REFLECTOR: Auto spark plugs

[aminetech at bluefrog.com]

I replaced the Denso X27GPR-U plugs with $2 autolite plugs (seems like that should be illegal at only $2).  What a difference.  The engine runs great, CHTs are all the same.  These plugs are supposed to be one heat range lower.  The Denso's worked great when new, so it will take time to tell if there is a difference.  What experience do others have using auto plugs with EIs?

John

--- sbjknox at earthlink.net wrote:

From: "sbjknox" <sbjknox at earthlink.net>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Subject: Re: REFLECTOR: Running LOP -- Climbing or Cruising
Date: Fri, 12 Nov 2010 16:17:49 -0600

No, the thread depth does not change, only the structure of the ceramic 
insulator.

Sid

----- Original Message ----- 
From: "Brent Bourgeois" <bjb3013 at yahoo.com>


The hot / cold of a plug is the measure of how much heat the plug conducts 
out of the cylinder. The thread depth (length) changes not the ceramic or 
the electrode. Search hot / cold racing plugs on the internet

Brent
N61VB
New Orleans


From: aminetech at bluefrog.com <aminetech at bluefrog.com>

Are you saying the cooler plug has a shorter center electrode? Can I file 
mine off to make them shorter? I'm planning to get some cooler plugs, but 
they won't come until next month and I really need to keep flying now.

John

From: "sbjknox" <sbjknox at earthlink.net>

>> That's interesting. I'm currently have spark plug issues and I'm
>> planning to try a cooler plug. Could I simply add a washer to my
>> existing plugs to get less reach and effectively make it cooler?
>> John

My opinion (not a fact) is just the opposite. The washer would create a
longer path for heat to flow from the plug body to the cylinder. You want a
lower heat-resistant (shorter) path from center electrode to the cyl...that
is why a colder plug will have a shorter exposed (exposed to the hot
combustion gas) center electrode insulator.

Sid Knox
Oklahoma

Velocity 173 RG N199RS
Starduster N666SK
KR2 N24TC
W7QJQ


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