Aftermarket FPR on NA?

[Thumper]

So I have seen where guys have removed the stock FPD and changed their fuel lines to a parallel setup with an aftermarket FPR. Would this setup be good for a NA motor with a Walbro fuel pump? Or would it be better to to just run a Marren FPD with the stock fuel line setup and keep the oem FPR?

[jerd_hambone]

On an NA, I'd just do the FPD delete. I doubt you'd ever tax the stock fuel system.

[Thumper]

Ive both the pros and cons about doing the FPD delete, and I would rather not do the banjo bolt thing just to be on the safe side.

[NoDOHC]

Actually, I have know two people to install aftermarket FPRs on NA engines. Both of them removed the stock FPR and installed an aftermarket adjustable vacuum-biased FPR. They both set the fuel pressure (vacuum relative) to between 32 and 33 psi (stock is about 40) to improve power output from the engine.

This leans the engine up from the stock tune and allows it to make significantly better power. The stock tune runs filthy rich. Unfortunately, they both experienced strange symptoms on VDI actuation, 6PI activation and throttle transients (not terrible, but noticeable). I think it also would make the engine start hard, but I don't remember either of them mentioning this as a symptom.

Advancing the timing about 5 degrees from stock will also improve power output.

For reliability, either install an S5 primary rail or replace the Pulsation Dampener. I don't recommend removing it (although I did it myself with no ill effects).

[Thumper]

Use the S5 fuel rail in conjuction with the aftermarket FPR?

[Thumper]

This is an S4 BTW

[RETed]

jerd_hambone is right - you will never tax the stock fuel system, unless we're talking big bucks in terms of mods (in which case, you would've answered your own question already).

Else, unless you just like to waste money and show off your mods...

The handful of people who claim the PD delete caused problems probably don't know WTF they are doing or just flat out lying.
99% of the people who do...have zero problems.
Remember, the FPR itself is a PD by design.

I'd also not recommend dropping the fuel pressure just to lean out your fuel curve.
A better way of doing this is to get some kinda fuel computer (i.e. A'PEXi AFC) to fine-tune instead of broad adjustment.
Dropping the fuel pressure also degrades the fuel atomization, and you lose idle quality and sacrifice fuel economy slightly.


-Ted

[Thumper]

Originally Posted by RETed

jerd_hambone is right - you will never tax the stock fuel system, unless we're talking big bucks in terms of mods (in which case, you would've answered your own question already).

Else, unless you just like to waste money and show off your mods...

The handful of people who claim the PD delete caused problems probably don't know WTF they are doing or just flat out lying.
99% of the people who do...have zero problems.
Remember, the FPR itself is a PD by design.

I'd also not recommend dropping the fuel pressure just to lean out your fuel curve.
A better way of doing this is to get some kinda fuel computer (i.e. A'PEXi AFC) to fine-tune instead of broad adjustment.
Dropping the fuel pressure also degrades the fuel atomization, and you lose idle quality and sacrifice fuel economy slightly.


-Ted

So you suggest just doing the FPD delete, leaving the OEM FPR and running some sort of fuel computer, right? I just want to make sure I am following. I dont plan on doing more than a street port (For now any way).

[RETed]

What are your eventual goals of the car?

My philosophy when tuning and building cars is to set a goal and work backward.
It is very easy to just start modding without setting goals, and this usually ends up with you wasting money and time with unnecessary things.

I've seen AFC tuning just leaning out the fuel curve produce 5 - 10hp gains across the board.
That's a 5% - 7% increase without changing anything other than slapping on an electronic box.
That's not bad for <$200 worth of electronics...

Your stock fuel pump can support 200hp at the wheels (DynoJet).
There's no reason to bump it up to an larger capacity fuel pump unless you're doing very radicals mods.
Very few normally aspirated 13B's can make 200 unless we're talking radical porting.


-Ted

[jerd_hambone]

Or hours upon hours of tuning and tweaking.

[diabolical1]

Originally Posted by RETed

What are your eventual goals of the car?

My philosophy when tuning and building cars is to set a goal and work backward.
It is very easy to just start modding without setting goals, and this usually ends up with you wasting money and time with unnecessary things.

+1

i learned this the hard way a few times.

[Thumper]

I just want to see how much power I can squeeze out of it with a large street port. I asked because I have seen where aftermarket FPDs have been retrofitted to work and I was looking at the parallel setup on FC3Spro, and I want to know if this would be the same for an NA. I was only going to upgrade the fuel pump because I need a new one anyway, and thought that I might as well upgrade since I may want to do a T2 swap in the future.

Thanks for the info so far guys I really appreciate it.

[NoDOHC]

ReTED is right, lowering the fuel pressure hurts the atomization.

I ran for about two years with banjo bolt mod.

I was only listing the reasons that someone would install an aftermarket FPR on a NA FC.

I had no fuel pressure issues on the dyno @ 216 WHp. Bone stock 460 cc/min injectors (63% duty cycle), Stock FPR (Turbo-style), stock fuel pump.

I think that you could get about 300WHp out of the 460 cc/min injectors using peak and hold (90% Duty cycle). The stock fuel pump should be able to handle that. (This assumes an NA build, it appears that Turbo engines are hard pressed to make 200 WHp on 550 cc/min injectors). Chances are, unless you know a lot about porting, you will not make anywhere near 300WHp.

The S5 fuel rail has a much better pulsation damper than the S4 fuel rail.

The FPR is on the secondary fuel rail.

[RETed]

You're welcome to convert your stock system to a parallel fuel rail system (like on my website), but it's going to cost you some serious cash.
You're probably not going to see serious gains doing this mod, but I guess you'll have peace-of-mind that your fuel system will be working at it's best efficiency.

The non-turbo 13B's biggest disadvantage to making lots of power is it's stock intake system.
You'll need to scrap the stock intake manifolds if you're going for serious power on an NA 13B.

Side note, the 13BT maxes out the stock 4 x 550's at a hair under 250hp at the wheels on a DynoJet as a conservative number.
I'd serious doubt 4 x 460's could hit 300 at the wheels even at best case on an NA 13B.


-Ted

[NoDOHC]

Originally Posted by RETed

I'd serious doubt 4 x 460's could hit 300 at the wheels even at best case on an NA 13B

I don't know (as I have never done it) but if my engine can make 216 at 63% duty, it is possible to make 300 at 90% duty.

216/63 = 308/90.

Like I said, I can't prove it as it has not been done, but it should work that way (as long as the BSFC remains constant with a more powerful engine).

I think this is a mute point anyway, as there is no reason that the OP needs to worry about his fuel system for an NA build, if he goes lean from fuel starvation, he may lose power... It isn't going to mean an engine rebuild for him.

Thumper:
If I were you, I would take jerd_hambone and RETed's advice and worry about the intake manifold. you will see significantly more gains from prudent intake modifications than you will see from spending a lot of money on an already functional fuel system.