NineMeister

We have tried exhaustively and eventually (reluctantly) gave up trying to get the Motronic system to control the boost valve accurately. Nomatter how we set up the system, it is always the torque spike at 4500rpm that throws a fraction too much boost into the manifold and brings in the MAF limit function.

The last car we worked on was exasperating. It was a GT2 with K24's that refused to hold a steady 1.0bar, and even after pulling the base setting back to 0.9bar on the dyno it would flash 1.1 on the road in certain conditions.

When the car came back in I fitted an Apexi AVC-R and mapped it to 1.0 bar on the dyno, and it would flash to just 1.03bar but a slight tweek of the 4500 duty cycle point prevented MAF limit intervention. On the road it held rock steady at 0.99bar in any gear. On the dyno it made 544bhp & 755Nm, putting down 485bhp at the tyre.

Reluctantly we now recognise an external boost controller as probably the best way forward when you are tuning to over 500bhp with over 0.9bar.

K24madness

Ninemeister Shoot me a PM. I have an answer for the MAF limits that you experance. I would be happy to share with someone that thinks outside the box like I do.

FWIW the Apexi AVC-R is a awesome boost controller. I like the fact you can adjust boost on a RPM basis if needed.

Since Geoffrey pointed out that he uses the factory valve successfully with MOTEC I have to believe that the lack of a MAP sensor is part of the problem when tuning the Motronic.

Jean

Colin, for someone with your knowledge there is absolutely nothing I can help you with unfortunately, but here are just some thoughts that should be taken carefully . It seems like the K24s are more difficult to manage by the Motronic for some reason. Whether the Motronic can manage boost perfectly is not debatable I think, it can't. Just how well (or bad) and easy, is the question. In fact, my understanding is that the 993TT Motronic does not control the boost as pressure per se, but rather through throttle position and rpms which are then translated into the appropriate frequencies to control boost. The proof is that racing GT2 EVOs had other systems (TAG) which were more appropriate for better flexibility.

I don't think many (if any) people can have the Motronic keep a stable boost "on demand" across the different RPMs like an external EBC will, and I don't think there is a need to do it either as you will be limiting performance (like a K Jetronic for instance vs EFI), however some of them have ways to avoid the massflow error driven by overboost through the programming and some are running 1.5 Bar in peak with variable boost, controlled strictly by the Motronic. With that being said, I am only talking about controlled overboost, whithout removing the fuel or knock cutoff that the system generates as overboost safety.

K24madness is only partially right as well, pressure sensing or MAP can give better control over boost, but do not expect to control boost perfectly either even with MAP, also going pressure sensing, you would be talking about a whole different approach altogether.

I use MAP and Motronic, and I am running fixed boost through an external EBC in my setup, which is what many high hp tuners have been doing for years.I believe the reason why I am running an EBC even with MAP is because boost cannot be controlled properly. The only reason I went with pressure sensing was to explore hp limits beyond the MAF limitations while keeping the knock sensing and Motronic rather than to control better boost.

I think one just has to optimize the mapping to his most likely used setup and compromise on having the best performance across all circumstances, unless you want to go with Motec or the likes, or go to one of the very few Motronic experts with access to some codes apparently, and pay a fortune.

NineMeister

Thanks Jean, at least it is good to know that I am not alone in my approach of adopting the EBC. For the level of tune that we are running with near standard engines, I think the EBC looking after the boost and a remapped Motronic on MAF with larger injectors is probably close to ideal.

The issue with Motronic is that it is relatively easy to find the fuel/ignition/boost tables and adjust them to suit, the problem is when the ecu does not then work how you think it should. I guess that the boost controller runs under some form of PD control (proportional derivative) and although the table numbers can change I think the PD parameters may be unsuitable for the faster boost response of the larger turbos. The bad news is that we cannot deduce where the PD parameters are hidden in the chip file without having the Bosch "A to Z" chip directory (can't remember what the file is called). If anyone can enlighten us further I would be delighted to exchange information, but I suspect that those equipped with the Bosch data would be highly unlikely to let anyone know that they have it, let alone release it, since it was released for internal use only at Bosch.

Kevin

Folks, It is the programmer of the Motronics that will make our break the case when adjusting the cells for the "boost map" I have heard this issue for more than 2 years, that people can't control the boost with large turbochargers WITH the factory Motronics. Well that is NOT the case.. It can be done. If you have the source code, you can control the boost.. I have seen it done very recently. We were experiencing uncontrolled/high boost levels 1.45 and 1.65 bars. When programmed correctly the boost came in correctly and was managed and manipulated to our needs. So all in all it is the ability of the programmer, and not the short-comings of the Motronics.

Geoffrey

Colin,

I think you are exactly right on here. The Motronic computer is every bit as capable and technically advanced as an aftermarket MoTeC ECU type system, however, it has been optimized for other goals (emissions/economy/reliability, etc.) and has additional features that a MoTeC does not have. I believe, as you stated, it is the ability to find the PD table that is limiting, and without the Bosch reference file that gives the addresses, you are limited to searching the code. I have the Bosch file for the 996TT and there are over 3000 tables.

