colossus281

What's the difference between a long and short glow plug? Thanks

proanti1

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The length of the threaded part of the plug. Long plugs are generally only used in airplane engines.

downunder

For normal (non turbo) plugs there are 3 different lengths. There's the usual long and short reach plugs but also the medium length plugs made by OS and Enya. Short reach plugs are generally only used in the smallest of engines. Ideally a plug should come flush with the surface of the combustion chamber and it's easy to check what's needed (if the instructions don't specify it) by taking out the head button and lightly screwing in a plug. It's not all that critical though so if it seems the plug is half a thread too long or short it's no real worry. Plug washers though come in different thicknesses from different brands so I tend to keep old washers to use to shim a plug up or down a fraction sometimes. This comes in handy sometimes if you want to use a normal long reach plug in an OS or Enya engine which could be designed to take their medium reach plugs by using two washers under the plug.

HerrSavage

Doesn't make any difference unless you're running a non-turbo OS engine..

For SH big blocks, I only run OS.. OS A5 in a Dynamite Big Red, Mach 427, LPR 28, Losi 454, etc... Best plug IMO, whatever the length..

Only really know about 21-28 engines, so no idea for .18's, etc..

1QwkSport2.5r

Almost all car engines use long plugs. You can use any plug you want, but the shorter plugs will have a slightly oblong flame propagation and can cause odd engine behavior. In general though, the compression will be slightly less using a short plug in a long plug engine.

OS standard plugs are medium reach. Os' LR numbered plugs are long reach. I use McCoy long hot plugs (mc59) in all of my engines because they run great and are $3 cheaper per plug. I have one airplane engine (Enya 30ss) that uses a medium plug and I just use 2 washers under the plug to have the plug flush with the combustion chamber.

HerrSavage

Little bit off-topic, but I do encourage anybody with an SH big block - Mach, LRP 28, etc.. to try an OS A5 plug. The performance is notably better(though the idle suffers a bit..) - especially on top-end..