How much boost should I be seeing?

[dest]

On my boost gauge I was seeing 10-11psi (0.68 bar) running standard.
I have just fitted the homefry loan ecu, and am now getting 15-16psi (1.03 bar)

Should I be seeing more? I thought it should be around 20psi?

I have not got silicon hoses yet, could it be that they are getting sucked shut?
Jamo also said my N75 was fitted backwards, could that affect anything?

Tests were done in 3rd gear and above

[Matt_D]

You should see 1.4 bar on overboost which is around 20psi

For overboost you have to be under 3000rpm and on full throttle

Not sure on the N75 might be worth spending 20 mins and swapping it around

[Lloyd]

I get 1.7 bar initially (overboost?) then levels at 1.5 bar to red line.

[S2central.net]

Forget RS2 numbers here - thats just confusing !

A healthy homebrewed ABY runs to 1.4bar mid range, dropping off gradually to 0.8bar at the redline. Those are in 4th or higher with a WOT run from ~2k rpm.

Sounds like dest has a not unusual air-leak... or maybe a slow WGFV.

Oh but if its fitted backwards then it aint gonna run right.
The LONGEST hose on the WGFV should be in the MAF hose - lets call that 3 o'clock.
The WGFV hose to the turbo is at 6 o'clock
The WGFV hose to the WG is at 9 o'clock

Make sense ?

PAul

[sheppardnias]

Given that your boost levels have changed the N75 valve is at least operating. I would fit it correctly if it isn't in the right way now. It really does only take a couple of minutes to do. If the N75 was doing nothing then you would be limited to the mechanical pressure on your wastegate which as standard is 0.4 bar. The homefry would make no difference at all in the pressure seen under those conditions.

It is most likely going to be a boost leak I would say. By increasing the pressure in the hoses the amount leaking will increase but overal you still see a higher pressure in the system overal.

Check all the hoses for obvious signs of holes and perishing and check all the clips are on securely and tight and that they fit cleanly on the hoses (no crud under them). It doesn't take much to see a drop on boost pressures.

I would also check the diverter valve whilst playing with the N75 valve, they don't last forever and are not expensive to replace.

My S6 had a faulty N75 valve when I got it and the diverter valve was not great either. Changing these fixed my issues with boost, fortunately.

After checking these you will need to pressure check the system. Not a difficult job but you'll need to beg the loan of some bungs from someone.



Hope you get it sorted soon and thanks for the tailgate lock... Got it welded in (broken stud in the boot) the other weekend and finally my Avant doesn't sound like there is an irate seal in the boot thats trying to mate with an air horn. I've even managed to get rid of the 6" of water that I was lugging around in the spare wheel carrier too...


Best of luck

[dest]

Ive been out to confirm things.
Sitting at 2k in 4th, then flooring it is seeing a rock solid 16psi held all the way to the red line, with no hesitating or holding back, which I was experiencing when I had all the boost leak issues.

I fitted a new WGFV about 4 months ago, so I know thats fresh.
I will try turning round the N75, and confirming all the connections to the WGFV.
Sadly it will have to be tomorrow morning now due to going to work soon!

[sheppardnias]

The Audi instructions for leak testing on the standard system say to floor the car in 4th gear at 60km/h. You should see just over 2 bar before you reach 3000 rpm if you have the internal boost display. On an external gauge you should see just over 1 bar.

Simple test but an easy one whilst driving.

[Paulgo]

Out of curiousity, and sorry to slightly hijack the thread, whats the norm for a homefried 3B planted on full boost - obviously missing the overboost element!?

cheers

Paul

[Rusty]

If you're running an RS2 IC then the boost may be a little lower as the inlet air temps will be lower, I'm sure Paul can caonfirm or deny this. I see around 1.25bar at full chat in the 3k to 5k RPM region with Samcos and an RS2 IC.

[UrS4Eben]

How strange.. I was thinking of asking the same question this morning with my daily drive to basingstoke... I have an AAN UrS4.. I have seen it measure , on digital OEM guage, just over 2 bar (overboost I suppose) but i more often see around 1.8 or 9 when I put my foot down. Is this normal or what should it be?

[mcandmar]

Subtract 1bar from AAN dash reading for the actual figure, with Pauls homefry the most i've seen on the dash is 2.1 bar on overboost. Fairly sure i have a boost leak somewhere so that may be a bit lower than normal. I seem to recall him mentioning 2.2-2.4 being normal.

[Smith_S2]

If you're running an RS2 IC then the boost may be a little lower as the inlet air temps will be lower, I'm sure Paul can caonfirm or deny this. I see around 1.25bar at full chat in the 3k to 5k RPM region with Samcos and an RS2 IC.

Silly question but since the RS2 IC is bigger and the turbo has to work a little harder to compress more air, will this not mean more L...........A...........G?

[UrS4Eben]

The Audi instructions for leak testing on the standard system say to floor the car in 4th gear at 60km/h. You should see just over 2 bar before you reach 3000 rpm if you have the internal boost display. On an external gauge you should see just over 1 bar.

Simple test but an easy one whilst driving.

I did this and got 2 bar but no higher. Is this acceptable of should I have the N75 checked as I replaced the diverter a couple of months ago...

Mind you it might be the turbo has some wear after 209 000 miles

[dest]

Right, update!
Turned the N75 round (the vacuum hose now points left, not up)
Checked all the plumbing to the WGFV, and it is all as it should be.

Went out for a test, and everything is exactly the same :mischeif:

I have checked the clips on all the hoses accessable from above and they are fine, at the weekend I will check the ones on the turbo and IC.

What else could it be?

[S2central.net]

I think there is big confusion here...

My information was on the WGFV - that is the 'N75' valve... The solenoidy-looking thing with an electrical plug that is attached to the MAF hose.

I suspect the valve you have turned round, by reference to the 'vacuum hose' is the throttle bypass valve (TBV).

The expression D'oh springs to mind.

Check the TBV isn't leaking, and that WGFV is correctly fitted - renew it if its not a recent one. Other than that, it will be an air leak from a split/loose hose.

Worst case a holed intercooler.

A leak-test is required...