mzgp5x

I have found that the stock F-body fuel supply line is very restrictive to flow. I changed to aftermarket an lines (Summit stuff). I have since moved to twin Walbro pumps. I think a single Walbro with KenBell BAP and larger fuel feed lines will work with @ 10psi.
App,,, 1997SS 383-D1 MM6.
B.

MikeGyver

Very unlikely unless you can supply actual pressure drop numbers. There's people making 1000hp on the factory supply line.

DirtyDaveW

I've been running the original stock '96 pump that came in my car and an inline NOS pump (from the NOS 5176 kit) since 1999 and I'm running a T76 turbo at 15psi and my boosted A/F ratio is 11.x under boost. Stock lines, stock regulator, stock wiring/relays and stock style filter. I bought a racetronix Walbro but haven't installed it yet because so far, I haven't needed it. To the OP, something just does not sound right about your results as far as pressure. What's the fuel pressure at atmosphere? The fact that it doesn't escalate under load sounds like the regulator is not responsive to me. Maybe I missed a crucial post here but that pressure response(or lack of) sounds suspicious to me.

Kevin Blown 95 TA

You'll go lean, it just hasn't happened yet. Just about everybody had a setup like yours at one point, then you go one step over the line in power and it falls on its face. What is happening to him is exactly what happened to me - I was fine until I switched to a bigger blower, and at that point it just couldn't supply enough fuel. Having the meth/water injection really helped save the engine, though tuning was difficult since there was not enough gas. I was actually at the track, it went 11.1, but I saw 14:1 on the gauge and the car had bogged doing the burnout - the next two runs had problems with the burnout, too. It was then that I realized the lack of fuel was causing it and that my tuning adjustments weren't having any effect. After upgrading it, everything was back to normal with tuning. So it was the larger blower that pushed my 383 over the power level that the single pump + inline would supply enough fuel for.

chief455

Kevin - can you help me wire the 2nd pump using the hotwire / relay kit I already have?

Since primary pump is all plugged in via hotwire / relay, I'm starting at the alternator with hotwire #2, into Hobbs switch, out to relay - then to pump #2

usin the relay provided with hotwire kit - please tell me where to put Hobbs activated power in and where to source pump #2 power from

looking at the diagram I'm thinking power in terminal 86 and power out terminal 30 to the pump.
Do I need anything out terminal 85? splived into the primary pump terminal 85 relay out?

thanks a million

chief455

follow up for thread readers:
Kevin and others were on point.
My solution was a second Walbro pump mounted on a spare sending unit - and mocking it up for my current pump side by side
I pulled out my single pump, mounted as twins with the pump ground wire up through the sending unit as studs. the 2 power wires sent up through and epoxied. I used twin power connectors for easy 1 - 2 pump swaps.
I used the stock feed line, opened it up to the 3/8" it really is and used a compression fitting to a 't' going to fuel injection hoses to each pump. similar to other set ups pictured in the stickies.
I ran a second hotwire kit because I had it.
I used an ignition positive source from the fuse box to the Hobbs switch. that goes to the 2nd relay.
so - pump 1 from alternator, to relay triggered as stock by PCM etc
pump 2 from alternator to relay powered by ignition then Hobbs 2psi to relay.
as a precaution I mounted a wire spade on one side and a jumper wire on the other to bypass the Hobbs switch terminals - can run pump 2 with just ignition if needed by just plugging that together.
I used it yesterday when pump 1 hotwire had melted through and shorted out during a drive that got me home until I found the short. since previous owner had installed that wire - I should have looked closer.
my car now runs ~ 32psi cruising with 15-20hgvacuum. Under throttle as boost passes 2psi I see fuel pressure jump to ~ 45psi and hold as the car rips up to ~12psi boost with no more fuel stumble or pressure drop.
Fuel system solved making twin 255 pumps using existing Walbro and hotwire, stock lines, a $60 hotwire, $25 Hobbs switch, $100 Walbro, fuel fittings and hose, a bunch of small vacuum fittings and wire connectors and a day in the shop fabrication and installing..

thanks guys!

