bosch spark plugs, bosch platinum spark plugs, spark plugs, bosch

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route. I'm not sure what the gap is but the center electrode cants
at about a 30 degree angle.

The results I was looking for and got were better idle with marginal
mixtures and better mileage as the result of better ignition at
part throttle. The only downside is the stock system may not be able
to handle the added voltage stress. I've heard of rotor buttons blasting
through to the shaft from the added stress.

john

From: jgd (John De Armond)
X-Source: The Hotrod Mailing list
Date: Aug 1992
Subject: Re: Plug gap

>-> varying the gap in a pressurized chamber (like used to be on the
>-> champion plug cleaning and testing machines) until the spark took the
>
> Gosh, I haven't seen one of those things in years.
>
> I seem to remember some controversy over the plug cleaning machines.
>Do they really work? I realize only a file or a pass with the moto-tool
>will give nice sharp corners on the electrodes like a new plug, but it
>always looked like it'd be useful to turn the insulator white again so I
>could see the results of the next jet change/boost increase/whatever.

Official Champion word and my experience is that those things, which use
abrasive sand, remove the glaze from the porcelean and thus make the
plug extremely foul-prone.

What I've found to work quite well, however, to whiten a plug up for another
check is to GENTLY bead blast the porcelean. 40 psi air or less.

John


From: emory!clockwise.att.com!jjnjw
X-Source: The Hotrod Mailing list
Date: Jul 1993
Subject: help: sparks plugs hot/cold
X-Sequence: 5808

Hello ..

I was looking thru my owners manual ( '90 miata) and I noticed they had
3 different plugs listed for my car .. as it turns out .. the extremes
are hot or cold plugs.. Please explain the difference and when you
should use a hot plug or a cold plug

[The cold plug would be approrpiate for extended wide open throttle.
By extended I mean several miles at a time. The hot plug would be for
conditions such as very extended idling where fouling might be a problem.
The middle plug is for average service. JGD]

AND ..

When i race the car (auto crossing) ... should i use a different plug
then what i would use when i am driving on the street ?

I don't mind changing the plugs when I get to the "event" and then
changing again before i drive home .. IF one plug type is better then
another for tre particular use... Some one told me that : If your plug
electrodes are 'white' then you need a colder plug and If they are
black/carbon-coated .. then I should use a hotter plug .. I have NO
idea ...

[I wouldn't bother changing plugs in a (mostly) stock engine. Modern
plugs have a fairly wide heat range and coupled with closed loop engine
management, you're unlikely to have any fouling problems. You really
can't read much from plug color with unleaded gas. IT just doesn't color
the plug like leaded fuel used to. JGD]


Please post here OR write to me directly ..
James D. Wynn
jjnjw@clockwise.att.com

thanks in advance ...


From: B.Hamilton@irl.cri.nz (Bruce Hamilton)
Newsgroups: rec.autos.tech
Subject: Re: "Hot" vs "Cold" plugs??
Date: Mon, 01 Sep 1997 18:47:47 GMT

Well, I thought I would see if anyone actually read my posts
by mixing up two major parameters for spark plug heat ranges
( length of exposed central electrode, and length of the heat
transfer region ) in the ascii drawings. Nobody noticed, even
though the drawings looked unbalanced. Altavoz followed up
- without detecting the deliberate error - as I expected, but
I though some of the obvious clue-laden readers might have.

Ah well, the correct drawings are below, and I've added to them
to show where the threaded portion is relative to the heat transfer
area, as the seat and threads are the major paths of heat transfer.
Obviously the overall heat range of the tip results from the balance
between the heat dissipated from the tip versus the heat transferred
to the tip from combustion and the plug body, which is greatly affected
by the design ( amount of exposed electrode, electrode material and
diameter, overall heat retention of the plug body, overall thermal
mass and conductivity of plug body, etc.etc. ).

It's also worth noting that the majority (67%) of the heat from
combustion ( which determines the temperature of the plug, and thus
the temperature at the tip of the central electrode ) arrives
via the metal body of the plug - predominately from the bottom
surfaces and the inside of the threaded area, and the exposed
insulator only transfers 20% of the heat to the plug, and the
exposed central electrode only 4%, and the exposed earthed electrode
transfers 8%. The temperature range of a plug arises from the
sum total of the heat flows within the plug, which determine the
temperature of tip of the central electrode and (less importantly),
the earthed electrode, not the ceramic - as originally claimed
by altavoz.

I previously wrote:-
>The heat range is defined by the length and diameter of the
>special conductive seal in the body of the plug and the position
>of that seal relative to the electrode tip. If the electrode provides
>a long path to reach the heat transfer region, then the plug
>is "hot", and if the path is short then the plug is "cold".