olddragger

iTrader: (3)

I thought I would like to open for discussion.
I know a number of us on the site know about the video in which this guy advocated partially filling in the lead sparkplug hole (making a slit instead of a round hole) to reduce the amount of blowby from rotor face to rotor face when the apex seal passes over that area.
That seems logical to me, but my gut tells me that there has to be more to this or Mazda would have done it?
What are others thoughts on this idea?
How could this be reliability done?

One other thought I have in addressing this blow by --and please shoot holes in this idea if needed--is by using a gapless sparkplug ( rx7 type)? The gapless plug can be moved closer to the edge of the housing reducing the size of that "hole" in which the blowby goes through?
The rx8 plug (ngk's etc) are recessed a fair amount making that "hole" larger. The larger the hole the more blowby you get--right?
Interesting? Is this worth discussing?

Harlan

iTrader: (3)

I've thought about using surface discharge plugs modified to fill the housing, but I've yet to be that brave. Mazda made the holes as big as they could reasonable get away with considering the differential pressure across each hole, probably has to do with initial flame propagation. Bigger the hole, easier it is for the flame to spread.

I've read of FD guys plugging their trailing holes, or otherwise modifying them to prevent knock. This all might be in the category of good enough. Maybe it just wasn't worth the cost to Mazda of designing completely custom plugs for marginal gains. It's really kinda sad because all the piston engine "marginal gains" have added up over the years.

wcs

iTrader: (2)

olddragger

iTrader: (3)

See ---I learn something every day.
But this is interesting: http://attachments.proboards.com/114...Sxhb6CztzT.jpg

besides we are running out of things to talk about and I plan on putting up a graft......

wcs

iTrader: (2)

It's too small a pic .. can't make it out

I know video you are speaking of where the dude makes a slit out of the Leading plug hole.
IIRC wasn't he thing that it reduced exhaust temp or was that because of the redesign to the rotor face?

olddragger

iTrader: (3)

Look at the brass looking plug where the leading plug usually is.
Makes it look like a trailing plug hole.

here is a link to where this is discussed as a spark plug adapter:

http://www.google.com/url?sa=t&rct=j...ZqhfWviEFsBR_A

it reduced the distance from the sparkplug to the charge in the rotary motorcycle engine. They designed this to reduce sparkplug fouling.

csl

the spark plug company always try to make the area of exposure as much as possible so that the fuel can be burnt off completely and achieve max power. Will making a tiny spark plug hole on the rotor housing works? Theoretically not convincible (I believe it will works until certain limit) but not too sure if it serves the purpose of modifying, I mean you can make it until almost zero loss but the air-fuel mixture may not fast enough to burnt off before the exhaust port opening (red line 8.5k rpm 3 passes per revolution). For me, I believe in 2 ways:

1. High RPM run.

2. Spark Plug FC3S Pro v2.0: Mods - Spark Plugs

When look at the HKS plug, I believe NGK and Denso already tested in many designs and etc before came out with a solution. Probably can try a stock spark plug on a housing without shim or weld/machine the spark plug tip so that it can be flush on a housing and minimize the losses without sacrificing the exposure area.

olddragger

iTrader: (3)

what do yall think about this type of plug?
Google Image Result for http://i.ebayimg.com/t/New-NGK-OEM-Spark-Plug-1975-1976-RE-5-RE5-Wankel-Rotary-OEM-Suzuki-E40-/00/s/ODk0WDEyNzg%3D/%24(KGrHqF,!jME8EydRjPtBPHvQdn85!~~60_35.JPG

designed for the rotary power Suzuki motorcycle and they do have a bad habit of fouling out fast. Still it is a little interesting to me?

The oem without a washer and careful adjustment of the grounding strap will get the kernal closer to the intake charge--that HAS to be a good thing. But, you need a washer on it for sealing--right?

HiFlite999

iTrader: (2)

That's a "surface discharge" plug, designed specifically not to foul. Downside is that they are very cold plugs. We have a "semi-surface discharge" plug, splitting the difference.

To run them further in, you'd have to tap the plug hole deeper and with a bottoming tap.

olddragger

iTrader: (3)

that is what an adapter could do without extending the threads in the housing. But with an adapter I would be a little concerned about adequately cooling of the plug area. Not sure? Things are usually more complicated than they seem.

The plug shown is not a surface discharge plug--look more closely--it has a grounding strap. you have to click on the link a couple of times for a bigger pic.

olddragger

iTrader: (3)

well how about that --i found some old articles from Mazdaspeed and Dave Drummond addressing tech for moving the lead sparkplug closer to the combustion chamber.
It was not an eye opening change--but it did make a little difference on the na engine--the 12A and 13 B.

Harlan

iTrader: (3)

Here's what I found so far:
NGK (2322) BUE Traditional Spark Plug, Pack of 1 : Amazon.com : Automotive
Oh and you also need to use them with no washer and a thin-walled socket, which is a no go for me.

I really want to see some surface discharge plugs with a longer reach. If anyone knows of a site to search spark plugs by dimension, let me know, everything I find is either too long or too short. Why drill and tap the housing when you can just machine the plugs to fit?

I guess I could haul a housing to the parts store and have them pull spark plugs until I find something I like, but I'd be worse than a woman purse shopping. "Oh I like that one, do you have it 2mm longer?"

olddragger

iTrader: (3)

even without the crush washer on the lead sparkplug is still pretty recessed.
Plus the space all around the tip of the plug and housing is easily visible. I am not sure if that is something needed due to different expansion rates of the metals.
I have an old housing and I think i will break out a heat source tomorrow and see what happens.

Sure looks like it could possibly develop into a hot spot for us boosted guys?

