Fueling & Injection - Fuel Pressure Still Dropping...

Twin 255 Walbros in tank - hot wired to run all the time
-8 Feed line to LS1 Speed Rails
60# Motos
Aeromotive FPR 1:1 at rails

50psi idle
~13 vacuum
+12psi
------------
75psi fuel pressure during WOT


pressure raises fine but towards 5k the fuel pressure drops and at redline its back to 60 or so psi..


Any1 else having fuel pressure dropping

How much power are you making?

725hp/765tq

Wlabros don't flow well at higher pressures. Search for a post I made that compared the Walbros at diffeent pressures to a -044Bosch. I removed my Walbro set-up and installed dual Bosch 044's for the same reason....it would ramp up then ramp back down....044's ramp up to 80psi and hold steady.

You could try a BAP on them.

installed dual Bosch 044's

how noisey are they? my twin 255's when I did the install were pretty loud..but after the shop did the -8 feed line..they quieted down quite a lot. I noticed the sound was gone right off the bat and another member with twin walbros asked why mine were so quiet.

Search for a post I made that compared the Walbros at diffeent pressures to a -044Bosch.
I am having trouble find the post...link plz

installed dual Bosch 044's for the same reason

I take it these are intank pumps? all you did was just remove the old walbros and install the new bosch pumps. nothing extra was needed? remove..and replace. not remove...replace..but had to replace this..and xxx to get it to work.


I also read on ls1tech that walbros dont like high pressure...and was wondering if I set them straight to 58psi with no vacuum/boost reference..would that let them flow within there rated range?

Shit, you can even sell your used 255 setup and recoup some of the cash, thoes things sell good :)

If you have a 98 tank 044's would be easy to install. I have a 99 plastic tank and wanted them intank so I went with a custom tank...can;t hear them.

If you have enough injector, you can set them to 58psi and they will flow better...just remember 58psi minus your boost psi = what the injectors see.

Are you checking your fuel preasure with a mechanical guage or are you pulling it into your boost controller for display purposes?

Is this happening with more than a 1/2 tank of fuel in your stock fuel tank? Just a quick sanity check to rule out fuel pump starvation under acceleration.

You're sure both 255 pumps are really working? They do have a weakness at higher fuel preasures but I don't remember the trigger point for problems.

Are you sure the boost reference source line to the FPR isn't leaking or coming loose?

We've been running at 60psi base fuel preasure on the Mototron 60s with the Weldon boost refernced FPR without any issues at 15lbs boost. We even had a cool day last November where we ended up cranking up the base fuel preassure some more to squeeze out a little more fuel during testing. The injectors didn't have any problems getting pushed this hard.

So I'd lean towards one of the pumps not being happy if the boost reference line looks ok to the FPR.

Rick

2001-WS6


full tank of gas
vacuum line is good (I always have 13psi of vacuum - if the line were to become disconnected or something...I would have 8psi of vacuum)
using a Autometer Cobalt Fuel Pressure Regulator
pumps probably have less than 500 miles on them


also have the racetronix wire kit for single pump

Hmmm... if the dual setup only has 500 miles on it, what were you running before? Just a single with the wire kit?

Rick

Ernest..

As stated before.. You sure obth pumps are on? Mine are much louder. Also I did a setup just like yours -8 breaded line all the way to the engine, W/a full return line. Dual Walbro's intank.

He's got a 396 LT1 with 11psi of boost and he's putting down the numbers, + his fuel pumps are quite loud when they prime up..

Maybe 1 pump is not happy, failing.. Maybe your not running both pumps. Like said in the other thread you need to make sure both are on..

Talk to you later.

Clint

Hmmm... if the dual setup only has 500 miles on it, what were you running before? Just a single with the wire kit?

