MEDIUM

Boost !

Serious power & torque gains can be easily had with revised software in the Motronic ECU. A number of vendors offer ECU upgrades for the S2. See below for details. These are available on both the 3B and ABY engines. Ideally I'd like to get information on real 'before' and 'after' figures for each of these, but that's a very tall order.

Any S2 owners got ECU info they would like to share with the www community ?

Because of the nature of turbocharged engines, a tasty gain of 40-50 BHP is possible with ECU reprogramming alone. The primary mechanism for achieving the higher power output on the S2 engine is an increased duty cycle of the wastegate frequency valve such that larger boost pressure is created. To complement these increased boost levels, a modified fuel map and ignition map ensure that knock is minimised and the correct fuel:air mixture is employed. The latter is very important as any turbo engine running too lean for too long will self destruct as the increased temperatures can lead to severe internal damage. A higher spec (3 bar) pressure sensor replaces the standard device (2.5 bar) within the ECU in order to measure the increased levels of boost pressure with the new firmware. 

Higher torque outputs can also be expected with a simple ECU upgrade - some would say that care needs to be taken in 1st gear with the 5-speed and early 6-speed gearboxes when torque outputs exceed 350Nm, but the later 6-speed box is heavier duty and should stand up to 450Nm. Your mileage may vary !

My personal preference would be with the German vendors who have proven Audi turbo knowledge but such knowledge is not unique to the German chip vendors. When researching any of these ECU vendors, DO ask for dyno and on-the-road performance comparisons against the standard specification. Always try to ensure you are comparing like for like e.g Does the car tested have a standard intercooler and exhaust system? Furthermore, all properly upgraded ECUs should retain the on board diagnostic (OBD) features for fault codes and output tests etc so don't accept any that fail to provide the diagnostic features built into the Motronic system.

Boing ! - A much revised section on the mysteries of the wastegate spring ...

To complement the ECU upgrade, a stiffer return spring in the wastegate is recommended. The reasons for this will be fully explained in the technical chapters in the very near future. In short, a stiffer wastegate spring provides a simple way of increasing the mechanical contribution to boost levels that are permitted in the engine. It also marginally reduces turbo lag.

To my knowledge, the 3B engines were equipped with a spring that allows the wastegate to open at 1.6bar of absolute manifold pressure (~0.6bar boost) whereas the ABY & ADU engines were fitted with a 1.8bar WG spring. This means that without the electrical control of the wastegate (via the wastegate frequency valve) the 3B would be capped at 0.6bar boost and the ABY at 0.8bar. This is good for engine preservation, in the event of electrical gremlins, and it allows the ECU to be the major factor in dynamically determining how much extra boost is permitted. In factory configuration, the ECU of the 3B engine permits approx 0.8bar boost and the ABY allows for controlled overboosting spurts of up to approx 1.1bar.

Lets say we have a ECU that runs the 3B or ABY engine at 1.2bar of boost (~2.2bar absolute). A good rule of thumb seems to be that the wastegate spring should be about 0.2bar below total system pressure and so a 2.0bar wastegate spring would be an ideal candidate for this configuration. By using the stiffer spring, there is also a fractional improvement in the time required to close the wastegate such that turbo spinup is marginally improved. The toughest wastegate spring available to my knowledge provides for a mechanical pressure limit of 2.2bar - so this would work well with an ECU designed to run at a lairy 1.4bar of boost.

The tension in the wastegate spring can also be fine tuned by adjusting the upper perch in the top of the wastegate chamber. In doing so, this can increase the amount of pressure required to crack open the wastegate and so provide a cheap and easy way of increasing boost. However - the practise is NOT recommended as the ECU may detect an excessive boost condition and go into 'limp-home' mode. Don't forget that the MAP sensor within the 3B ECU is only rated to 2.0bar of absolute pressure, so it would be pointless trying to get 1bar of mechanical boost on a standard 3B ECU as the MAP sensor would simply flatline and cause the overboost protection routine to cut in. An equally valid concern is that the ECU may not provide adequate fuelling and ignition settings for the now manually increased boost in the system. This applies to any setting with more than 0.8bar of boost - but there might be some tolerance in the ECU that allows for a little excessive boost. I suspect that is more true for the factory ECU of the ABY engine but I have no evidence and don't wish to use my own car as a guinea-pig.