Harlan

iTrader: (3)

Here's where I found them:
What Plugs? - Page 3 - RX7Club.com
Sorry it took me a while to find the link again. They are the coldest plugs possible, but the surface discharge makes them much harder to foul. So hot spots are a non issue, but they still aren't long enough. I would guess that Mazda didn't thread the spark plug holes any deeper to discourage idiot mechanics with long standard plugs. What I don't know is why they didn't put the spark plug closer while still maintaining a gap to the surface of the housing. Seems like a significant distance with no reason.

Edit: Just looked at the housing with stock plugs in place. The tip of the ground on the plugs is not that far recessed, but adding that distance plus what the tip takes up makes it seem bigger. Guess the engineers had plugs, stuck them in and called it a day.

Karack

why not fill the trailing hole, run leading only and use a true surface discharge plug for leadings?

now i'm getting ideas..

olddragger

iTrader: (3)

Aww Team--you know we are just having fun batting this around... We need something new to think about.

I HAVE to get a better caliper--so I can take actual measurements.
I can get some indexing crush washers for the plug--or can the lead plug be used without a washer?
Heat test today to check metal expansions.
Point to note--i do not run the oem sparkplug gap--i run a gap of 32 instead. This moves the grounding strap further down and increases clearance.
One thing to be careful about is manufacturer inconsistances referring to the sparkplug threads in the housing. Some may thread further down than others?
Seriously --I dont see how moving the sparkplug kernal closer to the combustion chamber can have any negative effect?

Surface discharge plugs require a stronger electrical system to perform as well as the oem ngk's dont they?

Point of interest--i heard that some guys are running trailing plugs in the leading position in order to have a colder leading plug ? Wouldnt that recess the spark kernal even further down?

dannobre

iTrader: (3)

I have a set of housings from Mazda with no trailing plugs holes...and using the surface discharge plugs. They were used for a generator that was running on Natural Gas. Fuel burns very clean and at a cooler temp than gasoline...and they were designed to run at a set RPM I belive...so Mazda has done this in the past.

Wonder how they would run on gasoline without the T plug?...might be worth the trouble to build a motor and see

olddragger

iTrader: (3)

well--i think i will back off on trying to reduce the sparkplug tip recession in the housing.
I just realized ( and after some more research) that getting the tip closer could really make a big difference in the heat at the plug tip. This could possibly increase the chance of a hotspot and detonation. For the small gain it may produce---not worth it for me.
What say everyone?
Now i think reducing the size of the lead sp hole may still be worth doing?

j9fd3s

just disconnect it... the NSU engines were all single plug too. the trailing plug speeds up the combustion process, basically. it also helps burn the gasses on the trailing side.

i've found the effect of the trailing ignition depends on the port, on a stock 12A disconnecting the trailing ignition is almost unnoticeable, mileage might be down a bit, and emissions will be higher.

on my Peripheral port, it'll barely run without the trailing ignition. power is down maybe 50%, and it won't idle, makes a huge difference.

my experience with the Rx8 engine is that the ECU is good enough that you can have a couple of bad coils and it still runs ok.

9krpmrx8

iTrader: (46)

olddragger

iTrader: (3)

extending the sparkplug further into the combustion chamber--i have realized is not a good idea--UNLESS some major tuning is done along with it.
You would need a colder running plug and extending the reach of the plug could be the same as advancing the timing 1-2 degrees. Not much for the na guys--but for the boosted guys--this is something you may not want to do without looking at your tuning.

The leading sparkplug recession is 4.5 mm deep with the washer (to the barrel of the plug--not the strap)--without the washer it is 2 mm. This is Tq of 25 ft lbs to the plug. Without the washer there is still plenty of room for the apex seal to pass when the gap is set at 32-35. I run denso plugs and its ok to gap those--with the ngk's you have to be VERY careful.
Extending the plug would also probably mean that they would carbon up faster and flood easier.

Extended reach plugs in the Miata ( 2mm longer) gave them 5 rwhp--which means nothing to us.

One thing I have discovered is that the denso sparkplug barrel fits better than the ngk's. There is less space between barrel and housing.


BE CAUTIOUS IF YOU TRY THIS. Personally I now do not think it is worth the bother/worry.

Harlan

iTrader: (3)

That makes a lot of sense. I still like the concept, but after going through several spark plug catalogs I can't find anything better than stock, at least not without major modifications. May still try the BUE plugs, they are cheap and close to what I want.

I guess in the end it was easier to add a couple degrees of timing then to reinvent the wheel.

Karack

in some setups i don't run trailings, it isn't worth the hassle of spending $500 for a separate ignition system for the slight mileage/power/smoothness improvements.

i have never tested it on a PP engine but every side port engine the difference was almost unnoticeable.

i have yet to actually fill the trailing hole though, it is a rather minor impact versus the leading which is much larger. the NSU housings have much smaller plug holes than the mazda leading versions.




that was a set from a '70 NSU RO80 that were sent for resurfacing, though he opted out of it because it was taking too long to setup to cut the much harder chrome surface versus the standard mazda housings which are rather soft. but NSU did also run trailings for the improved economy and power.

as you can see from the chatter at the trochoid peak and trailing plug they had their own problems.

olddragger

iTrader: (3)

wow-- look at those water jackets.
Thanks for posting those.
There are gains to be had my reducing the size of the lead hole by someone that knows what they are doing.
There are also gains to be seen by moving the spark kernel closer to the combustion chamber also--again by someone that really knows what they are doing.
I hope no one just goes out and throws a extended reach plug in there.

Karack

the casting is actually hollow, they aren't just straight through holes with the exception of the tension bolts holes. water runs through the whole housing versus in mazda's design which they pass straight through front to rear, around the back and then towards the front on the intake/exhaust half of the engine..