Here is a link to photobucket that shows the fuel hose and how it supports the gauge. And if you look you will see it has 8" of restriction which is what a stock air box had with no modification with the air cleaner lid on.
Photobucket
Photobucket sucks for not letting people post pics without paying money.

ROD

 

Thanks guys. The explanations and photos are a big help. That part is the 25in model which does seem like a lot of vacuum for the intakes on our cars. This is one of those curiosity things I tend to come up with as the weather struggles to warm up to where I can start driving the car regularly.

-- Chuck

 

Even though the gauge goes to 25" I would change the filter out at 11". In a pinch or when not wanting max hp(like a d/d)you could run it till it hit 15". At 15" it would cost you a few hp at redline but in a d/d you would never know it.

ROD
p.s. I never let my dissel truck hit 25" either, aways changed it out at 20-22"

 

I'm really just curious what the vacuum is so perhaps a 10inH2O gauge will be a better choice?

-- Chuck

 

Unless you hook it up after the TB to manifold vs where its supposed to go/Intake tube, Its not going to pull/read any vacuum unless you have an obstruction ie dirty filter/ too small an aftermarket filter. When I was NA I used it to help tune my custom intake. One filter I tried pulled 8" of vac at 7000rpm, so it was choking performance from there on. You don't want to see any vac pulled to redline on the gauge or you leaving performance on the table. Use it to verify your intake is size/working proper and or the filter is clean if you like, as it was originally intended.