Lexus/Riemer Air/Fuel Upgrade For 7MGTE
By Rob Carlile

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I Introduction

For the Toyota Supra Turbo MK III, there are a number of steps to take to increase the performance of the car. To use the HKS scheme of upgrades, by Stages, the first two stages are to eliminate the restrictions of the stock intake and exhaust. Stage 3 is the addition of a boost controller, either manual or (preferred) the electronic boost controller. With these mods, and the boost set to 11-12 psi, the car should make 285 hp according to HKS.

My 1991 Supra Turbo, with an RSR 70mm exhaust, K&N FIPK air intake and GReddy PRofec electronic boost controller was at an equivalent mod level. When I took my car to the dyno, I had the boost set at 11.75 psi and my car made 242 hp at the rear wheels. See Graph 1 in Section 6. Using the 20% loss factor cited by DynoJet for our cars, which includes a loss factor through the Independent Rear Suspension, this would put my car at about 302 at the crank. The car felt plenty strong, and I thought, "Well, this is good. I am satisfied". Ha!

It wasn't so much that I was having a Tim Allen attack and craved more power. It was just that that damn fuel cut off (FCO) was starting to become annoying. The FCO is a built in safe guard in the Toyota Computer Control System (TCCS). Whenever the computer sees air flow readings higher than some internal value it cuts the fuel supply for a second or so and issues a code 34 : Turbo Pressure too high. It assumes you have a high boost problem because of the amount of air flow it sees.

IMHO, it's a good thing to have an FCO, I just felt it was set at the wrong value for me. The thing about it was, with the stock CT-26 turbo, things really started happening at about 12 psi. The turbo starts to get into its own about here and really takes off to about 14-15 psi. This, I knew from my experiences with my '89 turbo on which I had a SuperChips upgrade installed. It really kicked ass up in the 12 to 14 psi range. So, I kept trying to get as close to the fuel cut as possible without actually hitting it. Easy to do on a one day test, but with all the changes in the weather and atmospheric pressure and density it had to be fiddled with every few days to be able to run right up to the FCO. Some days I could run .85 bar and other days I could not. Heavy air, light air, this all affected the boost related FCO.

So, the next step up for me was a fuel upgrade to supply more fuel and some way to raise the FCO. HKS actually says that an intercooler is the next step, but for me, I don't think it is really necessary at this stage. It makes a greater contribution under continuous high boost operation. For me, boosting up occasionally on the street, my stock intercooler has plenty of time to cool off between boost-ups. The fuel upgrade is a more necessary item and will yield a much higher bang for the buck.

HKS has two stages of fuel upgrade, the PFC F-CON, the programmed fuel computer system, and Vein Pressure Converter (VPC). The FCON is a computer which piggy-backs on the stock system and modifies the injector pulse as computed by the stock TCCS computer. It comes with a fuel cut defender which raises the FCO. It does not, however, provide the larger injectors needed to supply the increased fuel demand above 14 or 15 psi. The VPC replaces the stock Air Flow Meter, which is restrictive at higher flow rates, with a system that is less restrictive and will flow more air at the upper rev range. It comes with another computer which allows adjustment to the air/fuel ratios for various conditions, like idle, entire curve, and throttle response.

Well, if I wanted to get past the fuel cut I would need an FCON, about $1,000 US, which comes with an FCD. Then, if I wanted to further upgrade and maybe even get the sport turbo, I would need the VPC, another $1,000 or so. And with a bigger turbo, I would need the 550 cc injector and PROM kit, about $1,500. About $3,500 by the time I was done, and I would still be wanting the sport turbo and intercooler.

In researching all this, I came across an interesting alternative. Reg Riemer, president of SONIC, the Canadian Supra club, and tuner extraordinaire for the SONIC One-Lap Mk IV developed a system to replace the stock air metering system with a larger unit from a Lexus V-8. It would use larger injectors to balance the larger air flow meter (AFM) and yet use the stock TCCS computer. This would take advantage of the great adaptability of the system and its ability to "learn" the fuel map by experience, and was, I felt an elegantly simple solution to the whole engineering exercise. At the time I was looking into all this, his 7M-GTE (installed in a MK II) was making 340 hp and over 400 ft-lbs torque, at the rear wheels. (425hp & 500 ft-lbs at the crank) This was with, basically, my setup, the Lexus upgrade and an HKS sport Turbo. This was pretty serious for so few mods. I was impressed, and I knew I had found my upgrade path!

