FD Spark Plug Tech 2013
09-20-13, 06:53 PM
#27
Racing Rotary Since 1983
Thread Starter
iTrader: (6)
thanks for the link 00SPEC.
here's the Pettit SPM Mod:
while it doesn't clearly show, Cam chamfers the top off of the spark plug boss.
in addition to causing loss of compression and non-linear apex seal wear the lifting of the apex seal is the primary reason for chatter marks on the housing.
Cam and i discussed SPM a couple of years ago and he suggested the chamfer mod which i adopted.
lowering SPM starts w running colder plugs and AI.
howard
here's the Pettit SPM Mod:
while it doesn't clearly show, Cam chamfers the top off of the spark plug boss.
in addition to causing loss of compression and non-linear apex seal wear the lifting of the apex seal is the primary reason for chatter marks on the housing.
Cam and i discussed SPM a couple of years ago and he suggested the chamfer mod which i adopted.
lowering SPM starts w running colder plugs and AI.
howard
Last edited by Howard Coleman; 09-20-13 at 06:55 PM.
09-20-13, 07:30 PM
#28
"An engine" is singular tense. Of course. Nonetheless thanks for clarifying.
I understand the info but at what point does this really make a difference though? I've seen enough mildly modded turbo rotaries last 100-150+k miles. Is this more of an issue with high HP motors?
Also, is the issue heat range or spark plug design? It isn't clear to me in your original post. I'm inferring heat range but wanted to verify.
Thanks.
09-20-13, 08:47 PM
#29
Racing Rotary Since 1983
Thread Starter
iTrader: (6)
"Is this more of an issue with high HP motors? "
i do think as CCP and CCH rise w output SPM gains elevation.
"does this really make a difference"
a good question.
i suppose it depends on how you wish to view it. often i receive a motor that runs and has put down 100,000 miles... the owner wants a refresh and more output. without exception i find the carbon wings along w chatter marks. the chatter comes from SPM as do the wings.
in many cases the motor could continue to provide useful service.
i will admit when i see the housings i feel for them.
nowadays we have vendors that provide really good housing renewal so most often the housings, which are crazy priced new around $800+ these days, can be made dead straight and almost as good as new. and that includes leveling SPM.
another SPM issue is that any time the apex seal is not in contact w the housing surface it rapidly gains heat. the apex seal transfers significant heat into the rotor housing face but not when it is up in the air.
generally the product of seals not being in contact w the housing is a flat shoulder and a sharp trailing edge. i see it often.
i doubt that by running colder plugs, AI and chamfering the boss that SPM can be totally conquered. it certainly can be reduced and i have seen clear evidence of this with my motor and the Pettit picture adds support.
as to heat range and plug design... heat range probably trumps design in most instances. in higher hp apps design becomes relatively more important. i do like the lack of a ground strap as power rises. there are numerous recorded instances where a strap was lost in a high output motor.
i am not selling spark plugs
, i just thought i would share my first hand experience w the AR3932X... prior to Lance mentioning to me them pretty close to nobody was running them and they seem to be a solid rotary option.
howard
i do think as CCP and CCH rise w output SPM gains elevation.
"does this really make a difference"
a good question.
i suppose it depends on how you wish to view it. often i receive a motor that runs and has put down 100,000 miles... the owner wants a refresh and more output. without exception i find the carbon wings along w chatter marks. the chatter comes from SPM as do the wings.
in many cases the motor could continue to provide useful service.
i will admit when i see the housings i feel for them.
nowadays we have vendors that provide really good housing renewal so most often the housings, which are crazy priced new around $800+ these days, can be made dead straight and almost as good as new. and that includes leveling SPM.
another SPM issue is that any time the apex seal is not in contact w the housing surface it rapidly gains heat. the apex seal transfers significant heat into the rotor housing face but not when it is up in the air.
generally the product of seals not being in contact w the housing is a flat shoulder and a sharp trailing edge. i see it often.
i doubt that by running colder plugs, AI and chamfering the boss that SPM can be totally conquered. it certainly can be reduced and i have seen clear evidence of this with my motor and the Pettit picture adds support.
as to heat range and plug design... heat range probably trumps design in most instances. in higher hp apps design becomes relatively more important. i do like the lack of a ground strap as power rises. there are numerous recorded instances where a strap was lost in a high output motor.
i am not selling spark plugs
, i just thought i would share my first hand experience w the AR3932X... prior to Lance mentioning to me them pretty close to nobody was running them and they seem to be a solid rotary option.howard
09-23-13, 02:07 PM
#31
I plan on using the 10 equivalent. I think this will be a good chance to test howmuch abuse they will take
09-26-13, 10:46 AM
#37
"Elusive, not deceptive!”
