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campbellr · Joined: 25 May 2010 Posts: 6 Location: UK

I've got a UK Series 2 turbo and have just had the wastegate removed as it was making a (very) loud clicking noise when you pressed the gas pedal quickly. We found damage to the internal walls of the spring housing and it looks like the spring was not being retained propery. It was quite a mess!

I've just bought a second hand US spec wastegate as a temporary solution. The spring housing has an iron insert at one end which holds the spring properly (which my UK housing did not have).

Now to the questions!

The US wastegate spring is about 2" shorter than the UK spring. I guess this is because the US cars ran with less boost but 2" seems a lot. Can anyone confirm what the spring lengths should be?

Anyone know where I can buy UK/ROW spec springs?

I heard there was someone in the US selling new dual port wastegates; any ideas who they are?

What's the easiest way to measure the boost pressure once I get the wastegate back on? Is it a DIY job or will I need to take the car to a garage?

Is there a link anywhere on the forum which gives an easy to understand explanation of how boost controllers work?

New member : first post : thanks for any advice you can give.

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

Don't know the lengths offhand, but the US spring will be shorter and produce lower boost. If you get a boost controller, there's no need to replace the spring as you can use the controller to adjust the boost back to ROW (or higher) specs.

All boost controllers work on essentially the same principle, albeit with some variations in implementation. On our cars, there is a "boost actuator" line that carries pressurized air from the charge tube to the lower wastegate port. When there is enough pressure in this line to overcome the stiffness of the spring, the wastegate valve opens and bleeds off excess boost to the atmosphere, thereby preventing an overboost situation. What a boost controller typically does is to provide another bleed-off point in-line with the boost actuator line. By adjusting how much of the boost signal is bled off from the boost actuator line (i.e., the boost signal that is making it to the lower port of the wastegate), you can configure the car to see MORE boost at the intake before the wastegate cracks open.

The cool thing about our wastegates is that they are dual port already. The top fitting can be replaced with a line and banjo bolt. What you can then do is to take the bled-off signal from the boost controller itself (mentioned above) and route that bled-off pressurized air to the TOP port of the wastegate. What this effectively does is to prevent what is known as "wastegate creep"; in reality, the wastegate spring will begin to creep open even before the theoretical "full boost" level is seen at the bottom port. This is known as wastegate creep, and has the effect of making the onset of boost seem less responsive. Probably OK on a street driven civilized car, but not ideal from a top performance perspective. By using the boost controller's bled-off signal to hold the spring in place from the top, you can minimize the amount of wastegate creep, causing full boost to come on sooner since the wastegate isn't opening prematurely.

Tial are one of the leading manufacturers of lightweight, aftermarket dual-port wastegates. But on our cars, there's really no need to upgrade

unless you're looking to shave every last ounce of weight. The OEM unit, though a bit heavy by today's standards, is quite robust (identical to the 930 unit).
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erstwhile owner of just about every 924 variant ever made

9xx · Joined: 18 Jun 2006 Posts: 627 Location: Jarvenpaa, Finland

Smoothie · Posted: Wed May 26, 2010 4:31 am Post subject: Re: Wastegate advice please

campbellr · Joined: 25 May 2010 Posts: 6 Location: UK

924guy · Posted: Sat May 29, 2010 12:00 pm Post subject:

stock us spec series 2 spring vs 1.1 bar 930 spring...

stock spring in wg:

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Uploaded with ImageShack.us

assembled with diaphragm (before rebuilding):

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Eric
78 924
82 931 SE "smokey"
99' VehiCross
Y2K Honda Insight
http://www.cardomain.com/id/924Guy
Performance by Pasha

campbellr · Joined: 25 May 2010 Posts: 6 Location: UK

Rich H · Posted: Sun May 30, 2010 3:07 am Post subject:

Its a recirc dump valve. It dumps the boost from the pressure side of the compressor to the intake side. With a 'CLACK' at low speed

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1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

9xx · Joined: 18 Jun 2006 Posts: 627 Location: Jarvenpaa, Finland

peterld · Posted: Sun May 30, 2010 7:16 pm Post subject:

The wastegate spring tends to cock over at an angle inside the housing during use, and ultimately frets away at the inside of the housing causing grooves in symmetry to the coils of the spring. Although it looks horrible, unless the grooves are so deep as to actually wear through the housing, rebuild it with a new diaphram and set and forget.
I've rebuilt two 931/2 wastegates and a 930 unit, and they all exhibited the same problem, exacerbated by heavier boost spring, in the case of the 930. One other 930 housing was very badly gouged out.
BTW make sure the halves of the housing are indexed correctly before reassembly, otherwise you will need to pull it out and split the casing and do it all over again. Oh, and you'll need a fat friend to sit on the housing so that you can start the six little bolts, especially if you've installed a new or upgraded spring.
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80/81 932/8 ROW

RC · Joined: 25 Mar 2007 Posts: 2637 Location: Australia

Rich H · Posted: Mon May 31, 2010 4:55 am Post subject:

do you mind - I was eating...

_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

stevekat · Joined: 19 Jan 2008 Posts: 719 Location: Los Angeles, CA

Here are a few data points re: spring. No conclusive, but should give you a sense of things.

http://www.924board.org/viewtopic.php?p=273887&highlight=#273887
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"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Damn, Rog.

FWIW, length on these isn't the end-all. I have a .5, .8 (930) and a 1.0 (Weltmeister) and the lengths don't correspond at all to stiffness (no, Rog, NO)!
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

peterld · Posted: Mon May 31, 2010 9:44 pm Post subject:

+ 1 ^.......Isn't that what the actress said to the bishop?

I have a new 1 bar spring and a used 1 bar spring, amongst others, and none are the same length. In fact the used 1 bar spring is longer than the new 1 bar spring. The only way to properly test is in a spring compression machine, starting at the included height that the spring would sit in the wastegate housing.

Oh Rog.......just love your work!!
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80/81 932/8 ROW