Lorenfb

"I agree with Geoff, there is a difference between the 261 200 473 standard brain and the 261 200 483 Euro RS brain."

When Bosch makes an electrical change, i.e. different circuit design, the middle three digits
chamge and not just the last three which indicates a different EPROM (maps).

"I'll remap it, we can see the difference between a generic chip and one that is specifically built for this car."

You'll most likely find little/no difference, as the "custom" is a marketing ploy
and a joke for a basically stock engine!

Red rooster

Loren,

Not to get too boring but are you saying that all DME with the numbering
0261 200 XXX run the same hardware platform ? We both know that is not true. The Bosch number is only an allocation number when the DME went into production .
Sorry if I have missed your point . The Euro RS reference was meant to be a light , general interest point ,not some kind of deep , personal attack .
I dont have the time or interest in that kind of stuff.

All the best

Geoff

Lorenfb

Bosch DME Numbering Examples:

0 261 XXX XXX

968 - 200 070, twin board, 8 bit u-p, 256K EPROM, OBDI
944S - 200 195, twin board, 8 bit u-p, 256K EPROM, OBDI
964 - 200 182/450/473/483, twin board, 256K EPROM, 8 bit u-p, OBDI
993 ('95) - 203 675, single board, 512K EPROM 16 bit u-p, OBDI
993 ('96) - 204 008, single borad, OTP ROM, 16 bit u-p, OBDII
993 ('97/'98) - 204 649, single board, Flash, 16 bit u-p, OBDII

Second Digits Field, major DME circuit design change
Third Digits Field, 1st digit - minor circuit board change (jumpers/switch), 2nd/3rd digits - EPROM change

Some need to open the various DMEs and also compare the the various
wiring diagrams. Bosch's numbering was not random nor just sequential
based on date of production.

CWay27

I was looking into a chip from 911chips.com for cars with headers and no cat but if someone has one to send to Geoffrey for testing that would be great.

If in the end, you were to produce your own chip, I would go for it.

Good luck and hope the results will be positive

Red rooster

Loren,

I have a listing of all the Bosch DMEs .
Just considering the 0261 200 XX range ,a full range of Motronic systems/car manufacturers can be seen. No number sequence is reserved for a car manufacturer , indeed as car makers asign their own part numbers why would this be needed ?

All the best

Geoff

Colin 90 C2

Now I'm a bit confused.
My stock DME is 261 200 182, Porsche PN 911.618.124.02 and a Ruf DME I have is 261 200 450, Porsche PN 911.618.124.03.

Are these interchangable?

Red rooster

Colin,
A 964 DME is a 964 DME ! Just plug it in and go .

Where the difficulty lies is that it is not a 100% situation to just plug any 964 chip into any 964 DME .
The ideal situation is to have a aftermarket /replacement chip that is based on/identical to the chip that came with the DME .
Hope that makes sense !

Geoff

Geoffrey

There are also minor differences between the early DMEs and the later DMEs. In 1990 for instance, there is a fuel quality switch. The 91-later cars have plugs in the wire harness that are used for the same function. So, as Geoff said, it is not simply a 100% solution in all cases.

TR6

I'm considering a chip from 911chips/Steve Wong (the one for muffler bypass and cat bypass), so I would be interested in the results on their chips also. His website says he will also do a custom chip for an extra fee if you send him your air/fuel/dyno data. I'm curious how much difference the customization would make versus one of his off-the-shelf chips.

Lorenfb

"I'm curious how much difference the customization would make versus one of his off-the-shelf chips."

The "custom chip" thing is marketing B.S. Performance chips just basically change the TIMING.
For a stock engine, the AFRs are usually within +/-10% of the optimum of 12.6 for max
torque which results in little/no effect on performance by tweaking.

Bottom line: Don't believe everything you read, especially when it comes to performance claims!

Lorenfb

"Where the difficulty lies is that it is not a 100% situation to just plug any 964 chip into any 964 DME"

Not correct! All the 964 DMEs (182/450/473) in my stock ALL run properly by JUST changing a chip.
So, unless someone has a situation where they WON't run, let's hear it and get some REAL proof,
and not some historical hyperbole.