Here is the data logging from Tal's 993tt with Kevin's stage 2 turbos running a MoTeC M8 with the factory boost control valve. This was 1 dyno run near the end of the tuning process prior to the boost table being optimized. It rises to the preset boost level, the ECU then begins to open the valve and then controls the boost appropriately. Although it looks choppy, the difference between the highest MAP under boost and the lowest MAP under boost is only 5kPa or .05bar of boost. I could probably get it slightly better, however, generally if it is within 5kPa, I call it good. I have found the MoTeC ECU to be better than the aftermarket boost controllers I've tried (HKS and Greddy), although I've not tried all of them.

Jean

Kevin, you are right , and that is what is being said here. Only a handful of people will be able to, and you will have to pay the price. Among them Gunther I believe.

Even then, it will not be as accurate and programmable as a Motec with a MAP setup, but the Motec will not give you the other features of a Motronic. It is all about choices.

NineMeister

I am using a Motec M600 on a 993 engine that I have converted to single turbo, this is pulling around 530bhp at 1.0bar and is easily controlled within the +/-0.05 ripple that you experience Geoffrey. However after playing with the AVC-R on the GT2 I suspect that it is doing a much better job than the M600, such is the apparent fine level of the control. Like I said,on the road we see 0.99bar steady in every gear up to the redline with an occasional overshoot to 1.03, which implies control within +/-0.3 or maybe less. I doubt that fine tuning the Motec PD parameters would achieve this level, but +/- 0.05 is more than adequate in any case.

I know what you mean Kevin, we have access to the source code in the chip and have tried to adjust the boost table, but there is no obvious provision to improve the response rate of the valve to sudden boost spikes. I have no doubt that there is an answer in there somewhere, so hat's off to Mr Mandl for knowing where it is, but even with the raw hex file in front of you without the specific data location knowledge that he has acquired I doubt that anyone would achieve similar success. Don't get me wrong, I have played a lot with the boost table and even programmed in lower numbers to suppress overshoot, but in the case of this GT2 it would not stay away from the MAF limit unless we dialed in 11psi, which of course was unacceptable. After two weeks of playing around we had no firm answer, whereas after one day with the AVC-R I had a totally satisfied customer.

At the end of the day, commercial reality for job closure was the overwhelming factor, so although I like a technical challenge, in this case I reached my limit of what made sense to pursue. However (no offense Kevin) the purpose of posting my experiences are to possibly find the absolute answer, rather than just be told that it is possible if you know where to look, 'cause I have looked and cannot find!

Geoffrey

Colin,

Wait until you get the new MoTeC version 3 software...

TB993tt

Jean
I'm not sure that this is the proof which condemns the Motronic. From Paul Fere's "Porsche 911 Story"
(The racing GT2) is managed by a TAG instead of Bosch ECU. The main reason for the latter is that TAG being a smaller, but very efficient company, it can react quicker to eventual requirements for modifications in the specifications of the unit
So the better "flexibilty" you refer to seems more apt to describe TAGs working practices than its ability to manage the boost better than Motronics

vrus

My 993TT had K24 Race turbos on it and I had a custom program written into a '97 Motronic ECU. My car was programmed for 1.1BAR of boost and it worked flawlessly.

It all comes down to which tuner you use and what their capabilities are. I know first hand it can be done with a Motronic unit.

Also, my friend's car with a 3.8L pushing 1.6BAR boost w/twin plug heads and twin distributors is running on a 1997 Motronic ECU as well. You dont need to use an external boost controller.

Jean

TB I am a firm believer in Motronic, that's why I kept it!

I am sure Paul Frere is right in what he is saying, however I would not disregard the fact that another main reason was the flexibility of the TAG to control the separate wastegates that the GT2 EVOs had in their KKK27s, same as with the GT1 cars. Correct me if I am wrong but almost all, if not all, the independent racing teams used also non Motronic ECUs in their GT2 EVO race cars with separate wastegates, I know Fabian Roock did too for sure, and exactly for that reason.

vrus there is no doubt that Motronic can do an excellent job of course, otherwise how could all the tuners sell modified ECUs in their packages. I have an FVD ECU that boosts at 1.2 bar as well and does wonders.

fc-racer

Jean, which FVD package did you run before the big engine? How did you like it? Their 490hp kit seems like good value for the money.

Geoffrey

Jean,

Do you know if Todd used the 964 N/A ECU for your engine as he has done with most of his other systems, or did he use the 993TT ECU?

Jean

fc racer, I have a "540hp" ECU, whatever it really is. K24/26, mechanical rockers, camshafts, titanium retainers, LWF kit, sport cats, large intercooler etc, their typical complete kit. It is a very fast engine. I still have it.

Geoffrey, he had to go N/A because of the pressure sensing (and twin plug), same setup as a 964 N/A in many other aspects as well.