Automatic Trans and Brake Booster with Turbo

thatblue_67stang

Well-known member
Hello, i am turboing my 1967 Mustang l6 and as of now it is automatic c4. i would like to get a manual but that is out of the budget. i know the auto trans use vacuum to shift but im going turbo. how do i solve this. i know many people use a check valve but im planning on running about 15 psi and i dont know if that will handle it. also can i run a check valve on the brake booster aswell or do i do something different whith that.

Thank you
 
Manual valve body is the way to go, it will increase line pressure so the trans can take more abuse as well. I recommend Broader Performance. Stay away from TCI valve bodies.

The T/check valve in the modulator line basically just saves the modulator from seeing boost and being damaged. Depending on your internal governor, it may not auto shift without lifting the throttle to get a blip of vacuum. You can disconnect the modulator line now and run the car w.o.t throttle to redline and see if it auto shifts 1-2 and 2-3. This of course will simulate having T/check valve in the line.

I have used the T/check valve setup on the last turbo build, and the c6 would not auto shift on it own, I had to lift. I played with modulator pin lengths etc...to no avail. Being a plow truck and dailyish driver, I wanted the auto shift more than a manual valve body. Ran this combo as high as 21.6 psi.

I use a restrictor in the line near the carb (a small jet will do) and a large check valve to make sure the modulator sees no pressure. The check valves can be sourced from mid '80's Ford cars and trucks.

Only had 1 failure of a factory brake booster check valve, replaced it with another factory check valve and no issues...all the way up to 24psi and 7 turbo builds.
 
I will add that most n.a. engines will develop some vacuum at red line due to carb sizing so disconnecting and plugging the vacuum line to the modulator is a must to test. There can also be some venturi action (same way a carb delivers fuel under boost) depending on where the modulator line is connected.

There actually are ways to make auto shift work while boosted, but the effort is better spend at your job making money to save for a quality manual valve body that will help make that c4 a durable beast for years to come.

The Broader vs TCI debate is first hand experience on more than one build... :beer:
 
Sick6Turbo":674y3hjc said:
I will add that most n.a. engines will develop some vacuum at red line due to carb sizing so disconnecting and plugging the vacuum line to the modulator is a must to test. There can also be some venturi action (same way a carb delivers fuel under boost) depending on where the modulator line is connected.

There actually are ways to make auto shift work while boosted, but the effort is better spend at your job making money to save for a quality manual valve body that will help make that c4 a durable beast for years to come.

The Broader vs TCI debate is first hand experience on more than one build... :beer:

As much as I would love to do that I'm only sticking with this trans for a year until I get a manual, is it possible I could disconnect all lines then shift manually from 1-2-drive and driving being 3 or will it not shift into 3 when I shift into drive
 
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