To add a few caveats.
The area of ceramic and metal exposed to the combustion gases determines the heat of the plug that must removed. (a surface gap plug would absorb the least heat).
The latest generation housings have a better burn rate by separating the distance between the spark plugs.
This unfortunately decreased the water passage at the hottest point on the housing's surface.(this passage should be ported to mimic the original but only toward the housing surface, not toward the plug casting!)
In Howard's example the shading of carbon also indicates that the triangle piece was running on the right side.
The three spring contact points cause an imbalance (the forth is on the triangle).
This unequal snapping of the apex seal over the hump is what breaks the seal.
A complete paradigm shift would be to use Toyota/Denso's Laser plugs that don't require heat to keep them clean.
Barry
The area of ceramic and metal exposed to the combustion gases determines the heat of the plug that must removed. (a surface gap plug would absorb the least heat).
The latest generation housings have a better burn rate by separating the distance between the spark plugs.
This unfortunately decreased the water passage at the hottest point on the housing's surface.(this passage should be ported to mimic the original but only toward the housing surface, not toward the plug casting!)
In Howard's example the shading of carbon also indicates that the triangle piece was running on the right side.
The three spring contact points cause an imbalance (the forth is on the triangle).
This unequal snapping of the apex seal over the hump is what breaks the seal.
A complete paradigm shift would be to use Toyota/Denso's Laser plugs that don't require heat to keep them clean.
Barry
09-26-13, 01:19 PM
#40
interesting , continue on with said laser plugs??? could they be a direct replacement ? or what would need to be modded in order to use them?
do they require more power to well shoot laser beams at our rotors?
do they require more power to well shoot laser beams at our rotors?
Last edited by Tem120; 09-26-13 at 01:22 PM.
09-27-13, 07:42 AM
#41
Maybe its irrelevant maybe not , but these are my housings spark plug holes 
as you can see , NO signs of the wings . the housings themselves had 0 signs of carbon.
the engine was a JDM engine which I bought and drove for 12k miles . before it went boom .
The rotors on the other hand had plenty of carbon on them .
And the housings I just got with 20k miles on them also have the wings .
so why do mine not have wings? since I got the car I've been running NGK9's and I've been running AI ( aux injections ) some proof for the nay sayers that colder plugs + meth do help with the cleaning
as you can see , NO signs of the wings . the housings themselves had 0 signs of carbon.
the engine was a JDM engine which I bought and drove for 12k miles . before it went boom .
The rotors on the other hand had plenty of carbon on them .
And the housings I just got with 20k miles on them also have the wings .
so why do mine not have wings? since I got the car I've been running NGK9's and I've been running AI ( aux injections ) some proof for the nay sayers that colder plugs + meth do help with the cleaning
09-27-13, 09:53 AM
#42
"Elusive, not deceptive!”
Mazda research shows that the closer the plug tip is to the housing surface the more healthy the ignition sequence.
The real beauty of the laser is that it can focus the ignition point out into the rotor's pocket.
General News Parts - Lasers move closer to replacing spark plugs | GoAuto
The real beauty of the laser is that it can focus the ignition point out into the rotor's pocket.
General News Parts - Lasers move closer to replacing spark plugs | GoAuto
09-27-13, 08:10 PM
#44
Per my local Napa store, they said the entire west coast doesn't carry the AR3932X. It's special order. Local O'Reilly does carry the ASP AR3932 without the "X" which is why I was asking what the "X" meant. Thanks....... and by the way great stuff here Howard and others!
09-27-13, 08:23 PM
#45
Racing Rotary Since 1983
Thread Starter
iTrader: (6)
the X plug has four grounds that are part of the spark plug body. similar to the OE FD plug.
the non X 3932 has the traditional ground strap and like the "X" is a racing plug. it does have the advantage of being able to be gapped to your spec,
the plugs are available from NAPA. they have to order them from a NAPA warehouse or source located in Detroit.
not a biggie.
howard
the non X 3932 has the traditional ground strap and like the "X" is a racing plug. it does have the advantage of being able to be gapped to your spec,
the plugs are available from NAPA. they have to order them from a NAPA warehouse or source located in Detroit.
not a biggie.
howard
10-06-13, 11:06 AM
#47
Racing Rotary Since 1983
Thread Starter
iTrader: (6)
update re AR3932x
"upon further review" of the dyno sheet i see squiggles from around 5500 on. it has been pretty much proved that these are a result of too much spark plug gap. the 3932X is not adjustable as to gap.
additional evidence of misfire is the DynoJet losing the RPM signal further up the RPM plot.... around 7800. this is probably because some of the spark energy was leaking on the exterior of the plug to ground since there was too much CCP.
i am in debt to Cam Worth for bring this to our attention. Thanks Cam. i talked to Lance on it and he was in general agreement and offered an additional fix which was longer, almost impossible to install/remove spark plug boots. both Cam and Luke just focused on gap.
so we grabbed my NGK 6725 plugs and gapped them at .02. (did not have a set of AR3932 immediately avail)
the dyno retained the RPM signal immediately to redline.
