Spark plugs

Road-race engines and ancillaries - general discussion
MinorTC
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Re: Spark plugs

Post by MinorTC » August 23rd, 2010, 3:37 pm

Is there any chance of some freebie trial samples from Champion, Sandro? ;)
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Sandro
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Re: Spark plugs

Post by Sandro » August 23rd, 2010, 3:50 pm

Hi Minor TC

the ones I will be making for my engine will be prototypes and I am happy for them to go on my car but I cannot send any out as if anything happens to them then there is no warranty. Although nothing should happen !!!!! but I would prefer not to take the risk

As for production spark plugs the ones Guy recommends will cover all states of tune as they are a cool heat range and fine wire precious metal too so have the benefits. Nearly 20 years supply of this part number should give you enough confidence...

regards

sandro
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kpsig
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Re: Spark plugs

Post by kpsig » August 25th, 2010, 11:43 pm

Hi, I just found this old thread and decided to pose a question here.

I own a supercharged (Rotrex) Alfa 166 2.0 Twin Spark, facelift model with forged pistons for 9.5/1 CR. Latest boost figures are 0,75+@7000 rpm.
I have changed original BKR6EKPA and PMR7A to colder heat range plugs, BKR8EIX and CR8EIX in order to cope with higher exhaust gases temperatures (with suceess: managed to reduce around 50 oC!).
Although the throttle (electronic) response is bettered and engine operates very smoothly, i have noticed a decrease in performance over 5000 rpm in high gears.
I took the plugs out and I saw that they were at very good condition.
Could it be that the reason for the loss of power is the shorter tip of BKR8EIX than the BKR6EKPA? (almost 3mm shorter)
Please note that I have not regapped the BKR8EIX although I am thinking about it, bringing the gap at 1mm (from almost 0,7mm). I know it is difficult to gap iridium plugs but i have done it once with sucess.

I have also seen that DEnso iridium spark plugs are also that short, except the L model which is not available in Europe (it is used in Subaru cars at IKL24 version).
Any ideas?
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NickRP
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Re: Spark plugs

Post by NickRP » August 26th, 2010, 9:50 pm

Hi Sandro,

Thanks for the very useful information on spark plugs. I have a few questions you might be able to answer /present your view:

1) What is the time scale of the video that you have posted? Under which conditions has the video been generated (especially in terms of mixture generation and flow around the spark plugs)?
2) Was the behaviour shown on the video consistant among bigger number of cycles?
3) Your oppinion on spark plugs with multiple ground electrodes.
4) Your oppinion on multiple spark events spaced about 1 ms apart (present only on low revs) generated at the same spark plug - a feature very common today.

Many thanks,
Nik
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Sandro
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Re: Spark plugs

Post by Sandro » August 27th, 2010, 4:10 pm

Hi,

I will try an answer the two threads above. I will tackle each one separately.

For the Alfa twin spark...

I assume the supercharger is an aftermaket modification as they were never made that way....

I need some more information on the changes you have made...
You say that you have reduced the temperature of the exhaust gas by 50 degrees C, is that just by changing the plugs? I need to understand what changes you have made to the engine, mapping etc before I can give an honest opinion.
However from the sounds of the problem it does not sound like a spark plug issue, generally ignitability is noticed at low speed low load, thats were the OEs measure it. The shorter projection will have an effect on ignitability as combustion is closer to the cylinder head when it starts so more energy is lost. But you do need to consider that you are feeding the engine better with a supercharger so it can balance out.
You have done the right thing by going to a colder spark plug when you have more power but the new plug you use I dont know as it sounds like an aftermarket design. Can you post a picture of it please so I am 100% sure I know what it is.
High speed high load ignitability is generally not a problem to a certain extent from a spark plug design point of view. I assume you have had the engine remapped too to to ensure you get the best out of the supercharger modification?

