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Let's Play: What does this do?

 
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bacook  
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PostPosted: Fri Aug 31, 2001 6:57 am    Post subject: Reply with quote

What purpose does the screw cap on top of the waste gate serve? I just got the head removed on my 931 ( I had oil in the coolant) and I noticed the cap was just resting on top of the wastegate. Could that have contributed to my rough idle?

Also, I found that the hose between the intake manifold and pop-off valve was not connected. How could that affect the car?

On another note, I am glad to be doing this chore because I can finally access all those hard to reach things I've been needing to do like:

  • Replace the washer on the turbo's top oil feed line
  • Replace the rotted water pump gasket
  • Re-thread the bolt hole on the inside turbo-manifold flange
  • Compare the head to the spare 931 head I have lying around (it's good!)

I'm sure I'll find more as I go.
Any suggestions of things I should do while I'm here?
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larso  
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PostPosted: Fri Aug 31, 2001 9:49 am    Post subject: Reply with quote

Its a porsche 930 wastegate, the 930s in the 80s have two lines, one going in at the top, one out the bottom. The 931 they just put a plug in it and used the bottom only.

u can pop it off and use it for more effecient boost, less wasted boost at lower rpms.
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John H  
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PostPosted: Fri Aug 31, 2001 3:39 pm    Post subject: Reply with quote

The screw top on the top of the wastegate is a vent. You should put a fhose fitting into it when you've got it off and run a hose up to the top of the engine bay. You can then use this to wind up teh boost of the car.
With a regulator in this line you feed boosted air back into the top of the waste gate. The waste gate then has to overcome the spring and the pressure you have set the vale to to open.
Advantage with this way is it stops the wastegate partially opening at about 5 lbs and also stops the valve in the waste gate fluttering.
With the pop off line disconnected you would get rough idle and probably a slightly richer running motor as the air from the manifold id going oput to the atmosphere ratehr than back into the motor through the turbo - The CIS measure air flow and hance would be seeing more air going through it than going into the motor and sending more fuel to the injectors.
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Rick MacLaren  
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PostPosted: Sat Sep 01, 2001 12:29 am    Post subject: Reply with quote

This thread is really informative.

Does anyone have a drawing or schematic of the system hooked up properly for maximum performance?
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924RACR  



Joined: 29 Jul 2001
Posts: 8794
Location: Royal Oak, MI, USA

PostPosted: Sat Sep 01, 2001 3:11 am    Post subject: Reply with quote

I have the schematic John sent me describing; I will have to post it on the website...

Stay tuned...

Vaughan

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Vaughan Scott
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'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
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924RACR  



Joined: 29 Jul 2001
Posts: 8794
Location: Royal Oak, MI, USA

PostPosted: Sat Sep 01, 2001 3:17 am    Post subject: Reply with quote

OK, I have uploaded the file; sorry, but it's in Excel format right now. If someone would be kind enough to convert it to jpg or PDF format, then I will upload it and all can see, even those with Macs...

The file can be reached by looking at the Turbo page of the Tech section, or by clicking on this link:
http://www.924.org/techsection/wastegate.xls

Thanks for the file, John!

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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype
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bacook  
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PostPosted: Thu Sep 06, 2001 5:15 am    Post subject: Reply with quote

I made the doculent into a PDF file for anyone who wants it.
http://members.rennlist.com/bcookt06394/wastegate.pdf


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Rick MacLaren  
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PostPosted: Thu Sep 06, 2001 6:10 am    Post subject: Reply with quote

What purpose does the screw cap on top of the waste gate serve? It makes the 'whistle' noise we know and love when turbo pressure pushes up the springy and opens a valve beneath the plunger to let exhaust gases escape with impunity.

Jon made me a schematic of this as well. I'm a bit confused:

WTF happens with the ignition control unit? I thought I understood this until that damned box appeared. What's with that?

What the heck is ECU? Exhaust control unit? Do you mean ICU? Ignition Control Unit, or what??? It looks like the ignition box, but this can't be - the box can't read pressure. So...do you mean the Pressure Control Switch that cuts off the fuel pump?
_________________
1980 Porsche 931 C2H5OH/H2O injected 15 PSI
1979 Porsche 924

[ This Message was edited by: Rick MacLaren on 2001-09-06 06:21 ]
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John H  
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PostPosted: Thu Sep 06, 2001 9:13 am    Post subject: Reply with quote

ECU - stands for Engine Control unit - and on the digital units - 1981 there is a line from the manifold to the control unit. This measures boost pressure and tells the control uint to do something to the ignition curve.
If you pull the cover of the box there is a rubber bellows behind the connection and this from memory connects to a switch of some sort. I haven't pulled the control unit apart for about 5 or 6 years so I've forgotten exactly whats inside them.

As far as winding up the boost and the ignition control - I think you can forget about the ICU as your unit (1980) doesn't have the digital control. The principle is the same - you feed boosted air into the top side of the waste gate- it reduces flutter on the waste gate and you should notice slightly better response as the wastegate starts opening at about 5 lbs.
Drop me a line if you what further info - my engines out of the car at present so I can take a few photo's showing the setup if required.
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Rick MacLaren  
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PostPosted: Tue Sep 25, 2001 1:27 am    Post subject: Reply with quote

John, I've tried to do this, but am having significant difficulty in finding a metric sized piece to fit into the top of the wastegate...did you retap the aluminum piece on top of the wastegate?
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larso  
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PostPosted: Tue Sep 25, 2001 4:55 am    Post subject: Reply with quote

what size is it??

you have a thread gage?

I might have a banjo bolt kicking around that is the right thread, after stripping down my 931 to the bone, I kept every single bolt and have a good collection of fuel line bolts....
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