I'm looking to do an LS3 swap into my alpha and wanted to know what the size/capacity of the stock fuel pump was. Has anyone factually done a fuel pump upgrade?
Any ideas on any aftermarket upgrades that fit in tank? Walbro 255? Will it fit?

 

OEM fpm is around 60gph@60psi which is plenty for a stock 430hp-LS3.
What size fuel pump do I need?

 

Fuel feed is not an issue.

Why not keep the LH8 and mod it with a Low Lift Stage 2 truck cam with LS6 springs, Air Doc Intake, PP TB, Efan conversion, Cat back exhaust and a tune? You would be around 375-385 HP/TQ with a ton less aggravation and 100% reliability. Can you tell that is what I did?

You are going to have to tune the LS3 anyway. I would not be doing an LS3 motor into a truck because the power curve is set for lower weight cars and, more importantly, good low mile versions are getting harder to find. I am keeping my eyes open for a newer L9H to VVT delete with a cam swap when my 5.3 gets tired if I still want to play with it when it gets there.

 

The LS3 was really to reset the clock to zero miles as most of the rest of the driveline is new. A new crate motor is $6200 from Summit. Once you swap to the truck intake manifold, it's a truck power curve.
I would use the 204/211 stock cam it comes with because it has more low end Tq and idles like stock. I don't want any lope.
I can respect the reliability point.

I'm 'spinmonster' from the corvette forum and have developed many mods for corvettes. Motor swaps are old hat for me.

The stock H3 fuel pump is 45gph compared to the walbro 255 being 65ish, a 40% increase. Walbro has GMC applications to replace the entire pump assembly.

 

At 80 PSI the equivalent HP (high pressure) fuel pump will flow over 210 liters (50 gallons) per hour.

OEM replacement:

 

You are thinking like a "car guy" not a truck dude. You do the voodoo you gotta do, but.......... a truck cam in the 210-218 @ .050 range makes more low end and mid range power for heavy trucks, and with an LSA of 112 has a barely noticeable cadence, no chop. Unless you are a gear head most would not know the difference.

The LH8 Intake flows pretty darn well and is good for low end, but even the intake can add low end with mid range, like a ported TB SS manifold or the pricey FAST LSXRT, but I have digressed... Fuel flow is not going to be an issue because you are not going to wind out a motor to high RPM in a Brick shaped H3. Please carry on.

H3s ain't no hot rod, they are built for wheeling. Mine weighs almost 6000#s with off road goodies and me in it.

 

Is there a difference between the manifolds? I remember seeing some engine dyno runs of the Car and truck intake and they are nearly identical about 98% of the power curve


As for fuel pumps, is it easy to adapt a fuel pump? I plan on pushing over 500hp