The oem Vacuum Boost gauge is a 15 psi/ 30 in. Hg

But I will be running a 17% Helix pulley; so I want my gauge to show the vacuum and boost. My choices in the Stewart Warner line are:
Part # SSW 114537 Boost/ Vacuum, 0-15 psi/ 30 in. Hg, 2 1/ 16 in., Analog, Mechanical, Silver Face, Silver Bezel
Part # SSW 114380 Boost/ Vacuum, 0-25 psi/ 30 in. Hg, 2 1/ 16 in., Analog, Mechanical, Silver Face, Silver Bezel

Which will be better for a 17% pulley, producing how much boost and vacuum?

BTW what does in. HG measure? (I know it stands for inches of Mercury and has to do with vacuum but what is it measuring?) TIA Michael

 

I would pick a 20psi one....but that might just be me. I've HEARD that when you get up to 25/30psi gauges, you start to lose accuracy in the gauges, and 15 might be too lower....thus 20psi is right in the middle.

And someone correct me if I'm wrong, but you should see ~15-16psi with the 17.

-Cody

 

Thanks Cody but the problem is SW has a 15 and a 25, no 20

 

Have you considered the Autometer "Ultra-Lite" series of gauges as an alternative?

Here's a 20 psi boost / 30 "Hg 2-1/16" gauge, part number 4301:



They also make a 2-5/8" version, part number 4401.

Scott

 

It's measuring intake manifold vacuum. Generally-speaking, it will be lowest under full-throttle acceleration and highest under deceleration or part-throttle steady-speed cruising.

It can be useful to monitor for vacuum leaks in the engine's plumbing, and it will also tell you if you have an intake valve sticking.

Also, your fuel economy will generally be highest when manifold vacuum is highest. In fact, many of the "fuel economy" gauges, both factory and aftermarket, are simply manifold vacuum gauges with markings in MPG instead of inches of mercury.

Scott

 

Scott I have considered it, but to get the closest to oem both in daylight and nightime I want to go with the Stewart Warner so...

 

So.....15 might be pushing it, but I would go with 25. You shouldn't lose that much accuracy...it'll just be harder to tell exactly WHAT psi you are at....but for street use I don't think you would really care anyway (I would...but maybe that's just me ). So....if it were me, I would go with the 25.

Good luck! And post some pics when you get it!
-Cody

 

If I were you, go with the 20. That gives you the MOST movement. With a 30, the needle will just move slightly. With a 20, it'll be all over the place!

Good luck.

 

Just as an aside....

We have the factory Boost and Voltage gauges. They seem to work great. I love using the Boost gauge as a fuel mileage gauge as riquiscott points out.

The only problem I have with them is that the lighting is really dark compared to the other factory gauges (like the tach). I'd say they are about 50% of the brightness of the other gauges. Also, I can't seem to get my boost gauge to read any higher than 9%, but maybe that's all I can expect with a brand new bone stock 2006 Mini Cooper S.

I wonder if there's a "fix" to make the factory Stewart Warner gauges brighter?

 

I get much more accurate readings with my 30psi autometer gauge than I did with my 20PSI autometer.

the 20 jumped around ALOT and the 30 is more steady with its movements.

 

Good point Rick

 

Click the link in my signature for a link to pics of a good one!

EDIT: https://www.northamericanmotoring.co...ad.php?t=58578