Spark Plugs for Stroker 3.1

[z boy mn]

Good morning everyone, and happy holidays!

For Christmas, I was thinking I'd replace the plugs on my Z as it's been a few years, but I'm not sure where to begin getting the right one. I've read the forums here, and it looks like the best bet would be either the BPR6ES-11, BPR5ES-11, or BR6ES. The issue is that my car isn't stock, and I went through the NKG website and looked at every Z from 1970 through 1985 to get a feel for what they recommend.

(I attached the PDF from the site here to help make sense of what the letters mean.)

My engine is:

• F54 engine block, 3mm overbore; 83mm stroke, KA24E shaved flat-topped pistons, 3.098 liters (standard 3.1 kit)
• P90 head, ported, with stainless springs & valves
• 490 Lift – 290 Duration CAM
• 9.5 compression ratio
• Triple 45 DCOE Webers
• Electromotive HPX electronic ignition (no distributor)
• Campion 9007 plugs set at .035

A couple years ago I switched from NKG to Champion as I had two NKG plugs that went bad at the same time and I spent hours tracking down the issue...so I got the Champions out of spite! Now, though, I'm willing to return to something more stock.

Also, another issue is the gap. My electromotive manual says that stock street should be from .045 -.060 and performance street should be .030 - .035. I've got the Champion plugs now set at .035. (I've attached the manual for that, too, in case anyone's interested.)

I'm not sure how muh it matters, but the car came with BP7ES plugs...I don't know how the PO arrived at those, however.

My current guess is to go with the BPR5ES-11, and set the gap at .045. I'm not too worried about going up a notch in heat range as the engine runs plenty cool--barely getting to 180 under normal circumstances, and on the track it never went above 190. It also runs rich at idle (AFM = 10), so I'm thinking the hotter plug will help it start as well.

Finally, I did have it on the dyno this fall, and the results were pretty decent. Without the airbox I fabricated, it was getting 220 at the wheels, so I'm guessing with a 15% tranny efficiency loss, it's running about 250 at the flywheel. I've attached that file, too. I think my timing post 3K is low, so I'll be fiddling with that in the spring when the snow melts...but first I want to get the new plugs in.

So....any suggestions from the experts?

design_symbols_plugs.pdf

HPX Ignition Manual.pdf

Edited December 26, 2015 by z boy mn

[Chickenman]

In NGK " 6 " is the stock range for normal use and is usually suitable for mild competition sucha s Autocross. . The " 5's " are supposed to be used only used in the far North where warm up times are exceedingly long or on engines that are " tired " and are burning oil.  Hopefully your new 3.1 stroker is not burning oil!!!

 

I would definitely NOT run a " 5 " if you use the car for track days. Properly tuned, a cammed and triple carb Z motor should not foul the plugs, even in city traffic. Triple Webers can run a sharp as fuel injection with the right tuner. For track days, you may even want to switch to BPR7ES-11's, in fact it would be highly recommended. The last thing you want is a plug overheating, detonating and taking out your new engine. Combustion temps, fuel octane  and timing are what govern plug range. Water temp is much less important than EGT ( combustion temp ) for choosing plugs range. You can still melt plugs ( and pistons )  even at 180 F water temp.

 

The electromotive ignition helps out a bunch. Less prone to fouling if you are running a bit rich, and you can easily go with the larger gap BPR6Es-11 ( 1.1mm or .042" pre-gapped ) . .040" to .042" gap will give you a nice fat spark kernel and not stress the ignition. No need to go any bigger. Larger gaps are for lean burn engines.

 

Make sure you are running a good spiral core ignition lead such as NGK, MSD, Magnacore or Aurora.

 

BTW, I've bean running NGK, Bosch, AC Delco and Champion plugs over the last 40+ years of racing. NGK are by far the highest and most consistent quality. I've had 1 NGK failure in all that time. Two in a row is a bit strange... but very manufacturer has a bad batch slip through occasionally.

