049 Glow plug conversion perfected
04-27-2003, 03:02 PM
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049 Glow plug conversion perfected
Andrew,
I've got one of these tapered plugs. They're actually the same thread as a stock plug but the bottom bit has a taper for seal. Can't remember where I got it. I think it was at AVF hobbies in London. It's called "Dynamite Turbo Plug" and the package shows Horizon Hobby. Its also called a #7 medium so it appears that its available in a variety of heat ranges. That would be a lot of fun to experiment with.
Not cheap at 10.90 Canadian. This shop was very big in cars so perhaps this is a car item. I picked it up to experiment with but lack of roundtoits got in the way. Also, getting the correct taper kind of intimidated me.
I've got one of these tapered plugs. They're actually the same thread as a stock plug but the bottom bit has a taper for seal. Can't remember where I got it. I think it was at AVF hobbies in London. It's called "Dynamite Turbo Plug" and the package shows Horizon Hobby. Its also called a #7 medium so it appears that its available in a variety of heat ranges. That would be a lot of fun to experiment with.
Not cheap at 10.90 Canadian. This shop was very big in cars so perhaps this is a car item. I picked it up to experiment with but lack of roundtoits got in the way. Also, getting the correct taper kind of intimidated me.
04-28-2003, 01:36 AM
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Best heads and glow plugs
Guys, we used to race the norvel .049 and the only way to go for us was the head made buy Doug Gailbreth and the Nelson glow plug. The heads were 10.00 ea with more power than stock and way more than the modified heads for standard glow plugs.
Keith
BME
Keith
BME
05-01-2003, 10:15 AM
#58
049 Glow plug conversion perfected
`Guys, we used to race the norvel .049 and the only way to go for us was the head made buy Doug Gailbreth and the Nelson glow plug. The heads were 10.00 ea with more power than stock and way more than the modified heads for standard glow plugs. `
Has anyone compared a norvel `freedom XL` (why did they call it that?..sounds like an electric tooth brush..) To a nelson?
There has been much written in this coloum about plug `hole` chamber size/ thread seals etc.
I can only say that i made a conversion head for a cox td on an outboard motor with tuned pipe that i made.. as a joke..
in that case i had converted the cox head to water cooling and when the plug died, i tapped the adapter by cutting flutes into an old plug. This of course caused a very tight fit between the plug and head, if you use a tap there is a standard clearance builtinto the tap of about 0.15mm, e.g the tap is made about 0.15mm oversize.
in this case it was very hard to tell if there was any fluctuation in power, as the engin was running on a pipe at very high rpms.
.. If you compare the hole diameter and depth of a standard plug to that of, for example a norvel one, you will find the norvels one has much less volume, and i think that there is somthing in this.
The O.S turbo plug also has a very small diameter hole and is slightly shallower than a standard (o.s)plug.
I still have not had my engine running with the turbo yet, i am in construction at the moment, but i don`t expect any drop in performance, if anything i suspect i will see an improvement.
but still, has anyone compared a nelson plug with a norvel?
J.M
Has anyone compared a norvel `freedom XL` (why did they call it that?..sounds like an electric tooth brush..) To a nelson?
There has been much written in this coloum about plug `hole` chamber size/ thread seals etc.
I can only say that i made a conversion head for a cox td on an outboard motor with tuned pipe that i made.. as a joke..
in that case i had converted the cox head to water cooling and when the plug died, i tapped the adapter by cutting flutes into an old plug. This of course caused a very tight fit between the plug and head, if you use a tap there is a standard clearance builtinto the tap of about 0.15mm, e.g the tap is made about 0.15mm oversize.
in this case it was very hard to tell if there was any fluctuation in power, as the engin was running on a pipe at very high rpms.
.. If you compare the hole diameter and depth of a standard plug to that of, for example a norvel one, you will find the norvels one has much less volume, and i think that there is somthing in this.
The O.S turbo plug also has a very small diameter hole and is slightly shallower than a standard (o.s)plug.
I still have not had my engine running with the turbo yet, i am in construction at the moment, but i don`t expect any drop in performance, if anything i suspect i will see an improvement.
but still, has anyone compared a nelson plug with a norvel?
