cant afford to buy a new transmission,and t case,+ labor if your not into doing the work,you problably shouldnt do it,it seems the ones with full sponsors never break a thing,while those with just enough to bomb it, break everything and dont have another car/truck to get around while its down.

 

[Strick-9]

Snow man,



AMEN!!!!!



-Chris

 

[Cummins Corvette]

What's next in line for breakage after a billit input shaft and cryo'ed output shaft are installed?

 

[KatDiesel]

Originally posted by CAnderson

What's next in line for breakage after a billit input shaft and cryo'ed output shaft are installed?

transfer case, u joints.

 

[HoleshotHolset]

... . Axle shafts... ... ... .



Matt

 

[drice]

bad luck???

well maybe I just have bad luck but the frist and only time I raced in 4 hi I cracked my tail housing (but I smoked that phord) so I don't knwo how safe it is but from what I hear alot of people do it. I'm thinking about tring it again but it is about 400-500 dollar to fix if it does break.



but then again it could that darn luck!!!:{

 

[Cummins Corvette]

Re: bad luck???

Originally posted by drice

well maybe I just have bad luck but the frist and only time I raced in 4 hi I cracked my tail housing (but I smoked that phord) so I don't knwo how safe it is but from what I hear alot of people do it. I'm thinking about tring it again but it is about 400-500 dollar to fix if it does break.



but then again it could that darn luck!!!:{

On the back of the transfer case? I don't see how that has anything to do with the front drive being engaged. If anything it should be easier on the rear drive because the front is taking most of the stress.

 

[Snow man]

drice,ive seen quite afew chevy's and dodge's break the output housing on the Tcase,but every time it was due to a U joint that froze up solid ,one chevy actually split the tcase right open. I think you had a defetive casting on your T case,and the launch just did it in. It should not have broke that easy,IMO. I have onbly done 4 hi launches 4 times,but i plow with this truck in 4 hi for hrs,even days on end,and drive it weighing 11K,on sometime dry roads,and it does bind occasionally,up to now,knock on wood my truck has taken it in stride,I have the 241HD. I am very confident in what Dodge put under our trucks,its held up great considering the output of the Cummins.

 

[drice]

actually it was the on the transmission not the T-case. I haven't figured out how or why it would have cracked but it did. I'm guessing it was the torque but I was and still am clueless about it.

 

[Cummins Corvette]

Oh, you have a 5 speed. I didn't notice that before. If I had a manual, there would be no chance of me ever launching in 4x4. I would think that it would be way too harsh when you dump the clutch; that torque spike would be horrendous/break things.