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
 
Join Date: Apr 2014
Location: Christchurch, NZ
Posts: 30
Garage
Boost pressure difference

Hi all, long time lurker, but have finally got my car on the road and have a quick question...

Fresh engine, and I have started out with a 10PSI spring in my wastegate, but it only netted 7psi on my gauge (aftermarket, plumbed into the brake booster)

After a few hundred k's I upped to a 12psi spring, and now get approx 8-9 psi.

I know the wastegate line is fed pressure from the intercooler, before the air is pushed through the intercooler core, so was wondering if a 3 psi drop is common, or should I be seeing 10 and 12 psi as per the spring weight?

And if that is the case, do I ramp up the spring to 15-16psi so I can get 12-13 at the valves?

Only other thing I can think of, is that the throttle isn't opening all the way, but it sure as hell feels like it!

Thanks in advance

Old 01-14-2020, 01:05 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Registered User
 
Join Date: Nov 2003
Location: Tucson, AZ
Posts: 963
Garage
Any chance you have a boost leak?? Or a leak at the wastegate valve?? Did the waste gate have any shims under the spring??
__________________
Bill
1987 Marine Blue 911 Carrera Coupe RIP 01/2011
1987 Black 930 RUF Coupe Resurrected, 2488 lbs, EFI Technology, UMS Tuned - Mild & Wild, Ready for Paint
Old 01-14-2020, 01:59 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
Registered User
 
Join Date: Apr 2014
Location: Christchurch, NZ
Posts: 30
Garage
No shims. and 'should' be no leaks. Fresh engine build. Car runs fantastic.

Your answer would suggest I shouldn't be seeing a pressure drop... I have read about pressure drops through intercoolers on other cars, but this is my first 930 so wasn't sure.
Old 01-14-2020, 02:04 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Registered User
 
Join Date: Nov 2003
Location: Tucson, AZ
Posts: 963
Garage
There will be some pressure drop. Also note that a 10psi spring isn't exactly 10 psi. What boost gage are you using? Is it a Porsche wastegate or other?
__________________
Bill
1987 Marine Blue 911 Carrera Coupe RIP 01/2011
1987 Black 930 RUF Coupe Resurrected, 2488 lbs, EFI Technology, UMS Tuned - Mild & Wild, Ready for Paint
Old 01-14-2020, 02:49 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Registered User
 
Join Date: Apr 2014
Location: Christchurch, NZ
Posts: 30
Garage
Quote:
Originally Posted by brcorp View Post
There will be some pressure drop. Also note that a 10psi spring isn't exactly 10 psi. What boost gage are you using? Is it a Porsche wastegate or other?
Running a Turbosmart 45mm Wastegate, and a Turbosmart mechanical boost gauge.

I temporarily tee'd a pressure gauge into a line coming off the factory re-circ valve, and pressure was about the same as my boost gauge.

I'll tee a pressure gauge into the wastegate line tonight to see what pressure it is receiving.

I guess its feasible that the exhaust back pressure is helping to open the gate a bit early...

Thanks
Old 01-14-2020, 03:08 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Crotchety Old Bastard
 
RarlyL8's Avatar
 
Join Date: Jan 2000
Location: Huntsville, AL
Posts: 14,048
Garage
Springs are rated based on the pressure differential before and after the waste gate. If back pressure is greater after the waste gate it will open late, less it will open early. Typically the waste gates overboost due to bad plumbing design or other issues causing boost creep. Opening early is unusual. 45mm is sized appropriately for most 930 builds so that shouldn't be a problem. What exhaust manifolds are you using? I'd run a boost gage off the intake manifold to get an accurate reading of what the engine sees just to eliminate that as a potential issue.
__________________
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 01-15-2020, 06:48 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
Registered User
 
Join Date: Apr 2014
Location: Christchurch, NZ
Posts: 30
Garage
Quote:
Originally Posted by RarlyL8 View Post
Springs are rated based on the pressure differential before and after the waste gate. If back pressure is greater after the waste gate it will open late, less it will open early. Typically the waste gates overboost due to bad plumbing design or other issues causing boost creep. Opening early is unusual. 45mm is sized appropriately for most 930 builds so that shouldn't be a problem. What exhaust manifolds are you using? I'd run a boost gage off the intake manifold to get an accurate reading of what the engine sees just to eliminate that as a potential issue.
Have the factory ROW manifold. So far collected boost data from the brake booster, and the factory blow-off valve, and they both read the same (at WOT)

Will get a feed off the wastegate as well and report back. I'm guessing the boost at the actual engine valves is the important figure, so in some ways having a lower pressure could be good

Thanks again

Old 01-15-2020, 11:21 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 04:45 PM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2020 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.