>From: Bob Spidell <spidell@hpcc01.corp.hp.com>
>Subject: re: sparkplugs (fwd)
>On the subject of "indexing" spark plugs:
>>>plugs and put them in the spark plug holes, such that the line ends up
>>>oriented away from the inlet valve. It may take a few tries, swapping
>>>plugs amongst holes until you have an acceptable position for each.
>>...
>...
>I can't see how this indexing does any good, unless the idea is to
>"douse" the electrodes with the mixture. After all, the intake valve
>has long since closed by the time the plug fires, making the orientation
>of the side and center electrodes irrelevant. Can anyone elaborate on
>the supposed benefits of indexing the spark plugs?
Bingo. Pointing the plug at the intake valve is not the idea. There are two
reasons for indexing:
In *REALLY* high compression motors, there is a chance of the piston hitting
the side electrode, if it's downward. The obvious solution is to make sure the
electrode is towards the top. I had to do this on a 14.5:1 GP Spridget motor.
The second reason has a value ranging from questionable to nil. As the
mixture is compressed, it swirls. Some motors swirl more than others, but it
is a desirable effect. The theory is to make sure the spark is not shrouded
from this swirl by the electrode. So, which way do you point the electride?
Well, which way does it swirl. Odds are that, again, straight up is best.
Also not that this would be more effective on a big block chevy, where you
have a 4.5 inch bore, and the plug is all the way on one side. British designs
with their relatively small bores won't gain much. And, things like hemi-head
Alfa's will show no gain. Then again, Alfa used the elctrodeless Lodge plugs.
On a side note, someone asked about splitfire plugs. I've seen them, and
know some gokart racers that tried then. I highly recommend NGK BP6-EY (note
the "Y", not "S") plugs. (Spit and TR7 owners substitute a 5 for the 6)
Randy K Wilson
randy@taylor(.uucp)
...!uunet!chrysanthemum!taylor!randy
|