Rick

i was running the exact same thing....except i had stock lines. i had the shop install a -8 feedline to the rails and move the fpr to the rails also. i figured this would solve my falling fuel pressure...but it didnt.

i will re-inspect the pumps to make sure they are BOTH running.

check
dirty filter on upstream side
damaged/bad regulator
good power and grounds to pumps
good flowing Y block from pumps, no restriction inside the tank.
solid voltage to the pumps
weak pump?

when i was dropping pressure i ran new dedicated grounds to the pumps and re-did he y block and havent had a problem since

63psi is the most my dual 255s will hold after 90% or so injector DC. Like onfire said when pressure goes up, flow goes down with these. I have a dedicated 10ga wire to each pump (including grounds), nice Y in the tank, -8 all the way to the regulater etc and mine did the exact same thing when I boost referenced it. I was going to try a voltage booster but next step is dual external Bosch 420s for me when I decide to make some real power ;)

Fwiw we've ran dual walbros with no problems at -

995rwhp through a T400 and stock feed line, 43psi base pressure.

My own car which has made 898rwhp, 43psi base pressure.

And on a few customers cars at 70psi base pressure. (pushing 60's)

I would check the things MM has suggested. Also, does pressure bleed down or stay steady after the key is turned off? A pinhole in one of the lines inside the tank could do it as well.

Fwiw we've ran dual walbros with no problems at -

995rwhp through a T400 and stock feed line, 43psi base pressure.

My own car which has made 898rwhp, 43psi base pressure.

And on a few customers cars at 70psi base pressure. (pushing 60's)

I would check the things MM has suggested. Also, does pressure bleed down or stay steady after the key is turned off? A pinhole in one of the lines inside the tank could do it as well.

I'm planning the same set up...just curious what size injectors are ya'll using for the big HP cars and is the FP boost referenced?

We pm'd each other a few weeks back regarding this issue with stock feed lines...keepin' my fingers crossed!

We've been using 60lb motrons on the vehicles running the stock pcm. With as high as 70psi base pressure, 20lbs of boost, and 100% dc. Not an ideal situation, but it works.

We usually run 83's on cars with BS3, up to 1000rwhp.

I'd stick another gauge on there to verify the first. Do you have an Aeromotive FPR and and Autometer gauge? Seen plenty of gauges read bad.

Jim

Also, does pressure bleed down or stay steady after the key is turned off?

i turned the ingnition on...waited a sec for the pressure to rise to ~52psi...turned the car....pressure stayed at 52psi...didnt drop any..waited a few minutes.

but if i dont turn the ignition off...the pressure starts to slowly drop.

i take it that both instances i just described are normal?

I am pretty sure the fuel pressure is dropping it evident in my dyno runs where my A/F will start to decrease after 5k and no matter how much i open the injectors/PE vs RPM/VE table...the A/F curve doesnt richen up.

didn't the aeromotive FPR's have issue's with holding pressure?

Oh man i was just getting another 255 walboro pump in the tank Please keep us updated on your problem.

Anyone know where to get the 044 pumps for the best price? They are pretty expensive on the web. Also would one 044 pump be enough to flow 700-800rwhp SC'd car?

I just found this artcile which compare Walboro VS 044 pump.. http://www.stealth316.com/2-fuelpumpguide.htm#j6

They are saying there is a 255 high pressure walboro (GSS340-341-342) and 255 low pressure (GSS307-315-317). Which one are you running now?

340's

340's

In the article they are saying the 315's will flow better than the 340's at higher pressure due to different valve design whatever that is. It doesnt make sense to me because i thought the 340's was the high pressure pump.

i turned the ingnition on...waited a sec for the pressure to rise to ~52psi...turned the car....pressure stayed at 52psi...didnt drop any..waited a few minutes.
but if i dont turn the ignition off...the pressure starts to slowly drop.
i take it that both instances i just described are normal?

Your car should de-pressurize itself after like 30 min or so. Mine does the same thing- turn car off at ~60 psi......come back 10 min later with key on ~56-58 psi. Etc.

