chief455

iTrader: (21)

Thanks for sponsor and member help to get where I am so far with my fuel system.
LT1 383, D1SC, 12lb, 60lb injectors, single Walbro 255 w/hotwire ~560rwhp

I lose fuel pressure under load/boost at WOT based on my fuel pressure gage and brief engine stumble.
- otherwise all good. Runs hard as can be even going easy into low boost.

I have started a new in tank set up ready for twin Walbro 255, and another hotwire kit (purchased from sponsors)

Question 1:
What I have not found is a Hobbs switch to power my 2nd pump as soon as boost begins.

Ebay is a common answer - but I don't see anything like a true Hobbs switch.
I see ones that range 7lb - up, 3lb etc - I want my pump to start right away.
Can I get a preset or adjustable 1lb rated Hobbs switch?

Question 2:
My car is running on the factory rail mount regulator and I will be on single Walbro pump until booost demand with 60lb injectors- can I leave this alone? .
Will the factory regulator work under no boost and the return line absorb excess fuel from both pumps only under boost conditions?

This is a street car on a budget not intended to race often.
I am running out of money for parts and labor so need to run what can work - not what we would like to buy because bigger is better.
thanks

ls1curt

iTrader: (31)

i got a 1 psi hobbs off ebay. the guy will adjust them to whatever psi you want. the seller is jti5. i think racetronix has adjustable ones as well

BenLaz

iTrader: (6)

lsxtune dot com has a 1-3 PSI one that is preset at 2psi.

chief455

iTrader: (21)

refresh the question:
2nd pump on 2psi Hobbs switch works great.
Problem: with my stock regulator pressure when pump 2 kicks on during boost jumps to 45psi from 38psi on primary pump.
This causes the car to run flat on top end - lost rpm's and throttle response up there too.
Will an adjustable fuel pressure regulator set at say 42psi without the vacuum line on stop this pressure spike from pump 2 ?

lowbirdws6

iTrader: (62)

Anyone with an answer? My dual Walbro's do the same thing, when the second one comes on, activated by a hobbs switch it jumps up 4psi. I have an adjustable regulator mounted up front on the return side of the rails. Is this to be expected or is something going on? Thanks

chief455

iTrader: (21)

On another forum someone answered yes, expect a small jump in psi.

Others say they have this set up and see no jump in psi - only volume should increase as the regulator should be - regulating.
Another theory I heard was the return line is too restricted so the pressure backs up.

I realized my pressure increase was when the Hobbs kicked on, but that is also during boost - which the pressure should rise 1psi per 1 lb of boost..keep that in mind. It might just be doing what it's supposed to do.

I am installing an aftermarket regulator today and will post up results.

I plan to test by running on primary pump at idle, no vacuum to set 43psi - then I'm going to activate pump 2 at idle.
I should not see and increase of pressure if the fuel can escape down the return line and the regulator is working.

my concern is that my car does not like the second pump! my running at WOT changed from loss of fuel to having fuel but the top end flattening out.
I hope the regulator can get me fixed up.

wreckwriter

iTrader: (1)

I got mine from Dave (jti5) too, he adjusted it to .5 psi for me. Great to deal with!

lowbirdws6

iTrader: (62)

I'm running -10 in and -8 out as a return line. Way overkill but thats how I built it so there is no restriction in the line.