OTOH, Luke was hearing noise from peak torque up in the Link Knock Amp Headphones.
the headphones are awesome.... they keep you ahead of serious knock. we acquired them in January and Luke has adopted them for all his tunes.
here we are indebted to Richard Green (NZ) for the tip... here's an email from him a couple of days ago:
"Isn’t the Link knock block great. You can hear you’ve got a problem before you do damage – an early warning device if you will. Imagine how many tuners are needlessly destroying engines without this tool. Interestingly the engine I tuned today was quite noisy for the first 10 or so low boost pulls but then it cleaned up (sounded like worn apex seal grooves). It’s because the engine had zero miles on it before today and all the seals needed to bed in, even though they were new (most aftermarket apex seals seem to be supplied with a slight bow in them). So I suppose the noise was also like mildly bent seals… until they bed themselves in. And I guess mildly bent seals can cause pre-ignition…. which can be picked up through the headphones. Engines with flattened corner seal springs sound the same."
it appears that what we were hearing a week ago from the 6725s was a combination of a bigtime inductive ignition system (IGN 1A) and fine wire, long strap plugs being turned into a glow plug. this did happen to Richard last year and he switched to the thicker nickel/copper plugs which cured the noise.
we could not come up w another explanation. i think the 6725 plugs work very well in a CDI environment but may not work as well w inductive. the much longer spark duration being the issue.
so we swapped out the 6725 (11) and in installed AR3932s.
bingo. no problems.
for many apps the X may work fine. we are in the 550+ power area and it looks like the larger gap X plug may not be the ticket.
the AR3932 is a non resistor plug.
Autolite Racing does offer a similar plug that does have a resistor. it comes in (only) a one heat range warmer edition and is the AR3923.
howard
"upon further review" of the dyno sheet i see squiggles from around 5500 on. it has been pretty much proved that these are a result of too much spark plug gap. the 3932X is not adjustable as to gap.
additional evidence of misfire is the DynoJet losing the RPM signal further up the RPM plot.... around 7800. this is probably because some of the spark energy was leaking on the exterior of the plug to ground since there was too much CCP.
i am in debt to Cam Worth for bring this to our attention. Thanks Cam. i talked to Lance on it and he was in general agreement and offered an additional fix which was longer, almost impossible to install/remove spark plug boots. both Cam and Luke just focused on gap.
so we grabbed my NGK 6725 plugs and gapped them at .02. (did not have a set of AR3932 immediately avail)
the dyno retained the RPM signal immediately to redline.
OTOH, Luke was hearing noise from peak torque up in the Link Knock Amp Headphones.
the headphones are awesome.... they keep you ahead of serious knock. we acquired them in January and Luke has adopted them for all his tunes.
here we are indebted to Richard Green (NZ) for the tip... here's an email from him a couple of days ago:
"Isn’t the Link knock block great. You can hear you’ve got a problem before you do damage – an early warning device if you will. Imagine how many tuners are needlessly destroying engines without this tool. Interestingly the engine I tuned today was quite noisy for the first 10 or so low boost pulls but then it cleaned up (sounded like worn apex seal grooves). It’s because the engine had zero miles on it before today and all the seals needed to bed in, even though they were new (most aftermarket apex seals seem to be supplied with a slight bow in them). So I suppose the noise was also like mildly bent seals… until they bed themselves in. And I guess mildly bent seals can cause pre-ignition…. which can be picked up through the headphones. Engines with flattened corner seal springs sound the same."
it appears that what we were hearing a week ago from the 6725s was a combination of a bigtime inductive ignition system (IGN 1A) and fine wire, long strap plugs being turned into a glow plug. this did happen to Richard last year and he switched to the thicker nickel/copper plugs which cured the noise.
we could not come up w another explanation. i think the 6725 plugs work very well in a CDI environment but may not work as well w inductive. the much longer spark duration being the issue.
so we swapped out the 6725 (11) and in installed AR3932s.
bingo. no problems.
for many apps the X may work fine. we are in the 550+ power area and it looks like the larger gap X plug may not be the ticket.
the AR3932 is a non resistor plug.
Autolite Racing does offer a similar plug that does have a resistor. it comes in (only) a one heat range warmer edition and is the AR3923.
howard
Last edited by Howard Coleman; 10-10-13 at 08:43 AM.
