Fuel rail adaptor

[TominMO]

If you are planning on installing an adjustable fuel pressure regulator, you will need this fuel rail adapter to replace the OEM regulator. Scroll down and notice all the cars it fits, FYI.

Then you can go buy a cheap adjustable regulator like this one.

Here is the Permatex #1 sealant I used on the various threads.

I'll post up a couple of pics tmw of my setup, on my B6 SOHC. This adapter should work for any B-series motor. You might need to re-use the original o-ring or source a new one at McParts. I think that's what I did; it does not seem to come with one. Maybe the o-ring thickness is application-specific?

An adjustable regulator is probably still useful even on an otherwise stock motor, since factories tend to tune slightly lean, for fuel mileage. If you have an AFR (Air/Fuel Ratio) gauge, you can tune for the ideal 14.7 at a steady cruising speed, and get some more power. Stock might be 15.5 or something (higher # = leaner, lower # = richer). No point going lower than 14.7, it's just wasted gas.

Even if you don't have an AFR gauge, you can just bump it up a bit from the stock pressure of (IIRC) 37 psi, to maybe 40, and see if it feels peppier. Then after a while, check the tailpipe for sootiness. If it's too sooty, fuel is wasted, so back the regulator off slightly.

[TominMO]

Here's an upgraded gauge. The standard thread for these seems to be 1/8" NPT, at least for American ones. For the cheap Chinese ones, I'm not sure. I have one in my garage with a broken gauge, so I will take it to the hardware store and find out what thread is in the gauge port.

Comes in black too. And other variants. Click on Marshall Instruments to see them all. Make sure to get 0 - 100 for EFI (part # ending in 100), or 0 - 15 for carby.

Seems to me you could also use one of their 0 - 60 psi oil pressure gauges instead, for non-turbo applications. Readings in psi and same fitting on the back. More readable.

[TominMO]

Note that all the above FPRs are for EFI. Here is one for carbys, to use with a 0 - 15 psi gauge. Thread adapter for gauge.

[FestYboy]

??? Not to poop on your parade, Tom, but a quick search on eBay motors shows entire kits for nearly the same price as the adapter alone.

I give your posts great weight, but usually they come with a good anecdote to back up any directive written.

I'm not afraid to spend $$ if it's a good investment, so who is this the way to go?

[TominMO]

You're not pooping on my parade. I was unaware of the eBay stuff. I typically don't go there since I don't have Paypal. (A friend who does have Paypal bought the rail adapter for me.) Karl/sc72 and I were talking today @ the Hermann, MO meet about adjustable FPRs, and I told him I would do some research on what I had gotten for my Festiva, which was the stuff in post #1. Inexpensive and does the job.

My idea was just to share some knowledge, and you just added to the process, so all good.

It does look like the eBay ones will still need the specific rail adapter anyway, though. The adapter and cheap regulator in post #1 come to ~$39. I did not see any kit on eBay Motors that had the correct Mazda adapter for a gen1 Miata, but maybe I missed it. And any kit would still need the $4 sealant.

I wonder if it would be possible to drill out the stock OEM FPR, the way you can core out a catalytic converter, to turn it into the rail adapter (i.e. just a free flowing pass-through device), and then just buy the aftermarket regulator you want. I have several stock regulators that fell into my pocket at the JYs.....

[FestYboy]

I can see that as an attainable solution.

I did see several of the kits had an adapter that would fit multiple mounting points, so the only question would be the diameter of the o-ring flange, and I don't see Mazda using too many different sizes in that area.

[TominMO]

I can see that as an attainable solution.

I did see several of the kits had an adapter that would fit multiple mounting points, so the only question would be the diameter of the o-ring flange, and I don't see Mazda using too many different sizes in that area.

Looking at those eBay kits again, I saw some where the universal adapter might work, whereas I know mine does work. The ones I saw earlier seemed to have the adapter sitting flat on the table, which meant they had no part that actually fit into the rail. But I could have been wrong.

These adjustable regulators are super-simple machines. The only things that can really go out are the gasket and the gauge. I think I will take my broken-gauge regulator apart and look at the gasket. Do you know if anyone makes replacement gaskets for these? Or do we just fab them up ourselves out of gasket paper?

[FestYboy]

The gasket is also the diaphragm, so it's made of neoprene, and there's an aluminum plug that sits in the middle that acts like spring seat on one side and a plunger to regulate the fuel on the other.