Fuel System
Fuel System - Quick Access:
When I reached this point in modding OldSchool Supra, power levels had plateaued due to having reached the limitations of the stock Toyota fuel system & engine control. Toyota put into its "Toyota Computer Control System" [TCCS], a failsafe known as "Fuel Cut Off" [FCO] to protect the engine from abnormal (read: high) boost levels. On a stock engine, this is a very good thing, since the TCCS fuel map only extends to where FCO exists. But, alas! This certainly got in the way, when the goal was to triple boost output, all in the name of making more POWER! All thanks to FCO, my fuel system upgrades began to take shape.
The upgrades found throughout this section, not only addressed FCO, but ultimately addressed building a reliable foundation upon which to base future modifications. Descriptions & pics of the F-Con, VPC, GCC, RC 550 cc/min injectors, & Walbro fuel pump give you an idea of the path I took to an upgraded fuel system. Please note that any info regarding the Walbro fuel pump hasn't been posted yet...but it will be at some point.
This is the HKS fuel computer that rides piggyback to Toyota's Electronic Control Unit [ECU].
A component of HKS' Stage Five, this device uses a MAP sensor [basicly a pressure sensor] to measure boost, altering
fuel curve based on engine demand. The stock ECU contains a fuel map that tops out in the 11.8 to 12.3psi range of boost. The
F-Con's sole purpose is to provide an engine demand-based fuel map, while removing this limitation. Whether or not the F-Con
is additive, or completely replaces the fuel map has been the subject of much debate, but my real world experience shows
that it supplants the OEM fuel map from bottom to top. Regardless of detailed function, it serves the purpose of providing
more fuel to the engine, allowing higher boost levels to be run safely.
The unit is programmable via an internal pot-switch, & also utilizes changeable e-proms
to account for varying fuel injector sizes.
This is the HKS fuel meter that is a direct replacement for the stock Toyota Air Flow Meter [AFM].
A component of HKS' Stage Six, this device eliminates the restriction to air flow inherent to the original Toyota AFM. Instead of using the Karmann-Vortex method of measuring incoming air, the VPC uses Speed-Density- which assesses input from both MAP & temp sensors to calculate air flow into the engine, then provides the resultant signal to the ECU so that fuel requirements can be properly matched. A much higher air flow into the engine is achieved, & in conjunction with the F-Con, provides a means to run high boost, safely. The VPC has a set of knobs which allow minor adjustments to compensate for between-engine differences, while also including an 'Option-out' knob, which serves as a means to adjust the F-Con's settings in-lieu of the F-Con's pot switch.
Due to the prevalence of used VPCs on the market, many have asked me how to hardwire the VPC into the stock wiring
harness to eschew the purchase of the HKS harness, which can run upwards of $150 US. I've compiled a diagram showing
how this can be done...just follow the link.
This is the HKS Graphic Control Computer that allows fine
tuning of the fuel injection pulse duration at 5 RPM points.
The GCC is essentially a fine-tuning mechanism for the VPC/F-Con, providing adjustment to the air fuel map based on five different RPM ranges. Between points of adjustment, the unit interpolates the fuel map, attempting to make the fuel curve as smooth as possible.
The MkIII Supra comes stock with 440cc/min, peak/hold, low impedance fuel injectors. Depending on the guestimates of Brake Specific Fuel consumption [BSFC] one chooses to use, baseline fuel pressures, etc., this -can- equate to a fuel capacity capable of over 400 crank horsepower. Under normal circumstances, this is plenty of fuel for pretty much any stock turbo, or even modified stock turbo MkIII. So why change to larger injectors? Well, a couple of reasons. 1st, I didn't feel comfortable trusting my [then] rebuilt motor to a set of 12 year old injectors. 2nd, if I was going to go to the expense of getting new ones, I figured I may as well get larger ones. Since I already had the F-Con, & was installing a VPC concurrent with the injectors, all that was needed to compensate for the larger output, was a PROM swap in both F-Con/VPC. Besides, I figured the additional 'headroom' would come in handy for that fateful day I'd choose to upgrade from the faithful peashooter [CT-26 turbo].
