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R33 Brain Transplant

Discarding a Nissan R33 GTS25T Skyline's factory ECU and plugging in a programmable replacement...

By Michael Knowling

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In the past, the move to programmable management has meant rewiring the vehicle, farting around with ignition pick-ups and investing many hours - and dollars - to make it all happen. With the increasing number of plug-in aftermarket ECUs, however, the programmable management route is becoming much more appealing.

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Like most (all?) performance oriented Japanese-market cars, the Nissan R33 GTS25T's computer is calibrated to suit Japanese 100-octane fuel - a better brew than anything available at local Aussie pumps. As a result, a danger looming for these cars when sold as second-hand 'grey market' or 'import' cars in countries with lower-octane fuel is detonation, especially if modified with the turbo boost wound up. Short of adding potent octane boosters to the tank at every fill, there are a couple of ways around this for cars without easily-accessed engine management. One is to install an interceptor unit such as a UniChip or fit a completely new management system that allows almost infinite alteration of the fuel and timing maps. These solutions also offer the advantage of removing the Japanese-market 180km/h speed cut and providing tuning flexibility later down the track with any subsequent mods. Furthermore, the move to an all-new aftermarket management system can allow the removal of any airflow meter(s) through the use of MAP load sensing. This can reduce airflow restriction through the intake, if such a restriction exists.

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In this story we'll follow a modified Nissan R33 GTS25T Skyline being kitted with a current series MicroTech LT-12 plug-in replacement computer at Adelaide's RPM Performance Centre. This installation is typical of fitting an aftermarket management system to any factory-injected car.

Baseline Power and Drivability

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Our demo R33 had already been tickled with a big exhaust, recirculating aftermarket blow-off valve, aftermarket air-to-air intercooler, free-flowing Unifilter pod with cold air feed and - finally - a wastegate bleed to deliver up to 13 psi boost. An upgraded clutch had also been installed to take the punishment of the extra power.

The red plot line shows the car was capable of generating an average 178kW at the back wheels in third gear (as measured on a Dyno Dynamics chassis dyno). Boost pressure held between 12.5 and 13 psi, while full load air/fuel ratios ranged from about 12.2 to 11.8:1 at maximum power. This is quite rich, but not to the same degree as many other cars.

Driven on the road, the car performed glitch-free - no hesitations, no 'falling back' to idle, good throttle response and willing enough to pull away from a minimum 1200rpm in top gear. It behaved just as car running standard management should - perfectly.

The MicroTech Plug-In Conversion

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Before tackling any wiring work, Tim from RPM discarded the factory hot-wire airflow meter and whipped up a new air filter arrangement. The airflow meter was unplugged from its wiring connector and the combined AFM/Unifilter assembly was hauled out. Because the Unifilter ram has a bolt flange suited only to the airflow meter, it was then easier to stick a short length of pipe into the compressor inlet pipe and clamp a K&N pod filter over the end.

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Note that there won't be much flow difference between the Unifilter and K&N air filter.

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While focussing attention under the bonnet, it was the ideal time for Tim to fit the one additional sensor required by the MicroTech system - the intake air temperature sensor. This involved removing a post-intercooler induction pipe, drilling a hole through it and welding a 1/4-inch BSP tapping fitting into position. Once painted pretty, the pipe was reinstalled and a new Delco intake air temp sensor was screwed in. Electrical connection of this 2-wire temperature sensor involved hooking up a nearby Earth (to the body) and the signal wire to the computer (which was derived from one of the pins of the loom connector for the now defunct airflow meter).

The only other necessary provision for the new ECU was a manifold pressure feed hose (to hook into the unit's internal MAP sensor). Instead of routing a dedicated hose through the firewall, the RPM guys elected to tap into the vacuum/boost hose that connected to this car's in-cabin aftermarket boost gauge. There is no problem doing this - so long as the hose isn't disconnected from the back of the boost gauge and left venting to atmosphere.

Time to plug in the MicroTech LT-12 computer...

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Like most Nissans from the '90s era, the R33's factory ECU is accessible by removing the left footwell kick panel. When rummaging around, it was noticed that this particular car had already been fitted with a HKS fuel cut defender (FCD) - this serves to 'clamp' the airflow meter's maximum output signal, fooling the computer into allowing high boost pressure. Tim suggested this is also probably the reason why this particular R33 wasn't running particularly rich - the computer had received a lower-than-reality airflow signal. In any case, the FCD was de-soldered from the loom since the MicroTech computer has an adjustable overboost fuel cut defence.

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Plugging in the MicroTech ECU couldn't be simpler. Simply undo the screw holding the loom plug into the original ECU case, remove the factory job and plug the MicroTech unit into place. Note that a new MicroTech plug-in model, which incorporates the Nissan loom connector in the side of the casing, has now superseded this particular version - flying leads are no longer used.

