NGK BP6HS = Higher Compression?

i haven't tried an iridium plug, because i just don't believe the hype when it comes to "fancy" spark plugs, especially with an engine as low-tech as ours.

but, i do use NGK plugs, either the BH or the BPH series. the BP's are longer, and i haven't noticed any increase in compression. theoretically there should be due to it taking up more space in the combustion chamber, but to me and my motors, it doesn't seem noticeable.

any boost in performance would be so slight, it wouldn't be worth the money for anything more than a standard NGK.

that being said, i definitely recommend getting rid of the stock plug. they're so poorly made i just throw them away on every motor i get.

on another related note, one of my engines seems to perform better with the B6HS than with the BP6HS. dunno why, maybe it's a faulty BP plug.

as for your engine, nothing bad will happen to it running a BP plug. or most plugs for that matter. as long as it's sparking good, it's fine.

in my opinion, these motors could use some more compression, and i build them that way. if done right, you'll get many many miles of fun outta them.

plug gap i run at .030 i've tried every gap imaginable from real small to real big, going up and down till it wouldn't run or performance was noticeably affected, and i always come back to .030.

i also found no noticeable difference between .025 and .035, so i just split the difference.

The "P" in BP is for projected tip. This cools the plug better by sticking it out into the intake airstream. The standard tip is retracted enough into the plug that it blocks the effect. I think there's a mistaken idea that a larger number plug is better to the point of using BP7HS on a stock motor then wonder why performance is down. The motor comes with a "4" range plug, pretty hot, really. A B5HS is the ideal plug for the HT motor. If it's too hot take a step colder with a B6HS. Save the colder plugs for if and/or when you increase compression. My compression is very high, along the lines of 13:1. I get no ping using Shell V-Max premium fuel and a NGK BR9HIX Iridium plug and jaguar's CDI ignition box

NGK Iridium plugs have 1 ground electrode. Because of the cost of iridium the center post is very thin. NGK says not to gap the plugs because the center electrode will bust off. Iridium is a brittle metal. They come pre-gapped to .031, good enough for these bikes.

The compression comes from having a Puch Hi-Compression head from Treatland.tv. I got the head meant for a 50 cc and put it on a 66 cc. With the combustion chamber volume of just over 5 cc dividing 66 cc it works out to around 13:1. I'm going to have the head off here soon to put it on a 49 to have a 11:1 ratio then I'll get the right head for the 66, a Puch head meant for a 70 cc.

I'm thinking of getting a water cooled head. There's a thread by flybytaco where he made the jug water cooled but when you think on it most of the heat is actually in the head. I'll be leaving the fins exposed for cooling but water cooling the head. I got a junk Chevy Cavalier I'm going to pull the heater core out of. The 66 cc motor will become my "race" motor

CDI Ignition for the Chinese 48cc HT engine will get you to jaguar's CDI. I understand the unit will soon be sold by JNMotorsports at a higher cost so now's the time

...how far off from .031 is best? I know you're not going to bend the ground electrode on the Iridium plug, it's like 3-4 times the thickness of a stock-type plug.

Spot price on iridium right now is $1000 a troy ounce, $12,000 a pound. Gold is at $1500 for a comparison. When I was gold mining iridium was $2000 an oz with gold around $400. This explains the price.

Theory has it a microscopic amount of iridium is vaporized every time the plug fires. The metal helps to catalyze the combustion for a more complete burn, the same reason platinum or palladium is used in catalytic converters


oh, by the way, the spark plug actually fires twice every revolution of these two stroke motors. The ignition is triggered by the gaps in the magnet and there's no brain sensor to distinguish the difference between TDC and BDC. Leaving only one gap in the magnet would create a massive out-of-balance condition making these things vibrate worse than they do now. There's no fuel to ignite so there's no problem. It would be beneficial if there was no gap, the coil would have twice as long to saturate for a more intense spark but a V8 fires 4 times every revolution so I guess that's not a problem.

Having to close a gap to .026 shows you how weak the stock spark setup is. Garbage is the most polite thing I can say about it. Anything done to it is an improvement and worth whatever it costs in reliability, something very much lacking. jaguar's CDI goes a long way to correcting this issue. The ability to retard at high RPM's set it apart from the others. Because of this it will still be worth it for one of the units when they do increase in price. But it will also make it more worthwhile to knock-off. A few parts Class B wired to a breadboard, pretty easy to copy really and there are many here who could do it with ease(me included).