As part of this upgrade, I decided to install an HKS 75mm downpipe to complete the breathing mods to the car. I also decided to add HKS Exhaust Gas Temperature (EGT) and Boost gauges, both peak hold/warning meters. These were installed in the glove box and their peak hold functions would allow a closer scrutiny of the peak values attained under hard acceleration, when it would be imprudent to be looking anywhere but the road ahead. The EGT in particular, is very important, as too high a temperature would result in damage to the engine.

The downpipe came in early, along with the gauges, so I had them installed and re-dyno'ed the car. This time it made 255 hp at the rear wheels, or about 318 hp at the crank. See Graph 2 in Section 6. The car actually felt a lot stronger than this modest increase would indicate. It spooled up a lot sooner and seemed to be even more eager to run than before. I was anxious to get to the rest of the mod.

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II Description of upgrade and its parts

The gist of the system is to replace the AFM with one from a Lexus 4.0 litre V-8, which flows about 25% more air than the stock unit and to replace the stock 440 cc injectors with 550 cc injectors, a comparable 25% increase in flow rates. The larger AFM and injectors pretty much even each other out and the difference in the individual engines can be tuned out with the custom air screw and adjustable fuel pressure regulator.

Left: Side View of new AFM.

Right: Old and new AFMs.

Two more views of the AFM body showing relative sizes


Two more views of the AFM body. Note the honeycomb on the one end. This sets up the Karman vortex for the sensor to read to determine the airflow. If it is damaged at all, the meter won't read correctly.

The custom air screw allows adjustment of the amount of air going through the unmetered chamber of the AFM. Reg designed a special screw for our application which is longer than the stock screw and allows some fine tuning for fuel cut and idle setting. The stock AFM electronics module is retained and mounts into the new AFM with no modifications required.

Left: Bottom of AFM. Custom air adjustment screw can be seen.

Right: Close-up of adjustment screw.

Left: Close up of Custom Air Adjustment Screw

Right: End view of AFM. Air screw can be seen in smaller chamber.

The other piece of the puzzle is an adjustable fuel regulator to allow fine tuning of the injectors. Raising the pressure richens up the mixture and lowering it will lean out the mixture.

The adjustable fuel pressure regulator. It was custom built using a stock FPR and a machined upper housing with adjustment screw. It is a drop in replacement for the stock non-adjustable unit.

Left: the 550 cc injectors and their harnesses as received from RC Engineering.

Right: Closeup of one of the injectors.

For more information on the TCCS system and theory of operation, along with a complete technical discussion of the Lexus upgrade, see Reg's excellent article at the Sonic FTP site.

III Installation of the Kit

Installation of the system was fairly straightforward. I was quite familiar with removing the AFM and all the intake plumbing up to the throttle body. This was, however, as far as I had been previously. To install the new injectors, I needed to remove the fuel rail.

This proved to be a lot easier than I had first anticipated. To get to the fuel rail, I removed the EGR, throttle body, ISC valve, pulsation damper and cold start injector connection to the fuel rail. Having removed all that, the three bolts that hold the fuel rail to the head were now easy to get to. I removed them and the fuel rail was free. The injectors are a slip fit into cavities in the fuel rail and are sealed with an O-ring. I gently removed the old ones, twisting or rotating them while I pulled out and they came right out. I then installed the new injectors.

One important point here. When installing injectors into the fuel rail, always lube the O-rings with Lithium grease or, in a pinch, fuel itself. The O-rings are susceptible to being torn or nicked if they are dry. You may not even realize that one was damaged upon installation, but it will eventually show up as a leak in the pressurized system.

THIS IS VERY IMPORTANT. A fuel leak is the most dangerous problem you can have in an automobile. Other problems can cause the car to not run right or not handle properly. A fuel leak can burn your car right to the ground. (Not to mention you could be injured) Lubing the O-rings might seem like a minor detail.. it IS a detail, but IT'S NOT MINOR.

The new adjustable fuel pressure regulator was installed in place of the stock one. It is made from a stock pressure regulator with a new adjustable spring load in the top section, so it is a perfect replacement. At this point, I was finished with the fuel rail so I reinstalled it using new rubber washers where the injectors slip into the head. Probably not necessary, but they were $12 for the set of six and I sure didn't want to fool with it again later. Cheap insurance.

