<VV> water injection advice needed- now heat range

[corvairduval at cox.net]

That sounds better.

Combustion temperatures in a Corvair are over 2500 °F I would assume, since
EGR systesm were installed to keep combustion temperature at 2500 °F to
minimize NOx production. So 60 out of say 3000 is a small change.

The path of heat from the tip of the plug to the head is shorter with cold
range spark plugs. Pre-ignition can be caused by the red hot tip of the
spark plug setting off the charge before a spark is activated, and having a
shorter path will keep the tip cooler to prevent pre-ignition of this type.
You can usually see if pre-ignition is caused by the spark plug, as it
looks very white and misshapen when examined.

Frank DuVal

Original Message:
-----------------
From: Mark Durham 62vair at gmail.com
Date: Tue, 19 Feb 2013 10:52:12 -0800
To: corvairduval at cox.net
Subject: RE: <VV> water injection advice needed


Frank, I ran across that tidbit while studying spark plugs last year. I
should have clarified, it changes combustion temperatures that much,
not cht, however, lowering combustion chamber temps will lower cht's as
well. I'm sure you know that when the spark is fired and how much heat
is transferred to the head from the plug has an effect on internal
combustion chamber temperatures. I'm not an expert on the thermal
dynamics involved, just know I need to use colder range plugs in my
modified engine To keep it from pre-ignition. It happens to have
tapered seat plugs in it out of a Chevy 350 so it took a bit of
research and trial and error to get the plugs in a good temp range. I
kept having a intermittent miss going down the road I tried everything
to cure, finally got several sets of colder and colder plugs until I
got a set to work well. Someone had welded up the 62 102 heads and re
machined like a 62-150 but smaller chambers, and relocated the plugs
closer to the exhaust valve. It was some sort of performance mod done
years ago in the Seattle area, but I don't know by whom. The original
owner had a std set of plugs from a 350 in it that would last maybe 1k
miles then start missing. The beginnings of pre ignition were evident
on the plugs, so, I fixed the problem with a set of plugs 2 range
clicks colder than the standard plug.
Mark Durham

Sent from my Windows Phone
From: Frank DuVal
Sent: 2/18/2013 9:00
To: virtualvairs at corvair.org
Subject: Re: <VV> water injection advice needed
OK, I would like to hear how the plug design (distance from the hot tip
to thermal "ground") can change the combustion temperature/head
temperature  by 60 °F?
  The heat comes from the combustion of gasoline vapor. Whether it goes
quickly or slowly to the head from that pin point tip of the spark plug,
it still gets there.

Frank DuVal

On 2/18/2013 10:58 AM, Mark Durham wrote:
>
> Also, what heat range plug are you running? I would suggest the coldest
> range, that can itself lower cylinder temps by 60 degrees.
>
> Mark Durham
>

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