I currently have a Walbro 255.

What is the biggest direct replacement that will work with stock fuel lines?

Walbro 450?
Walbro 400?
Racetronix 340?


I know I need a new regulator too, I'll likely get the C5 filter/regulator kit from WS6Store.

We have drop in 340lph kits ready to go on the site also. Not nearly as hungry as the 400+ for voltage and amps.
Thats what i would recommend.

I have a Mechman 240 alternator, but I do want a pretty stout stereo at some point.

How much E85 horsepower can the 340 support?

Covered there. still id rather run the least amount of current possible to not build heat etc.

I think I edited after you replied...

How much E85 Horsepower will that 340 support with your C5 filter/regulator kit?

Depends on the target afr really but id say around 800 - 850 . Above that you really reach the upper limit of the stock lines.

Oh. That is more than I will ever do, even if I am ever able to get a Darton LS2 454.

I just changed my 255 out to a 450. It’s a direct replacement. Pumps are same size, except at the very bottom, the 450 blows out larger. Not a problem for me, as I don’t have a bucket for my pump to sit in.

What I found out the hard way, is that the corvette style regulator/filter will not work with the larger pumps. I ended up at about 75 lbs at the injector with that regulator, and I had to completely re-do my return side, and add a real regulator at the fuel rail under the hood.

I found a couple threads on here to support my findings, after I made the discovery.

Any potential issues with the 340 pump and the C5 style filter/regulator kit?

Looks like the Racetronix 340 runs at up to 80psi. I can't find anything on the limits of the C5 filter/regulator.

See post #12
https://ls1tech.com/forums/fueling-i...tallation.html

What’s more is that with my new engine install, I had a very hard time trying to get the car to idle/run, with a remote tune from Mast, who usually nails it for me.
I spent a LOT of time over the last month tuning my fuel/spark curves, only to find out it was a fuel pressure issue the entire time. Now I’m in reverse, trying to get the curves back to where we were...chasing my tail really...due to the regulator not being able to handle the pressure.
I’m glad I went the Aeromotive regulator route at the engine, with a return line at this point. It made the pump, which is in tank, much quieter, as though it’s not having to work so hard.

"450 pump but my main concern is the factory regulator"

It reads like they are talking about the stock F-Body regulator. I am talking about the RPMSpeed C5 Vette regulator/filter.

"duel 255's then" LOL. I guess the two pumps are having a battle.

I run a single aem340 in my tbss. Still using factory returnless setup with the original intank regulator. This pump has done great with a cammed, full bolt on ls2 spraying 200. I would guess at 600+ rwhp. Havnt had any issues. Been in there goin on a year now.

Used 93oct pump fuel only. Cant say with e85.