RTEC / SplitSecond fuel computer

If you need some further help or more information
just send an e-mail to Roger Gerl

For the installation just follow the steps given in the instructions and you'll be fine. Of course, always disconnect the battery before you start to do any work on the car !

The job is pretty easy to do ... even without much understanding of what is going on under the hood. The procedure is simple, as the stock MAS must be unconnected and unbolted and the new MAF is just placed into the same position. Due to the round outlet of the MAF the stock rubber intake part (the stock MAS is oval) may need to be made a little bit smoother with the help of the silicone spray.

Here the stock MAS with the K&N FIPK adapter mounted to the inlet. Note the honeycomb and the restrictive paths for the air.

Here the view into the SplitSecond MAF from the rear with the new filter already attached to the front.

Usually, the ARC2-GP kit comes with a large filter and a MAF adapter but I had a good large Blitz SUS Power Filter left over from the VPC plans. Here the picture shows the stainless steel filter already mounted to the MAF with everything in place.

Originally, the SUS came with an adapter for the VPC and the diameter was definitely too large. But I only had to cut the piping welded to the Blitz plate and to drill four holes into it that lined up with the MAF. I also made a small rubber gasket as the plate was a little bent from the welder doing a "hot job".

The next step includes the wiring of the MAF to the ARC. The provided harness (good quality !) is cut in two half's (4 wires) and it can easily be routed through the grommet in the firewall. The splices and necessary connectors comes with the kit (some spares is always useful) and makes it easy to connect the wires together.

This is the wiring diagram for the connection on a 1st gen 3S car. The same diagram for the 2nd gen cars is also included in the kit. The drawing also shows the connection of the ARM1 A/F LED meter to one of the O2 sensor wires. This type of wiring allows you to reinstall the stock MAS within minutes and disabling the ARC by simply disconnecting the Gray and Violet wire. In my point of view, also the Tan wire should be disconnected as it provides a constant voltage to the ECU. To be honest, who wants to disable it ??

The ARC has two harnesses, one for the connection to the MAF and the other with the wires leading to the ECU harness behind the panel next to the drivers right foot. As already mentioned, the installation is not complicated and just make sure you attach the ARC wires to the correct wires from the ECU.

Note : The ECU harness has several white wires on the middle connector and two of them are the O2 sensors. Connect the orange ARM1 wire either to one of the two O2 sensors.

The installation of the ARC2 box is simple but make sure to find a good place for it. It is pretty large with the harnesses are coming out of its back. One of the best places is the armrest box and I mounted it the same way as George Kuo did in his Stealth (pictures below)

The ARM1 box comes with velcro tape and a good place is just upon the steering column. The harness simply goes in between the the gaps of the plastic parts around the dash. Please note, the LEDs are sweeping around when the ECU tries to get the mixture on a stoichometric level. Over a longer period, it is not necessary to look at it the whole time. It is necessary for tuning in as well as for controlling the behavior. I dimmed it all the time and will probably dim it more as the LEDs are pretty bright (at least the blue ones)

Important TPS note :
The Accel function is activated when the ARC sees a TPS voltage below 0.5V. On my car the setting was at 0.66V and it is usually not below 0.6V. To make the ARC act properly, you may have to control your current setting with a voltmeter. To adjust the TPS just unscrew the bolts holding it to the TB and slowly adjust it anti-clockwise. The new reading should be around 0.46V. This new setting has no side effects for the ECU but the ARC is needing it.

After the installation is done, just check out everything once again before you reconnect the battery !

As the title already says, the installation is done without changing the injectors. But we all know that the stock fuel system is as its end above stock boost levels and larger injectors are mandatory. But the MAF modification can be done easily without the injectors and the setting range of the ARC covers the stock ones too.

The following section describes in short terms what the different knobs on the ARC are doing :

*Low*	*Mid*	*High*	*Accel*
Richen or leans the mixture with a fix amount over the whole range.	Richen or leans the mixture in the mid flow-range.	Richen or leans the mixture at high airflow.	Adjusts the idle setting. It is activated by the ARC when the TPS voltage falls below 0.5 volts.

Of course, each owner has it's own goal on the fuel side. I for myself need a good driveabilty in any season with temperatures between 5 - 100°F as well as Porsche killing power on demand. Therefore, a good mileage combined with great low, mid and high end power is the goal I want to achieve.