[Chickenman]

Since you are running Track Days, you should be running a Wide Band O2 sensor. They are really a great tuning device. If you're not running a WB O2 sensor you better learn how to " read " plugs fast. Read up on the subject, look at color pictures and get a Plug scope ( or a big magnifying glass ).

 

Us " Old Timer's " never had the luxury of having any type of AFR gauge when we started racing. Plug " reading " was a skill you had to learn or you were in big trouble racing. Some people were really good at it... others not so much. But it is a very handy skill to develop. 

 

But, AFR meters can sometimes lie ( faulty ). Never trust them 100%. The plugs will always tell the truth. Usually the AFR meter ( or an EGT meter )  will correlate with plug readings. But, f the plugs are telling you the engine is running lean for instance  and the AFR meter is telling you the engine is OK or Rich, put more " weight " on the reading of the plug. ( Assuming you have the appropriate knowledge of Spark Plugs and how to read them of course ). 

 

O2 sensors have a definitive  life span and give false reading as they age or get contaminated . Racing or Track Days can shorten their life span tremendously due to over heating of the sensor or contamination from exotic fuels/additives or Silicone gasket sealers. 

[gnosez]

Ditto re: O2 sensor(s - I have dual exhaust). I would start with 7s for road use and go to 8s for track days. Gap can stay right at 0.035 to 0.040.

You made no mention of the octane level. I'd be running 93 on the road and 100 or thereabouts on the track.

I ran my 3.1L with 9s on the track and 110 in the tank. The new 3.2L (13.7:1 CR) will run on 110 plus(when available) and with BR10EGs gapped to 0.035. No in car dyno numbers yet as I need to determine which clutch/flywheel to use depending on the tranny (280ZX or Preston/Datsun). I'm expecting 280+hp@rwhs with triple Mikunis and a very aggressive cam.

Edited December 27, 2015 by gnosez

[nix240z]

Rebello used B8es in my 3.2L

[Zed Head]

Rebello used B8es in my 3.2L

I was going to say if that's a Rebello motor why not ask Rebello?

 

And heat range is more about keeping the electrodes hot enough to stay clean but cool enough to avoid pre-ignition.  Indirectly related to engine temperature but evaluated independently. 

[z boy mn]

Wow, thanks for all the feedback everyone! And, sounds like I was going to guess wrong on the plug options so thanks for saving my engine. A few comments/follow-ups...

 

The engine is new, and it doesn't burn any oil.

 

I do have an AFR gauge (installed last winter), and it really helped tune up the webers. Before, I was reading the plugs and I had it tuned pretty well, I thought, with just a slight hesitation through the progressive circuit. When I got the AFR hooked up, I could see that it was actually leaning way out in the progressive circuit, jumping to 18-20. It was also running a but lean after 3K, so I adjusted the idle and main jets until it is even throughout. At idle (~700 rpm), it runs around 10, but anything past 1200-1500 or so it's in the 12-13 range. If I turn in the mixture screws, it's better at idle but leans out again in the progressive circuit. Also, cruising at 55-60mph ends up on the lean side, too (15) and I'd rather burn more fuel than risk the engine. (I thought about drilling out the progressive circuit holes some, but I simply chickened out. )

 

I have heard that the AFR gauges aren't always accurate and that they become less accurate over time. I put in an Innovate 3844 model has a Bosc oxy sensor and a meter which you can re-calbrate to compensate for hours of use, and I like it. The seat-of-the-pants gauge says the car is happier, too.

 

As for two the bad plugs in a row, I couldn't believe it either, which is why it took me so long to figure it out.

 

The HPX ignition is great, especially for a novice like me. It just wires up to power (I have it on a separate circuit straight to the battery so the power is clean) and then goes directly to the plugs. It's an older model, so you can't attach a computer to it, but there are 4 knobs for adjusting timing at 0-2999, 3K, 8K, and an rpm limiter. Right now, the initial timing's set at 12 and goes to 24 after 3K. I think I will try a larger gap with the BP6 as well...makes sense to me. Also, it has 8mm Taylor wires on it from MSA...not sure if they have a spiral core or not.

 

I run non-oxy pump fuel, but 92/93 is the best I can get here in central MN. I don't have access to anything higher than that.

