I have 330 cc injectors controlled by MS. The max duty cycle I have seen on these is about 65% when I was NA, at 7000 rpm and 13.5:1 AFR.

I'm pretty sure I will be at 95% or more DC when in boost, so I think an AFPR is the cheapest solution for me. My question is, will a regular fixed rate AFPR like a Vortec or a JR work? All I need is to increase pressure at a 1:1 rate. How do I do this with what is essentially a rising rate regulator? Unplug the vacuum signal line?

 

You can definately use a RRFRP like the vortech. A begi would be the best option because it allows adjustment below 4:1 but you can use a vortech at 4:1 and just pull fuel as needed.

 

FWIW from what is reported here trying to tune MS and at least a RRFPR is a PIA.

You can run the stock injectors without a AFPR up to 6 psi but you are right they will be near 100% on duty cycle. I did this myself until I got the RX7 injectors. Speaking of which, why not just blow off the AFPR and get larger injectors? It will cost about the same (for used, rebuilt ones) and be a better long-term solution. Plus you will end up with freshly rebuilt injectors as well.

 

I dont see how it would be difficult. but I'd weigh the cost of $120 cleaned 460s vs whatever you can pick a FMU up for. If you can find a 4:1 vortech for $50, then i dont see why it wouldn't work, if you feel that's the best way for you to go at it. but again, i dont see tuning being an issue at all, but it's not optimal.

 

you guys didn't get my question. i want to know whether an RR-FPR can be made to act like a 1:1 regulator? In other words, I want the base fuel pressure to be, say, 55 psi (like the NB) and increase linearly with boost just like the stock regulator, only the pressure is proportionally higher.

 

yeah sure....this is the most common one.

http://www.suprastore.com/aefuprre.html

 

What would be the advantage to your idea vs. just getting larger injectors? For your power goals on 330's, what does the math say your fuel pressure will need to be?

 

Advantage is more power for cheap if you have stuff laying around, and I'd imagine it's easier to make it idle smooth.

 

The smooth idle is somewhat true, though I have mine idling fine on the 550cc injectors at about 13.5:1 AFR. The key for me was to retard the timing in the idle cells.

One thing I have been considering that might be nice about a fixed, adjustable pressure for the ODB-II cars is this. Though it is not a problem where I live yet, if one had to do the back-to-stock thing once a year for a detailed inspection, then it could make things easier: adjust the rail pressure back to normal, remove MS, plug the stock ECU back in, wire the wastegate open, viola, back to stock. It could be easier than swapping injectors.

Anyhow, I got your question pipefather. I just think it is easier to go with the larger injectors rather than mess with the FPR, and not much more expensive. Seriously, if you shop carefully, you can get used RX7 injectors and have them rebuilt all for less than $150. I think mine were $125 all together.

 

I've been running tan tops with an 8:1 disk for a few weeks now because the vortech was already on the car and I had disks laying around. I'll eventually stick some bigger injectors in there and remove the vortech when I find a great set at a good deal. It idles really good at 14.7:1 and was pretty easy to tune.

 

I don't understand how a 1:1 FPR is going to help the situation any. Assuming you haven't totally cannibalized your fuel rail, then you've already got one from the factory.

In all seriousness, you can get a set of four brand new 465cc injectors for $300, or cleaned RX-7 injectors for probably half that. My engine, with 465s and HR code, idles just about perfectly at ~14.5:1 AFR.

 

Ok, allow me to clarify the situation.

I got my 330's from a junkyard turbo probe for like $30. Haven't cleaned them, but I already put them on when the car was NA. Believe it or not, they idled and ran better than the stock injectors once dialed in. So I'm assuming they're ok.

My target is 200 crank hp. At that hp, the DC for the 330's is 96% @ 43.5 psi rail pressure. So I have two options really:

1) Upgrade to injectors bigger than 395 cc to keep the DC down to something sane, like 85%.

2) Keep the 330's and raise static fuel pressure to ~63.5 psi, again to keep the DC down to 85%.

Since I can get an old Jackson Racing RR-FPR for free from miataspeed1point6, I want to see if its possible to use that like the Aeromotive thing that braineack posted. In other words, the JR's job will be to act exactly like the stock factory FPR, only with 63.5 psi pressure instead of 43.5 psi. Is this possible? I don't want to deal with the complication of tuning a fuel map with a rising rate regulator in place, its just too crude for my tastes.

 

Ok, I'm starting to dig... Didn't pick up on the whole "I'm going to raise the static pressure differential to ~50PSI at all times" vibe.

I guess it makes sense, just don't see how you're going to do it with the JR RRFPR. Unless you can find an adjustable 1:1 FPR for less than the cost of a set of cleaned RX-7 injectors...

 

Picture of regulator in question if it helps any.