Guys

Preface:

Car: Nissan 300ZX
Motor: RB26 (550rwhp @18psi)
Trans: Built Th400, JW aluminum transbrake, precision converter (5000 stall)

I've got a weird issue I've never seen before, and several people I have talked to have never seen....

Last night I got the nitrous system completed, and I went out to see if the nitrous would actually get the turbo spooled on the transbrake, and get the motor up on the converter.

The initial test went just fine, I hit the nitrous button, the turbo spooled, and my RPM's reached 5500 or so....now here's the problem.

When I released the transbrake, the car didn't really go anywhere, it just kinda crept forward a bit. Basically nothing happened.



Now move on to scenario B.

I put the car up on the transbrake w/out nitrous this time. I could only make like 5-6psi, and the car would only get up to 3500-4000rpms. I can release the transbrake and the car has a pretty good initial 'hit'.....however since its not past the stall point (5000rpm) it really doesn't go anywhere after the initial shock of releasing the transbrake.

Any idea why my car isn't moving anywhere when I release the transbrake at 5500rpm, and 18psi?

PS - The tires weren't spinning either, I checked that, lol

Thanks in advance for any help

 

Could the tranny be slipping, or the converter too loose?

It sounds like you need a 2 step to get the turbo spooled, either that or activate the nitrous off the transbrake so you're getting the hit of that right off the brake and the turbo will spool probably 20 feet down track.

 

I've had a similar problem since I put just a 2300 stall on my TH400, but its usually when i give it gas and it downshifts 3 - 2, people are like oh your tires are spinning, im like um no theyd be screaming at 5000 RPMS if im not moving forward

 

Is this Andy?


I'd try a two step as mentioned above, but it does sound like there might be an issue with the tranny itself.

 

Thats how I have the nitrous setup now, its wired into the transbrake. The car has full boost when I release the transbrake..........and as long as the car is up on the stall when I release the tranasbrake, it should carry that boost out of the box...

 

Sam, what up fool?

Yes, its me, i Decided I wanna go fast.........

 

might need a tighter converter.......



cough... cough....

 

Not much, same old same old.....

This may be overly obvious, but check the fluid. TH400's are real sensitive to fluid level and if you're even a little overfilled it could be foaming and letting the pickup pull air up, thus causing problems. Just a free idea to try.....

You gonna be at the MDA show next week?

 

Fluids good, checked that

I'd like to make it to the show, however my bro's wedding is that day

Not to mention, the Z might not like 75 miles one way on a 5k stall........1:1 3rd gear, no OD, and a 4:10 rear gear, lol..

 

That car should be fast enough to max that out before the 1/4, right? You might need some taller gears...unless you're spinning to 9000 RPM, I don't know jack about import motors.

 

Oh no, I'm only making like 540rwhp or so right now on pump gas through the auto (guesstimation- i made 555rwhp @ 18psi on pump gas with the 5spd)

Car is 3600lbs, I'd need 750-800hp to go 145 in the 1/4....lol

I have a 4.10 in the car right now, If I ever get to the point I'm maxing the gears out, I can switch back to the stock 3.73

 

I FIXED THE PROBLEM!

After 4-5 hours on the phone with my trans builder, precision torque converters, JW transmissions, and a few other people, we came to this conclusion....

Symptoms -

When car is at 3500rpms and low boost, it would launch
When car is at 5500rpms and high boost, it wouldnt launch, just creep forward a bit.

What we determined

The new JW aluminum pro-transbrake does not come with a gasket that goes between the separator plate, and the case. The instructions explicitly stated one was not needed.

After talking with the precision guys, he suspected that since I did not have a gasket, the line pressure for 1st gear was bleeding off into another chamber. This is possible because the TH400 cases are not known for their rigidity, and overtime can actually warp, especially at all the worm passages.

So basically, when I was on a low load, the line pressure was what it was supposed to be, and thats why I was able to feel a 'shock' when I released the trans-brake. When I was on the stall, and high boost, 1st gear line pressure was bleeding off into another chamber, so when I released the transbrake it didnt have enough pressure to fully release the brake and engage first gear.

JW had great customer service and overnighted me a gasket. I took some pictures today of the install....

He're's the trans with the oil pan off



Removed the valve body, you can see the passages I was referencing



Here's the valve body with the separator plate sitting on top



Separator plate removed



THe new gasket, and put in place





Cleaned up and ready for install




I went out in the country and got the car up on the stall, and LOTS of tire smoke followed, lol. I am only running around on MT ET Street Radials, so hopefully I can get some traction at the track.

 

I'd bet you lost alot more RWHP than that, didn't Grant lose a bunch? I mean, you're going from 100% engagement (clutch) to a convertor with slippage and a tranny known to eat some HP. I'm sure its still faster than a stick though.

What are you goals ET wise?

 

Very interesting.. Thanks for the info.

 

Mid 10's on pump gas if I can get it to launch well......9's on race gas

It made 680 @ 24psi on Torco 112.....which is getting pretty close to the ceiling for a stock block/head

 

LOL I am just reading the thread and that fix is the first thing to come to mind

Good luck!