Dont regap the plugs, you may have issues with the dielectric performance of the plugs as:

1) bigger gaps need higher voltage, plug with higher compression pressures plus supercharger the voltage will increase significantly- will the std ignition coils cope with it? if they cannot you will have misfire.
2) these higher voltages may punture the ceramic. You need to understand the effect of what you have done on voltage demand..we have all the test equipment to measure it to be sure. When I mentioned a 1mm gap earlier in the thread I was referring to naturally aspirated TCs. Turbo / supercharged engines usually are specified with smaller gaps, 0.7 - 0.8mm, but they have to achieve a durability target too. If you are to increase dont go above 0.8mm to be safe, but be careful because incorrect gapping can break / crack the ceramic core nose...then you will have pre ignition problems should the engine run.

If you can provide more information on what you have done and how you have measured these differences...that would help a lot.

In response to the video questions on the last thread.....

1) The timescale was equivalent to the time of one combustion event, measured in milliseconds, clearly slowed down so you can see the effects. This was done in a pressure chamber with no flow as we wanted to show the differences a firing end design had with no other outside influence.
2) This has also been measured on an instrumented engine where we measure the pressure in the chamber during combustion, the results match what we have measured. We have seen this also from many OEs and our competition.
3) Multi ground electrode plugs....in my honest opinion, I dont like them,I have tried them in my cars and I have felt the difference in engine smoothness - again this is my opinion. Again I look at designs specified for OE programs where we have specific targets to meet, durability, cost, ignitability, voltage demand etc. In general ignitability is worse on these designs although this is engine dependant, ie what turbulence you have in the chamber. I worked on a project with Renault a few years back that they claimed only a double ground electrode plug would work, I still dispute that but again they have a series of targets to meet. For you guys in the aftermarket plugs can be changed when you want to a certain extent, OE manufacturers want them changed at certain intervals. Porsche and BMW specify a multi ground electrode design on one of their engines but again they have targets to meet. BMW incidentally have moved away from them back to single ground electrode designs. The majority projects I work on now in Europe (in fact I cannot think of one new engine at the moment coming out) are specified with single ground electrode designs - anything requiring a service interval of 60,000km or more need precious metal, ie Platinum, Iridium or Gold Palladium fine wires, turbo applications need platinum also on the ground electrode to control the gap growth for voltage demand issues as mentioned above.
4) Multi spark concepts have been developed principally for low speed low load applications where carbon fouling of the spark plug is an issue. The multi spark events help clean the firing end and ensure you always have a spark. These are usually couple with multi ground electrode designs that have semi surface discharge characteristics (ie the spark travels partly in air and partly over the ceramic core nose - spark passing over the core nose cleans the carbon away - in simple terms). These concepts swith off once a certain load and rpm is reached and go back to a single spark.

I hope I have answered everything asked - I apologise for writing war and peace here...I could have written a lot more but Guy would have something to say!!!!.

Let me know if you have nay other questions....

thank you

sandro
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Guy Croft
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Re: Spark plugs

Post by Guy Croft » August 27th, 2010, 4:49 pm

What can I say?

MODEL POST

Thanks very much Sandro, your professional attention to these questions is very much appreciated.

GC

kpsig
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Re: Spark plugs

Post by kpsig » August 27th, 2010, 5:23 pm

Sandro,
The engine is a modified one with Rotrex Supercharger.
Mapping is done to the original ECU. We do wideband lamda analysis vs exhaust gases temperatures. At this moment we have backed up something like 4-6 degrees in advance at medium-high rpm.
Lamda ratio is at the rich side, around 11/1 full throttle. Always 14,7/1 at cruise
My EGT were around 910 Celcius @ 6th gear @5800 rpm at cruise (straight road) with trend to exceed this. Lowering advance made nothing but decrease performance while richening the mixture made response really sluggish.
So, I tried those spark plugs from NGK, which claims that colder spark plugs can reduce combustion chamber temperatures.
True, at the same conditions I see not more than 870 degrees now.
The spark plugs are NGK BKR8EIX instead of BKR6EKPA (special for Alfa Romeo Twin Spark 16V) and CR8EIX instead of PMR7A.
Yesterday I took out the BKR8EIX and put back the OEM. The car is again as before, really strong.
I measured the BKR8EIX gap and show that it was something less than 0,7mm. So, I did regap them today at 0,9mm. I know that Denso recommends 0,8mm-0,9mm for their similar IK24 (for Alfa Twin Spark) so I did the same. Actually, 0.9mm is the gap for the first generation of NGK iridium plugs for Alfa Romeo (aftermarket).
Also, note that the NGK BKR8EIX are used in Honda VTEC engines at 1,1 mm gap and Peugeot Rallye 1.6 8V with compression of 12,8/1 with Punto GT coil @0,9mm gap with sucess.
So, now I will do a trip to check EGT again and the refit the regaped BKR8EIX to see the results.
If I see misfires I will try 0,8mm.
Last edited by kpsig on September 2nd, 2010, 7:08 pm, edited 1 time in total.
Kostas, Greece

