Looking for some advice on boost!!

[the wombat]

Used the Q4 for a weekend away, and other than some idiot kicking the wing mirror off early Saturday morning, the car performed really well.

It is the first time I have driven it for a long distance since the 20th anniversary run. I did a full service including belts last week and all seems good.

One thing though, a bit of a doh! moment for me, I had been reading the boost gauge as bar (it has a big 1 0 - note the gap, and there is actually a little black dot between them), which is entirely incorrect. I noticed while I was driving it that the boost gauge is actually in inches of mercury (which appears to have the units numerically on the scale) and PSI (a smaller scale with no units).

So, it looks like my car is developing about 0.8 bar boost after a quick conversion. I will be getting a Bar boost gauge in the near future!!

The question is, it seems that 0.8bar is about standard, and the car pulls like a train on this, but the engine has been built to take around 1.2 - 1.5 bar according to the builder, so how to raise the boost a little?

Without looking at the receipts, I don't have all the specs for the engine, but it has got uprated con rods, pistons, cams, head gasket, hybrid turbo, so should be able to handle a little more. The ECU is standard though, as is the exhaust (non-cat). I do have a mongoose exhaust and turbo outlet to fit at some point (per Integrale with some mods to make it fit).

I am not looking for huge amounts of power, and the car is pretty good as is, but feel it should release a few more horses based on the spec.

What next steps have people generally used as a development path?

[Steve Webb]

Sounds to me like the pierburg valve isn't functioning correctly, 0.7 bar is the base boost, any extra is taken care of by the pierburg which keeps the wastegate closed for longer.
Check all the connectors, electrical and small bore air to make sure nothing is adrift.

Welcome to the wacky world of overboost!

[the wombat]

Thinking you might be right.

I switched the two bottom hose connections on the pieburg a short while ago to check it had been connected up properly. As expected, less boost.

Swapped the connections back again, and re-plugged the wiring, and whatever the gauge reads (still trying to work this out), it has gone to 10-12, to 15-16.

I looked up an inches of mercury to bar conversion for 16 (that is foot on the floor overboost), and got 0.54 bar. The car pulls like a train, so not sure if this is right.

Did 16 PSI to bar and get 1.1 bar which seems a bit more like it. Also did a conversion for psi relative to atmosphere to bar relative to vacuum (whatever that means) and got just over 2, which seems high.

Based on that, I will check all the small bore vacuum pipes, and clean up the connections per Steve, to see what I get. I will get a bar gauge as well, as inches of mercury seems to be what Noah or Sir Frances Drake might have used!!

The car goes well though!!

[wrinx]

Isn't inches of mercury a reading for Barometers...does the weather change when you're on boost?

wrinx

[the wombat]

Isn't inches of mercury a reading for Barometers...does the weather change when you're on boost?

wrinx

The world became dark and I heard thunder, or was that the car starting to tear up the tarmac!!

Does anyone know who supplies new pierburgs?

[Steve Webb]

Pierburg. Its a brand name if I remember correctly.

There must be some good used ones about as some people have moved over to separate boost controllers.

[the wombat]

I had a bit of a fiddle with the electrical connections and hoses last night. If the gauge is in PSI, then converted I got 1.1Bar on the gauge after fiddling (if its inches Hg, I got 0.54 Bar which seems wrong).

I would say from this the place to start is check all the hoses per above. Given a few other things I have discovered about the car, I also wonder if the waste gate set-up needs checking. Lots of other stuff was loose or not correctly adjusted (timing belt was so loose the front run was slapping the bearing behind the front balancer, balancer belt installed but shafts not anywhere near correct positions etc - the engine is like a magic carpet ride now in comparison).

So a few things to do, but I am going to leave this until next year as almost at the end of the season for me and the car (back to school next week). I still think there is a case to drop the engine and tidy everything up, and I have a minor oil leak that I would like to resolve, plus the power steering is still whistling the Italian National Anthem which needs some investigation.