As far as the pressure dropping, I saw a video on hereI think of someones Procharged car with an in-car 1/4 mile video focused on his FP gauge. It dropped pretty good. If someone has the link/knows the setup maybe they can chime in.

Good luck
Andy

Mine with a single 255 pump starts at 62psi and drops to 40psi at 6K RPM 630rwhp.

Mine with a single 255 pump starts at 62psi and drops to 40psi at 6K RPM 630rwhp.

Not supprised.. Be careful with that 40psi of fuel pressure.


any updates Mecham...???

Twin 255 Walbros in tank - hot wired to run all the time
-8 Feed line to LS1 Speed Rails
60# Motos
Aeromotive FPR 1:1 at rails

50psi idle
~13 vacuum
+12psi
------------
75psi fuel pressure during WOT


pressure raises fine but towards 5k the fuel pressure drops and at redline its back to 60 or so psi..


Any1 else having fuel pressure dropping

Aeromotive FPR... Return type system?

hopefully the pic link works

http://community.webshots.com/photo/549050781/2831394170076734921LxBlsP

using the stock line for return

Not supprised.. Be careful with that 40psi of fuel pressure.


any updates Mecham...???

not clint...might dig into the fuel system tonight...to verify that both pumps are active...

hopefully the pic link works

http://community.webshots.com/photo/549050781/2831394170076734921LxBlsP

using the stock line for return
That, if you have set the FPR to 50, and the vac line was off, and blocked, engine idling, that the pressure will be pulled back about 4-6psi.[Helps clean up idle]
Your math is, I think incorrect, in the subtraction of the vac value, you show as 13, will only allow the FP to rise that 4-6psi, I mentioned. This will occur as the engine progresses into boost. At that point, zero vac, zero boost, the FP should read the original set point. [50]
As the boost comes on, and rises to 13psi, the FP gauge should read 62+/-, a #, or two, not 75....

You may want to consider a larger return line, as supporting that much HP with a small return, is a bit risky.

Just my $.02...

Old G

my car has 13psi of vacuum at idle...always has from the days I was supercharged.

50psi fuel regulator (vacuum line attached to regulator)
13psi vacuum
12psi boost
-----
75psi

I am intrigued as to why I would need a bigger return line?

Not supprised.. Be careful with that 40psi of fuel pressure.


any updates Mecham...???

Yes i know... We stopped there and we wanted to add another walboro pump, -8 feed line, FPR and Speed rails, but now im concerned because of the problems MECHAM having. I would like to keep my 62psi base fuel pressure and increase it by 1:1 until 13-15psi of boost. That should put me around 75-77 psi of FP. Now i see that the Walboro dont flow good at that high pressure!!!

Old G

my car has 13psi of vacuum at idle...always has from the days I was supercharged.

50psi fuel regulator (vacuum line attached to regulator)
13psi vacuum
12psi boost
-----
75psi

I am intrigued as to why I would need a bigger return line?

That the car has 13" vac, but that value is not used to calculate the PSI that you will/should see at boost. [Once the vac goes to 100PKA, the engine is at the onset of boost, and vac has nothing to do with the operation of the regulator.]

I suggest you look at the gauge reading with the engine idling, vac line off, and blocked. If you do this, you will see that the 13" of vac has only a 4-6PSI effect on the pressure reading you will see, not 13 PSI.
Let's look at doing a "test" setting.
Base pressure desired is: 50PSI
So, engine idling, vac line off, and plugged, we set the regulator to 50PSI, lock it down.
Reattach the vac line, and the PSI will likely drop to 44-46.
Take the car out, and run WFO. If the 1:1 regulator is working correctly, AND the pumps are working correctly,
at 13# boost, the FP should be 62, +/- a #.

As for the fuel line sizing:
A. An OEM line that was sized to support an engine at 400HP, could be on the borderline when used on a modified system. [Except at WFO, that OEM line is expected to flow nearly twice it's intended volume.] May work, but most aftermkt systems recommend return lines near the size of the supply line.