Kevin Blown 95 TA

Sorry, I didn't realize your PM was referring to the questions above about wiring the relays or I would have answered them for you. Somehow I must have looked at the wrong thread.

chief455

back up:
after a full day of driving I see now at WOT/ full boost my engine does not rev as high or quickly as it did with the single pump.
As a test I unplugged pump 2 (2psi boost switched)
with single pump:
car rips quickly up to ~6400 rpm, pulls super hard to ~ 10psi boost - but always stumbles and drops fuel pressure at WOT some time during the pull. Dead stop full shifting pull the car is a quick reving animal - with a stumble up top.
with both pumps:
car rips quickly up to ~6000rpm, pulls super hard to ~ 10psi boost, never drops pressure or stumbbles - but rpms are doggish above 5000 and after hitting 2nd gear really tops out at ~5900 rpm as it pulls super strong.
basicly - I lost about 800-1000 snappy top end rpm with the added fuel volume.
I can feel it less responsive when boost hits ~ 5psi during a full shifting from a dead stop pull. About same power - but not as 'snappy'.
The cars tune is so spot on with the single pump - I hate to mess with it. Idle, part throttle cruising, full throttle response until it stumbles - one of the best tuned cars I've owned.
suggest I get the car tuned with the twin pumps ie; remove fuel from the high end/ WOT fuel area - or -
try to squeeze more from the primary pump, put a higher rated (5-7psi) Hobbs switch in - which way should I go?
I am happy how it is and feel safer it has enough /too much fuel under boost until I can afford the solution.

Kevin Blown 95 TA

Sure sounds like you're running rich. Do you have a wide band sensor & gauge? If not, you need that and it's also good to be able to log it to see what is going on. If your stock regulator is losing regulation of fuel pressure when the second pump comes on, that could be a problem, too - may mean the regulator or return circuit can't handle all the extra fuel. You could probably tune around that. My regulator goes up maybe 1-2 psi if the second pump is activated at idle or slow speed - not sure if it does that at high speed, though, when more fuel is being used.

chief455

I was just about to get a wideband a/f gauge with logging ability. Seems I'll need it now. I want assurance I'm not going lean anymore for sure!
My pressure gauge goes from 32psi at idle / low rpm to 45psi with pump 2 switched on manually.
at WOT / boost by Hobbs it goes from ~ 38psi to 45psi
I was toying with the idea of putting an aftermarker regulator on so pressure rises 1 psi with 1lb of boost as explained to me earlier.
That in itself may lower the impact of the 2nd pump into a more 'tune' friendly reaction - while still preventing my volume loss issue under boost.

I will say - the stock regulator works okay with my setup, but an aftermarket one designed to work with boost might be what I need.
Somehow I feel I will have to spend time on a dyno with a tuner - the car came from Nevada to Ct, now I have added fuel to the tune - it likely needs tweaking I guess.

I do not like dyno tuning though - I've had my cars run so much better - and quicker - tuning at the track for actual better driving rather than max power.
I just don't have that ability now wth the LT1..

what about the guys that send you a handheld, take your tune, modify it and send it back to you to flash?

that might work for me with an a/f wideband as my guide..who are they??

Purple Poncho

The stock regulator is a 1:1 so fuel pressure should rise one PSI per pound of boost.

chief455

I had no idea! thought they just pulled fuel out during vacuum and zero vacuum / boost would = full pressure of fuel.

chief455

Kevin nailed it. Running rich.
I installed an adjustable FPR but with 2nd pump the car bogged during boost. just pulling the fuse to 2nd pump the car runs almost perfect on single pump at ~44psi base fuel. i'll get it tuned on a dyno now. the base fuel pressure and regulation was my initial problem, causing the car to flatten out on top end. it still needs to transition into boost from part throttle better but WOT runs from a dead stop are sweet.