J.M
05-01-2003, 12:24 PM
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Plugs
J.M.
Although comparison of Nelson and Norvel plugs is kinda like an apples and oranges thing, I have made some comparisons. It's possible that when comparing, unless your carefull that the set up is the same for both, that you will come up with results that are influenced by the set up rather than the differences in the plugs and won't get a true picture of what's best. What you will see is the best set up performing the best and you will think walla! the best is brand X! The combustion chambers are way different. And, if you keep the set up as close as possible, you'll find that the norvel will outperform the nelson even though the norvel chamber is larger than the nelson head which should produce less power. (8cc vs. 6cc) So, in comparing the Norvel head to the Nelson head, notice I didn't say "plug", the norvel head will outperform the nelson head by a 1,000 to 1.500 rpms. Now, if you consider the cost, Nelson's win by almost a two to one margin. So, as always, if you want to make the power, you got to pay the price..... Rgds, jeff.....
Although comparison of Nelson and Norvel plugs is kinda like an apples and oranges thing, I have made some comparisons. It's possible that when comparing, unless your carefull that the set up is the same for both, that you will come up with results that are influenced by the set up rather than the differences in the plugs and won't get a true picture of what's best. What you will see is the best set up performing the best and you will think walla! the best is brand X! The combustion chambers are way different. And, if you keep the set up as close as possible, you'll find that the norvel will outperform the nelson even though the norvel chamber is larger than the nelson head which should produce less power. (8cc vs. 6cc) So, in comparing the Norvel head to the Nelson head, notice I didn't say "plug", the norvel head will outperform the nelson head by a 1,000 to 1.500 rpms. Now, if you consider the cost, Nelson's win by almost a two to one margin. So, as always, if you want to make the power, you got to pay the price..... Rgds, jeff.....
05-01-2003, 02:30 PM
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049 Glow plug conversion perfected
I agree with Jeff. I've tried the Nelson plug in a number of engines, Cox and Norvel and didn't find performance, (or throttling) any better and in SOME cases worse. Some of them used a blank available from Nelson and some were heads I got from Larry Driskill. The best were the heads from Larry Driskill but while they gave a bit of an edge on power, throttling suffered. HOWEVER, the Nelson head and plug that comes with the VA MKII works best as far as throttling and power. It just shows that if you experiment with plugs, there's another step to take and that is to optimize that particular plug and head set up. The exception to the preceding is that when on the pipe, the VA would flame out occasionally upon rapid acceleration using the stock, Nelson head. For whatever reason. The cure to this was the adaptation of a Norvel plug. This allowed equivalent power with improved throttle response,,, but only on the pipe.
I also agree with J-Man that the cavity for the element can represent a substantial increase in combustion chamber volume and as well, it may also affect combustion behavior. I've run all manner of adapters, plugs etc in Cox, Norvel and VAs. Results have always been mixed with no clear advantage. In the end, the stock plug/head nearly always came out the winner. It's still an interesting observation though, that a stock plug in an adapter reduces power but nearly always improves idling and power. Why this is so is the question. It doesn't appear to be combustion chamber volume as this has been experimented with. It could be the heat range of any particular plug and/or the element's composition. Perhaps the combustion chamber shape. The latter is problematic because a stock plug is so large in relation to the head that its not possible to duplicate the shape of the stock plug/head. And so it goes.
Perhaps, if the weather co-operates, I'll revisit the entire issue and let everyone know.
I also agree with J-Man that the cavity for the element can represent a substantial increase in combustion chamber volume and as well, it may also affect combustion behavior. I've run all manner of adapters, plugs etc in Cox, Norvel and VAs. Results have always been mixed with no clear advantage. In the end, the stock plug/head nearly always came out the winner. It's still an interesting observation though, that a stock plug in an adapter reduces power but nearly always improves idling and power. Why this is so is the question. It doesn't appear to be combustion chamber volume as this has been experimented with. It could be the heat range of any particular plug and/or the element's composition. Perhaps the combustion chamber shape. The latter is problematic because a stock plug is so large in relation to the head that its not possible to duplicate the shape of the stock plug/head. And so it goes.
Perhaps, if the weather co-operates, I'll revisit the entire issue and let everyone know.
