Spark plug recommendation for my other parts?
 

I have a '79 Cali 930 motor, and I'm updating my ignition system. No complete history on the motor, stock 3DLZ turbo, stock fuel system & CIS.

Due to a cross country move and redoing my suspension, I don't have a lot of miles on the car, so I don't have any historical performance to base a plug choice on. The fuel mixture is a bit rich and I need to set timing as well, but the car starts and runs fine, no ignition related problems that I'm aware of. Parts replacement is driven by "while I'm there", clean baseline, etc.

I'm currently installing:
- Classic Retrofit CDI+
- Parts Klassik CDI Ignition Coil
- Magnecor Plug Wires

Since I'll be installing the plug wires, I figured now would be the time to install new plugs.

I've seen the NGK 2668 BKR8EIX IX Iridium's suggested on the forums before, but I've also found conflicting information about the "R" in the part number standing for resistor/resistive, and I'm not sure if that would be a bad thing with CDI. I'm aware of the CDI+'s reputation for having consistent/high power throughout the RPM range, not sure if that should factor in.

I also looked into getting the original spec Bosch W3DPO, but at $38 apiece from Pelican (as opposed to $10 apiece for the NGK's) I'd like to get more opinions before spending over $200 on plugs.

Application is spirited street driving and road trips. Little to no track.

Please let me know if any other info would be helpful for a recommendation. Thanks in advance.

if you still have CIS then go with the w3dpo. just feel lucky you didnt twin plug it and need 12

Have you always used the Bosch W3DPO? Any comparisons with other plugs in a 930?

Video comparing/measuring resistive versus non

NGK Part number cross ref

Interestingly enough, using the NGK lookup for 911's it lists a "BP" instead of "BK", but it's resistive as well.

Does anyone know if the Bosch W3DPO is non-resistive?

Update: it's non-resistive

Some more notes:

The Bosch plug is W3DP0, ending in zero, not the letter O

R0ckAut0 page for W3DP0, it's non-resistor

Somewhat related quote from Mangecor: "On production vehicles used exclusively on the street in standard tune, often the vehicle manufacturer's original spark plugs are a good choice, except where a double platinum version is available — which is a better choice. Always use resistor spark plugs if the vehicle manufacturer specifies them, as the resistance is there to not only to help reduce RFI, but also to extend the life of spark plugs by reducing tip erosion."

From M&W Ignition CDI install instructions:

"Non resistor spark plugs will greatly enhance ignition performance however some installations will require the use of resistor spark plugs for correct ECU operation.
When using resistor plugs measure their resistance as part of regular maintenance. Open circuit or high resistance may cause damage to spark plug wires, ignition coils and CDI. "

Same instructions but for what looks like to be the M&W model for 6pin CDI

yes always have ben told unless you go with efi nest to stick with them. never had any plug issues

I have run the W3DP0 on the top since I have had the car. A few years ago I considered replacing them but they looked good so I reinstalled them. At that time I found this crossover chart. The BP8ES is about $3.50 compared to the $38 for the W3DP0. This is all I know and look forward to the results of your research.

http://forums.pelicanparts.com/uploa...1651660885.JPG

My bottom plugs are NGK D8EA

Here is a cross reference list from NGK

Most of what I'm reading says that it's not good to use resistor plugs in a CDI ignition.

I know that Chris at Turbokraft recommends the NGK BKR8EIX, but some say that is because he's mostly doing inductive builds (without CDI).

NGK Part finder (click on "Cars,Trucks,SUV" then "Part number")

Looking up BP8ES, it's a solid copper core, with 1 Ohms of resistance. Your D8EA's are also 1 Ohm of resistance.

Note that NGK also makes a BPR8ES which has 5000 Ohms of resistance.

In comparison, the BKR8EIX is listed at 5000 Ohms of resistance.

I forgot to note the source and the exact quote, but there was mention in an article that both the resistance of the plug wires and the plug itself is overcome to move the energy from the coil across the plug gap.

I know the Bosch silver ignition coils have a reputation for a high failure rate. I wonder if any of that could be associated with too much resistance in the plugs? I'm not an EE here, just a guy with a Porsche trying to figure it out.

