Spark Plug Differences autolite 45 vs 124

[Eoth]

Ok... I have a stock 1969 302 and I have been using Autolite 45's. I dont remember why those and not others but they were installed a long time ago... Anyways I decided that they were looking rusty and old so its time for a change. Going to the parts store they look it up and it says that a 1969 Ford Bronco takes the Autolite 124. Upon further research I see that there is a different reccomendation between trucks and cars.... It is my understanding that there isnt a difference between engines destined for cars or trucks (at least back then) so whats the story? Should I stay with the 45's or change to 124????

 

[Quick & Dirty]

The 45 is an extended tip (Powertip in Autolite advertising), the 124 is standard tip.

The extended tip is supposed to stay cleaner, without going a hotter range. The extended tip is also closer to the center of the combustion chamber for slightly better flame travel. They became common in the smog era, as axle gearing was changed to drop engine rpm. Good for stop and go, start easier with poor mixtures.

Standard tip is often preferred for high performance, high rpm engines, as they resist detonation better. Also less likely to be hit, and pushed shut, by a pop-up piston as the rods stretch at high rpm.

 

[Eoth]

Wow.. Excellent explanation! Seeing the obvious difference (the tip on the 45) really had me uneasy. I threw them in last night (boy the last one closest to the driver was a B-tch to get at) but I was holding off on firing it up until I could understand the differences. Looks like I am going for a drive after work today. Thanks again!

 

[broncnaz]

124 is a colder plug plug than the 45. The 124 is a standard tip as was said and the 45 so called power tip is realy the same just that hotter plugs have longer tips. So they market it as a power tip. The 45's are usually better to run just due to the longer times broncos spend at slow speed.