Starting the new year out with some bang — been driving around on our boosted 500hp FR-S for a couple months now and dealing with one of the nuances of making more and more power — the need for fuel system upgrades and tweaks. Now it’s time to go over what I’ve done to the car, what options I went with, etc.
The Turbo Kit
I was very close to building our own turbo kit for the FR-S — however PRL Motorsports had an option available and as I already have a very good relationship with them I decided to give their kit a try after we had some back and forth. I did make a few tweaks based on what I like to run on turbo vehicles — making it a little custom “VitTuned” off shoot, but the heart of the kit is their work and fabrication.
Before you say you can’t find it on their site — you’re right, you can’t. You can contact them directly, or myself — and I can help you build the package that’s right for your FT86.
Now getting into it– I chose to run a Comp Turbo CT4X-5862 .82 a/r turbocharger on my car. This is quite a bit larger than what most people run (it’s a large 4″ in, 2.5″ out cover — most kit options will have something like a 3″ in and 2″ out cover, which is quite a bit “smaller”). But I knew I was going to shoot for more power — and I just happened to have the turbo sitting on a shelf as well.
Basic fuel system upgrades included a DW300c in tank fuel pump and Deatschwerks 900cc port fuel injectors.
Let’s See Some Power Figures!
OK, enough with the build info — what’s this thing make? I have to say, I was quite impressed with the power output of this motor with this turbo. On 4psi (wastegate pressure) we made roughly 100hp more than stock on 92 octane fuel.
Cranking it up to 12psi running a conservative tune for the 92 octane fuel, we were able to hit just shy of 320whp. Quite a solid power figure considering this was more than 2 times stock power and still running on the stock clutch.
Speaking of the stock clutch — when I tried to crank it up a couple weeks later on E40 (40% ethanol content) it let go. So I put in an ACT 6 puck sprung setup and got back on the dyno with E55 (55% ethanol content). Boy did it make power… 16.5psi made an awesome 450whp, 3 times stock power!
About a week later I came back in with E75 in the tank to push it a bit more. Did it pick some more up? You bet, she put down 485 whp without even breaking a sweat at 18psi (3.2x stock power relatively).
But this is where some of our troubles begin… And no, it’s not the motor. I’m happy to report it is currently running smooth and strong.
Oh The Fuel System Woes — Fuel Return Time!
You got it — at this power level the stock returnless fuel system is complete maxed out. As you can see from the following datalog plot — port injector run at 17ms pulse width — this is beyond even 100% “duty cycle”. Since this is a dead head system, I did not have a fuel pressure sensor mounted yet to monitor the fuel pressure — but one can assume it was about 20-25psi “differential pressure” (actual pressure over the injectors), given the PW the ECU was commanding to hit fuel targets.
So it’s time to build a fuel return.
There are a couple ways and already a couple kits out for the platform — some that I don’t particularly like (because, bluntly — the fitment is complete shit). I chose to build a return the same way I have done it on other platforms. Over the course of troubleshooting the fuel system, I also chose to run a new -6 AN feed line in addition to the -6 AN return line. Here is a rough parts break down of the fittings necessary.
- 3/8″ Straight EFI Hose End
- -6 AN bulkhead fitting for the top of the bucket.
- Two 5/16″ EFI Hose Ends
- -6 AN Male “T” adapter/union
- Three 90 degree -6 AN Hose Ends
- Two Straight -6 AN Hose Ends
- 180 degree -6 AN Hose End
- 20-30 feet of -6 AN Hose
- Aeromotive 1:1 Rising Fuel Pressure Regulator
- VitTuned FPR Blank
The fittings and line were sourced from SummitRacing.com — I used mostly Russell items, with some odd balls dropped in depending on what was in stock (or what I had available already).
I used the stock rails and recommend you do the same (less line and less fittings, better fitment). I had a set of aftermarket rails, they fit terrible, no room to mount the DI computer (which is grounded to the head via the mounting bracket — your car won’t run otherwise), couldn’t clip in one of the injector clips… it was so bad I threw them in the trash.
To give you a verbal description of how the fuel return works — start at the tank. The feed comes out into a 3/8″ EFI fitting and goes into the matching hose end. The feed line then snakes into the engine bay and splits with the T fitting.
The T fitting then splits and one end runs into a 5/16″ EFI hose end into the DI pump. The last out on the T runs into the side of the regulator. Then you start at the next regulator side and feed that end into the port injector rail with the remaining 5/16″ EFI hose end — or in my case (as the pictures show) you run this into your flex fuel sensor, and then into the rail. Same exact concept though. Side note — you can with a fuel return relocate the flex sensor into the return line. I chose not to do this since I already ran the flex sensor with the dead head fuel system and it was “easier” to leave it in the feed line.
The final line — is the return line off the bottom regulator running back into your tank via the bulkhead fitting.
In the cage itself — you do have to replace the stock regulator with a blank to feed all the fuel into the feed line and towards our external regulator — as the following 3 pictures depict.
Now some people might debate this choice of blocking off what is known as the “Venturi” feed in the cage itself — and might be concerned about the in tank siphon from one side of the tank to the other on the FT86 platforms. I have been doing fuel returns this way for years when converting dead head fuel systems — it works, and it works great.
Here’s some facts about the Venturi feed — it is NOT designed to work the in tank siphon. The in tank siphon works like any other siphon — gravity and pressure! Simply put, the pressure in the tank will normalize the fuel level between the two sides. I’m not just saying this — I have been driving the car like this, the siphon works perfectly FINE without the Venturi. What the Venturi is designed to do is create a type of vortex/swirl feed at the inlet to the factory cage — this is designed to create a low pressure area that pulls fuel into the cage and helps keep it full during low fuel level conditions in the tank (and works so-so as anyone that’s ever done any aggressive driving on high powered vehicles can tell you — my dead head fuel systems running 100% OEM cages will starve the pump still). This is an effect you ultimately break the moment you use your return to feed the Venturi — under power the return line flows very little fuel and pressure, whereas the OEM Venturi is fed directly by pressure from the pump! With a Walbro 485 in the tank — I can hit it in boost with 1/4 of a tank and still maintain fuel pressure. Ultimately for someone running aggressively at a track event — a surge tank setup with their fuel return is the way to go (no in tank setup will ever be 100% when it comes to avoiding fuel pump starvation).
So what did all this work net us? Tons of room on the fuel system — at the normal 15psi boost pressure I run day to day, I have a ton of breathing room to push it harder if I want to in the future. Without the return, I was already at 13ms pulsewidth on the port injector, now I’m not even at 10ms.
Maybe more power in the future? We’ll see…