05-01-2003, 03:19 PM
#61
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049 Glow plug conversion perfected
Hey has anyone asked the top competitors (in cl speed, combat and mostly free flight) what head sthey use?? I bet they are using what works the best for top end (which may not be the best for RC).
If it was just a compression issue with a plug VS a head, you can easily compensate for the compression (shave the head, increas compression back to the original) so it must be a combustion issue IMO.
Maybe next winter I will do a detailed experiment with a Cox vs Norvel vs Nelso vs threaded cox head with a standard glow plug. Same engine/fuel/prop just different heads. Thats the only way to see whats what!
Andrew
If it was just a compression issue with a plug VS a head, you can easily compensate for the compression (shave the head, increas compression back to the original) so it must be a combustion issue IMO.
Maybe next winter I will do a detailed experiment with a Cox vs Norvel vs Nelso vs threaded cox head with a standard glow plug. Same engine/fuel/prop just different heads. Thats the only way to see whats what!
Andrew
05-01-2003, 05:15 PM
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049 Glow plug conversion perfected
Keep in mind anytime you change the shape of the inside of a head including the hole the glow coil is in itself. You will also effect the characteristics of the combustion pattern thus changing the performance of the engine. The smaller the combustion chamber the more this holds true. A couple thousandths here and there in a cox head is going to make some difference. So between the combustion chamber shape and the compression there are 2 issues at hand. Also when you shave or lower a head to gain compression you will also be making some changes to the combustion pattern as well but it should not be as noticeable.
I have a few cox engines on the way to tinker with. I generally use norvels but thought I needed some engines to tinker with hence the cox engines. The norvels are just so good stock that there isn't any need to tinker.
M_Saint
I have a few cox engines on the way to tinker with. I generally use norvels but thought I needed some engines to tinker with hence the cox engines. The norvels are just so good stock that there isn't any need to tinker.
M_Saint
05-02-2003, 03:35 AM
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049 Glow plug conversion perfected
If you caught it, I meant to say that a stock plug in an adapter reduces power but nearly always improves idling and acceleration.
Andrew,
I've been in contact with a few competitors, (don't know if they were top), but the Nelson is mentioned a lot and specialty engines like the CS and that other one from Russia always use a glow HEAD. And yes, they're not concerned with throttling as we are. This just proves that a stock plug in small engines just isn't a good working proposition. The OK Cub used a stock plug set up but it would be an interesting test to see what would happen if you adapted a Norvel plug. Uh oh, another experiment to try. Still, I've only seen a loss of 500 rpm in the .074. that's not bad. Perhaps some tweaking of some other element might get that back.
Msaint,
Agree with your observations. Also to be considered is the size of the combustion chamber. For instance, octane is important in car engines but not so in the weed eaters some of us fly. Why? Because the combustion chamber is so small in the typical gas model engine, that flame speed and characteristics just aren't a factor. In glow, I'd bet that combustion characteristics are similarly different. Imagine if you could see the flame in a TD .010 and compare that to an OS 1.08. I'd bet you'd see all kinds of unforeseen differences. Could be why the .010 is so hard to throttle well. At least with a conventional throttle.
This thread has prompted the following experiment, conducted just today. For the .074, I made up an adapter that would take an OS #3 plug. Like the first one I made for this engine, I made a hemi shaped combustion chamber with lots of squish band. However, this time I installed the plug offset from center. I'd observed engines in the past that had the glow plug offset from center. I believe they were biased towards the bypass port side. The adapter I made could be rotated 360 degrees and this is what I did. I tested it at 12, 3, 6 and 9 o'clock. My loss was now about 600 rpm. But, no matter where I placed the glow plug, there was no difference in rpm or throttling. This seems to prove that with such a small combustion chamber, a lot of elements that would affect a larger engine, just don't do dat in the small stuff we run.
Andrew,
I've been in contact with a few competitors, (don't know if they were top), but the Nelson is mentioned a lot and specialty engines like the CS and that other one from Russia always use a glow HEAD. And yes, they're not concerned with throttling as we are. This just proves that a stock plug in small engines just isn't a good working proposition. The OK Cub used a stock plug set up but it would be an interesting test to see what would happen if you adapted a Norvel plug. Uh oh, another experiment to try. Still, I've only seen a loss of 500 rpm in the .074. that's not bad. Perhaps some tweaking of some other element might get that back.