If you are running the stock injectors, the printed start values for the ARC are way off as they point to 550cc injectors. At the beginning the tune-in of the ARC was not easy as turning the Low up 2% needed to change the Accel. Also after finding the Mid too low, increasing it caused to restart with the settings for Low and Accel. The High then was necessary to tune in for a proper amount of WOT fuel delivery.

The following section shows combined logs from the TMO datalogger before and after the ARC2 installation :

The first picture shows one of the first logs the car runned smoothly. Check out the area with the pink (stock) and light blue lines (injector time in milliseconds) as well as the green (stock) and dark red lines (knock amount).

Step 1: Looking at the knock area (green and dark red) you can see that dark red line (new) shows much more knock compared to the stock fuel setting. The injector times above shows the cause for this as the light blue line is much lower and represents about 78% IDC at max while the stock fuel system is at 100% around 14.5psi. Also note the steepness or rising rate of the injector time as the light blue line is flatter than the original pink one. Interestingly, the car already runs RICH as the lines below the knock are represents the O2 sensor and shows healthy 0.9 volts. BUT knock was there !! I just don't know how one could find this out without the datalogger software !

The following log was again the old one and the new with changed ARC settings combined :

Step 2: After consulting GT PRO and SplitSecond I changed the settings to the suggested ones and tuned the High level at first to get rid of the knock. As you can see the result shows that there is stil lthe same amount of knock but later in the rpm. Also the injector times are showing almost the same values but overall, the injectors were less maxed out. Also the timing (the lowest two lines) was more advanced afterwards (red line) as the ARC gives the ECU constant low values (like at sea-level) and therefore the ECU wants to advance it a little bit more. The O2 sensor curve show the same high values as it did before the ARC.

To this point I was able to tune in the ARC properly and the car runned as good as usual. Of course, a little fine tuning was always necessary as the step into the area where the Accel works should be smooth. Please note, all these runs where made with 98 ROZ (93 RON) fuel, without water injection and no octane boosters boosting up to 14.5 psi.

The last log shows the final tuning and a boost that peaked at 1.08kg/cm2 (15.4psi) :

Step 3: Rising boost about 1 psi to 15.4 psi resultet in a bit more power and I increased the High value by another 2%. The result was a more richer mixture at WOT and a noticeable gain in the midrange. This is proven by the datalogger when you look at the combined pink (stock) and light blue line. When shifting into 2nd gear, the injector time rises quicker and reaches the peak earlier than with stock. The same, but not that extreme, can be found after shifting in third.

The bad thing here was, that during a run I hit fuel cut ! Of course, I had the logger switched off then and therefore no record of this behavior. Also I don't like it very much and therefore I was not willing to do the run again. The solution was just to crank down the high level at least 2% and FC never appeared again.

Conclusion, Results (stock 360cc injectors)

The car was not on the dyno as I have only 720cc injectors ready and I wnated to do a back to back comparison between the stock and only a little bigger ones. But I never got them as one promised me.

Anyways, after driving the car around for some weeks now, my first aim, good mileage, was proven by 28mpg during a long and easy highway run. With my normal driving style and city traffic, the result was around 24mpg. This because I managed to get a good stoich. mixture during part throttle, cruising and idle. Good and healthy :) Regarding the more power, the mid band is improved as I really feel a better response after shifting. The top end seems to be the same. My current settings for the stock systems are :

Low	+ 4%	+6% in winter
Med	- 16%	depends on turbo size
High	+ 16%	depends on WI activation
Accel	+ 2 %	(1 click from 0)

Fuel config : 360cc, stock fuel pump, 13g turbos

Attention : Split Second changed the settings during their revisions. This is for Version 0.x

Definitely, the ARC2-GP is much easier to install and to be tuned in as the HKS VPC/GCC. With the comparable price and no need for any specific program, the ARC is a very good way to improve the fuel system on our cars. But again, my tests showed that the injectors are totally maxed out and fuel cut appears earlier when increasing the high value for more fuel at the top end. Therefore, larger injectors are a MUST and I'd go for the 550cc for the real power. It is also possible to get a 6-pack of the DSM 440cc but this is the poor mans solution as in a few months you may want to have more power anyways (no question if you have them anyways). After installing the new injectors, of course the ARC must be tuned in again. But only the Low for the overall amount of fuel and the high for the rich condition at the top. If you upgrade the fuel system just don't forget to install a better fuel pump too.

My next step is to install the RC 720cc injectors sitting around and I wonder what then will be possible :)