Adjustment of the wastegate spring is best left to serious tuning professionals, and maybe only in conjunction with a revised ECU to make everything run sweetly.

RAMPANT

Consider the RS2 !

The ADU engine of the RS2 Avant is the ultimate factory specification of Audi five cylinder turbo engine. No surprise that it represents the last in the lineage of the evolution of Audi's turbocharged I-5 engine. The technical assistance from the turbo gurus at Porsche was used to develop the RS2 engine so it is worth studying how they achieved figures of 315BHP by modifying the induction, exhaust and ECU systems of the ABY engine which seeded the ADU motor.

First off - good news for ABY owners, the short engine of the ADU motor is identical to the ABY. That puts great confidence into the minds of ABY owners wondering how much their standard 'bottom end' will take. The ABY internals can comfortably handle > 315bhp if the software and hardware is there to create it ! The clutch and gearbox is another question, which is considered elsewhere, but there is concensus that the Torsen quattro system can handle torque outputs in the region of 450Nm. It is worth noting that the RS2 has a heavier duty clutch than the ordinary S2.

In addition, the ADU and ABY engine both utilise the same direct ignition technology with tiny coil packs at each spark plug, so much of the electrical wiring in the RS2 engine bay is common with the ABY-S2. Details to follow...

The magic of the RS2 is in the ancillary components bolted onto the engine :

Larger turbocharger (K24/28 hybrid versus the K24 in the 3B and ABY motors)

Larger intercooler (reducing heat soak on the inlet side)

Modified exhaust camshaft profile

Modified exhaust manifold

Modified inlet manifold

Different mass airflow meter (MAF)

Higher flowing fuel injectors

Higher spec fuel pump

Modified fuel, ignition and boost maps in the ECU

I took some time to study much of the engine part information on the 3B, ABY and ADU motors to get a fuller understanding of their evolution and guage what parts are common and which needed to be modified for the RS2. Here is a summary of my findings. It is not an exhaustive list, but it is reasonably extensive.

I was particularly interested to note that the same cylinder head and valves are used on all three engines. In fact, of the 24 engine components listed below, the 3B, ABY and ADU share 8 parts. A further 6 components are common on the ABY on the ADU motors. When time permits, I shall also investigate the AAN engine from the UrS4, as it appears to have a great deal in common with the ABY. The biggest difference on the UrS4 is that the bigger engine bay of the Audi 100 allows for a much less constrictive route for the air intake plumbing that also benefits from a larger intercooler (I think).

So if you have the time, the money and inclination, an RS2 power plant can be easily cloned with a willing ABY motor and a very deep pocket for shiny new RS2 parts - unless you happen to find a rear-ended RS2 in a breakers yard !

It is also possible to upgrade a 3B engine to RS2 specification, but there are significant complexities with respect to differences in the ignition systems of these two engines such that the prospective builder is well advised to simply use the wiring loom from the ABY or ADU engine. In addition the cylinder head cover of the 3B engine is different from that found on the ABY and ADU motors to accomodate the direct ignition packs attached to the spark plugs. A timing reference sensor on one of the camshafts, used on the ABY & ADU engines, would also need to be added to the cylinder head from a 3B motor - this makes the distributor on the 3B->RS2 conversion entirely redundant !

Visitors to the S-Cars and the 20V_Kruemme mail lists will know of Tommy Arnberg's success with a 3B -> ADU conversion (for a modified Audi 200TQ) which retained much of the original 3B wiring loom before an ECU from the ADU was grafted into it. No mean feat, but it is not recommended for those without solid automotive electronic knowledge and plenty of time on your hands.