M103 - What happens when the ignition timing advance increases at 3,200 RMP?

[Michael K]

The M103 in our 300 SL REALLY, REALLY comes alive at about 3,500 RPM. It’s like a power switch goes on, you’re pushed into the seat, and bam it’s at the maximum engine speed in seconds. Below 3,500 RMP power is adequate but subdued. Over 3,500 she’s a raucous beast. I found the table shown below and noticed, in the ignition system section, the 3,200 RPM number. This got me thinking about several questions.


1 - What happens when the ignition timing advance increases at 3,200 RMP?
2 – Is it normal for the power to increase so dramatically?
2 – What is the EZL ignition system (see picture) on the European version M103?
4 – Is my EZL set correctly to run on the premium fuel she drinks?

[coleyjf]

Hi Michael

I know what you mean. I guess my 88 300SL has the same Euro engine but being an auto I also get the kick down kicking in as well at about the same time so there's quite a push in the back at just over 3000 revs - I've never looked at the rev counter closely as I've always been busy controlling the car as it surges forward but it must be about 3.2krpm.

My engine was set up a couple of months ago by a great local indie who spent ages getting the mix & timing spot on(it had been a bit weak) so I guess it's a built in thing to allow you to accellerate slowly when you want (below 3,2) and quick when you feel like it (past the 3.3mark).

It's an early hot spring in the UK and I've got the hard top off - 18dec C already at 10am so I'm off out in the sun later - in APRIL - it's not normal but GREATTTTTTTTTTT

Happy Motoring

Jim

[ctaylor738]

Nothing really happens at 3200 RPM, the 40-44 degrees of advance is simply the spec for the engine to run correctly.

On your other question, I have the Haynes manual for this engine. Since Haynes is in the UK, it has some information on the EZL, which as you know, does not come on US 103's. What the EZL does is adjust the advance curve based on a resistance setting, which can be changed by turning the dial.

According to the picture in the manual, you are set for '95 RON premium unleaded' fuel.

The US versions have a fixed value resistor in place of the EZL. There was a huge and interesting debate a few years ago on the Tech Forum as to whether removing the resistor and thus allowing max advance improved performance.

WRT how your car runs, I think you are seeing the difference between the US and Euro versions of the engine. My 300E 5-speed was the opposite - great at the low-end and mid-range, but started to get anemic at 5000 RPM.

[Michael K]

Thanks guys. Great information.

Chuck, I can't tell where my EZL is set. Is it on the "S" between the white hash marks?

Not that I plan on futzing with it, but what would happen if I adjusted it up or down?

The settings range from "1" to "7" with "S" for 4 and "N" for 6, what do the "S" and "N" stand for?