B. Return line restrictions can cause backpressure at the regulator, pump[s]. [Causes heat, and may cause incorrect FP readings]

I'd suggest you modify the wiring to the pumps, so that off boost, you run with 1 pump. Here's a part # for a GOOD quality HOBBS switch.CCS Model 607GK.
Last fone # I had was 818-341-4610.
1 pump operation will cool things down, when you are not at "WFO"....

Lastly... Be sure your gauge is accurate. I flow check alot of the little, "mini gauges", and find them off as much as 5 psi, +/-. The best I've seen were only a # off, the worst, 7#. :eek2:

Don't always trust what you read here... I have never had a problem with running out of fuel pressure..

I'm pushing about 14psi with my setup and over 700RWHP..

Keep us updated Mecham. Depending on how you have your pumps setup, you could just pull the fuse to the primary pump to see if you still get fuel pressure from the 2nd pump..

Good luck.

Clint

your running too much fuel pressure, kick it back to say 3 bar (43psi) key on engine off and then re trim your injector flowrate.

less pressure will allow the pumps to flow more

your running too much fuel pressure, kick it back to say 3 bar (43psi) key on engine off and then re trim your injector flowrate.

less pressure will allow the pumps to flow more


But wouldnt less pressure make the injectors flow less? The way i understand is that the more FP u run the more the injectors would flow. I understand that the pump will flow better at a lower FP, but what about the injectors. For example, the 60lbs injectors will flow that much at 43psi of FP and could go to being a 85lbs injectors at 87psi of FP.

that is true, you have to bandaid the weaker of the two by favoring fuel pressure.

but he is not using the max of the injectors right now, and therefore can run the pressure down to help the pumps

But wouldnt less pressure make the injectors flow less? The way i understand is that the more FP u run the more the injectors would flow. I understand that the pump will flow better at a lower FP, but what about the injectors. For example, the 60lbs injectors will flow that much at 43psi of FP and could go to being a 85lbs injectors at 87psi of FP.

Yes, turning the FP down, will reduce flow, out of the injector. [A 60# inj at 43.5=60PPH, at 60PSI, it is 70.5PPH, at 40PSI, it's 57.5PPH.]
But, the pressure you MUST deal with is called "delta P".
That is the NET PSI the injector is working with.
IE:
Set the base, line off, to 60PSI. Reconnect reference line.
13# boost.
The FPR, if working at 1:1, should show operating PSI as 73PSI., at 13# boost.
Remember, that the outlet end of the injector is seeing the same 13# boost. Therefore, the NET, or DELTA P, is still 60PSI, and that's the flow, in #/hr, that the injector will flow.

BTW, the increase to 87PSI, from 60PSI, will not make a 60# inj flow 85#. It will flow 72.25#, if it will work at that elevated PSI....Some will not.......

Mecham. Erneast..

People here are correct, having your FPR Fuel Pressure Reg hooked up to see Vac seeing 13Hg of Vac causes the Pressure to go down, but remember just a light touch at the Throttle the FP jumps as much as 5 to 13 psi as the Vac has gone from 13Hg to almost zero, then all the way to 13psi at WOT past 3000 rpms.. this 26 + - Fuel Pressure is hard to control, and might be hard on the pumps..

I would hook the hose line form the Fuel Pressure Reg to the Tubing of the Turbo, or anything before the Throttle Body blade. And I would set your Fuel Pressure to 58 or sotck for a ls1 motor.. Still have it so that when the Regulator sees Fuel Pressure it will go up. though Mighty Mouse is right, Having your pumps at 70 psi of pressure at these bigger lines -8an is though, and to just keep it at 58 to 60 psi might be the best..

Remember when you came over to the house, I mentioned that the Regulator needs to be hooked up before the TB Blade.. Also, Reason your running Rich in the Mid Range, is the tuning I setup for you is a liniar pull, going richer as you see the boost. Well the injectors are also seeing about 15% more fuel when the boost kicks in because the FP Reg is feeding it. I can tune this for you so it provides a consistant 11.7 A/F ratio for you, but as you know your running out of fuel for all the above reasons mentioned above and in the other posts. Having your pressure constant will be easier on the pumps and easier on the tune.

