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-   -   Glow plug question (http://www.rcuniverse.com/forum/glow-engines-114/11349894-glow-plug-question.html)

Mr-Punk 12-30-2012 01:07 PM

Glow plug question
I'm running a 46 AX with a Macs pre-tuned pipe and getting 13500 (a little rich) with a 11x8 MA on the ground. I've been running os #8 plugs. Originally the stock plug lasted thru 2 gallons of fuel with the stock muffler of course. I know a pipe will eat a few more plugs. But since I've piped it it seems to eat one every other weekend. I'm not running it too lean and using Wildcat 15% nitro 18% synthetic oil. What plug would be more robust? Is a #6 a tougher plug? And how does Fox rate their plugs? Those OS #8's are getting expensive.

Thanks and Happy new year,

Pete Bergstrom 12-30-2012 01:15 PM

RE: Glow plug question
Get some head shims for you engine and I start them between the cylinder liner and the head. The problem is not the glow plugs but the increased compression ratio that comes with using a tuned pipe. Start with .004-.005" shim and keep adding until the problem goes away.

Pete<br type="_moz" />

MJD 12-30-2012 02:04 PM

RE: Glow plug question
Pete may be on the money, but one thing has me wondering. The pipe may be pretuned, but what rpm range is it pretuned for? 11x8 is a big shaft load for a .46 - in my books that's a .60 size prop. I would be mildly surprised if a pretuned .46 pipe system is set up for that prop, unless you asked specifically for it to be or have tuned it yourself for that rpm range via header length. So I wonder if the pipe length may be too short, that can beat the tar out of plugs.

And how many rpm back from peak are you setting it on the ground? You need more headroom than for a muffled engine. As rpm climbs due to supercharging from the pipe, the mixture will head farther in the lean direction than on a muffler. For a muffled engine 200-300 back from peak is typical, but on a pipe, depending on the state of tuning, more may be called for.

Also, a large prop can exaggerate compression issues.

I'd run a 10-6 or 10-7 myself. Or 11-6 tops. But pipe length has to be adjusted to the rpm, or there is no point having one.

1QwkSport2.5r 12-30-2012 02:08 PM

RE: Glow plug question
I have one engine on a pipe, and I never blow plugs. I'm running up in the 16,000rpm range. If it were me, I'd drop some of the nitro. I would also richen it farther from peak on the ground. Maybe 600-800rpm instead of the typical 300-400. When it comes off the pipe it ends up being lean and pop goes the glow plug. I run 5-10% nitro and HOT glow plugs; McCoy MC59 or Enya #3's.

This is only from my experience, and I don't fly my engines yet.

fizzwater2 12-30-2012 07:03 PM

RE: Glow plug question
I was also thinking that the prop size was awful big for a .46..

Warbird40 12-31-2012 12:58 AM

RE: Glow plug question
I went up in pitch from and started having problems with plugs and tuning, so I also suggest going down on pitch and see if that helps.

ronwc 12-31-2012 05:06 AM

RE: Glow plug question


ORIGINAL: Warbird40

I went up in pitch from and started having problems with plugs and tuning, so I also suggest going down on pitch and see if that helps.

11x8 is way to big for a 46, try a 11x6. Also, if you keep burning out plugs, try an idle bar.

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