Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > 911 / 930 Turbo & Super Charging Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Registered User
 
clexton1's Avatar
 
Join Date: Jun 2008
Location: Katy, TX
Posts: 159
Boost leak?

I have a '76 930 with the original 3.0 and a few mods which include Kokeln IC and k27-7200. My problem is that I am not getting the full 1 bar boost, I can get it up to .7 or .75. When I first got it 2 years ago, I could get 1 bar so I know it has a 1 bar spring which the PO also confirmed. I changed all the o-rings but didn't fix the problem so I figured it might be a cracked injector block and just decided to live with it for a while. I was recently having a problem with the distributor and fixed a stuck advance plate and in the process found that the vacuum pot has a leak, a slow leak when checked with vacuum pump, it would still function but would bleed off. I was sondering that since this would also be under boost, could the leaking distributor pot bleed off .3 bar of boost?

Thanks,
Paul
__________________
'76 Turbo Carrera
Old 04-14-2010, 07:33 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Registered User
 
e170drvr's Avatar
 
Join Date: Sep 2006
Location: Evansville IN
Posts: 261
Garage
Paul,
sounds like you already have it figured out. Those lines to the dizzy are pressurized on boost, so yes that would explain why you aren't seeing full boost. In addition to the boost leak you may be getting a vac leak off boost. Any smoke on boost? Sounds like you need a new pot. Keep us posted.
Eric
Old 04-14-2010, 09:22 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Forced Induction Junkie
 
WERK I's Avatar
 
Join Date: Jan 2003
Location: Wisconsin
Posts: 3,291
Garage
Paul,
I doubt the slow leaking distributor pot would bleed off .3 bar under boost. The K-27 could easily make up for that volume of air bleeding off that small of air volume going to the distributor pot. I take it that the wastegate never opens now?
If you have an air compressor, set the regulator pressure off the compressor to about 20# and hook it up to the boost line of the wastegate with the engine running. You should hear the exhaust being rerouted through the wastegate. Also, check to see if there is any exhaust pressure coming out the wastegate exhaust pipe with the engine running. Anything that bleeds off exhaust gas pressure before the turbocharger will prevent the turbine from compressor efficiency.
There are other more complex issues that can cause this, such as fueling and ignition timing.
Other areas could be the hose going to the BOV, BOV valve diaphragm ruptured, o-rings on the throttle body and turbocharger nipple o-rings.

Easier to start with the more common problems mechanical items and go from there.
Good luck.
__________________
Dave
'85 930 Factory Special Wishes Flachbau
Werk I Zuffenhausen 3.3l/330BHP Engine with Sonderwunsch Cams, FabSpeed Headers, Kokeln IC, Twin Plugged Electromotive Crankfire, Tial Wastegate(0.8 Bar), K27 Hybrid Turbo, Ruf Twin-tip Muffler, Fikse FM-5's 8&10x17, 8:41 R&P
Old 04-15-2010, 08:12 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Crotchety Old Bastard
 
RarlyL8's Avatar
 
Join Date: Jan 2000
Location: Huntsville, AL
Posts: 13,563
Garage
I would look at your BOV. Do you hear a metallic "clank" when you blip the throttle?
Any escaping or bypass compressed air will stall the buildup of boost. Your distributor vac port should not be large enough to do this (I actually forgot to plug a small port on the underside of my intercooler once and ran it for a week before I noticed).
Waste gate function is such that it will not open too wide (bleed off too much exhaust gas) but rather open too little, not at all or possibly stick open or shut.
__________________
RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 04-15-2010, 09:58 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Registered User
 
clexton1's Avatar
 
Join Date: Jun 2008
Location: Katy, TX
Posts: 159
Werk1, I was thinking along those lines also, that's a lot of boost to bleed through the distributor pot. It is something I need to fix regardless. I have looked into some of the common things like O-rings and recently replaced all of the hoses hoping to solve the problem. There was only one o-ring I couldn't get to, the one at the aluminum adapter for the K27, I have to do some more work to get to it. Probably should just weld the adapter to the turbo.

It's odd, the boost will come up and hold steady at 0.7+ like with a stock spring, but it used to go to 1 bar like it should. It's been like this for a while and the car is still quick at .7, but it's not right. I'll go back through the usual suspects.

RarelyL8, I don't hear a clank, is that with the stock style BOV? I have the 965 style BOV but not sure how to check it. I have a 934 boost gauge and the tattle tale spikes up to 1.2-1.3 bar when shifting under hard acceleration and full boost. I assume the BOV is doing its job but not sure.

Thanks, for the help.
Paul
__________________
'76 Turbo Carrera
Old 04-15-2010, 11:13 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Registered User
 
mark houghton's Avatar
 
Join Date: Jul 2008
Location: Central Washington State
Posts: 3,776
My money's on the wastgate valve not seating entirely- carboned up seat and/or valve guide sticking up the works.
At idle, loosely stuff a wad of paper into the WG dump pipe, rev the engine a bit and see if the paper blows out. There shouldn't be any exhaust coming out of there unless you're on boost.
__________________
Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 04-15-2010, 01:49 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
Registered User
 
aseem's Avatar
 
Join Date: Jan 2002
Location: Oslo, Norway
Posts: 543
Garage
Quote:
Originally Posted by RarlyL8 View Post
I would look at your BOV. Do you hear a metallic "clank" when you blip the throttle?
What is the source of the "clank" sound you are referring to here? I have that sound when I blip the throttle.
__________________
Arnljot
1980 930 GT35R, TurboKraft IC, 965 P&C, 964 Cams, Tial WG, ported heads, BLWUR, RarlyL8 hdrs&mfflr, Zeitronix logger & wideband
1989 928GT
1972 BMW 3.0S
Old 04-15-2010, 02:51 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Registered User
 
mark houghton's Avatar
 
Join Date: Jul 2008
Location: Central Washington State
Posts: 3,776
Quote:
Originally Posted by aseem View Post
What is the source of the "clank" sound you are referring to here? I have that sound when I blip the throttle.
Boost recirculation valve. There's an internal spring-loaded piston that moves up and down in response to vacuum when you're off the throttle. At each end of the assembly is a cap - with a silicone gasket between it and the housing. The gasket also serves to cushion the piston at the end of it's travel so it doesn't slap metal-to-metal against the cap. Replace the gaskets, stop the noise.
__________________
Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 04-15-2010, 05:26 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 06:23 AM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.