Msaint,
Agree with your observations. Also to be considered is the size of the combustion chamber. For instance, octane is important in car engines but not so in the weed eaters some of us fly. Why? Because the combustion chamber is so small in the typical gas model engine, that flame speed and characteristics just aren't a factor. In glow, I'd bet that combustion characteristics are similarly different. Imagine if you could see the flame in a TD .010 and compare that to an OS 1.08. I'd bet you'd see all kinds of unforeseen differences. Could be why the .010 is so hard to throttle well. At least with a conventional throttle.
This thread has prompted the following experiment, conducted just today. For the .074, I made up an adapter that would take an OS #3 plug. Like the first one I made for this engine, I made a hemi shaped combustion chamber with lots of squish band. However, this time I installed the plug offset from center. I'd observed engines in the past that had the glow plug offset from center. I believe they were biased towards the bypass port side. The adapter I made could be rotated 360 degrees and this is what I did. I tested it at 12, 3, 6 and 9 o'clock. My loss was now about 600 rpm. But, no matter where I placed the glow plug, there was no difference in rpm or throttling. This seems to prove that with such a small combustion chamber, a lot of elements that would affect a larger engine, just don't do dat in the small stuff we run.
05-02-2003, 07:29 AM
#64
A bit more on coil hole volume..
interesting experiment, actually my conversion head for a standard plug has a bit of offset.... this comes from more environmental factors though.. 
Just a bit more on coil hole volume,
If anyone has a cox 020, or better 010 head, i would be interested in hearing how the coil hole volume compares to a standard plug.
I suspect it will be a bit smaller, this because the smaller the engine, the smaller the combustion chamber and so potentially the coil hole can start to make up a larger percentage of the total combustion chamber.
this dosen`t seem to be optimal for combustion- it is very difficult for the scavenging gases to blow the exhaust gas from out of the coil hole. so if it is making up say 1/3 of the total combustion chamber it may start to really knock off some power. this may explain why standard plugs- even with tight threads- cause a drop in power.. but you know the more i thought about this... :stupid:
That said its a bit hard to know exactly why the volume is different.
In our glow engines we are running a static compression ratio of somthing like 10/1. this means very roughly that ten times the volume of the coil hole is squashed into it - picture this if you can- on a standard plug the hole is about 6mm deep- 10.6mm =60mm long stick of mixture is squashed into that hole.. and what happens? BANG! it ignites and suddenly becomes many times its origional volume and so leaps out of the coil hole like a spring...
Now what happens? who knows! (actually all of this is conjecture dressed up in pants) but I`d say it acts like a seed, propagating combustion in the rest of the combustion bowl. and i think this may make the proportions of that hole rather related to a particular engine and / its application (high rpm/ low down slugger etc)
for example, what if it leaps out with too much velocity?
or not enough? or is too small?
what if i am totally wrong about all of this?
Ha Ha .. much fun to chat about though!
Cheers,
J.M
Just a bit more on coil hole volume,
If anyone has a cox 020, or better 010 head, i would be interested in hearing how the coil hole volume compares to a standard plug.
I suspect it will be a bit smaller, this because the smaller the engine, the smaller the combustion chamber and so potentially the coil hole can start to make up a larger percentage of the total combustion chamber.
this dosen`t seem to be optimal for combustion- it is very difficult for the scavenging gases to blow the exhaust gas from out of the coil hole. so if it is making up say 1/3 of the total combustion chamber it may start to really knock off some power. this may explain why standard plugs- even with tight threads- cause a drop in power.. but you know the more i thought about this... :stupid:
That said its a bit hard to know exactly why the volume is different.
In our glow engines we are running a static compression ratio of somthing like 10/1. this means very roughly that ten times the volume of the coil hole is squashed into it - picture this if you can- on a standard plug the hole is about 6mm deep- 10.6mm =60mm long stick of mixture is squashed into that hole.. and what happens? BANG! it ignites and suddenly becomes many times its origional volume and so leaps out of the coil hole like a spring...