Well, it all sounds straight forward & easy, but I tell you- my life was much simpler before this decision was made. Once those injectors went in, simply turning up the boost was no longer good enough to call it a day. All of a sudden, the concept of -tuning- became a mantra that I not only had to bite & scratch to learn, but it became a way of life. Instead of going into a long treatise on how implement larger injectors, or how to tune here, at this point, I'll just offer up a few pics, & links to where you can go to get more info. I will say this...tuning fuel injection seems a lot more complicated than jet-swapping on dual carbs back in the day, but it all boils down to the same concept. Get to know the guys at your local Dyno shop really well, & learn the value of tuning by Dyno & wide-band oxygen sensor-equipped Air/Fuel ratio meters.
Click on the RC link to get more info on choosing injectors. Follow Rob C's link to check out how he upgraded to larger injectors by going with the Lexus-Riemer setup.
I took these pics from Rob C's Site.
Thanks, Rob.
An in-progress shot of the injector wiring harness 'project.'
Here's a close-up of injector wiring harness #2.
NOS brand mechanical fuel pressure gauge.
These are the parts you get when you purchase the Walbro GSS315 fuel pump kit.
This is one area of modifying the MkIII that gets a lot of air play, but many defer to the later stages in their modification plans. I vehemently disagree! Why? It all boils down to age. OldSchool Supra was pushing 10 years old when it got its new fuel pump...10 long years of service that the OEM pump had handled just fine; but much too tired to handle the severe duties of elevated boost.
There were several options available when it came time to upgrade:
Here's a table of outputs in gallons/hour derived from
Dave Henry's [now famous] fuel pump tests:
| Fuel pressure | Tired OEM | MkIV Turbo | Cosmo | Walbro |
| 20 PSI | ||||
| 26 PSI | 151.8 | 228.6 | 233.2 | 227.1 |
| 30 PSI | 132.9 | 209.7 | 217.7 | 219.9 |
| 40 PSI | 99.6 | 178.7 | 183.2 | 193.1 |
| 50 PSI | 63.2 | 141.2 | 143.8 | 166.2 |
| 60 PSI | 30.3 | 108.6 | 106.0 | 141.2 |
| 70 PSI | 62.5 | 62.8 | 121.5 | |
| 80 PSI | 79.1 | |||
| 90 PSI |
Up to the point where Dave did the testing, I had already decided on going with the Cosmo pump. This was due to its known ability to support mad power [in the Mazda 3-rotor Wankel], as well as the fact it's manufactured by NipponDenso- long known for reliable components. Unfortunately, at the same time this upgrade made it to the tank, I was also dealing with a [not yet known] malfunctioning fuel pressure regulator. So, the day after this pump went in, it was removed...to be replaced with the Walbro GSS315 255 liter/hour pump. It was this pump swap that brought the bad FPR to light!
Sometimes this modding business can really stretch your patience, not to mention your wallet. Although I got the Walbro for a reasonable ~$150, I was out $285 thanks to the Cosmo pump purchase! Now you know why it's sitting on my For Sale Page. A couple side notes here- 1st, there have been reports of reliability issues with Walbro products. Not many, but enough to give me 2nd thoughts on selling the Cosmo pump, & keeping it as a spare. 2nd, the Walbro is NOISY. I don't care what anyone else has to say about it, the whining drone it puts out is downright annoying.
Performance?
Thus far, after ~2 years of service, the Walbro has been a stalwort performer. So, there are no complaints insofar as its
ability to put forth the fuel. If it weren't for its noise level, I'd probably just leave well enough alone; but when that
day comes for me to install an adjustable fuel pressure regulator, & all of it's commensurate lines & fittings,
rest assured, if I haven't yet sold the Cosmo pump, it's definitely going in! If you're in the market for a fuel pump, &
you're sensitive to noise, keep this in mind. At idle, the 85mm exhaust doesn't cover it up; only the stereo at mid volume
or up makes the noise -go away-.