A340 Valve Body Upgrade

[P Bateman]

Through the process of building turbo 1UZ E36 BMW, I'm changing the valve body so it can handle boost more effectively.

PROBLEM - the Soarer 1UZ A340E valve body uses:

• cable from the throttle body to control line pressure (the more right foot you give it, the more pressure you get)
• solenoid to control accumulator back pressure (modulates the clutch/brake application to make it smooth or firm)

This is fine for NA engines, where you'll only see zero manifold pressure on full throttle, but a turbo engine will achieve positive manifold pressure on only 1/4 throttle. Insufficient line pressure on boost will result in cooked oil, slipping clutches/brakes and an early retirement.

SOLUTION - installing a Prado A343F valve body provides:

• solenoid to control line pressure (mapped to boost instead of throttle position)
• accumulator pressure is internally linked to line pressure (two birds with one stone)

The engine in my car is run by a Haltech 2500 Elite and since last year, the software now has the capability to run an electronic auto as well. The only wires in are for shift solenoids (S1 & S2) plus the line pressure solenoid (SLT).

The valve body bolts in without any issue and the wiring harness is an easy swap. The only issue is that the A343F has no drain hole under the Clutch-0, so the Soarer accumulator has been replaced with the Prado unit - it fits without any issue, but makes it hard to install the valve body in the car.

Further to this, I used the casing plug from the Prado to plug the hole left once the throttle cable was removed. I've also fitted the Prado oil pan as it takes another 5 litres of oil.

The only drawback is the Soarer has a linear solenoid for the torque converter lockup (SLU) and an internal oil temp sensor
The Prado uses an on/off solenoid to run the torque converter lockup and the temp sensor is fitted externally in the cooler outlet pipe.

Once I have the car running/tuned and have some time to play around with the Haltech auto configuration, I will post some results.

 

[ivan129]

Interesting idea. Couldn't you achieve the same result by adjusting the line pressure cable so that the throttle pulls the cable earlier. I haven't had any problems so far with my A341E still running cable line pressure. I'm only making about 1 bar but boost comes on at around 2200 RPM. Using my own design electronic trans controller, auto and tiptronic.

 

[P Bateman]

Yes and no - yes because adjusting the cable will give you more line pressure, and no because having a linear relationship between throttle and line pressure is only ideal for NA applications... and somewhat to supercharged engines.

If I was building a race car, then cable line pressure would be fine - but in a street car application where turbo response and boost can be variable, along with lag, there will often be times where higher line pressure isn't required on low to medium throttle. Mapping line pressure to boost gives the additional pressure when its necessary.

Given the choice though, would you prefer to have electronic control over your line pressure?

 

[ivan129]

Yes, however I didn't want to over complicate the way I control the trans so I've tried to mimic the OEM setup using the throttle to pull on the line pressure cable. When pressing to go pedal line pressure increases for firmer up shifts. On back off (when your foot comes off the go pedal), the controller takes care of multiplexing the LP solenoid to reduce line pressure on down shifts. If you don't knock off some of the line pressure when down shifting, the transmission will hit the lower gear hard and causes the wheels to skid. There are manuals on the net for the A340 series trans that will help you to develop your shift, LP control and TC LUP mapping. Keep us posted on how you go. Good luck.

 

[P Bateman]

Cheers mate - the Haltech software is excellent in this regard and can be setup for closed loop learning on pressure.
Will definitely share the results.

These are the basic options - they can be expanded significantly