Guy Croft
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Re: Spark plugs

Post by Guy Croft » August 27th, 2010, 5:37 pm

Make life simple: use the pre-gapped NGK race div plug B10EGV


GC

WhizzMan
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Re: Spark plugs

Post by WhizzMan » August 30th, 2010, 11:47 am

kpsig wrote: I measured the BKR8EIX gap and show that it was something less than 0,7mm. So, I did regap them today at 0,9mm. I know that Denso recommends 0,8mm-0,9mm for their similar IK24 (for Alfa Twin Spark) so I did the same. Actually, 0.9mm is the gap for the first generation of NGK iridium plugs for Alfa Romeo (aftermarket).
Also, note that the NGK BKR8EIX are used in Honda VTEC engines at 1,1 mm gap and Peugeot Rallye 1.6 8V with compression of 12,8/1 with Punto GT coil @0,9mm gap with sucess.
So, now I will do a trip to check EGT again and the refit the regaped BKR8EIX to see the results.
If I see misfires I will try 0,8mm.
You are comparing with NA engines here. You should be comparing with forced induction. As Sandro stated, higher compression requires a higher voltage to ignite with the same gap distance. If you increase the gap distance, you are also increasing the voltage required. Stock Alfa coil-on-plugs aren't designed for these voltages or for forced induction engines. I'd stay away from larger gap distances.

Your engine is most likely a CF3 engine. These don't do a "waste spark" setup like the CF1 and CF2. In stead, they spark both plugs of the same cylinder with one coil. You could get more oomph out of the coils if you were to reprogram your ECU to do a waste spark setup between cylinder 1/4 and 2/3. That way one of the plugs per coil would be sparking in a non-compressed chamber and you will be using two coils per spark. Do check if you have a CF2 or a CF3 setup, there is a difference and swapping ignition parts between them is not plug and play.
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Sandro
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Re: Spark plugs

Post by Sandro » August 31st, 2010, 9:34 am

Hi kpsig,

I started to write a response on Friday then stopped as I wanted to have a think about the problem...

your problem is interesting.

First of all i need to clarify a few points

for identical designs of spark plugs with differenct core nose lengths, ie colder or hotter....this will not have any effect on the combustion temperatures given the same operating conditions / parameters. What changes is the temperature at which the spark plug operates, that is why we have to identify the correct heat range for each engine using thermocouple spark plugs, so I am intrigued to know whats going on here. So a colder plug can be put in a more powerful engine than the standard (ie yours v the std Alfa TS) becuase it has a lower operating temperature and will have the correct safety margin against pre-ignition.

I know the NGK plugs for the Alfa twin spark because I worked on that project. The gaps of 0.9mm for a standard engine work fine, but your engine is not standard. Denso recommend the gap for a standard natuarally aspirated application not a supercharged application, be careful. With a supercharger the in cylinder pressures are higher and therefore so are the voltages.

I dont recognise the plugs you are using, as I said the more retracted the spark position the more effect you will have on the combustion. The reduced exhaust temperatures are to do with the change in combustion you are getting due to the retracted spark position, and clearly this is having an effect on the performance.

