Hobbs Switch

[TOMT]

Hey there guyz, Is there a better safety out there other than the ""Hobbs"" fuel pressure switch???? I use a 5psi preset.

Due to Another faulty hobbs I have melted another motor!!! well that and the bloody temp on the day I know the hobbs did work, as when I do a fuel flow check I also bluff the hobbs to think that there is no fuel and she shuts evrythin down.
Were we raced the temp went up n down, I was loosing up to 2-2 1/2 psi on the fuel side. I have had this happin b4 at this track, first I thought it was battery voltage playing with the fuel pumps, as both the NOS pump and Carb pump both loose pressure.

So combineing the fact that the fuel was all over the place I thought we were safe if it was a concern, figureing the hobbs would shut evrything down, but alas at max rpm of 7800 she melted....
When we got the car back to the pits I thru the gauge on the NOS fuel to find it was down to 4 3/4 psi!!!!! I had set this to 7.5psi ( which is .5 higher than were my static pressure usually is for this hit) just b4 the run.

I know it is due to the temp/alt of this track as 3 other racers I know were havin the same issue with fuel pressure.

So when we can find the funds to rebuild I want a far better safety....
Any thoughts of what else is out there???

[John_Heard]

My personal opinion of the hobbs switch is that it's better to use for a light inside the car than shutting off the system. Seems like a lot of people have trouble with them and they really aren't very precise. The problem with losing pressure looks like the real issue and needs further research. Bad pump, clogged filter/s, voltage, regulator/s, etc. all need to be checked out.

This is where a data logger is very valuable, you could tell if this was a pump pressure problem, regulator or voltage based on your last pass if you had that data. Those things pay for themselves quickly when troubleshooting things like this. If you set your fuel pressure when you got to the track before making your first pass - then I can't see where the temperature would have played that much of a part in the failure you ran into - even if your buddys were running into something similar, that doesn't make much sense. I've never seen temperatures affect fuel pressure that much myself.

[stroker1]

A couple of things come to mind for me. Was the 7.5psi dead heading into a regulator? What pressure does it hold when activated? Also, sounds like a voltage drop to the pump may have occured. Like John said, without knowing what your voltage was during the pass, its hard to put the fault where it belongs.

A F.P.S.S. is a good saftey to have but you cannot totally rely on it. After all, they are a relatively cheap made part to trust your engine to when you really think about it.

What if the fuel solenoid takes a crap?? There just ain't enough saftey devices available to prevent a melt down IMO. This subject needs some creative engineering.

[TOMT]

Hi guyz, yep I hear you bout the datta logga, but they a pretty damn $$$ over here, have always been wanting but..... Its going to set us back about 17-20K to rebuild to the next step.
I am pretty damn cautious when it comes to the fuel! more so on this motor as she was a 60K+ investment. So yeah might be lookin at 1 now..... any imput and makes???
Now the 7.5psi is my static pressure, for a 175hit. Flowing pressure is 6psi. The Nos fuel (BG 2Port) Reg has no bypass, But each fuel soleniod has a bypass to tank( seperate line) on the inlet to the soleniod. So there is no creep on the reg at all.
Front mounted fuel tank with a BG240. I have exsplained how I do my flowing pressures in a dif thread, which is way better I think than ur guys 1jet method as it checks if there is any fault with the soleniods.
Also the NOS is controlled by a Jacobs Nos Mastermind, And all is good with that as when I do a flow check, that is checked as well.

I here you bout the fact that temp shoudnt play round with the fuel pressure, But I,m telling ya, At this track it always does!!! no other track just this one.... Its not just me, its a lot of guys have issues with keeping fuel press rite there, the only ones that dont are the blown guys with mechanical pumps.
New guys to the track are always running lean 1 run ,then fat the next, and they cant suss it unless som1 tells them....
Weird aye?????

I have been down the loss of voltage, leakage, etc but evrything checks out ok.
Just so happins that this is the second motor lost here!!!!
I will hav a new plan wen running at this track in future, I will b checking fuel pressure as we are sitting ready in the stageing lane with 1 car to go.
ANd adjust to suit....

When I make the trip to were the car is ( my partner is 4hrs away) I will take some piks and show you how its setup, As this car still has to stay streetlegal, and a 23T it aint easy to fit evrything on lolololol

But I dont want to rely on a Hobbs again, so some input on diff safety devices?????

[John_Heard]

So it's kind of like a track in the Bermuda Triangle where everyone loses fuel pressure? That's weird... sounds like a track to avoid!

There are several of us here running the RPM Performance Data Loggers, Randy, the owner is a member of the board and moderates the Data Logger section here. Getting something like that is my best recommendation because we have no data to work with to know what actually went wrong with your fuel system. Without information we're just taking pot shots at it.

[TOMT]

Yeah you could say that John..... All I know is its been like that for years, since I first started racing there... Weird or I,m loosin it bud????
If I was havin fuel issues at the other places we race I would look further into our setup, But I dont have a problem anywere else.....
As you can see we have to tune "old school" buy reading plugs and seeing how she performs.
I will contact Randy and see what we can do/afford cause I here you bout knowing what is going on inside these motors.....