 

I didn't ask Rebello as they didn't build this motor. The PO assembled the pieces using directions available for the 3.1 stroker. I have them somewhere...from what I've read, it's a pretty standard build. I noticed in their website, though, they're turning out a lot more HP than I am, their stroker 3.1 was close to 325 I think. So, I need to find another 50 horses somewhere, could be in the timing...or the fuel. Either way, I'll start with the plugs!

 

So...BP6ES (with BP7ES for track days)...skip the "R"?

[Chickenman]

Stay with the Resistor plugs always. Resistor plugs with Spiral core wires will actually build a higher arc over voltage and current than non-resistor plugs. That is a good thing. Initiates a larger spark kernel.

I've never liked Taylor wires. From my experiences very poor quality. There high end Race stuff may be OK, but the regular 8mm and 9mm spiral core wires are not that good. And hopefully you aren't using there carbon core wires as those just seem to be junk. IMHO of course FWIW.
 

 

[Chickenman]

As for your cruise AFR of 15 to 1, I don't think that's too lean. At cruise, AFR  leaner than 14.7 to 1 are possible and desirable. Cruise conditions are light load, low throttle angle, that give a low " Dynamic " compression ratio. Volumetric efficinecy at cruise is very low and that reduces Dynamic CR. That greatly reduces the chance of detonation. At cruise you want to run as lean as possible with no " hunting " of engine. Lean mixtures at Cruise do require a homogeneous mixture ( which the Webers should provide )  and an Ignition system with a powerful spark. Your HPX system will provide that.

Engines with CR ( static ) of 9.5 to 10.5 to 1 should be able to run an AFR as lean as 15.5 to close to 16 to 1 with no ill effects. IF is is tuned properly, and IF you have well designed combustion chambers with good squish and high swirl  ( Early Style small chamber heads with flat tops or dished pistons )  and IF you have a strong ignition systems. Modern EFI cars ( no direct injection ) easily run 16 to 1 and even leaner with Direct Injection  these days.

David Vizard has an excellant book called " Performance with Economy ". ISBN # 0-9311472-09-1  He goes into all the details of how to build High Performance engines that still get reasonable fuel economy. Lots of tricks in there for older engines.

Edited December 30, 2015 by Chickenman

[z boy mn]

Hi again, Chickenman, thanks for the info. Clearly, I'm a novice and can only imagine how to adjust "squish" and "swirl" characteristics, but I'm learning!

When my car gets past 16 on the AFR it hesitates badly. I experienced this on the freeway at a constant 70mph....it jerked even at the constant speed/load. This was before I had the AFR in and realized it was so lean. Once I got different idle jets in there, it dropped down and seems much happier. Maybe it's another issue, though?

Also, very helpful information on the wires and plugs. The wires came from MSA and the PO bought them. I can add replacing them to the list while I learn more about how they're made.

I did make an order over the weekend for some BP6ES plugs, and they're on back-order now at O'Reilly's. Now I'm thinking maybe I should keep the "R". How much difference do you think it will make in spark?

Incidentally, they also said the BP7ES plugs aren't available anymore, though I did find them other places. So...just a heads up, seems that NKG may be discontinuing the cooler options or maybe they'll just become harder to get. They recommended I order a bunch if they're the right ones. I'll see how the BP6ES's feel, and if I like them I'll order a pile just in case.

Also, I just added Vizard's book to my Amazon list (one of the places I found the BP7ES plugs, BTW), I'm looking forward to as many tricks as I can get! :-D

Edited December 30, 2015 by z boy mn

[z boy mn]

I wanted to post an update to my last post regarding the availability of NKG plugs. I hadn't heard from O'Reilly's so I called them and asked about my special order. The person on the phone sounded confused and went back to check. He had a full set of BPR6ES's, BP6ES's, BPR7ES's, and BP78ES's on the shelf and said they were all standard stock items. So, looks like they're going to be available for the foreseeable future...sorry for the mis-information!

[CDL1542]

Any suggestions on spark plug wires or is there an ideal size/type for strokers
?