adjustable FPR
 

Doing a turbo build......searched to see what AFPR people are using and didn't find any discussion about it. I need to decide what is best to use for my FI build. Looking for something capable of supporting 400whp....

I am new to FI and really don't know what to look for, thanks for your help!

I'm assuming you mean a fpr to adjust base pressure with something like a MS?

I guess.....
I have a MS3, I know the stock will be ok for a little bit but don't want to wait for it to fail. So I am really not sure what I need, hence the thread. Thanks!

Never heard of them failing.

You can get 400hp with just injectors. People use some sub $100 FPR's to avoid buying $500 in bigger injectors, but it's not a failure point.

I have a walboro 255 and ID 850 injectors......

I'll let Braineack chime in with some maths to find out what that's good for, but my guess is you may need id1000 or 1200 injectors. I could be completely wrong.

What's the engine?

The vast majority of us are not using any aftermarket FPR, adjustable or otherwise.

If you're seriously shooting for 400HP, this will justify bumping up the fuel delivery capacity at the pump a tad. Some back-of-napkin math says you'll be flowing somewhere in the vicinity of 600-700 cc/min of fuel at that power level, meaning that some id1000s are probably a good choice which will give you a bit of headroom.

700 cc/min per injector (I'm going worst-case here) is about 44.5 gallons per hour. Assuming stock rail pressure, that's right at the limit of what the Walbro 190 is rated for, and well in excess of OEM. So a Walbro 255 is easily justified here.

There is a substantial body of anecdotal evidence to suggest that the 255 fuel pump flows more fuel than the stock FPR can effectively bypass at idle, resulting in elevated idle fuel pressure. This was problematic in the days of stock ECUs, but with a Megasquirt or similar you can adjust your fueling table to compensate. There will be a slight degredation in idle quality (as the injector duration at idle will need to be even smaller than it would be with 1000cc injectors at stock pressure), so it's largely a value judgement here. If you really want to optimize for best idle, you might spend the extra money and replace the stock FPR with a larger aftermarket unit having a 1:1 ratio. If you don't want to spend several hundreds dollars on a new FPR which you might not even need (which is what good ones cost), you can always try it with the stock unit. You're not going to blow up the engine just by firing it up and tuning the idle.

Joe,
Thanks for the input! I went with ID850's. My goal is really 300-350ish but want to see what the EFR6258 is really capable of and I think I can get really close to the 400whp mark and want to error on the side of over built. This is a daily driver for my wife so idle quality is important and if a adjustable FPR will help then I don't mind spending a few bucks. I know a lot of SM guys use the AEM for like $130. I will be very happy with 300whp I am sure. Low end throttle response is paramount to me, hence the EFR....

you will be happy with 300whp for your wife's daily driver lol...

Very interested in following your progress with the EFR, how is the motor built?

its not yet.....still waiting for my oil pump I paid for 6 weeks ago....

pistons, rods, headwork?

Supertech 8.6:1 83.5mm
Manly
Port/polish +1 valves VVT

Find my intro thread, I list my build specs in there.....

I have the aem FPR mounted to the firewall, because I've got an 044 in the tank and that WILL over power the stock fpr. I couldnt figure out a very clean way to setup the fpr on the stock rail so I just went with an m-tuned rail with a single feed. One end of the rail is the inlet and the other end is the outlet that goes to the fpr. Easy as pie. You can hear the fuel flowing though the aem if you mount it to the firewall.

come on, the math isn't hard.

(BHP x BFSC) / (# of injectors x Duty cycle) = lbs/hr X 10.5 = cc/min

so

(425 x .55) / (4 x .8) = 73 x 10.5 = at least a 766cc inejctor.

also keep in mind your 850cc injectors flow more like 955cc at the 55psi you're probably seeing at the rail with the 255. So as long as the fuel pump can keep enough fuel supply behind the injectors, they should be sufficient to spraying enough fuel at your given HP goal.

Brain, would it be easier to get a reliable, steady idle with a aftermarket FPR?

I dont see why ID850s would give you trouble idling. they have fast enough deadtimes where idle quality and AFRs should be easy to maintain. Unless you're crazy and are running MSI and non-sequential fueling.

if you did want to go that route, then get a SUPER FMU that can adjust the 1. base idle pressure in vaccum 2. crossover pressure at atmospheric. 3. rate of rise in boost

like these:

Super Fuel Management Unit | Vortech Superchargers

2035 FPR For Aftermarket Turbo and Supercharger BEGi

how is that trolling? is providing great technical answers on this site trolling now?

RRFPR is needlessly complicated, though. He's got enough injector to meet his power goals without it.

Chris, I use the Fuelab 545-series FPR on Theseus. With big fuel pumps, the fuel pressure fluctuations at idle can cause unstable fuel pressure, which is why an aftermarket FPR is helpful. The 545 is a single in/out, fully E85 compatible, 25-90psi adjustable, and uses standard -6AN union fittings instead of the pricey ORB fittings that Aeromotive seems to like. I've yet to see an aftermarket FPR that I like more.

Thanks Andrew!