Author Topic: Hobbs Switch? (Read 4551 times)

texaseric · « **on:** February 07, 2006, 06:47:34 pm »

Where can you get a 20 psi Hobbs pressure switch (or an adjustable one adjustable to from 10 to 25 or so psi)? I'm having zero luck on Google and eBay. Need a source. It's for a boost controller.

:roll:

malone · « **Reply #1 on:** February 07, 2006, 10:49:14 pm »

Quote from: "texaseric"

Where can you get a 20 psi Hobbs pressure switch (or an adjustable one adjustable to from 10 to 25 or so psi)? I'm having zero luck on Google and eBay. Need a source. It's for a boost controller.

:roll:

The Hobbs switch can be found at Lordco, a general auto parts store. I don't know if the US has these stores. Try calling Autozone and Pepboys?

RabbitGTDguy · « **Reply #2 on:** February 08, 2006, 02:50:14 am »

If you can wait a day or two, I can get you the P/N from the hobbs switch I used for my propane injection (boost sensitvie) setup I was running on the IDI engine. I bought it locally from NAPA pretty cheap...and its adjustable.

Joe

texaseric · « **Reply #3 on:** February 08, 2006, 04:51:42 am »

Thanks for a part number. I can wait.

jackbombay · « **Reply #4 on:** February 08, 2006, 08:29:13 am »

I just buy them from the local part store, they have several different models with varying pressure activation levels, 5-15 PSI 10-20 PSI 15-25 PSI, or something along those lines.

fatmobile · « **Reply #5 on:** February 10, 2006, 12:34:14 am »

I just got a hobbs switch at Napa. It looks like they are normally used for oil pressure switches.
It's the 15psi version but there is a little rubber plug that can be removed and an allen wrench can be used to adjust it either way ... they said about 3 psi.
Item #7011577.
Price $27.21 ... plus tax= 29.11. It was more but I said hey can you give me a better price ... that has worked every time lately, even at the dealership.
I hooked it up to a relay and used it to control a dual vacuum switch off a '91 Golf. Wastegate is open to the air below 15, over that it feeds boost to to the wastegate.
Used Jake's method to blocked off the bypass so it wouldn't release pressure over 10psi.
It got to 15 I heard a click ... and the egt gauge needle dropped to nothing and the boost kept climbing ... blew a fuse.
Vacuum switch was junk but it's OK I have 2 of them. :lol: Check 'em for 20 ohms before you install them.

fatmobile · « **Reply #6 on:** February 11, 2006, 02:24:03 am »

I can't remember who inspired this, I think it was from the old forum and I'm just now getting around to building it.
Here's the hobbs switch, relay and vacuum solenoid that I'm pretty sure is from a '91 Golf gasser:

The hobbs switch had something like 10m1 threads, not what I wanted. I ran a 1/8" NPT die down them so I could screw a 1/8" barb (not pictured) to it. I've had buzzing coming from my boost gauge and heard that a restrictor would keep turbo pulses from getting to the gauge. I didn't want pulses getting to my hobbs switch either so I plugged the end of both 1/8" barbed fittings with solder and reduced the hole to the size of a pin. It stopped the buzzing on the gauge so it probably helped keep pulses from the switch too.

A better look at the dual vacuum solenoid. I slid pieces of vinyl tubing over the ends of a couple of the nipples so the rubber fuel line would fit tight over them without having to use a reducer (green arrows). When the boost is low, the wastegate is connected through one solenoid to atmosheric pressure. When boost hits 15psi, the other solenoid routes boost pressure to the wastegate and it opens.
The piece of metal tubing next to it is what I cut off the metal wastegate line to make hose routing easier.

This is on my '91 Golf, which has 2 studs attached to the firewall. I cut a piece off the original vacuum solenoid mounting bracket. The 2 holes were already there so I just twisted it and used it to mount the solenoids to the firewall.

...and the controller mounted to the firewall and plumbed. I thought I took a better picture than this but if you look past the spaggetti (AC and fuel lines) it's not too hard to see what's going on: