Which M117 to fit into W111 250SE

[rgafitanu]

Hello all, Gael,
I read Gael’s 10 year old posts about the M117 5.0 V8 into his coupe.
I will have to install a V8 too, the L6 is really too slow.
There are many opinions about which M117, 4.5, 5.0, 5.6 D-jetronic, K-jetronic, anybody has any experience and advice? Stay away from the 3.5 M116?
Gael, if you are reading this, any reason why you replaced the original with megasquirt? This triggered change of the injectors and manifold?
My car has the original automatic transmission that I intend to keep, do I still have to enlarge the tunnel?
Thank you all,
Radu

[Bruce Rudin]

My 67 250 SE has a full 280 SE 4.5 driveline.  Torque converter 3 speed and 3.27 rear.  $,5 subframe.  The car is seriously great.  More than enough power, gearbox shifts perfectly and the rear end ratio is perfection.  This is the easiest swap you can make as well of it is bolt in.  I believe the original builder used the donor car engine harness.

[rgafitanu]

Thank you for the info. A 4.5 with K-Jetronic would be nice considering it’s the least “electronically’ controlled. Stronger front springs should take car of the heavier cast iron block. The transmission should be better than the original 2.5l. I already have the 3.27 rear. I’m curious how extensive mods, if any, are needed for the exhaust.

[lpeterssen]

Dear Radu

Some months ago I did a wiring harness conversion for a customer which had a w113-230SL on which a 560SL drivetrain was installed.

That engine, even when is Kjetronic, was heavily controlled by an ECU that required many signals not available on the w113.

So, my advise in your w111-v8 conversion project,  is to STAY AWAY FROM KE-JETRONIC, because will be very engineering demanding to make it work as should.

On any drivetrain conversion you make, you will need, as a starting point,  the original engine wiring harness that came with it; and you will have to modify, in a huge extend, your original w111 harness to work properly with it.  The engine control harness should be kept ORIGINAL, that because from time to time due to heat exposure you will need to replace it.  Then, it’s better to make all the necessary modifications only on the car (w111) harness as it will stay in place much longer without deterioration.

Basic things that should be made to your OEM W111 harness will be:

1. Increase its power handling capacity in all the circuits related to T30, and T15 feed
2. Modify the position of many of the accessories.  V8 Kjetronic engines tend to have the ac compressor on the left side instead of the right.
3. Change all the circuitry going to your ignition tumbler switch, since more power will be handled
4. Add new lines as T16 to ignition coil from starter
5. Change the the fuel pump power supply logic.  On a w111 fuel pump gets power as soon as you turn ignition switch.  On Kjetronic, depending on version you have, a dedicated fuel pump relay, which works in conjunction with the ECU, manages power to it.
6. Eliminate all circuits that will no longer be in use, as cold starting circuitry, automatic transmission looms, etc.

If you need further assistance from the wiring point of view contact me  (DM) or go to my website www.Wiredoktor.com

Best regards
Eng. Leonardo Peterssen

[rgafitanu]

Thank you Leonardo for information.
This came to me because I will have to do some serious rust repair that may require removing the engine. And since it’s not the original 2.5, it’s a (more desired) 2.3 from an SL, I was thinking to replace it with a more powerful V8. And now I have to decide considering that I would like to have more power (5, 5.6), less weight (Al block) with least electrical pain (for the reasons you mentioned). In the end there isn’t much difference in power between the 4.5 and 5. And the US neutered 5.6 is not much gain with a lot of emission stuff. I am still not decided between the D and K Jetronic, some people say to stay away from the D because injectors on K are not individually actuated.
My W111 does not have A/C so I would remove the compressor and I think all the extra sensors are already on the engine so, yes use the original harness. In the end it would be a salvage donor car from copart.com. I still cannot find a correct chart with M117.XXX, it would help to know the precise XXX for block changes, D vs. K, US, etc.
Thank you,
Radu

[lpeterssen]

Dear Radu:

In that part of knowledge (engine designation) I can not help you, since I have not investigated much, and therefore my knowledge is limited.

K-jetronic systems are built having in mind robustness. On the other hand there are many tutorials online which show you how to tune them.

D-jetronic has individually controlled injectors and I think it is also a good system.  Maybe people does not like it because of an aging or defective engine control wiring harness which may lead to many failures.   They age a lot because of heat exposure.

But if you match your DJetronic engine with a BRAND NEW or refurbished engine wiring harness, then there will be no problems for many years to come.

DJetronic engine in 3.5 liters was used on the w111 at the end of the production run, so we can do an installation that looks much more like original, with the ECU on the front right fender.

What to do depends on you and the availability of an used drivetrain on a junkyard.  Look around to see what you find.

Regarding g the AC is not so difficult for me to let you all the wiring ready for that, think in the confort you will have.

Well you know how to contact me if further assistance is needed.

Best regards
Eng.Leonardo Peterssen