Take care.

Clint

I would hook the hose line form the Fuel Pressure Reg to the Tubing of the Turbo, or anything before the Throttle Body blade. And I would set your Fuel Pressure to 58 or sotck for a ls1 motor

Clint...so this is how i should hook things up then?

Mecham. Erneast..

People here are correct, having your FPR Fuel Pressure Reg hooked up to see Vac seeing 13Hg of Vac causes the Pressure to go down, but remember just a light touch at the Throttle the FP jumps as much as 5 to 13 psi as the Vac has gone from 13Hg to almost zero, then all the way to 13psi at WOT past 3000 rpms.. this 26 + - Fuel Pressure is hard to control, and might be hard on the pumps..

I would hook the hose line form the Fuel Pressure Reg to the Tubing of the Turbo, or anything before the Throttle Body blade. And I would set your Fuel Pressure to 58 or sotck for a ls1 motor.. Still have it so that when the Regulator sees Fuel Pressure it will go up. though Mighty Mouse is right, Having your pumps at 70 psi of pressure at these bigger lines -8an is though, and to just keep it at 58 to 60 psi might be the best..

Remember when you came over to the house, I mentioned that the Regulator needs to be hooked up before the TB Blade.. Also, Reason your running Rich in the Mid Range, is the tuning I setup for you is a liniar pull, going richer as you see the boost. Well the injectors are also seeing about 15% more fuel when the boost kicks in because the FP Reg is feeding it. I can tune this for you so it provides a consistant 11.7 A/F ratio for you, but as you know your running out of fuel for all the above reasons mentioned above and in the other posts. Having your pressure constant will be easier on the pumps and easier on the tune.

Take care.

Clint

I disagree.
1.The FP does not drop 13psi, due to the regulator seeing 13" of vac.
2. The injectors are not seeing 15% more fuel, as the boost is not only on the regulator side of the flow, it's also seen at the nozzle end. They cancel each other out, and the fuel volume is then controlled by "delta P", AKA, "net pressure".

Clint...so this is how i should hook things up then?

set the base pressure to 58psi and from there it will be 1:1

will i need to re-scale the injectors clint?

Mecham...

the Diagram looks good!.. Does the WasteGate need to see Boost and Vac? I'm not sure.. Ya hook the F P R up to the turbo tubing so it sees only boost, ya boost baby boost.. ;)

1:1 ratio is fine, ad the 58psi should work fine. The Ltrims will be slightly off, but not a big deal with the added Fuel Pressure.

I run both pumps at the same time, have been for over a year with no issues, so I would not worry too much about heat from the fact your running 2 pumps..


talk to you later.

Clint

update Apr 29

verified both pumps are working. i would assume that if they turn on that they are working. no leaks...verified.

hooked up the system like the above pic, so the fpr only sees boost and rises 1:1.
static fpr 52-53psi

fuel pressure is still dropping during WOT runs...for 7psi no...13psi yes.

any1 running 3 pumps? cheap route to add another pump gss340...


or


should i drop the static pressure down to to 43psi like MM suggest and try that?


:confused:

update Apr 29

verified both pumps are working. i would assume that if they turn on that they are working. no leaks...verified.

hooked up the system like the above pic, so the fpr only sees boost and rises 1:1.
static fpr 52-53psi

fuel pressure is still dropping during WOT runs...for 7psi no...13psi yes.

any1 running 3 pumps? cheap route to add another pump gss340...


or


should i drop the static pressure down to to 43psi like MM suggest and try that?


:confused:

Whats your injector Duty Cycle at 13psi?

Whats your injector Duty Cycle at 13psi?


at 5856rpm they are 16.4 and 16.9

You Could Try with 43 psi like MM said..

