transam69230

iTrader: (49)

Well long story short this is 3rd 4L80E that I have burnt up in less than 1500 miles.

I am looking at switching the trans to vacuum modulated to take out the EPC unit to take the line pressure tuning variable out of the equation.

My questions are :

Is this a good idea ?

What is need for vacuum modulator to work properly with a high HP car?

The car made 1000rwhp on 17.5lbs of boost.

This trans has a 36 element sprag , billet shafts, and all the good parts.

Currently it is slipping in 1st and 2nd (this is clutch pack it keeps burning up).

Went and pressure tested the trans none of the pressures were over 200 at positive vacuum.

I want this to be last time this trans needs to be rebuilt this summer!!

jimmyblue

iTrader: (11)

Questions are -

- can you find a vacuum modulator that responds to
positive pressure in any way?

- Would you want line pressure to be anything less than
all-in at 100kPA anyway? If no then you don't care
about the first question.

- Can you reasonably relate vacuum / boost to the line
pressure needed to hold motor torque, or at least
overestimate it safely?

Now, all that said, you might be able to do a better job
by keeping the EPC and reprofiling the line pressure
(steady and shift). Depending on the setup. You'd need
to spend some time scanning and doping out what the
trans needs to hold, and what you can get the PCM to
command. Stock setup is poor on the F-bodies, and with
more motor and boost on top you sure don't want to
stick with that mess. At least clean the force motor
table of stupidity.

Now the other issue with the EPC is that any foolery
as far as air mass, or any wrongness about how the
air mass to motor torque figuring goes, will tell the PCM
you're making way less torque and need way less line
pressure than reality. "Lean is mean" will eat your
frictions if you let it.

transam69230

iTrader: (49)

Here is the HPT file if anyone wants to review it and have input.

Jake's Performance

iTrader: (2)

200 psi is enough to support over 1000 RWHP.

I would set it up with fixed line pressure. No modulator, EPC not effective.

transam69230

iTrader: (49)

Isn't that hard on parts inside the trans?

This is a street driven car as well. I drive it every weekend and put 3000 miles on it a summer when it isn't broke.

Won't the shifts at light/part throttle be very hard?


Can you elaborate as to why you wouldn't use a modulator on a high HP boosted car?

NorthTexasConverter

Fixed line pressure is hardest on the pump, which will wear out much sooner, and yes part throttle shifts will be very firm, but not necessarily unbearable (but that is a matter of opinion of course). If you don't drive it a lot, fixed line pressure is ok, however if you do drive it a lot, I would put a vacuum modulator on it (and set the pressures before beating on it).

Jake's Performance

iTrader: (2)

We have extensive experience with the 4L80E and boosted applications. If you have any further questions call the shop. 877-433-5099 and I will explain time permitting. There are several reasons to avoid the vacuum modulator for your setup.

You've killed 3 4L80E's so far. There's a saying about repeating the same pattern and expecting different results.

transam69230

iTrader: (49)

According to my builder the parts that you (Jake's Performance) recently sent were not identical to the parts that we had initially in the transmission (parts we got from Jake's Performance). I was told it was using a 4T80 northstar clutch and now has a different stack and clutch in it (ford truck one?)

So technically there are different parts in the trans.

I am not a builder and I am just learning and going off what I can read and learn from people around me.

What needs to be done so that the trans has fixed line pressure? I am willing to try whatever so that the transmission won't burn up.

Jake's Performance

iTrader: (2)

Yes,
Your builder thought he was having intermediate clutch failure due to a lube flow issue. I told him I doubted that was the case bit provided him a different drum under warranty. We've changed our design on that drum to use C6 clutches instead of the 4T80 parts. Functionally there isn't any difference.

It seems I was correct that the failure wasn't caused by the drum.

Jon seems to be a knowledgable builder so I'm not sure what the issue is without seeing it but I have a couple of ideas.

transam69230

iTrader: (49)

Can you provide any insight as to what your theories are?

I just want to drive my car without issues, and go have fun with my friends! I am begging for help/advice so this doesn't happen anymore!

Jake's Performance

iTrader: (2)

I gave you advice earlier in this thread and offered to help by phone. It may be best if you have Jon call me since he's the builder.