Thread: To HP or not to HP...that is the question.

I am asking because I need to buy a fuel pump for my track project.
It will be a DE for a while,then VE eventually.
More than likely I will never boost it,but its not out of the question.
I just figured if I have to buy one,I would rather go ahead and plan for future upgrades intead of buying a stock replacement.
My questions
1.)What is the REAL difference between the Walbro 255 and the HP version?


2.)Should I just get the HP and be done with it,or save the ten bucks and get the std.255lph?

3.)Will it make the car run rich with a stock ecu and stock(bolted) DE with the stock FPR

4.)If so,should I just dial it back with an adjustable FPR,rather than buy a stock replacement pump?

I read in another thread about adjustable FPRs that you won't need one unless you are going to be running 4bar. The stock FPR will only yield stock FP, or 3bar, no matter the pump. Stock, walbro, or HP, just stick with your stock FPR. Even the stock pumps are rated for 60-70 psi, but mine stays at about 38 on idle, and 43 under throttle.

I would not trust the stock FPR as it is designed for stock fuel pump pressure. Buy and adjustable one and the 255 and be done. This will be plenty for the VE and even go to 4bar if needed.

Hp or no HP,that was the question.

eggman, the main difference is that the high pressure pump will still flow fuel at the high pressures required for turbo cars. The regular medium pressure pump (not to be confused with the low pressure pump for carbureted engines only) has the same flow rating, but looses flow quickly as the pressures rise to turbocharged territory.

This graph should really answer your question.



You will be fine with the regular 255 if you're N/A or low pressure boosted, but high pressure turbo is a different story.
I always think about the potential future owner of the car, and how complicated it could be for them if you got the medium pressure pump and they wanted to boost it. They'll never do the research to find out which Walbro 255 pump you put in, and they will have one hell of a time diagnosing a fuel delivery problem since they will assume you put in the HP pump.


As for the fuel pressure regulator, in theory the stock one will do just perfectly. It regulates your fuel pressure to be 3-bar (relative to vacuum input) no matter what input pressure you get. It's that simple.
In practice, I've heard stories of people running slightly richer than normal in open loop. Nothing I'd worry about. For me with the stand-alone when I went to a Walbro 255 lb/hr HP pump I had to lean out the tune the tiniest bit in what would normally be the closed loop section (so your ECU will do it for you) and nothing changed in the higher flow parts of the map (I was N/A still by the way).

I'd go ahead and get the high-flow pump. Since your plans are still a little unsure, it's better to have a good foundation to handle whatever you decide to do with it. At least you'll know that whatever setup you decide on in the future, your fuel needs will be met regardless.

I'd also recommend installing a stronger aftermarket fpr. I'm with squirlz on that one. The stock fpr is great for what it was designed for, but the added stress of higher volume and psi is asking for a failure at some point. That's a gamble I wouldn't be willing to take.

I trust stock and factory FPRs above and beyond all aftermarket FPRs. Especially adjustable ones. Don't do it! When have you ever heard of a stock FPR failing?

Great info Ben.exactly what I was looking for.Thanks!
It seems like my thought of just getting the HP was correct.
Might as well get the best option so I am not limited in the future.
I will probably start with the factory FPR first,and go from there.I will have an inline gauge to keep an eye on it.

Yes. The stock fpr is great, and all most will ever need. But like any regulator, surely, it is designed for pressures it was meant to see? I was just going on the theory of when you start adding higher than normal pressure at the input side, at some point it would exceed or hinder it's capability to regulate properly. I'm no expert at this stuff, and I've never tested the stock fpr's ability. Probably never will. Just going with a "better safe than sorry" approach if Eggman is going for serious pressures.

Do you know just how far the stock unit has been tested to? I've wondered myself.

That's the beauty of pressure regulators. They only see the pressure they create. Without the FPR there, you'd get almost no pressure in the line. With the FPR there, you get the 3-bar in the rail, and negligible pressure on the return line (as long as flow doesn't overwhelm it). The only pressure differential to worry about is the 3-bar rail pressure versus the vacuum source pressure. And that doesn't change any from stock (unless you turbocharge).

I've personally seen the stock RWD SR20 FPR handle a maxed out Walbro 255 HP pump at 25 psi and around 450 WHP. I have no doubt it could handle plenty more.