Can you send in a photo of the plug you are using just so I can see what the spark position and firing end is like...I dont recognise that part number sorry.

regards
sandro
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NickRP
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Re: Spark plugs

Post by NickRP » August 31st, 2010, 9:49 pm

Hello Sandro,

Thanks for the clarification.
Sandro wrote: 1) The timescale was equivalent to the time of one combustion event, measured in milliseconds, clearly slowed down so you can see the effects. This was done in a pressure chamber with no flow as we wanted to show the differences a firing end design had with no other outside influence.
I see. The reason I asked for time scale was to find out how fast is the flame front traveling. Another interesting video, real combustion chamber, with piston position given: http://www.youtube.com/watch?v=sEf8va1S7Sw (hope Guy won't mind).
Sandro wrote: 2) This has also been measured on an instrumented engine where we measure the pressure in the chamber during combustion, the results match what we have measured. We have seen this also from many OEs and our competition.
Can you please explain the differences recorded with the real engine? Which parameters were assessed? We often use BMEP variation as the measure of combustion stability, but if you used some other method, I am interested to hear about it.
Sandro wrote: 4) Multi spark concepts have been developed principally for low speed low load applications where carbon fouling of the spark plug is an issue. The multi spark events help clean the firing end and ensure you always have a spark. These are usually couple with multi ground electrode designs that have semi surface discharge characteristics (ie the spark travels partly in air and partly over the ceramic core nose - spark passing over the core nose cleans the carbon away - in simple terms). These concepts swith off once a certain load and rpm is reached and go back to a single spark.
I have made an experiment with multi spark multiple ground electrodes on my car (Tipo 2.0 16v), that has relatively unstable idle when running lambda = 1. Short details about setup:
[*]high performance (motorsport) Ford EDIS coilpack (wasted spark configuration, 70 mA of spark current, spark duration 2.5 ms).
[*]Bosch FR78 Super 4 spark plugs (deliberately chosen to be a bit hotter, gaped at 0.9 mm).
[*]OE HT leads (DC resistance 500 ohm).
[*]RP Lab programmable Weber Marelli IAW ECU with the OE maps.

Looking into BMW secondary (spark) voltages, I noted that at low revs, they let the spark "burn" for about 0.8 ms, then they recharge the coil for about 1.2 ms, then let it spark again etc. I have programmed the same into engine management, and then experimented with various settings of spark duration and coil charging for secondary sparks. However, no matter what I did, I could not achieve better results (improve combustion stability) in comparison to single spark - actually, I struggled to find a set of parameters at which it would work with the same level of "smoothness" as with single spark. My conclusion was that this concept only makes sense if spark energy is relatively low (which is often the case with modern pen coils), but coils have short charging time. My engine simply liked having single long strong spark, which motorsport EDIS coil was capable of producing.

Furthermore, I have performed some tests to compare effects of different ground electrode design to the engine behavior. For the comparison I have used 3 different spark plug designs, OE (RN7YCC, single ground electrode), NGK V-Line (BUR 6 ET, three ground electrodes) and Bosch Super 4 (FR 78, 4 ground electrodes). I was logging engine revs accelerating from 1000 to 7000 RPM in third gear (approx. 20 - 140 km/h) and did statistical analysis of the numbers. At engine speeds above 3000 RPM, there was no statistically significant difference between the three. However, both NGK and Bosch have yielded better results in low revs, especially in the range between 1500-2000 RPM, where improvements are also obvious to humans (engine is a bit hesitant there with OE spark plugs at high load). My assumption was that multiple ground electrodes were increasing ignition probability - but I could be wrong, of course. Do you have some explanation for the performance improvements I have measured?

Best regards,
Nik
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kpsig
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Re: Spark plugs

Post by kpsig » September 1st, 2010, 10:27 pm

Yes, my engine is a non waste spark. It is CF3. But to be honest, I have no idea on how to reprogram stock ECU to do waste spark. I will ask my mechanic.

