Direct Ignition - The Unofficial BMW M5 Messageboard (m5board.com)

Nene · 25th October 2001, 18:22

Hello-
I've read that the 1995 3.8L M5 comes with a direct ignition system on it (read, a computer controlled coil for every cylinder). Does anyone know if it is possible to convert the earlier 3.6L cap and rotor system over to this newer, more efficient direct ignition system?

Nene

Alan Archer · 25th October 2001, 18:52

No, i wouldn't think so, seeing as the 3.8's have a different engine management system + wiring loom to 3.6's....also the motronic sensors are different too...

IvanDias · 25th October 2001, 21:13

I agree, I saw this system being taken apart at a local specialist. It`s pretty different.

The 3.8 isn`t just 300cc more;

The coils as you know are different, and obviously the bore and stroke (up from 93.4mm x 86mm to 93.5mm x 90mm).
The inlet and exhaust valves are slightly larger, the air intake system has been revised to improve airflow, the crankshaft is new and the flywheel is lighter.
Just to finish, there are new aluminium pistons which allow the compression to go up from 10:1 to 10.5:1

All this is how they get extra 25Bhp and 30lb/ft from it.

Makes the six hamster wheels under the bonnet of my 1990 3.6 seem a bit low-tech

The point is, that assuming you did have all the bits you would need, and the time and skill to do it, then once the new ECU and wiring loom is in, someone is going to have to reprogram it to accomodate all the "missing" items, as the computer would be expecting all the bits from the 3.8

Looking back over what I have just written, I wonder how much is actually gained by the ignition system. The other improvements that Motorsport came up with seem to me to be the lions share of the extra power.

Ivan.

Nene · 25th October 2001, 23:28

I wasn't really looking for more power necessarily, but I wanted to get the power band that the 3.8L has. It's so broad and useful, unlike the 3.6L where it's all about top end. Maybe there's another solution...

Nene

Alan Archer · 26th October 2001, 16:02

I did my sums on the difference in power to weight from the 3.6 to the 3.8,

how about dumping the heavy electric seats, spare wheel & a couple of other items and you'd probably loose 100kg and equal the p.t.w of the 3.8 !!

( my original idea was to get an early 3.6 instead of the more expensive 3.8 and totally empty it of every non vital piece of kit !!)

Al.

Nene · 26th October 2001, 23:35

Alan-
Your idea is good, and I do plan for something of the likes in the future, but what I was trying to get from the direct ignition can't be done by weight alone. The 3.8 has 90% of it's torque available at 1800RPM! The only way to do that is to have a completely programable ignition system where you can set the ******ation just right for torque down low and advance it for high RPM power as well. I guess I'll have to "live" with what I have for now.

I'll just keep the revs above 4000 at all times (read:What gas mileage).

Thanks for your input,
Nene