I was wondering what the normal vac. readings on my boost gauge should be. At the moment I have roughly 21 inHg showing on my gauge at idle. As I rev the motor slowly, the gauge seems travel to about 8 inHg all the way to redline then settle back to 19-20ish inHg as the car hits the limiter.


I was under the impression that a suitable souce for the gauge would be any vac line directly attached to the manifold. I used the one associated with the FMU. Shouldn't I be seeing positive pressure (boost) somewhere in the RPM range? Does that only happen under load? Is the 3.66in pully too weaksause? Im pretty sure the blower is making positive pressure.


I haven't been able to install all my gauges, EMU, wideband, injectors, etc in a permenent sense as of yet. I have most of these things, just not enough time to install them. I was puttering around the garage and decided to hook up the boost guage in a temporary sense. Hence my n00b questions.


My setup is;

110k mi. DE-K, Stillin 5th gen charge piping, V2 S-trim, vortech 8:1 FMU, and aux fuel pump. 3.66in 6psi? pully. Basically all the original stillin kit parts. Stillin lightweight flywheel, ACT 6 puck, etc,etc. Gauges are glowshift.


I have a 3.125in and a 2.87in pully and intend to get one of those in as soon as I can. I would like to have the walboro 255, EMU, injectors, and wideband up and working before I do away with the FMU and start to up the boost. Then eventually get a professional tune.


I dont drive this car much, it sits most of the time in the garage or under a cover when Im wrenching on somthing else. I will say that the damn thing is pretty fast. Faster than the I/H/E, 00VI, and street tuned 4th gens I have put together. This is all subjective, because I have never had it on a dyno. However, I would like to see this thing reach its max potential.


Thanks for reading and sorry for the paragraph.

 

I am around 20-22 at idle and then around 1-8 under a load

can't help with redline since im under boost by then

 

Ok, seems 20-22 is normal.

Not seeing any boost through out the RPM range is sorta weird, guess I'll do some reading.

Thanks.

 

IdK, ive used some vacuum sources on the mani that didnt give me any readings before. I switch it back to my previous source and i get the readings again. I say try to find another source, and if possible not feeding anything else.

 

Well, after reading for a few hours I wasnt able to figure this out.

I did solve my problem after I noticed a restrictor in the little plastic tee which came with the gauge. The thing would show inHg perfectly just no positive pressure. I also tried various vac lines and got the same results.

So, after seeing the restrictor in the tee I decided to ditch it. I then connected a 1/16" brass one I had laying around from some pneumatic HVAC controls I demo'd a while back.

Worked like a charm. Starts building boost at around 2800 rpms and pegs out at 9psi at redline (6800ish).

Hopefully this doesnt trash the gauge, if it does I'll just buy a better one. I only paid $42 for this one so no big loss.

In conclusion, if you are using a glowshift brand boost gauge, throw the tee included with the kit away.