DaveC said:

...how far off from .031 is best? I know you're not going to bend the ground electrode on the Iridium plug, it's like 3-4 times the thickness of a stock-type plug.

Spot price on iridium right now is $1000 a troy ounce, $12,000 a pound. Gold is at $1500 for a comparison. When I was gold mining iridium was $2000 an oz with gold around $400. This explains the price.

Theory has it a microscopic amount of iridium is vaporized every time the plug fires. The metal helps to catalyze the combustion for a more complete burn, the same reason platinum or palladium is used in catalytic converters


oh, by the way, the spark plug actually fires twice every revolution of these two stroke motors. The ignition is triggered by the gaps in the magnet and there's no brain sensor to distinguish the difference between TDC and BDC. Leaving only one gap in the magnet would create a massive out-of-balance condition making these things vibrate worse than they do now. There's no fuel to ignite so there's no problem. It would be beneficial if there was no gap, the coil would have twice as long to saturate for a more intense spark but a V8 fires 4 times every revolution so I guess that's not a problem.

Click to expand...

Very well quoted...I have a built engine with a Jim's straight intake, Jim's billet head, 18mm Mikuni, chamber, 34 tooth Jims billet rear sprocket, port work...AND if a little spark plug will give me POWER I'll get one..The colder the plug the more power as a cooler engine produces more power..Get a basic BP plug and be happy..

in theory, a cooler engine doesn't produce more power. it's the optimum operating temperature you're looking for.

i still believe (based on experience) that a simple spark plug won't give you any real increase in power. obviously, a quality plug like an NGK is superior to the stock piece of crap, but iridiums, triple electrodes, or other fancy plugs just cost more money, and if you can't change the gap, you can't tune it.

it's just the way these motors are. they're not designed to take advantage of a "high-performance" plug.

but, if it makes you feel better, go for it...

bairdco said:

in theory, a cooler engine doesn't produce more power. it's the optimum operating temperature you're looking for.

i still believe (based on experience) that a simple spark plug won't give you any real increase in power. obviously, a quality plug like an NGK is superior to the stock piece of crap, but iridiums, triple electrodes, or other fancy plugs just cost more money, and if you can't change the gap, you can't tune it.

it's just the way these motors are. they're not designed to take advantage of a "high-performance" plug.

but, if it makes you feel better, go for it...

Click to expand...

Very well said

All internal combustion engines are designed to run at a certain temprature. Cooler doesn't mean more power. (too cold & too hot both mean less power.)
Every part inside the engine (especially the piston) was designed to expand with engine heat to the proper size & fit. That's why you should always warm up a engine before using it.

& just as said above; a spark plug will not give any power increase; It can only make the engine run properly.
There can be a small compression increase from a longer plug; but it's not really noticable.

I'm very pleased with the BR7HS, for a resistant plug, it puts my bike right where I like it to be.

Hi
If anyone is interested here is a link to NGK spark plug codes
http://www.math.uwaterloo.ca/~rblander/NGK.txt

DaveC said:

...

oh, by the way, the spark plug actually fires twice every revolution of these two stroke motors. The ignition is triggered by the gaps in the magnet and there's no brain sensor to distinguish the difference between TDC and BDC. Leaving only one gap in the magnet would create a massive out-of-balance condition making these things vibrate worse than they do now. There's no fuel to ignite so there's no problem. It would be beneficial if there was no gap, the coil would have twice as long to saturate for a more intense spark but a V8 fires 4 times every revolution so I guess that's not a problem.

Click to expand...

It doesn't. The trigger circuit in the CDI uses a single diode so everything between the begining of the first gap to the end of the second seems the same (no voltage) to it.

yes

There seems to be some bit of misinformation in this thread about plug life in premixed, old school 2 cycle engine operation.

These HT engines are definitely old school.

If you consistently mix your fuel and quality oil ratio and pull and inspect and gap/clean the plug at service intervals you shouldn't need to change them very often.

I had a 1960's Yamaha step-through 50 cc bike I regularly commuted to work on for 3 years, that I would get over 5k miles between plug changes running 32:1 mix. This was before E10 fuel, in the 1980's.
.
I'd change the plug at that period even though it really didn't need much more than checking the gap and a wire brushing. It probably would have ran for 10K before it really carbon fouled. I'd pull the head and scraped carbon off the piston and head at 10k intervals on that bike.

There's really little more you an do for these if you're not racing or otherwise running them beyond their recommended use. These engines were originally designed to power heavy old Flying Pigeon single speed bicycles as commuter powerplants in PRC before they became popular here in the US.