Spark Plug Gap
Thread Starter
Racer
Joined: Dec 2002
Posts: 306
Likes: 1
From: N. Charleston SC
Spark Plug Gap
On the 427/400hp with R43N plugs, the service manual calls for a gap of .035". When would you want to either increase it or decrease it?
... in other words, how can you use variation in gap to aide performance?
Thanks
... in other words, how can you use variation in gap to aide performance?
Thanks
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
Re: Spark Plug Gap (Red69)
... in other words, how can you use variation in gap to aide performance?
Race Director
Joined: Jun 2001
Posts: 16,483
Likes: 1
From: The Only Corvette in Gila Bend, Az.
St. Jude Donor '09
Re: Spark Plug Gap (Mike Ward)
The only time I have ever seen anything on increasing plug gap, was with my truck when I installed a MSD ignition. they told me to open the gap up 10 to 15 thousands to allow a larger, hotter spark.
But you have to remember this is with a big increase in voltage.
But you have to remember this is with a big increase in voltage.
Le Mans Master
Joined: Sep 2000
Posts: 5,635
Likes: 4
From: Orlando Floriduh
Re: Spark Plug Gap (Desertdawg)
Spark plug gap is determined by the coil. If the coil doesn't have the capacity to jump a larger gap then a larger gap will overneat the coil and the spark may not be consistant resulting in mis-fire. Now if the gap is too small the spark will jump very easy but not very hot. GM "HEI" (high energy ingnition) put out higher voltage so they use plug gaps up to .060. I think one year they used .080. In all cases condition of the plug wires is very critical. An old wire with breaks interally is a huge strain on the ingnition system.
Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
Re: Spark Plug Gap (Red69)
if yur running stock ignition stay with the stock gap. If you run a higher output coil then you can experiment with larger gaps. but as stated above, too much gap will make it difficult for the spark to jump the gap. too much gap can cause mis-firing and hard starting
Advanced
Joined: Oct 2002
Posts: 83
Likes: 0
From: Cumberland RI
Re: Spark Plug Gap (Red69)
I know this doesn't answer your question but I just installed Bosch Platinum series Spark plugs in my '70 350/350 and I can't believe the difference! I used the 0.035 gap recommended in the specs. The plugs were 3 times the cost of Champions but they came with a money bacl guarantee from Bosch so I said, "What the heck."... I recommend them.
-Bill
-Bill
Melting Slicks
Joined: Oct 2002
Posts: 2,106
Likes: 0
Re: Spark Plug Gap (vett70)
Well when i regapped my plugs i set them to .035 because thats what the gap on the 350/350 motor was, but after reading this thread should i set them to . 042 like it says on the firewall and in the book?
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Le Mans Master
Joined: Sep 2000
Posts: 5,635
Likes: 4
From: Orlando Floriduh
Re: Spark Plug Gap (battsup)
If you have the GM HEI ignition you need the bigger gap to take advantage of the hotter spark. If you are using an aftermarket set-up, use the gap reccommended by the mfg. of the system.
Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
Re: Spark Plug Gap (battsup)
Yup the ignition system is stock, could this explain my some of my bad emmisions results and why my car sometimes diesels after i turn it off.
