Low boost with light modifications?

[Vic Rattlehead]

Hi all.

Recently fitted a VDO mechanical boost gauge. WOT in 3rd 4th and 5th is showing 12psi.

Now, I was thinking I'd be seeing more along the lines of 15psi, with the modifications on the car.

Lyndsey boost enhancer, 3bar fpr, promax chips and baily blow off valve. This was already fitted when I bought the car two years ago and it looks like the previous owner wound out the boost enhancer to nearly it's maximum, as according to rennlist they say the factory 10psi setting is about 4 visible threads.

So anyway, I've just done the wastegate test and clamped off the line from the intercooler hard line (as acceptable as clamping off the line from the cycling valve acording to rennlist) and got the same results, which is leading be to believe the wastegate is dead.

I was wondering if anyone here had done the wastegate test clamping the line from the hard pipe. Or is it not as reliable as clamping the line from the CV

Also, the VDO gauge isn't wired into a switched 12v yet, I'm assuming as it's a mechanical gauge it wouldn't need power to work correctly?

Cheers in advance.

 

[Diver944]

If you can't get more than 12psi with the wastegate line clamped then it sounds like your spring is so weak it is opening under exhaust pressure alone.

If it's a mechanical gauge then the 12v supply will just be to illuminate the light

 

[sulzeruk]

Sounds like your wastegate spring is US or soft. I have a reshimmed wastegate from a 250 bhp car set to 15 psi here if you need one,
Alasdair

 

[edh]

See my ad in spares - I have a good wastegate I want to get shot of.

I would expect boost pressure to fall back to ~11psi at 6k rpm with that sort of setup, but it should be easy to hit peaks of 17-18psi or more in the midrange with a LBE.

 

[logan]

Everyone offers sound advice, but I would also check the accuracy of the gauge. If you can find any local turbo specialists phone them and ask if you can bring the gauge down for them to test the accuracy.

We have three different makes of pressure testing rigs at work for the big turbo's on our excavators - and above 10psi, they vary by up to 3psi each - and these bits of kit range in price from £1500 to £3000.

If its a decent gauge from a reputable manufacturer it should be fairly accurate, but if not then definitely check it. Other option is if you know anyone with another gauge locally, then swap them and see what readings you get from each gauge in each car, if they agree with each other then you are probably ok, if they disagree wildly, get them both tested.

 

[rickware]

I agree it sounds like a weak wastegate spring although if you haven't bypassed your cyclic valve then this maybe opening at 12psi dependant if the overboost protection is still in the settings of your chips set. How fast is it? If you find a place to run a quarter of a mile then you should get to about 100 mph on 280 hp. That will tell you if you have a faulty gauge!

 

[Vic Rattlehead]

Thanks for the input chaps.

Posted on this Rennlist too and had similar replies. I'm currently fancying a Tial 38mm WG that I've seen for a good price so could be the excuse I need.
I'll try and get under the car and pressure test the WG and see if it opens. Or try the WG dump pipe test (if it's warm at idle then the WG is possible stuck open)

With regards to the Tial. Could it be installed and run in single port mode? The intention would be to go to a black knob boost controller and run in dual port mode. But that won't be until next year.

One thing I'm never sure on is the LBE. Someone said that it would only provide the cars stock boost level (11ish psi) and just allow it to come on quicker?

As for the gauge. It's an original VDO. Brand new out of the box. I wanted an accurate gauge, and not something that will display every colour in the rainbow like some I've seen []

 

[Diver944]

Yes you can run the TiAL in single port mode with just a boost enhancer to control it.

It is possible to wind the LBE in and increase the boost a little through the midrange but it will still bleed off a little at higher RPM's. Just remember that the standard AFM and DME will not be able to adjust the fueling to match and so you could start running a little lean

 

[AndrewS]

ORIGINAL: Vic Rattlehead

. . . One thing I'm never sure on is the LBE. Someone said that it would only provide the cars stock boost level (11ish psi) and just allow it to come on quicker?

The Boost Enhancer is a boost pressure relief valve (rather than a boost controller). Full details on how it works and what it does can be seen here.

The BE just allows the peak boost to roll on sooner (as no air signal reaches the wastegate until the BE opens). To increase peak boost (for example, up to 15 psi), you will need a boost controller and also modified software for the DME.

Regards,
Andrew

 

[Vic Rattlehead]

ORIGINAL: AndrewS

ORIGINAL: Vic Rattlehead

. . . One thing I'm never sure on is the LBE. Someone said that it would only provide the cars stock boost level (11ish psi) and just allow it to come on quicker?

The Boost Enhancer is a boost pressure relief valve (rather than a boost controller). Full details on how it works and what it does can be seen here.

The BE just allows the peak boost to roll on sooner (as no air signal reaches the wastegate until the BE opens). To increase peak boost (for example, up to 15 psi), you will need a boost controller and also modified software for the DME.

Regards,
Andrew

Cheers Andrew, that's how I thought the BE worked. Thanks for confirming that.

 

[edh]

This car had a LBE, chips (AMD), no boost controller. Looks to me like it allows increased boost above factory levels in the midrange that rolls off once the LBE opens. What do we mean by "peak" boost? Is that the max. figure reached, or is it the figure acheived at max. rpm - say 6k?

 

[Vic Rattlehead]

Nice. I actually had a nice stretch of clear road in front of me on the way to work the other morning and gave it some welly in third. Gauge hit 14psi. Couldn't get it to do it again.

I've got a weeks holiday coming up so I've decided to pull the intake manifold and replace the vac lines as I'm sure ther'll be a few boost leaks under there. Also investigate the wastegate.