Now what happens? who knows! (actually all of this is conjecture dressed up in pants) but I`d say it acts like a seed, propagating combustion in the rest of the combustion bowl. and i think this may make the proportions of that hole rather related to a particular engine and / its application (high rpm/ low down slugger etc)
for example, what if it leaps out with too much velocity?
or not enough? or is too small?
what if i am totally wrong about all of this?
Ha Ha .. much fun to chat about though!
Cheers,
J.M
05-02-2003, 08:21 AM
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049 Glow plug conversion perfected
J-Man,
It's 5.30 AM here and I can't sleep. I'll bet that its something like the middle of the afternoon in the land of the rising sun. Thank god for the Internet for chronic insomniacs.
OK coil hole volume. Interesting ideas. Valid conjecture I think. Here's something to ponder. You may or may not be familiar with the Glo-Bee plug. If not, this plug has a spiral element that is not buried in a cavity like conventional plugs. This eliminates the undesired dynamics of the combustion process that you've so eloquently described. I can't recall what they ever did for me in my bigger engine days but I've had some experience with them in Coxs and Norvels. The original Glo-Bees went out of production a few years ago but Lite-Machines helicopters found them to be better performers in their helis than stock Norvel plugs. So, LM went and made a similar plug they called Spiralite. On my throttled TDs they gave more power but none of my Coxs throttled as well as I liked so any deterioration in throttling performance wasn't relevant. However, on my perfectly throttling Norvel .061s, I could gain 5 to 600 rpm on the top end and the engine's tone seemed more steady. But, for this gain, I realized a higher idle. I normally set the engine for a best idle of 5K. Actual flying idle is at 6K and this gives you a buffer of 1K for best reliability in the air. With the Glo-Bee, static, best idle goes up to 5.5K and while I still fly at 6K, I loose 1K buffer. Typically, I'll up the flying idle to 6.5K just for that extra reliability for stall turns, touch and goes and the like.
It appears that the shrouded element, as found in conventional plugs, does rob a bit of power at the top end for the reasons you describe. However, like the idle bar plugs of old, the coil, deep in the cavity, seems to be protected somewhat at idle, from the onrush of the incoming, cooling, fuel charge.
I've heard of some folks, perhaps competition types, that would carefully extract the element from out of the cavity in conventional plugs. As I recall, this had some benefit but the plug didn't last as long as it might. And so it goes.
Here's a thought. Make the cavity with a broad taper. This minimizes the shrouding effect but still provides some protection for the element from the shock of combustion. Wonder if any manufacturer of plugs has tried this.
The coil and hole volume in the .010 and .020 is proportionally smaller, as you might expect. Even the element diameter is smaller, all in the right proportions.
It's 5.30 AM here and I can't sleep. I'll bet that its something like the middle of the afternoon in the land of the rising sun. Thank god for the Internet for chronic insomniacs.
OK coil hole volume. Interesting ideas. Valid conjecture I think. Here's something to ponder. You may or may not be familiar with the Glo-Bee plug. If not, this plug has a spiral element that is not buried in a cavity like conventional plugs. This eliminates the undesired dynamics of the combustion process that you've so eloquently described. I can't recall what they ever did for me in my bigger engine days but I've had some experience with them in Coxs and Norvels. The original Glo-Bees went out of production a few years ago but Lite-Machines helicopters found them to be better performers in their helis than stock Norvel plugs. So, LM went and made a similar plug they called Spiralite. On my throttled TDs they gave more power but none of my Coxs throttled as well as I liked so any deterioration in throttling performance wasn't relevant. However, on my perfectly throttling Norvel .061s, I could gain 5 to 600 rpm on the top end and the engine's tone seemed more steady. But, for this gain, I realized a higher idle. I normally set the engine for a best idle of 5K. Actual flying idle is at 6K and this gives you a buffer of 1K for best reliability in the air. With the Glo-Bee, static, best idle goes up to 5.5K and while I still fly at 6K, I loose 1K buffer. Typically, I'll up the flying idle to 6.5K just for that extra reliability for stall turns, touch and goes and the like.
It appears that the shrouded element, as found in conventional plugs, does rob a bit of power at the top end for the reasons you describe. However, like the idle bar plugs of old, the coil, deep in the cavity, seems to be protected somewhat at idle, from the onrush of the incoming, cooling, fuel charge.
