Spark plugs & ignition coil ?

[blairwag]

As you can tell, per all my posts, I'm preparing to overhaul the ignition system of my 1971 280 SL.

I plan on instaling the Crane XR700 electronic ignition conversion kit. I plan on installing a Bosch 26KV coil, and replacing any/all ballast resistors with one 1.8 ohm resister. I plan on purchasing a set of Bosch Spark plug wires (Bosch p/n 09023). And, of course, plan on installing a new set of spark plugs.

Questions:

1) How do I specify/select the correct ignition coil? All web sites I see don't offer any options. Just bosch Ignition coil p/n 00027.

2) I'd like to install multiple ground electrode spark plugs. But Bosch doesn't specify a set for the 280 SL. None of the parts ordering web sites suggest any plug other than the Bosch W7DC or NGK BP6ES.  SplitFire offers their goof-ball V-tip (TP6B).

Any input?


--
~~~~~~~~~~~~~~~~~~~~~~~~~~~
William Blair Wagner: blairwag@earthlink.net
Education is not always knowing the answer,
...but rather knowing where to look for it!
~~~~~~~~~~~~~~~~~~~~~~~~~~~

[Richard Madison]

Just to fill in any gaps (pun intended) of knowledge, here is my limited info about Bosch spark plugs:

The nomenclature "W7DC" breaks down as follows:

W means 14mm diameter, 7 is heat range (higher numbers 8 or 9 are hotter plugs), D is the length of the thread (how deep the plug goes), C means copper tip (an S plug has a Silver tip, P is Platinum.)

Common wisdom says that a colder plug (7) reaches operating temperature faster, more resistant to overheating, and does not foul as easily...

W7DC is the Bosch plug most commonly recommended for these engines.
W7 is a colder plug for warmer climates and high rpm or highway driving.

W8's and 9's are hotter running plugs and might indicated for colder climates and stop and go traffic. 8's and 9's are used by some drivers in "normal" driving conditions with satisfactory performance and plug life so the heat range does not seem critical in most applications.

An "R" as the last letter (W7DCR)indicates a Resistor plug. R might help supress Radio RF static but most agree that Resistor plugs are not good for these engines.

As to Copper, Silver, or Platinum, Bosch guarantees improved performance from the Platinum tip or money back http://www.boschusa.com/AutoParts/FAQs/SparkPlugs/

Perhaps Dr. Benz or others will answer Bill's question which I cleverly avoided.

Richard M

[n/a]

Blair,
Did you give any consideration to the PerTronics electronic ignition?
Basically, how did you settle on Crane? I am an old muscle car guy, so I am familiar with Crane in that application.
I am curious as I have been considering converting to electronic, but do not want to mount an external box - I want it to look original.

Regards,
Stan

[blairwag]

Richard, thanx for the breakdown. I searched for hours on Bosch's web site for the breakdown (http://www.boschusa.com) for a LONG time before finding it. Anyway, Very Helpful.
I've done a lot of research, and came to several conclusions:
1) Double tip Plattinum with copper core IS the way I want to go.
    It offers optimul performance with long degree of resiliancy.
2) I want a hotter plug than the standard for the engine, because
    it does burn some oil. A hotter plug will help burn off some of
    the deposits, reducing plug fouling. The plug will not last as
    long however. That's fine with me.
3) SplitFire is NOT the plug to go with. The FTC has slammed them
    for misAdvertising and false claims (some time ago)
      http://www.ftc.gov/os/1997/05/c3737cmp.htm
      http://www.ftc.gov/os/1997/05/c3737.do.htm
      http://www.ftc.gov/opa/1997/05/petapp26.htm
   I fear you pay a little more with no reward, for SplitFire plugs.

Here's a couple of really informative web pages on plugs:
http://www.sparkplugs.com/faqmain.asp
http://www.sparkplugs.com/sparkplug411.asp
Here's Bosch's info: there's a link for designation codes:
http://www.boschusa.com/AutoParts/FAQs/SparkPlugs/

4) Iridium is just too freakin' expensive!

5) I'll likely NOT go with a multi-ground plug, as likely, the M130 engine combustion chamber is not suited for plugs with the ground electrode firing to electrodes on the side.

6) I'll probably go with a Bosch Platinum Plug W8DP

As far as Stan's question on "why Crane" - basically, based on the info I read in the Technical Articles, given peoples experiences (see http://www.sl113.org/articles/engine/ignition.asp), and based on other input from this forum.

I'm STILL looking for some help with the ignition coil. Bosch's web site is most useless, as far as I can tell!


--
~~~~~~~~~~~~~~~~~~~~~~~~~~~
William Blair Wagner: blairwag@earthlink.net
Education is not always knowing the answer,
...but rather knowing where to look for it!
~~~~~~~~~~~~~~~~~~~~~~~~~~~

[George Davis]

The Bosch "red" coil is a common coil upgrade for these cars.  The current version isn't really red any more (earlier ones were red, I understand), but that's still how it's known.

Give Ray Paul at SL Classics a call, he can fix you up with red coil and correct ballast.



George Davis
'69 280 SL Euro manual

[n/a]

Geez.. I stirred up a hornets nest.

My comment about multi-point was too offhand, however.  The plugs I have experience with are two-ground Nippondenso, and the car was a Mazda (25yrs ago).  They were used because rotaries are sucsepitble to detonation, and the double gap (and double plug per rotor) make sure the mixture burns.

I have no 'direct' experience with the split-fire, but all of these plugs were designed with the same philosophy.  If the FTC went after them, why not the other derivative plugs?

The research you posted is excellent!  That will help me make a decision on whether to change the Platinums out later.