To fine tune fuel at high load I used APEXi SAFC, again most popular among turbo junkies fuel piggy-back computer. It intercepted AFM signal, converted it according to user's wish and sent converted signal to ECU. If your intention is to run leaner at certain rpm range you have to feed ECU with disinformation, in this case you have to tell ECU that engine is consuming less air, SAFC did it perfectly. Now big question was how far you can lean out. Optimal AF ratio for moderate boost is around 12.5, and less for higher boost on pump fuel. We have to run as rich as 11.0 - 11.5 for additional in-cylinder cooling to prevent detonation. I am talking here stock ECU scenario, programmable EMS is completely different case. Best solution to fine tune motor is on dyno with WB O2 sensor, but 4-5 years back there were no such places in my country and I had to rely on myself and helpful info from SOGI list. WB sensors even 4-5 years back were very expensive and I purchased my first WB O2 in 2003 when price dropped to more affordable 900 bucks. It was FJO with datalogging capability, display was plain ugly and would look more in place on Soviet submarine, rather than on the car's dashboard. Though it was professional quality tool and I was very happy to own it. Prior to affordable WB era I used only EGT gauge (always kept pre-turbo EGT less than 830 - 850C) and KnockLink.
It was possible to make around 400-450 whp on Lexus/Riemer setup, real hardcore guys used HKS VPC to get rid of stock AFM in favor of speed-density. From today's point of view VPC was inflexible and crude device, for such simple things like upgrading injectors user had to buy new chip from HKS. Time has changed and today for the quarter of VPC setup price you can buy something like MAFT which is more flexible than VPC. I don't mean it was impossible to make big numbers, some VPC equipped motors produced up to 1000hp.
Ultimate choice if you are serious about power and want complete control over your engine is to go standalone engine management. I began considering this when I realized few years back that stock ECU sucks. Most of all I did not like it when car was becoming sluggish after 2-3 full boost pulls. My Supra felt very strong when I drove it away from the garage and warmed it up. After flooring it few times she suddenly felt like loosing at least 100 hp, building boost too slow, it was clear stock ECU was pulling timing for no reason. I was absolutely certain engine did not detonate, I had good intercooler, cooling system, meth/water injection, rewired knock sensors, etc. I was fed up playing with stock ECU and piggybacks and wanted something that offered full control over my engine.
There was no plug'n'play programmable EMS for the 7MGTE on the market 3-4 years ago, I started gathering information from the Web in attempt to choose what would work better for me. I considered many names, like Electromotive, Motec, FJO, Link, Haltech, Autronics, etc. Top priority for me was user support availability and open information about EMS. In other words - I wanted to read user's manual before buying actual thing. My knowledge about electronics and EFI was quite limited and I wanted to be sure I would manage to install and tune EMS. If you ever browsed web sites of EMS makers I named above you know that info given there is close to zero. Only one maker was appealing to me - SDS. It was mainly due to very good explanation of basic EFI theory, how SDS EMS works and all aspects of it's tuning. Everything is written in plain English and I would still recommend this reading to the beginners. I decided to buy SDS EMS, not because I particularly liked it, but because I knew in advance how to install and tune it.
Then in 2003 AEM announced their intention to produce plug'n'play EMS for 7MGTE. Before that I was not interested at all in AEM, though I knew some people were already running Honda box on their 7M. I downloaded AEM Pro which is freely available on AEM forums and after some reading realized I finally found what I was looking for. It was not as simple as SDS, but I had enough time to learn it. In spring 2004 AEM released their first box for 7M, nearly 1 year after they actually announced their intention to do this. At he same time I placed my order with old Suprasport on complete AEM package, but due to some reasons received all parts only in October 2004. Then I had to go back to the ship and finally I installed AEM EMS in August 2005. I used calibration file downloaded from AEM forums, where users share their knowledge, this is another aspect I like about AEM.
I expected to have problems after swapping AEM in place of stock ECU, but motor started right away and I felt like the happiest man on Earth. Term "plug'n'pay" does not mean you can plug AEM EMS into the stock harness and drive away. It means AEM EMS works with stock sensors, but since every car is different and all of them are heavily modified owner has to tune EMS. Calibration file I used was driveable for me and I remember I filled 30 ltrs of gas to my tank and after about 60 km tank was empty again. This is 4.7 mpg. Ignition map was overly conservative in boosted area, throttle acceleration settings did not suit my 76 mm TB, etc. Learning curve was pretty slow for me, it took about 1.5-2 months to make my Supra behave like any other civilized stock car. Tuning is nowhere close to finish, programmable EMS is perfect for people who like tweaking their motors, it will keep you busy for long, long time.
I think installing AEM EMS is the best thing I have done to my car. It can help to release full potential of engine's mechanical modification. Despite seemingly high sticker price of EMS in the end it is cheaper than heaps of piggyback devices. Another factor, sometimes forgotten - it is far safer then stock ECU combined with piggybacks. Here are just few very usable functions offered by AEM EMS:
- secondary injectors control
- various sensors wizards, basically you can use any sensor included in the list
- VTEC control
- secondary rev limiter (2-step)
- anti-lag
- 512k of internal datalogging memory
- shift light vs. gear
- boost control (boost control solenoid valve sold separately)
- O2 feedback (cruise, boost - you choose)
- user defined knock control
- high EGT fuel enrichment (4 channels, EGT sensors sold separately)
- various fuel and ignition trims including user defined trims
- WOT gears change on manual transmission
- nitrous control
- automatic transmission control
- fuel pumps, electric fan and many more drivers
- traction control
- etc.
I do not mean to say other similarly advanced EMS can't handle it, AEM wins here simply because all info is free and open for users (and potential buyers as well). Try to change 2.5 bar MAP sensor to 3.5 bar on APEXi Power FC. Wish you luck, you have to send ECU to the dealer. With AEM this is matter of few mouse clicks.
Tuning fuel table of AEM is piece of cake. I did not use automapping, just datalog my normal in city driving, cruising and WOT runs and tune map afterwards. Off-boost area is tuned cell by cell, upper boosted part of the table uses boost compensation correction table, this is so called hybrid fuel map.
Tuning ignition map
is more of the challenge and can't be done properly without dyno or at least
accelerometer. Engine's spark advance requirements depend on too many
parameters, like rpm, load, AFR, air humidity, coolant and intake air
temperatures, fuel in use, shape of combustion chamber, etc. The point here to find optimal spark advance angle which will put
engine's PPP (peak pressure position) at around 15 degrees after TDC. This is
how maximum torque achieved. Too early and you either loose torque because
combustion starts too early before TDC which is counterproductive, or even worse - engine
detonate. Too retarded spark advance - and peak pressure will be too low and too
late. Illustration on the left explains it better than words. I set my timing
table as per recommendations from AEM tuning guide, can be
found here Widely accepted technique to tune ignition timing is to increase it in small increments till you see the torque is still rising. When with further increase of timing you gain no torque or loose it - back off one or two degrees, this is MBT (Minimum Best Torque timing) for your engine. By backing off degree or two you will achieve some safety margin, though maybe sacrifice few horsepower.