Hobbs switch fuel pump and meth
TECH Enthusiast
Joined: Jan 2012
Posts: 557
Likes: 9
From: Bowling Green KY
Yes, just run the wire from the hobbs switch to both relays, the one for the pump, and the one for the water/meth system.
Run 1 side of your hobbs switch to a 12V source, and then the other wire coming out of the hobbs switch, split it and run it to both relays. Run the other wire on the trigger side of each relay to ground.
That should make it work.
Run 1 side of your hobbs switch to a 12V source, and then the other wire coming out of the hobbs switch, split it and run it to both relays. Run the other wire on the trigger side of each relay to ground.
That should make it work.
I wouldn't run both off of one Hobbs switch. If the Hobbs switch fails you won't have your second pump or your meth. If they are both separate at least you will have one of the two in case of failure which might be enough to keep the motor from melting down.
TECH Apprentice
Joined: Feb 2012
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From: Montreal
What he said. ^^^^^^^^^
TECH Enthusiast
Joined: Jan 2012
Posts: 557
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From: Bowling Green KY
Well you know if you run 2 you have double the probability of a failure. If either meth or fuel are cut you will probably do damage. So have you doubled your chance of failure? Maybe. Just another way of looking at it. I learned this from airplanes, twin engine airplanes that are incapable of flying on one engine have a higher crash rate than single engine airplanes. Basically 2 chances for an engine to fail vs 1.
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if worried about hobbs failures, why not wire 2 hobbs both to the same 2 relays. So that either hobbs switch can fail and still activate both relays.
Heck why not wire 4 or 10 hobbs switches to 4 or 10 relays. Redundancy ftw
If an engine is very expensive you should be running a stand-alone capable of monitoring fuel pressure and shutting down the engine in the event of fuel pressure failure. The same ECU can also control the water/meth relay.
Heck why not wire 4 or 10 hobbs switches to 4 or 10 relays. Redundancy ftw
If an engine is very expensive you should be running a stand-alone capable of monitoring fuel pressure and shutting down the engine in the event of fuel pressure failure. The same ECU can also control the water/meth relay.
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Restricted User
Joined: Mar 2014
Posts: 7,192
Likes: 109
From: Ohio
I tried the fuel pump and meth both on a hobbs switch. I ran the ground for the fuel pump relay and the ground straight from the meth pump to one side of the hobbs switch, and then the other was a ground to the frame.
I ended up getting weird feedback between the 2, and my 2nd fuel pump would run constantly once the key was on. The 1st pump would prime like normal, the 2nd would prime and stay on, even when the car wasn't running. If the key was on, so was pump 2.
Unless you're running dual 450s or a corvette regulator, I would just run both pumps full time.
I ended up getting weird feedback between the 2, and my 2nd fuel pump would run constantly once the key was on. The 1st pump would prime like normal, the 2nd would prime and stay on, even when the car wasn't running. If the key was on, so was pump 2.
Unless you're running dual 450s or a corvette regulator, I would just run both pumps full time.
TECH Enthusiast
Joined: Jan 2012
Posts: 557
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From: Bowling Green KY
You know to think of it, I wouldn't run meth off a hobbs switch at all, I'd use a map sensor and progressive controller. That's the way my car is set up. It has a separate 2.5 bar map for the meth controller, and the more boost the more meth. They aren't that expensive. That way you don't have the same amount of meth at 7 psi as you do at 22 psi.
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Joined: Feb 2012
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From: Montreal
Originally Posted by ScottyBG
You know to think of it, I wouldn't run meth off a hobbs switch at all, I'd use a map sensor and progressive controller. That's the way my car is set up. It has a separate 2.5 bar map for the meth controller, and the more boost the more meth. They aren't that expensive. That way you don't have the same amount of meth at 7 psi as you do at 22 psi.
You know to think of it, I wouldn't run meth off a hobbs switch at all, I'd use a map sensor and progressive controller. That's the way my car is set up. It has a separate 2.5 bar map for the meth controller, and the more boost the more meth. They aren't that expensive. That way you don't have the same amount of meth at 7 psi as you do at 22 psi.
TECH Enthusiast
Joined: Jan 2012
Posts: 557
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From: Bowling Green KY
The controller regulates the pump, which in turn regulates the pressure in the system. At higher pressure the same nozzle flows more. The meth system I have goes as high as 250 psi. A lot more meth gets introduced at max methanol pressure 250 psi, which is at about 15 psi boost, vs the 50 psi or so when the system first kicks on, at about 4 psi of boost. The pressure of the meth ramps up from the 4 PSI boost entry point through the 11 psi gain to hit the max of 15psi, where it levels off at the max the system can spray. The controller is fully adjustable, but that's how its set now. More boost = more meth. This is just the same as we do with timing, more boost = less timing.
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From: Ohio
Progressive controllers were all the rage with 4-cylinders.
99% of us don't bother with them. Too much work for so very little return.
My meth kicks on 100% at 8 PSI. The problem with a progressive controller is how fast you build boost. With a centri blower, it makes more sense. With a turbo once you start building boost, you'll reach peak boost with 1 or 2 seconds. Progressive controller is a waste in that case. I go from 8 PSI to 20 PSI in ~1 second.
99% of us don't bother with them. Too much work for so very little return.
My meth kicks on 100% at 8 PSI. The problem with a progressive controller is how fast you build boost. With a centri blower, it makes more sense. With a turbo once you start building boost, you'll reach peak boost with 1 or 2 seconds. Progressive controller is a waste in that case. I go from 8 PSI to 20 PSI in ~1 second.
Progressive controllers were all the rage with 4-cylinders.
99% of us don't bother with them. Too much work for so very little return.
My meth kicks on 100% at 8 PSI. The problem with a progressive controller is how fast you build boost. With a centri blower, it makes more sense. With a turbo once you start building boost, you'll reach peak boost with 1 or 2 seconds. Progressive controller is a waste in that case. I go from 8 PSI to 20 PSI in ~1 second.
99% of us don't bother with them. Too much work for so very little return.
My meth kicks on 100% at 8 PSI. The problem with a progressive controller is how fast you build boost. With a centri blower, it makes more sense. With a turbo once you start building boost, you'll reach peak boost with 1 or 2 seconds. Progressive controller is a waste in that case. I go from 8 PSI to 20 PSI in ~1 second.
also, if you have it set to 100% meth by 20psi and you are only running 15psi, if the engine overboosts now you get extra meth.
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Joined: Mar 2014
Posts: 7,192
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From: Ohio
You shouldn't be using excess meth as overboost protection. You should be using your timing/fuel tables to dump fuel and pull timing.
Want to know the most common cause of preventable engine failure? Poor planning and overcomplicating the setup. Once you start throwing in progressive meth (without actually knowing anything about the flow rates and their effects on detonation), Hobbs switched secondary fuel pumps, multi-stage boost controllers, etc, at some point they won't be working in harmony anymore and you have a failure.
Run a large return line, keep both pumps on all of the time, and spray your meth either on or off. No complicated tuning, no failed Hobbs or grounding loops taking out your engine.
I'd want the ECU to control the meth then. I wouldn't trust an external switch/relay for something that important. I wonder if HP tuner can configure an output for switching meth on and off.