I then reconnected the piping to the adjustable FPR and reinstalled the pulsation damper and its hard piping. The pulsation damper is the inlet point on the rail for the fuel and the FPR is the exit point for extra fuel and pressure than is bypassed by the FPR. I was also ready to reconnect the piping for the cold start injector at this point.

The 550 cc injectors I used were from RC Engineering, and from initial conversations with Reg, I knew they were not interchangeable with the stock injectors with respect to the electrical connection. Reg told me that the injectors would not mate to the stock harness and that I should cut the old harnesses off the car and solder in the new ones I got from RC Engineering.

Well, I thought, this would make it very hard to refit the stock injectors if I wanted to go back to stock, so I decided that instead of soldering, I would use a sealed automotive connector. Then I could make harnesses for both sets of injectors and easily swap back and forth between them if I so wanted. I went through a lot of industrial automotive connector catalogs at work and finally selected a sealed connector by Amp for use here. The connectors (male and female sides) are shown below. The connectors have little rubber O-rings that go around the wires and seal the backs of the connectors where the wires enter the connector. This would assure a good tight seal for my connections.

These are all the parts that make up the connectors for the fuel injectors. The shell and contacts on the left were installed on the engine harness side and the shell and contacts on the right were built into the harness going from the injector to the engine harness.

I built up harness assemblies for the injectors and used braided sleeving over the wires for abrasion resistance and adhesive backed shrink tubing over the junctions of wire to connector to further waterproof the assemblies. After making up the six harnesses and installing the six mating connectors on the engine harness side, I was ready to plug them in and get on with putting it back together.

This is the one of the harnesses I built that connects the injector to the engine harness. The injector plugs in on the right hand connector and the left hand side plugs into the engine harness.

Left: Close-up of end mating to engine harness.

Right: Close-up of end mating to injector.

Left: Close-up of injector harnesses.

Right: another view, this time showing the adjustable fuel pressure regulator

The next major step was to swap out AFMs. This was relatively straightforward. The black plastic AFM sensor module must be removed from the old system and reinstalled in the new one. There was one O-ring around one of the posts on the sensor module which was held on to the AFM body by three screws

The meter part of the AFM assembly. This is the stock unit I removed from the stock AFM assembly.

The bracket that attaches the AFM to the fender of the car and the bracket for the wiring harness for the AFM itself must also be transplanted from the stock AFM.

I had previously measured the range of adjustment of the Lexus AFM The numbers are in terms of how deep below the surface of the AFM the screw head is. The minimum depth was 0.385 in. and the max depth was 0.607 in. for a range of 0.445 and a convenient scale upon which to track adjustments. With the screw adjusted all the way in, i.e., max depth, this would give the least amount of airflow, with the maximum amount of air flow being obtained at the minimum adjustment. Since this air screw adjustment directly affects the FCO, this equates to:

Low FCO = max depth = 0.607 in

High FCO = min depth = 0.385 in

I set the FCO at the minimum value and reinstalled all the rest of the plumbing. I wanted to start at the minimum setting because I did not know what it was and thought I'd be conservative.

The car was now ready to fire up and test/setup.

IV Testing/Problems Encountered

I had several problems with setting the car up, all of which were my fault, and were not in any way related to the upgrade itself, only my installation.

The first problem I had was that I could not get the FPR to raise the fuel pressure above 23 or 24 psi, stock being about 30. This was at idle with the vacuum hose connected. I was not familiar with the adjustment on the FPR and being the cautious sort that I am, I was too gentle with it at first, fearing I might break it. It turns out that where I thought the end of the adjustment was, was actually the beginning of it, and after a conversation with Reg, I decided to turn the adjustment screw a little harder (clockwise). Now it was starting to adjust! Reg had told me that his car was set to about 7 psi over stock so I set mine to 37 psi (at idle with vacuum hose attached).

My other problem, which was a real dumb oversight on my part, was that the two hose clamps holding the rubber hose connecting the "3000" pipe to the throttle body were loose, allowing metered air to escape under boost, which caused the car to run real rich under boost. I got enough black smoke out the rear that I looked like a mosquito fogging rig from South Fla. (Made $47 fogging for mosquitoes in two neighborhoods that day) After I got my band clamps tight, the car started running much better. Now I could think about adjusting the FPR and the AFM screw to optimize my mixture.

