What is a Hobb's switch?

[JStieger]

What is a Hobb's pressure switch? Is it the same thing as those oil pressure safety switches that shut off a fuel pump in a car?

 

[GWedekind]

YUP... . the Hobbs type switches detects a low pressure situation and depending which type of switch you have it either makes or breaks an electrical circuit.

 

[Forrest]

I bought the Napa 701-1577, nc, adjustable, & am using it for the wastegate controller. The idea is to keep the wastegate shut until a predetermined PSI, then open.



I screwed it into a rt angle adapter on top of the AFC housing. I adjusted it to close at 38psi. It's in series with a regular old aux driving light relay, so when boost hits 38psi, the relay actuates. The relay turns on a vacuum switch, a PDR Valet Switch. The Valet Switch is now in the wastegate circuit.



When boost reaches 38psi, the Hobbs Sw closes, turns on the relay, which turns on the Valet Switch, which allows the boost signal to get to the wastegate actuator. Works



I also adjusted the wastegate rod to keep the wastegate from being pushed open by boost psi. Simply cranked the rod so that it's shorter. Now, the wastegate stays closed until 38psi. Previously it started opening in the 20 psi range.



Boy can you feel the difference. It really raises the low rpm boost. Oo.

 

[JStieger]

You read my mind! I read about this on nwbombers.com so I want to try the same thing, but with a normally open solenoid valve. This way when the pressure is reached, it cuts the circuit and the solenoid is de-energized and "fails open". I just bought the NAPA 701-1578, nc, 15 psi. They also have the 701-1606, nc, 60 psi, but it wasn't in stock.



I asked the counter guy if it was adjustable, but his old catalog didn't specify one way or the other. So we took the plug off and it looks like it is adjustable. Which way do you turn it to increase the pressure switch? I'm going to hook up bicycle pump with a battery & light bulb to test it!



Do you have any pictures of your setup you can email me?

 

[Forrest]

... I started the whole investigation because of the NWB post.



I don't have any pics yet. Soon & I'll PM you.



You turn the hex head in/clockwise to raise the PSI rating. You're adding pre-load to the spring.



I put the Valet Switch on the fenderwell over next to the turbo. Pulled the hose off the wastegate actuator & it reached the Valet Sw just fine. Only had to run 1 hose from the other side of the Valet Sw to the wastegate actuator.



The aux driving light relay is mounted next to the Valet Sw ... all next to the battery.



Frank helped me wire it all up & did some investigation. He found that the big rig guys have been doing it for some time. Sure makes sense after you do it.

 

[JStieger]

I don't have any pics yet. Soon & I'll PM you.



... Sure makes sense after you do it.

Great - thanks! - It made sense to me too after I saw those dyno graphs, which made the torque come in sooner due to the pressure not bleeding the wastegate open early. I am adverse to using those allen scew adjustable elbows and even though my wastegate is set at 40 psi, I can hear it start opening around 25-30 psi and it makes the power-to-the-ground seem "peaky" for lack of a better description.



BTW nice gallery - that's quite the turbo collection and what happened to your engine?

 

[Forrest]

BTW nice gallery - that's quite the turbo collection and what happened to your engine?

Thanks ... I borrowed the HY & the HX35 for pic purposes. That HY had some DDII & Comp towing miles. :-laf



Engine is ok, nada a problem. If you're looking @ the o-ringing ... was done just as a pre-twins prep thing, up @ PDR. While the head was off for that, the pump was taken off & hauled next door to the pump guru for all the right tuning. No new internals, just making the best of the stock 215 pump. Haven't done the twins yet.



Yea, you can sure feel the torque early now. Feels like what I lost with advancing the timing I picked back up. Oo.

 

[BPonci]

When i was on the dyno last weekend i did get a few chances to play with the adjustments. You can really make the hp and torque go up and down forward and back in the rpm ranges. That really made me see how well it does work. Simple yet effective. My best #s that day were 663hp@2200 and 1632trq@2100.

 

[JStieger]

From where can I purchase a 12 VDC solenoid valve? Everywhere I look they are either 120 VAC or 24 VDC...



Thanks!

 

[Forrest]

Do you have any pictures of your setup you can email me?

The gallery has some pics now.

 

[JStieger]

The gallery has some pics now.

Great - thanks! I have all my parts on order now. I found a place on the internet that sells (hopefully) good quality solenoid valves rated for higher temps and pressures (especially for the high compressed air temps related to the boost signal).



I also figured that I needed to bite the bullet and clean up some of my wiring so I ended up getting the Painless Cirkit Boss from Geno's... as well as some Bilstein's :-laf So hopefully I hope to have this all installed by the end of the year.