Tim commented that many Nissan ECU plugs - such as the R33's - are prone to warping that leads to poor electrical contact. A slight jiggle with the plug demonstrate this - it was possible to make the engine stumble; something for all GTS25T owners to keep in mind should their car start running poorly for no apparent explanation.

Specs of the MicroTech LT-12 Plug-in Computer

At the time of writing, MicroTech were yet to release the specs of their LT-12 unit, but we're told it's very similar to the established MT-series. The biggest difference is the 'matrix table' tuning process for laptops - something similar to an Excel spreadsheet.

The LT-12 has all the features of the MT-12 - there are sixteen load points for fuel and timing from 30"Hg to 20 psi (as determined by an in-built MAP sensor). Mapping is at 500 rpm intervals, and there's adjustable acceleration and cranking enrichment, WOT adjustment, water and air temp correction. Timing is adjustable over a 45-degree range between 500 and 8000 rpm, with a two-stage adjustable rev limit. PC data logging and electronic boost control is included in the deal, as is air-conditioning control, auxiliary output switching, injector staging and a lean cruise facility.

Note that, unlike the standard ECU, the LT-12 does not have an active knock sensing function. This shortcoming applies to every aftermarket programmable system we've seen on the market.

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The MicroTech plug-in computer comes supplied programmed with a time-saving set of base maps - these are designed to start the car and run on fairly 'safe' settings (ie rich mixtures and conservative ignition timing). It's up to the entrusted tuner to extract the maximum possible power, drivability from the vehicle - while, of course, simultaneously maintaining the appropriate safety margin.

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After checking the base ignition timing - which was running at 18-degrees - Tim tuned the MicroTech system via laptop on his chassis dyno with a careful eye on air/fuel mixtures as shown by his wide-band meter. Note that the LT-12 computer can alternately be tuned using the MicroTech handset, though Tim says it's much easier to do it on a full size screen.

Tuning involves optimising relevant fuel and timing maps to suit the particular vehicle, setting the rev limiter (to 7500 on this one) and, in this case, slight adjustment of the factory idle stepper motor (which is pulsed by the MicroTech computer). This helped stop the car stalling at idle. Note that the LT-12's boost control function was not employed in this case; the existing wastegate bleed valve was left in place.

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After about an hour of dyno tuning, Tim was happy with the look of the fuel and timing maps - maximum load air/fuel ratios now hovered in the low 12s throughout the rev range (compared to 12.2 - 11.8:1 previously) and timing was altered significantly through the mid-range to achieve good mid-range torque and smoothness. Tim comments that it's important to back the timing off after the first stage of the R33's variable inlet cam phase adjustment - the engine is likely to detonate coming up on boost otherwise.

It was now time to ramp up for an 'after' power run and hit the street for a drivability check.

MicroTech'd Power and Drivability

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With boost untouched from the initial runs, the R33 reeled off a couple more power pulls so we could find an average result. As seen in the new blue plot, there was only a small gain found in the top-end - up from 178 to 184kW at the back wheels (a gain of just over 3 percent - negligible). On the other hand, check out the humungous improvement throughout the upper mid-range! Up to 20 percent extra grunt has been found prior to the point where power peaks and begins to nose-over.

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Back out on the road, the car felt considerably quicker, despite having only slightly improved top-end power. Away from the exact rpm of peak power - which you can explore for only a brief moment in urban driving, anyhow - the car was accelerating noticeably stronger. That 20 percent gain in the high-ish revs meant it was much easier to degenerate into wheelspin, however...

In terms of nitty-gritty drivability, the tuned MicroTech performed well. The only faults we could find were a 'snatch' when coming off the throttle, along with a more unsettled idle. The engine was more prone to stall when taking off gently from a standing start - a trait magnified by this car's aftermarket clutch.

Tim from RPM had no problem accepting these criticisms and suggests they could probably be ironed out with more extensive tuning.

Is It Worth It?

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The fitted and tuned price for the MicroTech LT-12 is somewhere around AUD$1900. In this case, the conversion gave up to 20 percent more power through the upper half of the rev range and a top-end power gain of just 3 percent (expect probably more on cars not already fitted with a FCD).

Is this a value modification, you ask?

Well - because many of the bolt-on mods have already been performed in this instance - the MicroTech is probably one of the next most cost-effective changes. Sure, the stockie turbocharger could be swapped for a larger non-ceramic item, but this would trade-off much of the grunty everyday feel of the car. As mentioned earlier, the new ECU also removes the annoying 180 km/h speed cut and gives the flexibility for tuning later down the track.

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We would not suggest the MicroTech plug-in as the most cost-effective modification in the early stages of a build-up - we'd see to the exhaust, intake, intercooler and boost before we looked at the management.

Of course, another concern is street emissions legality - or the lack thereof. Road registered cars are subject to certain emissions regulations, and your local state registering authority may not look too favourably at the fitment of an aftermarket ECU. The MicroTech ECU case is printed with the words 'For Racing Use Only' so don't say you haven't been warned!


RPM Performance Centre
+61 8 8277 2266

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