Hi,
yes I did searched, yes I read that mechanical gauges are not that accurate.
but, as I want to fit one and got 2 in hands, I must choose between my Omori and my old School HKS:

• But, for there is a "but", there's 10% of boost difference between both, when the Omori shows 1 kg/cm2 then the HKS shows 1.1...(simulated with a medical syringe).
Is one of these brand famous for precise reading? My guess is that Omori should be more accurate and the HKS seems older... but not proving anything. And I have no way to compare/calibrate that used stuff.
As a matter of style I wish to fit the HKS in my S4 as the look is really in match.

• Maybe if some can give the estimated boost of my S4 then I can compare :
it's full stock ( OEM airbox, filter etc... ) but a full and brand new 3" Racing Beat "Rev TII" exhaust ( from dp to mufflers ) and it's FCD. (and yes stock and unmodified wastegate... defo need a gauge!).

• There's a kind of reducer with the T (wich I'm uncomfortable to fit either on boost presure sensor or BOV line...), don't know where to use it and it's function, maybe to slow down the pressure variations on the plugged gauge line and/or to keep the original vaccum line speed of reaction?


Thanks for helping

 

Mechanical gauges are a toss up and to do a determination of the actual boost your car is capable of, and is actually making is nearly impossible. Without precision equipment it's dificult to determine which gauge is correct.
As far as a connection, there is a capped vacuum tube on the right rear of the engine, remove cap and hook up tube, or you can use the T connection as it will still indicate the boost and vacuum properly, naturally dependant upon the gauge.

 

Anyway I'll use it mainly to find overboost if some.
May I ask you where exaactly is this capped nipple? Any pic or drawing?
Thanks!

 

Take a look about 2" in back of the BAC valve and 1" down. Not a great picture, a little fuzzy, but:
http://i249.photobucket.com/albums/g...4/SUNP0056.jpg

 

There's nothing about a mechanical gauge that makes it inaccurate. Any gauge of sufficient quality will be accurate whether it is electrical or mechanical. The advantage of an electrical gauge is that you don't have to plumb what you are measuring (oil, water, fuel, air) into the cabin.

Gauges, whether electrical or mechanical, tend to drift with age and use. They are also made to a tolerance and will come out of calibration easily if they are bumped around. Some very cheap gauges aren't even calibrated at the factory.

Most have an adjustment screw so if you have a precision vacuum/pressure source you can readjust.

 

First thanks for the answers guys.
Aaron I'll have a look... when I'll have a know pressure source. I guess this is the price to pay for an used gauge anyway.

Turbonut I've looked on my car a while until I found the aera on the pic and mine is not like yours:


So left are all the command lines (both sides of the UIM) wich I can T, or the ones seen on the pics.
I ask there for my current/futur setup:
https://www.rx7club.com/2nd-generation-specific-1986-1992-17/acv-removed-egr-stays-what-about-rats-nest-777607/

 

Just "T" it in to the hose going to the boost sensor. Just make certain to use stay ties on all the slip on fittings.