Or I would Up the voltage to the Pumps at WOT, and here's the perfect thing to do it with..

https://www.casperselectronics.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=102130&Category_Code

My buddy is running this and it works well for him he's 550RWHP with 1 single pump.

what does your FP go to at WOT 13psi of boost?

if you dont manifold reference your regulator then wtf does your injector flowrate table look like?

easy to have a nice constant value and give it vaccum and boost. thats where they are placed for all oem (or are not referenced at all)

having it boost only certainly would have no affect on fp stability at higher pressures.

either you have a kink or break in the line inside or outside the tank, or your voltage at wot is not holding 13v.

every psi you turn the regulator down is one more psi it wont drop on you at wot.. yea maybe you should try what i said ;)

update Apr 29

verified both pumps are working. i would assume that if they turn on that they are working. no leaks...verified.

hooked up the system like the above pic, so the fpr only sees boost and rises 1:1.
static fpr 52-53psi

fuel pressure is still dropping during WOT runs...for 7psi no...13psi yes.

any1 running 3 pumps? cheap route to add another pump gss340...


or


should i drop the static pressure down to to 43psi like MM suggest and try that?


:confused:


I'm trying two A1000's.

Erneast..

I would do what MM said.. Now that I think about it the 255l per hour flow rate is at 45psi I believe. So it makes since you can max the Flow of your pumps by doing 2 things.. Lower the PSI to what MM said, and also upping the voltage to the pumps, from 12-13 to 16volts if you can..

Tuning your car for 43psi fuel pressure is not a problem..

Clint

thx clint...

was gonna order that casper do-dad u posted earlier...did a search on here and noyzee is selling a brand new one .. so i got it from him instead (saved about $40.

gonna lower the FP to 43psi too....increase the injectors...and pray my fp stays. if not....3 pumps here i come :emb:

update...

2...is better than 1....3 is better than 2. :devil:


yep...3 intank walbros...holy scheeit it was a tight fit. :judge: wasnt too bad EXCEPT the fuel pump relay went bad...at the same time I was adding the 3rd pump...took me about 6hrs to figure that one out...i cant tell you how many times i rewired the pumps...put it in..pulled it out...in..out...fuses..etc..etc :bang:

anyways..minus that detour :(


prelim 12psi tests show 0 drop in pressure. :)

its running really rich now...did that and the 2bar new tune so everything is out of whack.....again.

im getting lots of knock too...hope this is because of the richness? :confused: wideband : richness

Mecham...

I guess 3 Walbros are better Arnt they ;)

I suppose at that point people would have gone with that Aeromotive 1000 hp pump, but I don't think that flows 765L per hour of fuel.. It is amazing your car needs 201Gallons of fuel per hour flow but I guess it does. Impressive..

Not supprised your tune is off now..

we shall take care of that.

Clint

post some pics mecham, i may need a third one day, specially if the e85 thing works out

well...nix the 3 pumps. with the tank low, the heat of the pumps was too much and one of the pumps burnt out. and while undoing everything i broke off one of the inlets for one of the other pumps. so now my plan is... 2 pumps .. 43 psi .. and i hooked up the casper volt booster. gotta get another pump 2morrow.

Why dont u go with a one 255 intake and a 420 Bosch mounted outside the tank with a feed line going in then connect the feed lines from both pumps with a Y block outside the tank. Thats what we are trying to do now. The nice thing about the Bosch is that it will hold high pressure better than another 255 intank.

dont run any more than 1 pump ALL the time.

also i promise if you have two GOOD 255's in there and no restrictions on the pressure side between them and the rails (and a good regulator) you will not have pressure problems.

Earnest..

I'm sorry, but I must stress again.. Your 3 Walbro Pump idea was perfect, but don't know why you had all 3 on at the same time.. Like I said you need to have a RPM or WOT switch to activate the #3 pump. Seems like having 2 on is okay, but 3 will create Heat!! Also I hope you mounted these in your tank with a little space between each pump. Having all 3 touch each other metal on metal will cause a problem.. place some rubber between each. I did like MM did, I placed cut 3/8" rubber hose between each pump to cusion between and put a hose clamp on them.