I've heard of some folks, perhaps competition types, that would carefully extract the element from out of the cavity in conventional plugs. As I recall, this had some benefit but the plug didn't last as long as it might. And so it goes.
Here's a thought. Make the cavity with a broad taper. This minimizes the shrouding effect but still provides some protection for the element from the shock of combustion. Wonder if any manufacturer of plugs has tried this.
The coil and hole volume in the .010 and .020 is proportionally smaller, as you might expect. Even the element diameter is smaller, all in the right proportions.
05-02-2003, 11:16 AM
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049 Glow plug conversion perfected
Wouldn't you like to have a couple of hours picking Bill Atwood's (the TD designer's) brain? He worked out all of this stuff almost 50 yrs. ago! Without a computer or a pile of scientific instruments. 
05-02-2003, 02:12 PM
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049 Glow plug conversion perfected
Milt,
Dont forget the Atwood Shreik, Wasp, Cadet, etc... all good engines of the day, especially the shreik.
We CAN pick his brain, he has thoughtfully left us with literally millions of engines to look at, run, play with, disect, ect...
Andrew
Dont forget the Atwood Shreik, Wasp, Cadet, etc... all good engines of the day, especially the shreik.
We CAN pick his brain, he has thoughtfully left us with literally millions of engines to look at, run, play with, disect, ect...
Andrew
05-03-2003, 07:28 AM
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049 Glow plug conversion perfected
ZAGNUT/Dave,
I had good rapport with one Don Hatcher, parts supervisor and long time employee. From time to time, he'd intercept a cylinder for me before it went on to the next stage. Unfortunately Don retired a year or so ago.
Cliff Cotton of Estes/Cox has been most helpful of late though I haven't had need of blank cylinders for a while. If you have no luck, let me know and I'll see what I can do.
What did you have in mind? A 1/2A four stroke?
If so, reserve one for me !! 
I had good rapport with one Don Hatcher, parts supervisor and long time employee. From time to time, he'd intercept a cylinder for me before it went on to the next stage. Unfortunately Don retired a year or so ago.
Cliff Cotton of Estes/Cox has been most helpful of late though I haven't had need of blank cylinders for a while. If you have no luck, let me know and I'll see what I can do.
What did you have in mind? A 1/2A four stroke?
If so, reserve one for me !!
05-04-2003, 12:04 AM
#70
049 Glow plug conversion perfected
What did you have in mind? A 1/2A four stroke?
actually i'm getting back into 1/2A after a long break. i once took a non-spi twin transfer (single cut) cylinder and added an alum header adaptor that blocked one exhaust port and filled the slit all the way to the bore. i reshaped the transfers to a schnuerle pattern (sorta) and added a boost port. on a t.d. with a fibreglass pipe this made a big gain but i never got the standard plug and head adaptor to work right and gave up.
i want to try this again now that i see some solutions to the head issue and the blank cylinder seemed perfect for this.
also, are the turbo plugs for cars the same as the nelson in dimension? do they come in different heat ranges?
thanks,dave
05-04-2003, 05:44 AM
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Dave,
Your welcome :devious: But seriously, if you managed to modify a stock cylinder as you describe, you're way ahead of me. I tried just that with JB Weld and it didn't hold. Let me see if I can get you some blanks. And yes, they're threaded.
The car turbo plugs are the same thread as stock plugs. Nelson plugs are much larger in diameter.
On the subject of head conversions. I discovered today that the cavity in the OS #3 plug is the same diameter as the cavity of the stock Norvel plug. HOWEVER, the depth of the cavity is three times longer than the Norvel. In light of this, I shaved my conversion head (.074) even more and reshaped the combustion chamber. Substantially more compression ratio but still, no better than before. Still not able to overcompress and there's no more room for shaving. At the same time, I tested the Nelson conversion again. Today I was reminded again why it didn't find a permanent home in my engine. Power was up to par with the stock plug at 16.5K on a 7 X 3.5 Cox grey. However, while idle was solid at 4.5K, the engine kept quitting in the air during spins and the like. The needle WAS adjusted to suit the new plug. Even after trimming the idle to 6K, the quitting happened with snap maneuvers when on idle. The combustion chamber was hemi shaped. Next to try is to make one that duplicates the stock plug's shape.