First note: BKR8EIX are out of the picture. The difference of tip length between those and BKR6EKPA is almost 3 mms, which clearly created downgrade in performance. Putting back BKR6EKPA gave performance back almost entire rpm range, although I do see an increase in EGT: it is around 10oC higher now (however, this difference could be a result of pump gas difference between shops).
Second note: with CR8EIX instead of PMR7A i noticed some lack of performance after 5000rpm, with BKR6EKPA now installed. Gap was 0,7mm, as original plugs for NA TS 2.0 engine. I regapped them to 0.9mm (i know, contrary to theory for gapping when you supercharge an engine) just to see if coil could continue proper sparking (in any case, iridium plugs are "easier" to spark than platinum OEM, so why not). Performance was *better*, however @5000 and 6000 rpm some slight engine hesitation. Probably, misfires.
So I did a lot of research to see what people are doing in Italy where you can find Twin Sparks of any kind. So, BIG surprise for me.
ALTHOUGH some NGK dealers (Greece, UK etc) propose BKR8EIX and CR8EIX, those, in practice, have given bad results in NA and forced induction engines. Instead, they propose BKR7EQUP+PMR8A
and for racing: R7434-8 + R016-9.
I am not racing, so I will definetely go for BKR7EQUP+PMR8A which are widely used and not that expensive. Both have the same lentght of tip with OEM BKR6EKPA and PMR8A.
Last edited by kpsig on September 2nd, 2010, 7:09 pm, edited 2 times in total.
Kostas, Greece

Guy Croft
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Re: Spark plugs

Post by Guy Croft » September 2nd, 2010, 3:52 pm

BEFORE ANYONE ELSE POSTS HERE I WANT TO SEE PHOTOS.

ALL THESE BLASTED SPARK PLUG NUMBERS THAT MEAN NOTHING TO ANYONE AND REAMS OF DATA MAKE A DULL THREAD.

DON'T TREAT THE FORUM LIKE A PRIVATE PARTY - THIS SITE GETS READ BY A LOT MORE FOLK THAN EVER JOIN UP.

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kpsig
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Re: Spark plugs

Post by kpsig » September 8th, 2010, 6:35 am

f 001sm.jpg
Left: PMR7A (geometrically same as now installed PMR8A) tip intrusion from plug face 2mm, Right: CR8EIX tip intrusion from plug face 1mm
f 001sm.jpg (29.34 KiB) Viewed 3759 times
f 004sm.jpg
same plugs as above
f 004sm.jpg (27.6 KiB) Viewed 3759 times
f 006sm.jpg
same plugs as above. Note that ground electrode on CR8EIX is also shorter and gap of cr8EIX which now is 0,9mm. Did not work at 0,6mm and 0,7mm.
f 006sm.jpg (23.56 KiB) Viewed 3759 times
f 008sm.jpg
BKR6EKPA tip intrusion from plug face 5mm, BKR8EIX tip intrusion from plug face <3mm, BKR7EQUP tip intrusion from plug face >3,5mm
f 008sm.jpg (28.86 KiB) Viewed 3759 times
f 009sm.jpg
same plugs as above
f 009sm.jpg (31.48 KiB) Viewed 3759 times
f 012sm.jpg
PMR7A after 100.000 kms Note the small pits on porcelane. Typical from the high Sulfide Greek gas pump
f 012sm.jpg (26.75 KiB) Viewed 3759 times
f 011sm.jpg
CR8EIX after 500 km. When I installed CR8EIX and BKR8EIX my fuel mixture became almost 10% richer. Low combustion efficiency, probably, in relevance to before with OEM plugs
f 011sm.jpg (23.88 KiB) Viewed 3759 times
f 013sm.jpg
BKR6EKPA after 100.000km (not my engine)
f 013sm.jpg (28.15 KiB) Viewed 3759 times
f 015sm.jpg
BKR8EIX after 500kms on my engine
f 015sm.jpg (27.98 KiB) Viewed 3759 times
f 016sm.jpg
Brand new BKR7EQUP. Results from its installation soon. It is a semi surface discharge plug, used in tuned Twin Spark Alfa Romeo's (Iridium, after all, are not proposed by NGK!). Same plugs for Mini Cooper S supercharged and some modern Porsche
f 016sm.jpg (31.36 KiB) Viewed 3759 times
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Guy Croft
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Re: Spark plugs

Post by Guy Croft » September 8th, 2010, 8:48 am

That's more like it - well done,

G

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