Next time I head to Reno I'm going to have to PM you to meet up- to at least buy you a beverage for helping me out. I try to meet up with RankRam from Carson City everytime I'm there for lunch so the more BOMBers the merrier!

 

[Forrest]

Absolutely ... PM next time !!!! Glad the pics helped ... kinda hard to see, so I dup'd & zoomed.

 

[drrhoades]

I am looking to do this to my truck as well but would like to understand it a little better.



Here is what I think is happening, let me know if I am wrong.

What is happening is when the boost reaches a set pressure the Hobbs switch sends a signal to the solnoid to open so that the wastegate will activate.



My questions:

1. Do you have to do anything to the wastegate since you are blocking the boost signal to it?

2. How is everything wired? Does the positive from the Hobbs go to the positive on the solnoid? And the other two wires are ground?



Thanks,

Doug

 

[JStieger]

Here is what I think is happening, let me know if I am wrong.

What is happening is when the boost reaches a set pressure the Hobbs switch sends a signal to the solnoid to open so that the wastegate will activate.

This is correct! After doing some research I am going to use a 3-way "normally open" solenoid is when the solenoid closes the excess (residual) pressure from the wastegate to the solenoid is vented to the atmosphere. At least this is for my 3rd gen 24-valve.

My questions:

1. Do you have to do anything to the wastegate since you are blocking the boost signal to it?

2. How is everything wired? Does the positive from the Hobbs go to the positive on the solnoid? And the other two wires are ground?

I understand conceptually what Forrest is doing with his 12 valve, but I am still 12-valve illiterate when it comes to AFC's and such! My guess from the context is that the AFC combined with a boost signal controls the amount of fueling??? To answer your questions in a non-12 valve specific way though:



1. I'll leave my wastegate set at the 40 psi it is set at now. It already starts cracking around 30ish psi so even if the Hobbs and/or solenoid valve fails during high boost, the wastegate will still be there to save the day. I guess you could set it up to say 30 psi if you wanted to be even more cautious??

2. The Hobbs is just a switch and the instructions that came with mine said to connect to either terminal as long as the other went eventually to ground. Probably what I'll do is an ignition hot to Hobbs. Then from other Hobbs terminal to a solenoid lead. The solenoid has 2 leads or a special "DIN" socket with three terminals, but I hope it will have instructions to tell me how to wire it!



Hope this helps!

 

[JStieger]

When i was on the dyno last weekend i did get a few chances to play with the adjustments. You can really make the hp and torque go up and down forward and back in the rpm ranges. That really made me see how well it does work. Simple yet effective. My best #s that day were 663hp@2200 and 1632trq@2100.

I tried to call you again later on Friday, but it looks like the schedules didn't mesh. However, when I read through your posts on NWB and then reading between the lines over-and-over again I answered lots of my questions!



I have the book Maximum Boost by Corky Bell and he devotes maybe 2 small paragraphs to what you described as boost creep in terms of manipulating the torque curve peak! I couldn't believe it - only 2 small paragraphs for such an important thing.



This is such a simple, yet ingenious method for boost control - can't wait to get it hooked up and then some dyno time!



How do you adjust the Hobbs switch on the bench? I might try an ohmmeter, pressure gauge, and bicycle pump since I don't have shop air in my apartment (yet :-laf )...

 

[rockjeep73]

Just so I am crystal clear on the operation of the wastegate control, in order for this to keep the boost at a preset level (based on Hobbs adjustment) the Hobbs switch and solenoid will rapidly cycle open and close in order to keep the boost at preset level? Does this cycling occur quick enough to not effect the boost level, but rather maintain it?

 

[Forrest]

It does maintain the boost level. You can see the boost cycle as there is switching going on. I'm gonna do some playing with the adjustable elbow a little & see if that decreases the cycling. Not sure i'm even on the right track with the elbow, but it'll be interesting to dick with it a little.

 

[rockjeep73]

How much does the boost fluctuate as the system cycles? Im just curious if this idea is worth messing around with seeing as I just ordered a manual boost controller which is supposed to do the same exact thing, but without the cycling.

 

[JR2]

The simplicty of this idea is that you don't have to adjust after its set up. Wit a manual boost controller you will be adjusting it for your HP. At least that is what Diesel Freak said on the NW bombers post that started all this.





Anyone have a part number for a solonoid??

 

[rockjeep73]

The simplicty of this idea is that you don't have to adjust after its set up. Wit a manual boost controller you will be adjusting it for your HP. At least that is what Diesel Freak said on the NW bombers post that started all this.

Im not following you here?



Do you have a link to the thread on NW Bombers?