Jc803

iTrader: (2)

Currently getting my T56 problem fixed and going to sell that junk. Have a 500+ hp car with 100% full suspension and a lot of weight reduction. I'm ready for a big boy transmission so I can finally get out of 11s in the 1/4.

I know almost nothing about autos so hoping someone can help me out. Have a TH400 picked out that comes with a trans brake valve body. I thought a 4000 rpm stall converter meant one thing but as I'm reading I'm way off. What would I have to do to get the car to launch at say 4,000 rpm. That number isnt set in stone, just trying to figure this all out and get a parts list together.

And someone please explain the trans brake. Are there certain ones that will make it launch at a certain rpm or can you launch at any rpm with them or does it depend on the converter. Sorry for all the questions

ragtopz28

iTrader: (57)

Trans brake locks the tranny in reverse and first gear (car no move), release the button and reverse is released (feels like getting rear-ended by a dump truck). I would spec the converter at motors max torque (you have a dyno sheet?). A two-step is needed to set/limit the rpm you want to leave at. Some people don't use a two-step and just put the motor up on the wood and the converter will not let the motor rev past the converter rating. When I had my old drag car (TH350 with trans brake), I tried both two-step and no two-step. I had a 5200 converter and it would 60' the same. I will say that the two-step is better for consistency.
I AM SURE SOME WILL DISAGREE

Jc803

iTrader: (2)

Looks like I'm in luck. I have a dyno sheet and a LNC-2000. Looks like my peak torque is at 5,000 rpm. But I do like driving this thing on the street on the weekends. What would a 5k converter be like on the street with a TH400? Since the converter doesnt lock up does that mean I'd have to be close to 5k rpm for it to go anywhere or would the rpm be lower with a lot of slipping?

And how much past the converter rating can a trans brake hold? Thanks for breaking this down to me to where its easy to understand

ragtopz28

iTrader: (57)

I'm not going to get in over my head here (I have been scolded in the past ) Not all converters are created equal. If you have a motor dyno sheet, that needs to be sent to the converter company to spec the correct stall for your particular use.
Hopefully some converter and trans sponsors will chime in on your thread.

I just skimmed your build thread...holy crap what a beautiful car...care to comment on my upcoming 408 build...https://ls1tech.com/forums/generatio...-breather.html

Jc803

iTrader: (2)

Yea I hear on that. Not everyone agrees on everything. But you helped me a lot and made things a lot more clear so thanks.

And thanks for the compliment. I used to be an ASE certified mechanic but quit 5 years ago to join the army. Now I'm getting out in 3 months and cant wait to get back into. Building this car and another LT1 camaro was just my little hobby in those 5 years between.

ragtopz28

iTrader: (57)

Hopefully some TRANSMISSION and STALL CONVERTER sponsors will chime in here......

Jc803

iTrader: (2)

Its cool if no one does. I've been reading up and doing my homework so by the time I am ready to make the switch I'll have a parts list

ragtopz28

iTrader: (57)

Might want to add some touch-up bumper paint to that list

bbond105

I’m not a converter expert, but I don’t think a 4000 stall non-lockup converter will work very well in a street driven car. The lockup clutch in the converter is what allows that high of a stall to be street driven. There would be too much heat from the converter stalling and it would over heat the trans. You can’t add a big enough cooler to keep it cool.

Jc803

iTrader: (2)

Yea the whole thing seems to be falling apart lately

Jc803

iTrader: (2)

That's a good point. I've been trying to find threads with people running high stalls and see what the highest average is to get a good idea

mrvedit

Looking at the torque curve you want to maximize the 2D volume under it as this is the amount of "go juice". In 1st gear from a start, the stall speed defines the beginning of the area and the 1-2 shift ends the area. For 2nd gear, the gear ratio change plus the shift extension provided by the converter defines the beginning of the area and the 2-3 shift ends the area. Similarly for the 3rd gear, although that is likely to end at the 1/4 mile mark. The more "go juice" area you can squeeze into the 1/4 mile, the faster your ET will be.
If your peak torque were e.g. 5000, but then dropped off rapidly, a 5000 stall converter would be poor because the distance between 5000 and when you shift would be very narrow and hence be a small area. Your dyno curve stops at 5700 and we don't know what it looks like past that. If you plan on shifting at 5700 you definitely do not want a 5000 stall converter which might more suitable for a 7500 shift.

The process of fitting a complex polynomial function to your torque curve and complex integral calculus based on your vehicle weight, transmission and rear end ratios and converter parameters (e.g. STR) might give you the ideal stall speed.
However with your dyno curve, vehicle weight, transmission and rear end ratios, a converter expert, like one of the sponsors (FTI, CircleD, Yank), should be able to come very close. Give them a call.

ragtopz28

iTrader: (57)

I was referring to dragging the bumper when you release the Tbrake!!

Jc803

iTrader: (2)

Ha ha, oh. Well that would be a good problem. I'd even leave it that way.

I thought you were referring to the picture in my build thread where last Friday the tow truck guy almost took my front bumper off and the paint with it. I almost cried

Circle-D_Brian

Very smart people in here helping you out. I would like to know a complete run down on the car and I can better choose the correct billet front, diameter, pump, and stator choice to work for your intended usage. There is a link to our Ask Chris form in my sig if you want to send over some details and get a recommendation and price quote.

-Brian

Jc803

iTrader: (2)

Sounds good. Thanks Brian