switching from cold glow plug to medium/hot glow plug

[pelicanprentice]

i have a hpi savage x 4.6, i bought a os #10 from the LHS, as thats what the recommended. I took the truck to a local tuner and he seemed to warm it up on blocks and tune from there and he took it for a spin a couple times and it seemed good to go, however i just took the truck for a full tank of fuel and the ambient air temperature was basically the same however it was pretty groggy and seemed rich i guess. the tuner recommended a #8 plug as our temperatures in summer are usually around 20celcius to 30 celcius however i could only get #10 from my lhs.

my question is show i just try leaning out the engine a little more? i ran a whole tank mostly on full throttle but it was groggy and didnt really seem to wake up, i used my temp gun but wasnt really getting high temps around 185 degrees celcius (however i don't rely on my low quality ir temp gun), i tried the spit test on the cylinder fan head thing and it didnt sizzle or boil off so i do believe my temps are lower. Today however was a cooler day compared to the regular days, about 18 celcius.

Would you guys recommend i switch to a #8 plug and go from there? or is it better to keep the # 10 and i guess go leaner?

correct me if I'm wrong but it seems like he got the truck super hot arounfd 230 easily on blocks and he tuned from there, but it seems like i will never be warming up the truck that much before i want to bash and race, so doesnt that mean i should be going leaner anyways?

thanks

 

[olds97_lss]

Plug temp and engine temp and ambient temp aren't really related. Plug temp is related to compression and nitro content. If your running 20% nitro fuel, a hot/medium hot plug should work fine. With higher nitro content, you step down to a cooler plug. I run 25% nitro and medium temp plugs in all of my trucks. When I ran 20% nitro, I ran OS #A3's in everything but traxxas engines because they use a longer plug. In those, I used OS LC3's. Now that I run 25%, I use odonnel medium (purple) plugs and OS LC4's in my traxxas/OS TM engines. If I ran high compression/high performance racing engines, then I'd probably be using 30% nitro and cold plugs.

Plug temp is for timing the combustion to happen at the right point in the stroke, just as the piston gets near the top of the upstroke. If it fires too early (too hot of plug), then it will fire as the piston is low in the stroke and coming up, which causes it to fight itself. If it fires too late, after the piston starts back down, it will cause most of the power to go out the exhaust. Plug temp allows you to adjust for that.

As ambient temp and humidity changes, so will your tune. Nitro engines aren't a "set it and forget it" type thing. It's something you have to adjust a little bit nearly every time you run and sometimes while your running throughout the course of a day. Could be dryer/cooler in the morning, hotter in the middle of the day, cooler in the evening. 3 different tunes needed in one day.

For 20% nitro, I never had good luck with the #10/A5 OS Cold plug.