Thread: Boost springs
View Single Post
infraredcalvin infraredcalvin is online now
Non User
infraredcalvin's Avatar
Join Date: Sep 2007
Location: Ladera Ranch, CA
Posts: 1,359

Originally Posted by JFairman View Post
If you don't have a mechanical boost gauge you don't really know what your boost is.
The factory boost gauge and sensor are not accurate and even less so after 20 years or so.

The spring and diaphram in the stock electronic boost gauge sensor fatigue and become inaccurate after time so it takes less pressure to compress the spring in the sensor and it gives higher readings.

Also, the stock sensor is reading boost pressure from the intermediate manifold or intercooler above the throttle body, not below the throttle body in the intake manifold where you have slightly lower boost pressure.
This is the only place you can really get an accurate boost pressure reading that the engine is seeing because of the air flow restriction of the single throttle body.

Another thing that can happen is if a lazy or hung over mechanic ever cleaned the intermediate blow off valve housing in parts washer without removing that sensor, the solvent could get inside it and swell the diaphram in the sensor making it softer and it may give optimistic readings after that. Same thing goes for the overboost switch.

Good chance the one in yours is a stock spring.
Hence my response "might have what you need".

I guess I didn't make myself clear. I'm thinking the spring I got is a stock spring, which means that it will be extra stock spring that I will have sitting next to my original stock spring once I install my new 1 bar spring, so I'd be willing to part with it...

Since I have a "known" spring now (the 1 bar) the easy test for my gauge (aftermarket vdo, no factory boost guage on 76) is to install the 1 bar and compare the readings to what the previous spring showed.
Infraredcalvin - AKA Pat
'76 Turbo Carrera #311 - Factory LSD, Sport Seats
'75 914 GT clone project
'71 914 track car
Old 03-08-2008, 04:05 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #20 (permalink)