Increasing base boost / shortening wastegate arm (how-to)

[daveforber]

Thought I'd post this in case it helps anyone else. The procedure was carried out on a V40 2.0T, but I suspect most other engines are pretty much the same.

Here's the pre-requisites:

1. Your base boost is too low. This may be the case if you can't get above a certain boost level with your MBC, even if it's fully wound in (this was the case for me - wouldn't go above 12psi).

2. You have a boost gauge.

3. You don't blame me if your engine goes pop.

From my understanding, base boost is what the turbocharger will get to if you hook the red line on the BCS/boost controller directly to the yellow line (or wind your MBC fully out). It should be, if what I read is correct, about 4psi. Check it is that before you touch the wastegate arm!

It's a simple procedure and should take 1/2 hour tops. Here we go:

Step 1:
Make sure the exhaust is cold/cool. If you've just pulled onto the drive you'll get burnt!

You need a 12mm socket/spanner and a 10mm spanner.

Step 2:
Remove the heatshield at the back of the engine. On my car there are three 12mm bolts holding it in place. They were buggers to get out, requiring a 12mm spanner and a hammer to loosen them (my socket has seen better days).

This pic is taken looking slightly forward:



Step 3:
You should see something like this:



The job from here is simple:

1. Remove the retaining pin and don't lose it!
2. Loosen the locknut with a 10mm spanner. Again, mine was pretty damned tight, but some WD40 loosened it enough.
3. Lift the 'bit wot you turn' clear of the stud? that holds it. Now turn clockwise to increase base boost or anticlockwise to reduce it.
4. Put it back on the stud, tighten the locknut, refit the retaining pin, refit the heatshield and test.

It is very sensitive. Do NOT overdo it! I reckon on 1.5 turns (i.e. 3 half rotations) MAXIMUM. Ideally do it .5 of a turn at a time until the problem is resolved.

I tried 2.5 turns at first and it was over-boosting to 18-19psi on the motorway (bear in mind mine is a 12T low pressure with no remap, so I count myself lucky that I still have an engine) and I couldn't do anything about it on the MBC. I had to back it out on the wastegate as above.

When testing, wind the MBC fully out first and then readjust. Go gently - the first thing you'll find is it boosts earlier than before. You might find it boosts OK (say, to the 14psi you wanted) in first/second gear, but on a dual carriageway in third/fourth it might spike higher and stay there. So be very careful.

Again, I should reiterate you shouldn't be doing this unless there is a problem, and certainly not with 'blind boost'. And if your engine blows up, that's your responsibility

Comments/corrections welcome.

[princepugh]

Anyone know what the base boost is for a Mitsubishi TD04-16T (Phase 2 V70 T5)?

TIA

[Wobbly Dave]

Wastegate actuator should be set at 3-4psi - so if you have an accurate pressure gauge you can connect it to the actuator line and pump it to that pressure. Adjust the actuator nut aka "the thing wot turns" so that with the wastegate closed the hole in the actuator nut slips nice and easy over the pin on the wastegate arm.

Silverline do hand held trigger style "MityVac' pressure pumps but they are not cheap! The best price I found was 67 quid. This comes with the vital built in guage & does both pressure & vacuum - which is just as well as I can't remember which way the 3 - 4 psi should be.

[gmain1967]

Only comment would be that if the adjuster that fits over the spindle is tight to turn on the threads, it's a good idea to put a set of mole grips on the round portion of the arm, to effectively hold it. This will mean that if you need to grip the other portion to turn it, you are less likely to force the arm backwards, and damage the diaphragm. Some on the S40concepts.net site, seem to have managed to tear the diaphragm and end up with virtually no boost...

Good post, and pics too!