REFLECTOR: Automotive Spark Plugs

[John Dibble]

Looks like I need to to more research.  Here's what I'm sure of:

Higher compression engines need a cooler spark plug.

Here's what I'm sort of sure of:

The next to hottest plug is about right for my 10/1 Franklin.

Here's what I don't know:

What reach the plug should have.  The aviation plugs have 3/4" of thread.  The adaptor
adds another 1/4", so 1" of thread is needed to put the electrode at the same location in
the combustion chamber.  Brian, the auto store cross referenced your Bosch plug to a
Champion L86C (new # 306).  This has 1/2" of thread, so it is 1/2" short.  I am wondering
if this can affect the compression ratio.  The guy in the store is concerned that it
would foul.
The other issue is the adaptor.  The ones I have, have 1/2 of thread, so a plug with 1"
of thread will extend 1/4" past the adaptor.  Can this area foul with lead deposits and
make removal difficult?  I'm thinking I will need an adaptor with 3/4" of thread.

Any comments?

John

Brian Michalk wrote:

> I am using a Bosch 14mm plug on my Franklin.  Bosch W7AC, if I recall
> correctly.  I'll check when I get to the hangar.
>
> John Dibble wrote:
> ? I plan to convert my Rose ignition (Franklin engine) to automotive spark plugs.  I
> ? currently use the same plugs as for the mag - Champion REB32E.  Anyone know or have
> ? ideas as to what plug to use?
> ?
> ? Thanks,
> ? John
> ?
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