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Wonderful Wastegate wellbeing

Diver944

Diver944

Active member
There's been a few questions about wastegates on the forum recently so I thought I'd post my own experiences and a few piccies that I sadly took along the way. Hopefully this may help other Turbo owners who are interested in getting back up to full power or maybe going a little further [:)]

Please remember I am purely an amateur anorak and just coz I'm the 944 forum moderator it doesn't mean I know what I'm talking about [;)] Proceed at your own risk.

It's a known fact that over time the spring that controls the 944T wastegate gets weaker and opens too early, thus losing valuable boost pressure straight down the exhaust pipe [:(] I recently removed my wastegate following instructions at www.lindseyracing.com/wginstal.htm and when I applied pressure to the WG it actually started opening at only 2psi [:eek:] A new wastegate is supposed to hold 12psi (0.82bar) so mine was very weak.

An easy fix for this is to buy a Boost Enhancer valve from www.autoporsche.co.uk At £99 this device is fitted in under 10 minutes and controls the flow of air to the control line that goes into the wastegate to stop it opening too early.

I recently fitted a kit from Guru Racing in the States to increase my boost from the standard 0.82 bar to 1.1 bar. At this pressure the standard wastegate is forced open no matter what valve you fit into the control line, so something a bit more involved has to be done. The Guru kit comes with shims ( three 3mm washers) to fit onto the wastegate to provide some preload to the internal spring and thus increase the pressure at which the wastegate opens. Once the wastegate is off the car you simply remove the three Hex bolts holding the diaphragm to the main wastegate body and insert the three shims.


Wu604840070.jpg
 
With the wastegate off the car it is now easy to check the pressure at which it opens. Simply attach a pipe to the top of the wastegate where the control line normally goes and fit this to a standard footpump that you know has an accurate gauge. Slowly apply pressure from the pump and watch for the wastegate valve to open. In standard form mine opened at a measly 2 psi [:eek:] and was fully open at 4 psi - not good, the standard 250bhp is supposed to make 12psi (0.82bar) of boost.

I installed the three 3mm shims that came with the Guru kit as in the pic above and had the car tested on a rolling road. It now made 287bhp and 331 lbft or torque, up from a standard 250bhp [:D] but after 4000 rpm the power tailed off dramatically as can be seen in the power graph below.

Tr511579877.jpg
 
I installed an accurate boost gauge in the cubby under the radio and sure enough it could be seen that although the boost leapt up to 15psi (1.04bar) it started to drop down to 12psi (0.82bar) over 4000 rpm. I removed the wastegate again (in under an hour this time [:D] ) and tested with the foot pump which showed it was opening at 4psi and was fully open at 7psi.

Now came the experimental bit and an 'enjoyable' afternoon loosening the hex bolts and trying different widths of shim before back to the foot pump to check. Finally I finished with 9mm of stainless steel shims which resulted in the wastegate starting to open at 7psi (0.5bar) and is fully open at 10psi (0.7bar). It looked decidedly 'Heath Robinson' and I had to use some longer Hex bolts but after swapping numerous posts with Turbo ownners on Rennlist I found some people with 15mm shims in theirs so I was happy.

Reinstalled on the car it now looks like this:

Bz783299238.jpg
 
With the boost controller now adjusted to maintain 16psi (1.1bar) and the shims also in place, the boost gauge leaps up to 16psi and just starts to drop to 15psi around the 5500 rpm mark .

The aftermarket 'one size fits all' Guru chips are mapped for 15psi but ran slightly rich on my car so I spoke to Danno the Guru himself and he recommended adjusting to 16psi then head back to the Rolling Road. I hope to do that early in the New Year before this seasons trackday action.

I did all of this because of the Guru upgrade but the shimming will apply to any Turbo with an old original wastegate that wants to maintain its maximum power without resorting to a new wastegate at circa £700. If the car is on standard chips then shimming too much will produce more than 12psi (0.82bar) of boost and the overboost protection will cut in to stop damage to the engine. If this happens then you too can look forward to an 'enjoyable' afternoon with the footpump and metal washers

One final tip - before starting any of this, soak all the nuts on your wastgegate with WD40 or PlusGas and when reinstalling smear the threads of the bolts with copperslip grease. It took me a whole day to remove my wastegate the first time due to stubborn nuts but now I can do it in well under an hour. I replaced all the nuts and bolts with new ones also, they get very cruddy under there.
 
Thanks Paul. That's made it all very clear to me (albeit my standard wastegate is on Eddie Buckley's car!)
 
Top Man Paul.

Thanks for those details. I want to have a go now.

Do you get you wastegate off with the car on stands/ramps or do you have access to a pit/lift?
 
Tony,

You might want to think about replacing some of those 90 degree elbows with nice mandrel bent curves [8D]

Seriously, that explains the basics of the system quite well.

Again in a similar vein here's a vacuum diagram I found on Rennlist that I'm not sure I fully understand yet...

Ec890965253.jpg
 
Cheers John, I had you in mind as I was writing as I know yours needs doing [;)]

I did mine with the front of the car on axle stands and nice slidey lino under the car so I could slide in and out from the front. One stand on each side under the front jacking points (yes the ones that sometimes 'bend' the drivers footwell and cause the accelerator pedal to stick). I have found you don't even need to remove the undertrays as there is room to slide the wastegate out behind it.

I was glad of Tonys diagram a few months ago when for the first time it showed me how a weak wastegate spring could be forced open purely by exhaust pressure. Until then I really could not get my head around it, believing that the pressure was coming from the closed side of that valve. So thanks for that Tony [:D]
 
Shimmed my wastedgate today, I calibrated my cheap footpump gauge by testing the tyre pressures with my digital gauge and comparing the figures, the footpump was 3 PSI lower. I ended up with similar figures to Paul with 5mm of shims / washers. I would think if you go too far on the shims the wastegate may not open far enough - I would be a bit wary of 15mm. I only had hex headed bolts of the correct length but these just fitted and could be done up with an open ended spanner.
I was impressed that the wastegate mounting bracket had slotted holes so a shimmed wastgate could still be fitted easily - damn fine engineers these Germans [:D]
Tony
 
Hurrah [:D] Well done Tony, may the boost be with you [8D]

I know what you mean about having too many shims in there, but one chap on Rennlist swears he has 15mm of shim. I can't see how the valve could open fully with that amount, I'm still not happy with the way mine looks with 9mm. Oh well Tial wastegate here I come (At some point)
 
You obviously have to be carefull with that level of shims and boost, with the stock injectors. Once you are getting up to 15psi and trying to hold it to the redline you are risking a lean mix <14.7:1 with the obvious consiquences to your car. I have the shims in and the wastegate will hold 16psi to about 4800rpm then it starts droping to 15psi@5000 rpm and 12psi @ 6000rpm. Means i get a nice fat amount of torque around 4000rpm. I am going to get the 55lb injectors & a new wastegate next year, i wouldnt get the wastegate without the injectors. I hope to be about to hold 16psi all the way to 6500rpm, should give a nice pull ;)
 
ORIGINAL: George Elliott

Shims still working OK Paul [:D]
Click to expand...

Ha - I can't even remember what happened to that original wastegate, only that I don't have it any more [&:]

Edited to add - Actually I think I sold it to a name that us oldtimers should remember - Leigh Cromwell [:)]
 
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