Thread: spark plug length

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Ok I have two quetions here
1. I just pulled a spark plug out today to get a part number off of it and called part stores to see if they had that part. None did so i asked to cross reference some came up. So i go to the store and they handed me autolites(i dont think so). So I said how bout r44ts or r45ts(ac delco numbers) started to examine new and old and the new ones are short shank and the old are long is there a reason i should or shouldnt run one or the other. I mean the long shank never hit my piston or nothing so would it be better to get the spark as close to the piston as possible? Oh the long shank is a NGK part that came up as a racing app.
2. I was considering going back to q-jet over my proform carb. My proform is a 950 way to big. and I really am not into holleys(style) carbs but i never really owned a motor as the one that I have so would i be able to make good power on the street and the strip with the q-jet. I tried one on this motor once with no mods done and it had a mid range cruise speed lean miss although i did change jets and needles nothing better nothing worse came of it. Now i know if you pull the float cover off there are two spots that you can drill for mid range fuel flow. Will this help? I wanna get away from my holley
I hope this makes sense!!!

if i remember right, the length of the plug had to do with where it was located in the dish of the cylinder head, and nothing to do with piston at all. many many years ago i had a 305 motor that had the shorts, and i remember checking into it way back then. as for the carb question thats another whole can of worms there. the q-jets are very finiky and harder to tweek, but they are a great carb when they are working right. im not sure if id drill any holes in it, never heard of that before.

383 Chev,

A couple of things. The engineers at the factory spent a whole lot more time and money trying to determine how long or short the plug should be than you or I could possibly do. It is best to use somewhat close to what the factory used in the particular application.
As far as "I don't think so" for the Autolite plugs, I could tell you a story about that but it would take too long. If Autolite plugs are available to me I will certainly use them. They were the only thing that I found that would hold up on a brand new 1969 Camaro 396/375 SS for more than 300 miles without missing. That car was death on spark plugs.
As far as the Holly carb, I have use a lot of them. Thay can be a royal pain. If you can find someone that knows how to set up a Q-jet, they are a very dependable carb and will perform very well.

Ed