Motronic brain and heat

[Scott S]

Hi All -
I am in the process of lowering the seat rails in my car. I have measured 100x, making sure I clear the motronic brain/bits under the seat. However, the amount of air space above the unit will definitely be reduced.

Could this cause an issue with heat?

Thanks -
Scott S

[scarceller]

Most likely it won't be an issue to lower the seat closer to the DME. The DME doesn't really need that much air flow. It simply just dissipates heat via conductive heat sinks, no fans. Plus you'd be amazed how hot the winter heat in these cars can get under the seat with the heater ports flowing heat under the dash! I wouldn't worry much about the DME over heating.

[DRACO A5OG]

+1, you will be fine.

[Bill Verburg]

Originally Posted by Scott S

Hi All -
I am in the process of lowering the seat rails in my car. I have measured 100x, making sure I clear the motronic brain/bits under the seat. However, the amount of air space above the unit will definitely be reduced.

Could this cause an issue with heat?

Thanks -
Scott S

Move it to the area behind the seat.

[mrdieseldude]

Added heat = shorter life. Period.

You won't kill it tomorrow.... but you ain't doing it a favor either. Only you can decide if it is worth the trade off.

[Tippy]

The case is huge (large airspace). I doubt laying something on it would increase heat much at all. The cover is just stamped sheetmetal, no heat sinks built in.

I wouldn't sweat it.

[scarceller]

Consider that this same DME case and design was used in 80s BMW cars and put in much tighter spaces than under the seat of the 911.

In the 928 2 of these DMEs are stacked right on top of each other. Can't get much closer/tighter than this setup. Then they are covered up tightly by interior paneling!
where is the LH-ECU located ?
I know the DME type in the pic is slightly different but same basic design.

[mysocal911]

Originally Posted by scarceller

Consider that this same DME case and design was used in 80s BMW cars and put in much tighter spaces than under the seat of the 911.

In the 928 2 of these DMEs are stacked right on top of each other. Can't get much closer/tighter than this setup. Then they are covered up tightly by interior paneling!
where is the LH-ECU located ?
I know the DME type in the pic is slightly different but same basic design.

Actually, the ECMs used in the 928 versus the 911 3.2 are significantly different in
design. The 928 used separate ECMs for ignition (EZK) and fuel (LH) where the 911 3.2
uses a single ECM. Furthermore, the 928 has knock control and uses a MAF sensor
versus a AFM on the 911 3.2. The 928 units are mounted vertically which reduces
perpendicular forces from vertical vehicle vibrations causing intermittent connections
as occurs with the 911 3.2 DME ECM. The 928 EZK ECM uses a single crank sensor
to obtain the timing control versus two sensors (speed/reference) for the 911 3.2.

[scarceller]

100% Agree that they are different but heat dissipation is likely very similar. The main components that generate significant heat in these units are the Fuel and Coil drive circuits with the large Darlington Transistors.

Interesting point on the vertical vs horizontal mounting. I know first hand the 911 and 944 units fail often on the solder connections where the large transistors and heat sinks are. I've repaired many of these units. Are you saying the vertically mounted units don't fail as often? Very interesting.

Originally Posted by mysocal911

Actually, the ECMs used in the 928 versus the 911 3.2 are significantly different in
design. The 928 used separate ECMs for ignition (EZK) and fuel (LH) where the 911 3.2
uses a single ECM. Furthermore, the 928 has knock control and uses a MAF sensor
versus a AFM on the 911 3.2. The 928 units are mounted vertically which reduces
perpendicular forces from vertical vehicle vibrations causing intermittent connections
as occurs with the 911 3.2 DME ECM. The 928 EZK ECM uses a single crank sensor
to obtain the timing control versus two sensors (speed/reference) for the 911 3.2.

[mysocal911]

Originally Posted by scarceller

100% Agree that they are different but heat dissipation is likely very similar. The main components that generate significant heat in these units are the Fuel and Coil drive circuits with the large Darlington Transistors.

Interesting point on the vertical vs horizontal mounting. I know first hand the 911 and 944 units fail often on the solder connections where the large transistors and heat sinks are. I've repaired many of these units. Are you saying the vertically mounted units don't fail as often? Very interesting.

The 928 EZK (ignition) does not drive the coil directly as the 928 uses two separate
ignition modules.

"Interesting point on the vertical vs horizontal mounting."

Do a search on how most all aircraft electronic systems are mounted vertically.
Since the late '90s and on, most all vehicle OEMs mount modules vertically.
It should be obvious when one analyzes the forces on a circuit board what the
stresses and vibrations are, i.e. based on how the circuit board is mounted.

[scarceller]

Bill this is nice option. Do you think the harness for the 84-89 cars will allow for this? I know most of the harness comes from the back LHS just under the rear seat but portions of the harness feed forward as well.

Originally Posted by Bill Verburg

Move it to the area behind the seat.