Originally Posted by
H5606
Either forgot or more likely never realized there are mid-reach plugs; only thought longs and shorts w/w/out idle bar, various heat ranges...
Can you shim plug and achieve decent results?
Thanks all.
Plug choice has never been a huge issue with me [running wide open 99% of the time] unless I'm working with a super cold plug that my engine can't bring up to temp.
You want to monitor the condition of the combustion chamber and top of the piston. You don't want to see a clean, sandblasted surface. You want to see soot and a caramel finish in there.
If not, add head shims. Better to add too many than too few, you can always subtract as needed after you get the feel for what is going on in there.
A tuned pipe raises the dynamic compression ratio, so if you obliterate a glow plug you need to "detune" the things that you have control of like fuel mixture, pipe length, nitro content, head clearance and propellor load.
Too short of a pipe system or not enough volume causes excess heat.
A loose glow plug element rattling around inside your engine can get expensive.
When you hold your finger into the exhaust spray, you should see dark brown ooze and not black. Black means that the engine is over-compressed. Same exact symptom if you are tuning a diesel.