Reg told me that the car would idle best with the AFM screw all the way in, so this is where I started. Using the Montigney V/F meter as a guide, I finally settled on AFM screw at .607 (all the way in) and the fuel pressure set to about 28 psi (idle with vacuum). This is about 2 psi under stock. The car, however had a crappy idle, and I could not seem to tweak it right. I was sure, however, that I still had done something wrong, so for three days I kept looking at every vacuum hose, connector and widget I had touched to see if I could find the culprit.

After fogging the neighborhood for most that first day, I decided that it would not hurt to put in new plugs. I also found that the #6 plug wire had some insulation missing, so new wires were also a good idea. I ordered both (all factory Toyoto parts)and put them in when they arrived. Maybe this was my idling problem. But alas, it did not help. If anything, it was worse.

I had not changed the gaskets for the throttle body or the ISC valve so I decided to do this as I was running out of ideas. Well, it turned out the ISC valve gasket was leaking a little, so that when I put the car back together with new gaskets and tested it, the V/F meter showed a change in mixture. Well, at least I had affected it, so this was good. The car still would not idle smoothly, but now I was pretty sure it was somewhere in the ignition system.

Well, with the plugs and wires, I had managed to shoot myself in the foot again. The plugs are supposed to be pregapped, so I didn't check them, and just installed them. I had also installed the new plug wires at this time. The dyno runs I did the next day were with this setup, and a close examination of the curves indicated I still had ignition problems. After the gasket replacement, I thought about it some more and finally decided that I still had an ignition problem. I pulled the plugs, one at a time and checked the gaps. #3 was about .018 in. , while the rest were .025 to .030! Pregapped my ass. I regapped them to .031 and reinstalled them. I also found that the #2 plug boot had not been fully inserted into the hole and the contact was not fully snapped onto the plug and that the #3 plug wire was not fully engaged into the coil. Because the plug wires are all held in the looms when connected to the coils, this had restricted my access to the plugs. This made it hard to see what I was doing and to get the #2 boot fully inserted. I finally removed the all wires from the loom and put them back in one by one. When I put it back together this time and fired it up, the idle was much better. Now I could go back to the AFM screw and the FPR for my final adjustments.

I eventually settled on AFM screw at 0.385 (all the way out) and the fuel pressure set to 28 psi. With the system adjusted like this, the car idles smoothly and in the green on the VF meter. In fact, the VF readings look like they did before the mod. This was my tuning target, to make the car run the same, V/F-wise, as before the mod.

With it setup like this, I have no idea where my FCO is. My boost is set at 1.0 bar, and I have not hit it once since getting it tweaked in right. My peak hold boost gauge shows max boost during shifts is about 1.3 bar (19.1 psi) so it must be above this.

I also kept a close eye on my EGT gauge. The sensor is located after the turbo in the elbow before the downpipe, next to the O2 sensor. The highest EGT I have seen is 1400 F. Reg says my danger zone begins at about 1450 F, and that my readings are good. A note here about the location. A better location for the EGT sensor is before the turbo, which will read about 100 degrees F higher than after the turbo. It was not feasible to locate it here on my application, so the elbow was chosen as next best. The HKS sport turbo provides a port for mounting the sensor before the turbo, so eventually, I'll get it located there.

V Results and conclusions:

The biggest single advantage of the upgrade is the elimination of the FCO along with the provision for enough fuel to run the boost at 1.0 bar (14.7 psi) and above. With the stock system, 14-15 psi is considered the maximum amount of flow the fuel system can handle. With this upgrade, it's nowhere near the limit. This yields a system that has a lot of headroom to grow. In addition, a very health dose of torque was added: 64 ft-lbs at the rear wheel (approx 80 at the crank). The increase in torque is what makes the car feel so much stronger.

Graph 1 : RSR Exhaust, K&N FIPK intake and GReddy PRofec set to .8 bar (11.75 psi)

Graph 2 :
Green/Black lines : RSR Exhaust, K&N FIPK intake, HKS downpipe and GReddy PRofec set to .8 bar (11.75 psi)
Blue lines : RSR Exhaust, K&N FIPK intake, HKS downpipe, Lexus upgrade and GReddy PRofec set to 1.0 bar (14.7 psi)

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