Walbro 255 limit

[Directconnection]

Does anyone have any experience with the HP limitation of the high pressure Walbro 255lph pump?

[Pat]

Not sure where the limit is, but I can tell you I haven't found it yet at the 370-380 whp range.

Pat

[89DaytonaTII]

I've known of them to be run at 500+whp, but in applications with lower FP.

[Tony Hanna]

Yeah, pretty sure the upgrade pump for an lt1 f-body is 255 lph.
I personally have seen 450 hp out of a stock pump on one of those cars, so if the 255 is an upgrade then it should be good for more than that.

[87csx2.4]

I've known of them to be run at 500+whp, but in applications with lower FP.

Agreed 550 whp

[Directconnection]

Ok, then that's good news. Thought I might have to upgrade if pushing 28psi on my 2.5.


I still have the stock rail and +40's to contend with though. Any opinions? 2.5 forged pistons, ported head and manifolds and T3/T4 50trim.

[8valves]

Ok, then that's good news. Thought I might have to upgrade if pushing 28psi on my 2.5.


I still have the stock rail and +40's to contend with though. Any opinions? 2.5 forged pistons, ported head and manifolds and T3/T4 50trim.

I don't know, I had people tell me that I'm insane for still using a stock two piece rail, but I used one on my 370whp pulls. Everyone was telling me that it was only good till about 300 whp. Maybe I just didn't have even fuel distribution then... ?

I have seen the HP 255 support low 500 Awhp on DSM's and Honda's as well. It should be fine.

Aaron Miller

[Directconnection]

Aaron, what injectors were you using? 2.2 I assume and what boost were your runs at?

I have been told in the past by a DC engineer that the hollow rail technique is not needed in high HP situations. I'm leaning on the fence which way to go on the rail.

[8valves]

Aaron, what injectors were you using? 2.2 I assume and what boost were your runs at?

I have been told in the past by a DC engineer that the hollow rail technique is not needed in high HP situations. I'm leaning on the fence which way to go on the rail.

+40's w/ 43 base I think, i can't remember exactly, and at 26 psi on 93 octane without any injection of any sorts. We were getting close to my personal safety limits though, 72 lb/hr's are in line for this year.

I try to think of a fuel rail design being similar to a simple surge tank style intake manifold... just give it enough volume inside to have constant pressure and flow for each injector... ni biggie to me. LOTS of big power race cars have extremely simple hollow machined aluminum rails, no tricks.

Aaron Miller

[gasketmaster]

Ok, then that's good news. Thought I might have to upgrade if pushing 28psi on my 2.5.


I still have the stock rail and +40's to contend with though. Any opinions? 2.5 forged pistons, ported head and manifolds and T3/T4 50trim.

The problem I've found with the high pressure intank 255 is the lack of adequate dead head pressure if using a cal that requires a 55 psi static fuel pressure setting while running 30+ psi boost.

My HP 255 only made 85 psi maximum at WOT.

Using a cal tuned to a lower base fuel pressure is a blessing for us high boost guys.........it gives you more head room

[cordes]

The problem I've found with the high pressure intank 255 is the lack of adequate dead head pressure if using a cal that requires a 55 psi static fuel pressure setting while running 30+ psi boost.

My HP 255 only made 85 psi maximum at WOT.

Using a cal tuned to a lower base fuel pressure is a blessing for us high boost guys.........it gives you more head room

I think that the turbo buick guys mod the pump some how to solve that problem. Not sure how they do it, but perhaps some one will know.

[gasketmaster]

I think that the turbo buick guys mod the pump some how to solve that problem. Not sure how they do it, but perhaps some one will know.

Hey..........I AM a Buick guy.......LOL!!!

They were shimming the bypass spring with a piece of welding rod and a zip tie

My point is.........the wiser choice is to start with a lower static fuel pressure setting because as pressure rises volume deminishes when it comes to fuel pumps

If you can't get the job done by 85 psi at WOT something needs to change

[87csx2.4]

Yeah exactly once you get over 76 psi it falls off pretty fast.I set base pressure at 45 to start,you can use a grand national pressure reg.and it sets your base at 43.5 if your cal will support it.Make sure you are getting at least 13.5 volts at the pump mine gets 14.4 which boosts it a little more.At 70 psi 13.5 volts 56gph at 12 volts 46gph At 80 psi 13.5 volts it drops like 10 gph and so on.

[mech1nxh]

^^^^+1^^^
on the voltage and cal pressures.....
just for reference.....Attachment 397

[David Bohrer]

On my setup I run 72pph injectors on a 52pph cal. Base pressure is 20 psi with the NO vacuum. The key to getting the fp low enough is a large return line and that the regulator can flow enough fuel.

As for modding the 255 pump for high pressure you can order a high pressure mustang pump and mod to fit. OR drill out the bypass valve,remove the spring and then tap threads in the new cavity and install a allen set screw. Voila! Dead head capable.

But, why run a pump that hard? Get a modded cal and run a lower static pressure and get a safer amount of available fuel. Hence, my 20 psi of base fp.

[8valves]

On my setup I run 72pph injectors on a 52pph cal. Base pressure is 20 psi with the NO vacuum. The key to getting the fp low enough is a large return line and that the regulator can flow enough fuel.

As for modding the 255 pump for high pressure you can order a high pressure mustang pump and mod to fit. OR drill out the bypass valve,remove the spring and then tap threads in the new cavity and install a allen set screw. Voila! Dead head capable.

But, why run a pump that hard? Get a modded cal and run a lower static pressure and get a safer amount of available fuel. Hence, my 20 psi of base fp.

You do realize though that running injectors at such a low pressure is way less than otimal, right? Injectors need a certain pressure to maintain their spray pattern... does your car act tempermental at idle sometimes? Just a thought, I'm sure it works for now but look into getting it set up right for the 72's!

Aaron Miller

[David Bohrer]

The car runs fine with no hiccups during cold starts nor does it have problems with hot restarts. There is the occasional blip at exactly 3200 in part throttle at less than 25% load but, that is not enough to chase it down and fix it. The car gets 34 mpg at 90mph so I think the spray pattern is good.

EDIT: Besides, when I throw 30 pounds of boost at it the fuel pump is still in optimal range WITHOUT jacking up the voltage. And that puts the injectors in a perfect pressure/rating/area. IMHO. I feel better with this 72pph inj/52pphcal setup when running stupid amounts of boost just for the insurance aspect. If I have a boost spike the injectors won't get hung halfway open. That has happened to me TWICE with the 52pph injectors at 24psi (on pump gas 54 psi static w/o vaccuum) and then 28 psi of boost with 110 leaded with 50 psi static w/o vacuum. Now that this was done with two different cal, one for pump and one for 97 octane. But, my results were the same when I got to the @80psi range of fuel pressure the injectors hung and I cracked pistons. Also, it may be worth mentioning that I had the injectors flow tested and cleaned before and after each knock party and re-installed them in different injector locations as to try and isolate a weak unit. No dice. I still ended up driving a mosquito truck home.

Dave B.

[GLHSKEN]

+!^^^ You hear a lot about spray pattern. Gus used to run his car with +40's and 18-20 psi base... I'm all for lower pump pressure myself...