Several of the places I've checked in order to find a better price for the Bosch W3DP0 said they can't even order them. Not sure if that's just a retail failure or has some further meaning.

Here is a larger cross-brank heat reference

According to the above, Bosch 3's are equivalent to NGK 9's
According to the above, Bosch 4's are equivalent to NGK 8's

However the NGK cross ref shows some Bosch 3's equivalent to both NGK 8's and 9's.

Interestingly enough I just noticed the NGK cross reference lists the BP8ES as equivalent to Bosch W3DP0.

It is O and not zero on the end of W3DPO, in case you are trying to order them. Maybe one vendor had it wrong?

Might be, both Amazon and Rock Auto have it listed as a zero so I'm not sure, common mistake.

Bosch Spark Plug Part Number reference

Actually I think it's a zero, check 2nd page in link.

W3DP0

W = Seat shape and thread: 20.8 hex, M14x1.25
3 = Heat range
D = 19mm height incl seat, 17.5mm height excl seat, 3mm electrode height
P = Electrode Material: Platinum
0 = Designation Code: Differences from basic design

Another plug recommended by 930 owners is the Denso IW24.

Denso plug catalog

IW24:
- 14mm dia x 19mm length, hex 20.6
- gap of 0.7mm
- Resistance of 5000 Ohms
- projection of 1.5mm for "focus on heat resistance"
- spark position of 1.5mm is .5mm from normal (1.0mm)
- 0.4mm diameter iridium
- typically around $10 apiece

None of the plugs in this section are non-resistor.

Note that there is an "Iridium racing" brand/line around page 44, and "IW06" are all non-resistor.
"All IRIDIUM RACING plugs specify a resistor, and contain a highly reliable monolithic-type resistor that blocks noise that may affect electronic devices. (IW06 has no resistor.)"

IW06 plugs:
- 14mm dia x 19mm reach, 20.6 hex
- gap 0.6
- projection of 1.5mm
- ground electrode height 1.6mm

There are 3 heats (cross-ref via this chart):
- 27 - NGK 9, Bosch 3 - Denso P/N: 067600-1811 (IW06-27) (alt P/N: 5744)
- 31 - NGK 10, Bosch 2 - Denso P/N: 067600-1821 (IW06-31) (alt P/N: 5745)
- 34 - NGK 11, no Bosch equivalent - Denso P/N: 067600-1831 (IW06-34) (alt P/N: 5746)

And ironically the prices I see for the Denso 067600-1811 (which matches the same heat as the Bosch W3DP0) are $40 and up apiece.

It does look like some shops in Japan are selling them for around $20US.

What plugs did you end up settling on? I’m in a similar position and not sure if I need to just bite the bullet and pay $38 each

I run NGK BP8ES in my 964T. Car runs great - the plugs last about 20,000 miles. I'd pay more for a plug that last longer - but not $38 each (W3DPO)

well actually maybe I would - how long do they last?

Brandon
'91 964 Turbo

I ended up going with the Bosch W3DP0's. They're the highest quality non-resistor plugs I could find.

I ran with NGK BP8ES some time ago (don't recall if they were BPR's or just non resistor). I liked them just fine, no issues, electrodes looked good on inspection, etc. Other than originality I have a hard time swallowing W3DP0's having $30+ benefit over NGK. I also ran a substantial spark gap, supported just fine by the MSD ignition I had at the time. Something like .040 if I recall.

Heh. I twin-plugged and went EFI/COP - and still run Bosch OE plugs. Worked well with CIS and still do. Never had one foul, even when it was getting 6-10 mpg in-town with CIS.

Them being a heat range colder than the NGKs is supposed to be a hold-over from the factory originally thinking they were building cars for club racers to trash on the track for homologation purposes so they could go production-based racing. They made only incremental changes for emissions and never re-tested for the EPA until they went EFI with the 965 Turbo 2 (I think). And then they spec'd hotter plugs, IIRC.

Colder plugs apparently remove more heat from the combustion chamber and provide snappier throttle response - in racing, many run the coldest plug that won't foul. As spendy as they are, W3DP0's don't seem to for me in normal street usage. YMMV...