10-08-13, 09:41 PM
#49
So Howard, which versions do you recommend? The "non X" versions which ARE gap able or the "X" versions that are not? I would like to see how they work on my NA 20b with LS1 coils. The non "X" versions are in stock at my local Advance auto. One last thing, are you recommending these plugs in both leading and trailing locations?
One last thing, are you recommending these plugs in both leading and trailing locations?
10-09-13, 07:37 AM
#50
Racing Rotary Since 1983
Thread Starter
iTrader: (6)
i don't have a specific recommendation and am simply sharing what i have observed.
spark plugs are very important to get right since our motors are capable of easily generating lots of CCP and CCH.
while i was sitting in the passenger seat watching the logs as we made 575 at 25 psi i had zero indication that we were experiencing primary voltage leaks at the plugs.
zero.
looking at the dyno power chart at zero smoothing a different picture emerged.
the squiggles on the power line above 5200, (we were making over 400 SAE at 5000 so we had big time CCP at that RPM), the noise on the headphones and the dyno rpm signal being squelched at 7800 all tell the tale.
too much plug gap w the un-gappable AR3932X.
in went the only set of plugs we had that we could gap, NGK 6725 11 heat range at .02.
all misfire symptoms vanished for the first two pulls. no dyno RPM shut down, almost no noise and a smoother power plot. on the third pull power was down about 30, and the noise re-appeared.
after acquiring a set of AR3932 plugs gapped .02, no further symptoms occurred. we made numerous runs and experienced no noise, no RPM signal loss and the power returned to previous levels.
there are probably two important factors working here.
gap is important and even w a big ignition needs to be in the .02 neighborhood at this output level.
skinny long ground straps when forced to pass a powerful LONG DURATION inductive current may turn in to glow plugs. this is a speculative conclusion but is exactly what happened to Richard Green a year ago. he had the same noise and settled on the same cure: nickel large ground strap (cheap) plugs.
i do think if you are running CDI the NGK 6725s may be excellent as the spark duration is short.
if you are running INDUCTIVE, such as the OE coils, the OE coils and a Twin Power, FC coils or the Mercury Marine/ IGN-1A re-badge/AEM re-badge w a single turbo i would suggest you consider a nickel large ground strap plug. (the AR plugs are designed w a shorter "cutback" ground strap to reduce the chance of glowplugitus.)
there are NGK options in this area. i have always been a fan of Autolite Racing plugs and the 3932s seem to work well for my app. if you like the X design they may work very well at lower power levels.
check w board member Chris Ludwig for a FD friendly Mercury coil solution.
howard
spark plugs are very important to get right since our motors are capable of easily generating lots of CCP and CCH.
while i was sitting in the passenger seat watching the logs as we made 575 at 25 psi i had zero indication that we were experiencing primary voltage leaks at the plugs.
zero.
looking at the dyno power chart at zero smoothing a different picture emerged.
the squiggles on the power line above 5200, (we were making over 400 SAE at 5000 so we had big time CCP at that RPM), the noise on the headphones and the dyno rpm signal being squelched at 7800 all tell the tale.
too much plug gap w the un-gappable AR3932X.
in went the only set of plugs we had that we could gap, NGK 6725 11 heat range at .02.
all misfire symptoms vanished for the first two pulls. no dyno RPM shut down, almost no noise and a smoother power plot. on the third pull power was down about 30, and the noise re-appeared.
after acquiring a set of AR3932 plugs gapped .02, no further symptoms occurred. we made numerous runs and experienced no noise, no RPM signal loss and the power returned to previous levels.
there are probably two important factors working here.
gap is important and even w a big ignition needs to be in the .02 neighborhood at this output level.
skinny long ground straps when forced to pass a powerful LONG DURATION inductive current may turn in to glow plugs. this is a speculative conclusion but is exactly what happened to Richard Green a year ago. he had the same noise and settled on the same cure: nickel large ground strap (cheap) plugs.
i do think if you are running CDI the NGK 6725s may be excellent as the spark duration is short.
if you are running INDUCTIVE, such as the OE coils, the OE coils and a Twin Power, FC coils or the Mercury Marine/ IGN-1A re-badge/AEM re-badge w a single turbo i would suggest you consider a nickel large ground strap plug. (the AR plugs are designed w a shorter "cutback" ground strap to reduce the chance of glowplugitus.)
there are NGK options in this area. i have always been a fan of Autolite Racing plugs and the 3932s seem to work well for my app. if you like the X design they may work very well at lower power levels.
check w board member Chris Ludwig for a FD friendly Mercury coil solution.
howard
Last edited by Howard Coleman; 10-10-13 at 08:46 AM.