Disable the TVSV


What is this TVSV thing I keep hearing about?

It's a "thing" that allows the turbo to produce a little bit more boost pressure in 3rd+ gears. All of the GT4s have a TVSV - Turbo Vacuum Switching Valve. It allows about an extra 2psi of boost to be produced.

What sort of pressures do GT4s run?

165 ~7psi 1st and 2nd, ~9psi 3rd+

185 I "think" this is the same as the 165 ... Can someone help me out here?

205 ~11psi 1st, ~13psi 2nd+

Ooooh, that's clever, how does it do that?

It drains, or bleeds, off a little bit of air away from the wastegate actuator, so that the actuator sees less pressure than there actually is. This in effect allows the wastegate to open when there is an increased boost pressure i.e. for 165 ~9psi

Why do I want to fiddle about with this then?

It is desirable to run a consistent boost level when running some sort of boost controller.

Disabling the TVSV will allow you to run a constant boost pressure, BUT without any other form of boost control the car will run at the lower pressure in ALL gears, so it is pointless disabling the TVSV if you do not plan on fitting a boost controller.

In short - don't fiddle with it unless you are going to fit a boost controller.

What common ways are there to fiddle with the TVSV?

There's a few methods that have been utilised:

Cut and ground the TVSV wire
I'm not a fan of snipping wires, seems quite agricultural to me...this will however keep the VSV open and allow the higher boost pressure in all gears. If you were feeling adventurous then you could install a switched circuit to activate high and low boost as and when you feel like it.

Bore out TVSV
I've seen articles in the past discussing taking a drill bit to the hole that drains off some of the boost pressure experienced by the wastegate actuator. I am not a fan of this mod either. Drilling out the TVSV drain hole will cause the TVSV to drain away more air from the actuator, and thus increase the boost pressure. However, you are still left with the lower pressure in 1st and 2nd gear... Also, if you foul up the drilling it'll be hard to make the hole smaller again! The TVSV is a bugger to get at, and you really don't want to be fiddling about with a torch and an inspection mirror...

165 TVSV gizmo. Picture shows the inlet and outlet of the unit - note the smaller diameter hole


Block TVSV pipes
I like this one! Why? Because it is cheap, easy and almost fool proof! Blocking the pipe will cause the car to permanently run the lower pressure; unless a boost controller is fitted.

Okay, I'm going to fit a boost controller, how do I do this pipe blocking mod?

Like this...

(note all pics are from the 165)

The pipe work on the turbo is normally connected as shown here. 1 pipe from the turbo housing down to the actuator and then another pipe from the actuator to a solid pipe which runs off to the back of the block...
...the solid pipe runs off to the TVSV assembly which is bolted to the underneath of the inlet manifold...
...and looks something like this
Therefore to block off the TVSV from draining away some of the air pressure, the pipe needs to be blocked as shown here
This is a close up of the completed mod


Anything else?

I highly advise NOT fitting fancy coloured hose to the wastegate actuator. It looks pretty but it is not as robust as a dedicated rubber pressure hose. If it splits, it might cost you dear...

Things to do at the same time

This article is intended as a helpful guide and shows how I disabled the TVSV. If you are in any doubt, or not qualified, do not undertake this modification, consult a qualified mechanic. Always consult the manufacturer's manual. Alterations away from the manufacturers specifications are not recommended.