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Fuel System Upgrades- October 2007

An important part of turning up the horsepower knob is adding the fuel to go along with it. The Greddy turbo kit that I installed came with a Vortech fuel pressure riser which is extremely simple and effective for modest power increases, but ill equipped on Miatas when turning up the boost. As much as I wanted to stay at 5psi and the Greddy/Vortech FMU forever, the lure of more power is a strong one, and I decided to address the next item with my car: more fuel and better fuel control.

Since I planned on bumping the boost from 5psi to 10psi I did lots of research on the best fuel modifications for the Miata and called from my experience and what has worked well for me in the past.

The first step was getting my hands on and installing a Walbro 190 high pressure fuel pump. I got the kit from lightning motorsports and it has everything you need for the install.
Walbro fuel pump

After seeing some pretty rusty deck panels, I was happy to find that this one was in good condition.
Miata rear deck panel

For those that haven't seen it, here's what the gas tank and pump assembly mount look like.
Miata gas tank

Ahh, so that's what the inside of a Miata gas tank looks like. At this point, do your best not to drop your iphone in here.


Here's a shot of the fuel pump assembly with the new Walbro in place. Perfect fit! The stock pump is on the right.
Miata fuel pump

After completing the fuel pump, my next task was to get those teeny stock Miata injectors out of there.
Miata fuel injector plugs

Stock Miata fuel rail with injectors and fuel pressure regulator
Miata fuel rail

Since I planned on taking the Greddy/Vortech FMU out of the picture, I needed a good rising rate fuel pressure regulator. I went with this one from Aeromotive (part #13116), which is made for Hondas but bolts to the stock Miata fuel rail. The pics show the fuel pressure gauge mounted in the FPR gauge port, but that setup wouldn't fit. I ended up running the gauge in a separate location.
Aeromotive 13116

Here's a shot of the back of both FPRs. The Aeromotive unit uses an o-ring instead of the protruding piece that the stock FPR uses.
miata fuel pressure regulator

For injectors, I found a good set of Supra 430cc black tops. I had to wire in resistors, but that was no biggie. I replaced the o-rings and rubber isolators while I was in there.
Toyota Supra fuel injectors

Pic of the Aeromotive Fuel Pressure Regulator installed.
Miata Aeromotive Fuel Pressure Regulator

Another FPR pic, and you can see where I installed the fuel pressure gauge.
Autogauge Fuel Pressure Gauge

Lastly, I redid my gauge panel and installed a leftover autometer blinky Air fuel ratio gauge from an old car (until I get a wideband) and Knocksense. The Knocksense unit takes input from a Bosch Knock sensor and can output to an LED warning light and/or datalogger.
Miata dash

I also installed an old Apexi S-AFC that I had from years back. This is where I mount it if I need quick access. Otherwise, it lives in the glovebox. I used a GM 3 Bar Manifold Absolute Pressure sensor since the Miata does not have a true throttle position sensor. It's working great! Click here to read my 1990-1994 Mazda Miata Apexi Super AFC Install Guide
Miata gauges

Driving Impressions
Typically, I never do more than one modification at a time unless absolutely necessary. This one an exception because all of the items above work together in concert to add more fuel. My impressions of these modifications are very good. Under normal driving conditions, the car drives and idles exactly like it did with stock injectors and seems much more responsive than with the previous setup. Fuel economy is better also, as I'm now averaging 32-35mpg with about 60% highway driving. The best thing is now I have the ability to tune. After nailing down my settings I haven't touched them in months and the car drives great under wide open throttle with a nice, safe Air Fuel Ratio. For proof, check out the videos section. :-)

Thanks for reading!

-Tom