Your welcome :devious: But seriously, if you managed to modify a stock cylinder as you describe, you're way ahead of me. I tried just that with JB Weld and it didn't hold. Let me see if I can get you some blanks. And yes, they're threaded.
The car turbo plugs are the same thread as stock plugs. Nelson plugs are much larger in diameter.
On the subject of head conversions. I discovered today that the cavity in the OS #3 plug is the same diameter as the cavity of the stock Norvel plug. HOWEVER, the depth of the cavity is three times longer than the Norvel. In light of this, I shaved my conversion head (.074) even more and reshaped the combustion chamber. Substantially more compression ratio but still, no better than before. Still not able to overcompress and there's no more room for shaving. At the same time, I tested the Nelson conversion again. Today I was reminded again why it didn't find a permanent home in my engine. Power was up to par with the stock plug at 16.5K on a 7 X 3.5 Cox grey. However, while idle was solid at 4.5K, the engine kept quitting in the air during spins and the like. The needle WAS adjusted to suit the new plug. Even after trimming the idle to 6K, the quitting happened with snap maneuvers when on idle. The combustion chamber was hemi shaped. Next to try is to make one that duplicates the stock plug's shape.
05-04-2003, 11:59 AM
#72
049 Glow plug conversion perfected
Hi guys, just cruising the threads but i thought i`d better add this, but not meaning to be a know it all:
The thread size of the O.S turbo plug is a bit bigger than a standard plug at M8 fine, standard plugs being about 6mm for all of us metricly inclined.
The O.Sturbo plugs come in cold, medium and hot.. most usefully
J.M
The thread size of the O.S turbo plug is a bit bigger than a standard plug at M8 fine, standard plugs being about 6mm for all of us metricly inclined.
The O.Sturbo plugs come in cold, medium and hot.. most usefully
J.M
05-04-2003, 12:53 PM
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049 Glow plug conversion perfected
Even though I watch my cholesterol,, I've got egg on my face.
J-Man and AJC are both right, actually. I'm the bonehead that got it wrong. The Trubo-plug I was looking at is still NIP. Didn't actually take it out and look at it real hard. Also, the guy at the shop didn't know the thread but he assumed it was the same. I wouldn't have bought it otherwise. Anyone need a trubo plug??
Dang it. I ordered a bottoming tap to make a head for it. Trouble is, I ordered a 1/4-32. That's my punishment for mispeaking,,, as the politicians would say.
It's still correct though, that the Nelson plugs are much larger than the other two.
J-Man and AJC are both right, actually. I'm the bonehead that got it wrong. The Trubo-plug I was looking at is still NIP. Didn't actually take it out and look at it real hard. Also, the guy at the shop didn't know the thread but he assumed it was the same. I wouldn't have bought it otherwise. Anyone need a trubo plug??
Dang it. I ordered a bottoming tap to make a head for it. Trouble is, I ordered a 1/4-32. That's my punishment for mispeaking,,, as the politicians would say.
It's still correct though, that the Nelson plugs are much larger than the other two.
05-05-2003, 12:22 AM
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049 Glow plug conversion perfected
It would be my thinking that the longer hole in the plug would act as an accumulator no matter how much you shave off the head.
Originally posted by 1705493
Dave,
On the subject of head conversions. I discovered today that the cavity in the OS #3 plug is the same diameter as the cavity of the stock Norvel plug. HOWEVER, the depth of the cavity is three times longer than the Norvel. In light of this, I shaved my conversion head (.074) even more and reshaped the combustion chamber. Substantially more compression ratio but still, no better than before. Still not able to overcompress and there's no more room for shaving.
Dave,
On the subject of head conversions. I discovered today that the cavity in the OS #3 plug is the same diameter as the cavity of the stock Norvel plug. HOWEVER, the depth of the cavity is three times longer than the Norvel. In light of this, I shaved my conversion head (.074) even more and reshaped the combustion chamber. Substantially more compression ratio but still, no better than before. Still not able to overcompress and there's no more room for shaving.