Clint

yeah..i got 2 new pumps coming in tomorrow :)

i did not see that rubber hose between the pumps. will do that tomorrow.

What are you going to use to have the 3rd pump come on only at WOT??

What are you going to use to have the 3rd pump come on only at WOT??

nothing...im not doing the 3rd pump now. gonna see if 2 new pumps and the casper volt booster works...if not then I will either...yeah.. :bang:

I still think you will have the issue of fuel pressure drop with the 2 pumps. You have a lot of -8an fuel line to fill there Earnest.


Take a look at these RPM WOT controllers. You can get these to work your 3rd pump.

http://store.summitracing.com/partdetail.asp?autofilter=1&part=MSD%2D8969&N=115&autoview=sku

http://www.nitrousoutlet.com/catalog/product_details.asp?group=26&model=86&dept=11&product_id=964

http://www.nitrousoutlet.com/catalog/models.asp?group=26&model=86&dept=11

Of course you can get the mechanical one that mounts to the TB, when you go 80% or more WOT the switch turns on and you have your 3rd pump. When I go 3rd pump I'm going to do the window switch.. You can control both your 2nd and 3rd pumps like this is you like too..



Clint

why 3 pumps and have more of a risk of something going wrong then just buying a dependable single pump that flows enough.

place add here for single pump that is as dependable and flows as much as 3 walbros? p.s. include price of dependable voltage regulator for said pump.

also u forgot that said pump must install in factory location

Earnest any updates?

Clint

nope..im chaing 2 gremlins now..my fuel pressure and hp tuners 2 bar 1998 program http://www.hptuners.com/forum/showthread.php?t=6151

update
2bar 98 SD program needed a code fix and works great! thx HP Team

for 02SSLE as I see you are having the same problem.

i would try changing the base fuel pressure to 43.5psi and see if you still have a fuel pressure drop? I did this and still had a pressure drop with 12psi. 7psi no.

in your thread you said the fuel pressure dropped to 50psi? so your base is 58psi and add 1psi per pound of boost. so 58+12=70psi max pressure but at redline you are registering 50psi?

new plan is 3 pumps in tank...2 hot wired..and 1 pump to come on under boost only. ran fine for several years with 2 pumps on all the time..no problem. just need a little more fuel up top. :)

If the pressure drops on a boost referenced regulator up top, y'all are out of pump(s) at that pressure. Walbros don't flow well over 60-65psi.

Mecham.. I would not use a Hobbs switch for the Activation.

Use the RPM Switch by MSD for the Activation of the 3rd pump.. Set it for say 2800 rpms, which is where you'll be starting to get into boost..

Take care.

Clint

i use the built in hobbs switch on my e boost... and unlike superchargers you never know what rpm you will need the fuel ;)

Just in my experence I've had better luck with a RPM activated switch like the nice MSD unit that runs about $70 bucks from summit..

http://store.summitracing.com/partdetail.asp?autofilter=1&part=MSD%2D8950&N=115&autoview=sku

This is a nice unit and nearly guarantee's activation, VS, a cheaper boost sencative switch + When your shifting gears, the pump will turn on and off when you get off the throttle, Via the boost switch, then turn on again through each gear. I like the "ON" switch above a certain rpm, this rpm switch makes more since IMO.

But mighty mouse your the man, and don't let anyone tell you different! Being serious here!! I've always enjoyed your car, RWHP and fast 1/4 times..

Clint

i dunno about all that, but your point is good, it would always be on during a 1/4 run.

If you want to "make sure" any kind of switch doesn't fail y'all at the track, wire a shunt connector between whatever kind of switch you use. I use a hobbs on the street and just pop in the shunt in 10 seconds at the track. No worries about a switch.