Bottom line: Given that the torque is fairly flat (11.5<AFR<13.0) and that most
stock Porsche engines, i.e. running properly, have AFRs at WOT in this range,
tweaking the AFR via a "custom chip" yields little/nothing - a waste of time and
money.

Geoffrey

The optimum air fuel ratio IS NOT 12.6:1 at any point in the engine mapping and it will vary depending on engine load. 12.6:1 is too rich. I have not found that the stock programming of any Porsche 964 or euro RS to have air fuel ratios at full throttle to be within +/- 10%. In fact, during peak torque the engine run in the 11:1 AFR range which is too rich.

Modifying the AFR from 11:1 to 13.2:1 will gain you some power, however moving the AFR from 12.6:1 to 13.2:1 will not yield a noticable gain. It is the ignition timing as Loren suggests that makes the largest increase in performance, especially if you are using 93 octane fuel over the 91 octane fuel the engine programming has been designed for.

"All the 964 DMEs (182/450/473) in my stock ALL run properly by JUST changing a chip."

I have no arguement with your statements. However, the issue of swapping chips comes from swapping a 473 chip into a 483 brain or vice versa. I know this does not work, the engine will not run. 483 is the Euro RS/Cup Car brain. My proof comes from a 1990 cup car with a 473 brain with a stock Cup car chip and a second 473 brain with a stock C2 chip. Swapping either of the chips into the 483 Euro RS / 1992 Cup car brain will cause the engine not to run and vice versa. This is factual information.

Lorenfb

"The optimum air fuel ratio IS NOT 12.6:1 at any point in the engine mapping and it will vary depending on engine load. 12.6:1 is too rich"

Really, so you've discovered something which contradicts very basic automotive engineering, right?
And this conclusion results from sampling a LARGE number of automotive engines, right?

Reference: "Internal Combustion Engine Fundamentals", John B. Haywood, pgs 830, 831,
i.e. The theoretical max torque occurs at an AFR~=12.6.

Geoffrey

Once again, things are not black and white and there are so many variables that one cannot pull out of a book the "correct" answer. I doubt that Haywood said 12.6:1 AFR was optimum for all engines.

It is widely viewed in the industry that there is a range of air fuel ratios engines can operate at and give peak power. Examples of differences in engines that may affect optimum AFRs are a lean burn direct injected engine vs an inefficient hemi head air cooled engine. Bosch states "spark-ignition engines with manifold injecton (not direct injection) achieve their peak power output at an air deficiency of 5-15% of Stoichemetric meaning a lambda value of .95 to .85 or 13.9-12.5:1 afr."

Further, labratory tests from the Bureau of Standards have shown that there is a wide range of air fuel ratios where the engine will make within 5% of peak power, generally between 12.5:1 and 14.5:1. The conculusion is that air fuel ratio does not have a material effect on overall power within a fairly wide range. I agree with the above and have demonstrated it in my engine management classes on a chassis dyno with my Porsche 924.

My opinion is that the optimum air fuel ratio for an engine is the leanest AFR where the engine makes peak power AND does not melt down. Running an engine richer than that does nothing but waste fossel fuel. Based on my over 4000 hours of dyno time with programmable engine management systems, I have found that a performance N/A Porsche engine produces safe, peak power at about 13:1 AFR or .88/.89 lambda. I am comfortable with stating my opinion as factual information for the air cooled Porsche 911 engine and if it disagrees with John Haywood, so be it. Since the volumetric efficiency of a street 911 engine is less than a performance 911 engine and therefore does not produce as much heat, I would think that it can be run even leaner and still produce safe peak power, something on the order of 13.2:1. I will be tuning my 964 to something between 13.0-13.2:1 at full throttle.

Reference: Bosch Automotive Handbook 5th edition page 458.
Reference: Internal Combustion Engine Handbook by SAE
Reference: Report 189 Relation of air fuel ratio to engine performance by Stanwood W. Sparrow

I hope this helps.

Lorenfb

"The conculusion is that air fuel ratio does not have a material effect on overall power within a fairly wide range."

Right, which again supports my premise that tweaking the AFR is a total waste for a stock engine!