Larry,
You will have to ask your dyno guy why he picked .048". Did he even try a
run with your .063" gaps? In general, as you turn higher rpms, the energy
per spark decreases. In a conventional coil and breaker setup, with the
aforementioned gaps, the engine would probably start missing somewhere in
the 5-6k rpm range (depending on compression and other factors. As we have
discussed previously on the List, the purpose of the dual-point distributor
is to increase the dwell and get as much energy into the coil per discharge
as possible. .016" gap with a dual point is probably equivalent to about
0.08" gap or less with a single set of points. Of course, we all know that
the MSD, in addition to providing multiple discharges at lower rpms,
continues to give a single strong discharge at much higher rpms than even a
dual point system would. However, even an MSD system has its limits and if
the gap is too large, at some point the MSD will not generate enough voltage
and/or current to produce an effective spark. Of course the other thing that
can happen with a big gap is voltage breakdown, but this can happen at any
rpm. So, is there really any advantage to a big spark gap? In my experience,
I see a difference in terms of how smooth the idle is. I can't really say
that I see any more power at the high rpm end so you should take the advice
of an experienced dyno tuner on this count. I have been told by people who
should know that a new set of plugs is worth a few more ponies on the dyno.
Indexing the plugs is supposed to help too. BTW, based on the advice given
on the List and elsewhere, I index the gap in the region between 3 o'clock
and 6 o'clock. Again, without a dyno I can't confirm whether it really helps
or not.
Bob
-----Original Message-----
From: owner-tigers@autox.team.net [mailto:owner-tigers@autox.team.net]On
Behalf Of Larry Paulick
Sent: Friday, October 06, 2000 2:12 PM
To: Bob Palmer
Cc: Smit, Theo; 'Tigers'
Subject: Re: Dist. Cap
Bob, what are the advantages of gap, on both ends. I originally put
.063" on my plugs, and the dyno man backed them to .048". This is with
a MSD6AL, Mallory magnetic distr, 8mm Taylor wires, platinum plugs, big
Mallory coil, and 9.5 compression ratio.
Thanks
Larry
Bob Palmer wrote:
>
> Theo,
>
> The parameter that directly determines the spark voltage is the spark plug
> gap. Back in the '70's the auto manufacturers went to very large gaps -
> .070"-.090" - and consequently had to increase the cap size and make other
> improvements in voltage standoff capacity. I'm not sure what gap is normal
> these days, but bigger is better to a certain extent at least. I think you
> will see that MSD recommends around 0.055" or so, depending on compression
> ratio. For quite a while I ran an MSD with a standard Ford dual-point
> distributor with 0.055" plug gap and never had a problem. This was with a
> pretty high compression motor BTW. I think a good set of 7 mm wires will
> work just fine too, in case you are after that "stock" look.
>
> Good luck,
>
> Bob
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