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Nelson plugs how do they do it. ??

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Old 09-07-2017, 11:44 AM
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gmeyers
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Question Nelson plugs how do they do it. ??

I have a couple of engines using Nelson plugs, and a head adapter that uses one too . They all out-perform the same engine with standard sized plug. Anybody know how this is. Temp wise they are about the same, electrical resistance the same, shape is different but I am convinced that isn't entirely the reason for the difference. I've machined other heads to simulate the same shape and with different temps from cold to hot but the results aren't the same. Any thoughts anybody???
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Old 09-07-2017, 05:14 PM
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It is all in the way that the taper seals. The threads on a normal plug have a gap that doesn't work as efficiently. The turbo ones I think are better because the diameter is a bit smaller which makes a lot of improvement on a smaller motor like .15s or less.
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Old 09-13-2017, 11:17 AM
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Hi!
The difference is the how the plug seals and how smooth the combustion chamber surface is compared to ordinary glow plugs.

Last edited by jaka; 09-13-2017 at 11:55 AM.
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Old 09-13-2017, 02:33 PM
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Default Nelson plugs

Originally Posted by jaka View Post
Hi!
The difference is the how the plug seals and how smooth the combustion chamber surface is compared to ordinary glow plugs.
I'm not about to argue with your answer and I thank you very much. but I have several heads bored and tapped for those plugs and it seems they all bump up the RPM's regardless of their shape - one head I was working on I got a bit of chatter with my end mill and it was kinda wavy looking but it made no difference in the performance of the plug - still bumped it up by 2,200 RPM . the range of RPM gain has been from 700 to 2,500 with real nelson plugs.
I'm going to continue to experiment with combustion finish and shape for regular plugs and for Turbo plugs and if I have anything spectacular to report I'll do it here.
Thanks again
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Old 09-13-2017, 06:17 PM
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I have had similar luck with the turbo plugs too. Just a 100 degree countersink for a combustion chamber has worked well for the .049s that I tried. I ground up a ball end mill for some .074s to .25s that worked well too. At some point I will try the countersink on the bigger ones. I found the turbo plugs wear away the taper and protrude a bit after repeated tightening. The Nelson plugs have a shallower taper and do not do this. I will leave a bit more land on future turbo heads. Maybe a .010" step.
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Old 09-15-2017, 03:52 AM
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I suspect it is the size and shape of the
element cavity. A small shallow cavity
may "spray" fire wider and quicker than
a large deep one.

Jenny
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Old 09-15-2017, 05:45 AM
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Originally Posted by Jennifer Curtis View Post
I suspect it is the size and shape of the
element cavity. A small shallow cavity
may "spray" fire wider and quicker than
a large deep one.

Jenny
May be - I'll investigate that more closely. I'd like to find an answer.
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Old 09-15-2017, 06:05 AM
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I was talking to Al of Merlin plugs, and he was mentioning that some .049 plugs have a smaller hole around the element, and they give better performance, even though the heat range is wrong. They do not idle, so that is not in the equation. I got a few turbo plugs with the flat Glowbee type coil to try out. That might be even better. I have not tried them yet. There is no hole at all and the coil is like a stove element. I had some great results on an ASP .15 and even better on a CS .049. If the ASP would not burn out plugs and the CS would go a bit faster yet with the Glow Bee, they would make me very happy. (I might set a record even)

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Old 09-15-2017, 07:05 AM
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Originally Posted by aspeed View Post
I was talking to Al at Merlin plugs, and he was mentioning that some .049 plugs have a smaller hole around the element, and they give better performance, even though the heat range is wrong. They do not idle, so that is not in the equation. I got a few turbo plugs with the flat Glowbee type coil to try out. That might be even better. I have not tried them yet. There is no hole at all and the coil is like a stove element. I had some great results on an ASP .15 and even better on a CS .049. If the ASP would not burn out plugs and the CS would go a bit faster yet with the Glow Bee, they would make me very happy. (I might set a record even)
I wanted to go to FOX to meet Betty Fox and take a tour of the factory about the time it was in decline and while I was there studying the girls welding elements into the plugs Betty assembled me a special Eagle 74 ABC which I have never ran. Anyway I spent a couple of hours watching the glow plug operation and learned that FOX had about the best experts in the world at designing and manufacturing those little things. They opted to produce just three types for consumers - the standard, the RC, and the Miracle 4-stroke plugs all in both standard length and short length. They could have produced others but opted to provide for the largest demographics and leave others to deal with the rest. I truly wanted to get one of those welders but could not get past proprietary issues, When they closed the factory I tried again but ran into similar problems when MECOA bought the remaining inventory and machinery.
I have a K & B boat motor (7.5cc's RIRE) that has been changed to spin an airplane prop and it's 1 flight 1 glow plug no matter what I try to do. When I land the element is completely missing. I'd still like to get a welder - can I borrow yours for cloning purposes?
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