slow78ta

Whats the max power potential I could get from my Walbro 255? If necessary, I can copy my brother's twin 255 in-tank setup, but I'd rather not if I can support decent power with the single Walbro.

I haven't really decided on my power goals yet, I know its gonna be turbo, (5.3) but I really just can't decide how far I want to take it.

Stoichiometric

iTrader: (10)

Probably 500rwhp or so. You can add a boost a pump to eek out a little more if you need it. Also, a methanol kit can buy you more fuel without needing a bigger gas pump.

Big Thumper

iTrader: (1)

Short answer - about 500 HP on a basic turbo motor.

Long answer:

A Walbro GSL-392 flows 255 liters / hour (about 68 gallons / hour) at 1 bar (14.7 PSI of gauge pressure) and 12v - I've got their flow curve here in front of me

Base LS1 fuel pressure is 4 bar (58.8 PSI) gauge - the 392 will only flow 52 GPH at that pressure. If you're going to run, say, 15 lbs boost (worst case), you'll want to maintain the ~60 PSI differential across the injectors, so your pump will have to make at least 5 bar of pressure (58.8 + 14.7 = 73.5 PSI).

At that pressure, the pump will move about 45 GPH.

So, your worst case required pressure: 73.5 PSIG, giving a flow of 45 GPH.

To figure out potential power from that you work off of the engine's BSFC (Brake Specific Fuel Consumption - it's a measure of the overal engine's Power to Fuel Consumption efficiency, and is usually in pounds of fuel per horsepower by hour).

A safe estimate for a turbo gasoline engine is in the 0.5 - 0.55 lbs / HP-HR range. S/C engines will be higher (0.55 - 0.65 +) as the blower power requirements subtract from overall efficiency.

Gasoline is about 6.2 lbs / gallon (737.2 kg / cubic meter).

(45 gallons / hour) x (6.2 lbs / gallon) = 279 lbs / hour at 73.5 PSIG

(279 lbs / hour) / (0.55 lbs / HP-hour) = 507.3 HP

A couple caveats -

The BSFC number is a rough estimate. All of your engine's hardware will affect this - lower is better. I've seen BSFC's as low as 0.28 on turbo-diesel race engines and as high as 0.72 on supercharged alcohol-fueled engines.

The 507.3 HP is a crankshaft power number before any accessory power take-offs.

If you're using a rising-rate (vs. a straight-rate vacuum-referenced FMU), your pump will have to output an even higher pressure (some multiple of boost, instead of an equal offset), which will lower the power potential.

Conversely, if you're not running a vacuum / boost referenced pressure regulator, your pump will not have to output as much pressure (but your injectors will flow less as intake manifold pressure rises, so it's a bit of a wash).

Increasing voltage will increase flow - they have two curves on their flow sheet, one at 12v and one at 13.5 - using the 13.5v curve, the pump will flow 56 GPH at 73.5 PSI.

YenkoST

iTrader: (11)

There is some GNs using it to run 550rwhp on a single Walbro 255. So, that's a V6 turbo engine as well.

slow78ta

Big Thumper- a huge thanks for taking the time to give a thought-out answer with data to support. Now anyone can go through the same process to determine what any particular pump can support. Very much appreciated!

I think what I'll likely end up doing once I max out the single pump is running another 255 in parallel to increase the gpm at that same pressure. Perhaps a boost referenced switch to start the other one. I guess I'll work on maxing out one pump first though

Big Thumper

iTrader: (1)

No problem - done that math set a couple times. We run three in parallel (constant-on - just make sure you've got a big enough return on your fuel pressure regulator!) on the high-horse (1100+) twin turbo engines.

Here's the plot for the 392 for reference.

slow78ta

Thanks for the map! Do you have a resource for other manufacturer's pump plots?

TURBHOE

iTrader: (4)

so NA that single pump is more than enough. by my math something like 700 and some change. thats with a .45 bsfc. which is what i found on the rc injector web site. and that is at 12v not 13.5. thanks for that info now i know that one pump will work great for my 383. and still 644 at .50 bsfc

Big Thumper

iTrader: (1)

I've seen a couple plots for the larger Aeromotive pieces - honestly, though, the best thing I can recommend would be to run multiple 392's. They're damn near bulletproof... We've had a lot of trouble over the years with the fancy 'drag race' billet pumps that a couple outfits are building... Not a hiccup ever out of the little Walbros.

Bosch bulds a real similar pump in a couple different sizes, but it's a 'Motorsport' part and very large $$.

Every manufacturer should be able to get you a plot like that. If they can't, don't buy their pump, they haven't done their development work, plain and simple.

parish8

iTrader: (6)

we have seen 450rwhp in the fairmont with one 392 and over 600rwhp with one and a voltage booster.

i run 3 392's on my truck with no booster to over 1000rwhp. i that i am good for 1200+rwhp with this set up.