All you could ever want to know about Bosch W9DC vs W9RDC

[Jack M]

So I wrote to Bosch with the question of Why no more W9DC's?
and this is their reply. So their really is someone who will answer our questions. Not necessarily with the answer we want.

From: Wilkinson Mark M (AA-SP/MKT-NA)
Subject: RE: Request from Contact function: Spark Plugs

Date: Friday, August 6, 2010, 11:30 PM

Dear Jack M.

First, thank you for taking the time to express your concerns. This kind of feedback is invaluable to us here at Bosch.

I understand your concern, but unfortunately at this time we are unable to supply the W9DC spark plugs. We have upgraded this plug to the WR9DC+ as you have noted, which is a superior design in many ways. The fact that a resistor has been added only provides additional interference protection. It has virtually no effect on the operation of the plug or the amount of energy that is required to fire it or the power and duration of the spark.

In addition to the interference protection, the WR9DC+ has a tapered and V-profiled ground electrode, as well as yttrium enhanced center and ground electrodes. The V-profile provides for better ignitability and better flame growth. The yttrium enhanced ground electrode maintains a lower ground electrode temperature versus standard nickel chromium ground which you will find on competitor plugs. This is important in preventing pre-ignition which can damage an engine. Also, the nickel yttrium center electrode with a copper core has far superior resistance to wear versus standard copper core plugs (see pictures below...plugs were run at the same time in the same engine and operating conditions). The copper core in the center electrode ensures an ultra wide heat range versus plugs without a copper core center electrode...meaning it stays between the two critical temperatures, self-cleaning on the lower temperature limit and pre-ignition on the upper temperature limit, over a broader engine operating range. This keeps the plug from fouling and the engine from knocking.

Without Yttrium With Yttrium


I also thought I would clarify the effect of adding the resistor to the spark plug. See explanation below.

Current flow in ignition systems is measured in terms of milliamps, e.g. .001 volt. Therefore, the voltage loss due to the resistor can be measured as follows: [LEFT]

Voltage = Current x Resistance

Voltage = voltage loss for the purposes of the calculation

Current = measured in milliamps for ignition systems

Resistance = Ohms in the resistor, typically this is 5k Ohm or 5000 Ohm resistor

For example, in an 80 milliamp system with a 5K Ohm resistor the equation looks like this:

0.080 x 5000 = 400 volts

Therefore, as an example, in an ignition system capable of a max output of 25kv, 1.4% of the capacity is being consumed by / lost to the resistor (400 / 28000 = 0.016 or 1.6%). Also, in this 25kv system (or any other ignition system), one would never need anything close to the max output to actually cause the sparking event to occur. There is a margin of error built into each system by the manufacturer. Common values for bridging the air gap of the spark range from between 5-6kv at idle to 10-12kv under load...with the added resistor it will take an additional 0.4kv...which will have no effect on power or duration of the spark. It is simply added RF interference protection for other system components.

In summary, if it were possible for the resistor in the plug to affect the spark / drivability, then then there are most likely other problems with the ignition system, e.g. connections, corrosion, coils, etc... This very small voltage requirement caused by adding the resistor should have no impact on the system or driveability.

All that noted, we would welcome the opportunity to have our spark plug application engineer examine a vehicle exhibiting issues that are attributed to our WR9DC+ resistor plug versus a non-resistor plug. We strive to bring the best product to the market, but anything is possible and it could be a learning experience for all of us.

Finally, thank you again for taking the time to express your concern. Customer feedback is critical to our success and our bringing the right products to market. Please keep it coming. I hope some of this information is useful to you. Feel free to email me directly if you have further questions.

[FONT=Arial]
Mit freundlichen Grüßen / Best regards,


Robert Bosch LLC
2800 South 25th Avenue
Broadview, IL 60155 USA
www.boschusa.com
[

[nobby]

That gave me a head ache.

Can't I just look at pictures?



Good info but it certainly won't stop the debates.

[Jack M]

I agree with those who have tried resistor plugs and found poor performance. Actual comparisons are superior to technical processes and procedures.
Maybe if we write Bosch with our actual hands on results we can get them to start to manufacture them again. LOL J

[Graham]

Originally Posted by Jack M

I agree with those who have tried resistor plugs and found poor performance. Actual comparisons are superior to technical processes and procedures.
Maybe if we write Bosch with our actual hands on results we can get them to start to manufacture them again. LOL J

Jack,
One thing Mark did not cover, was use of resistor plugs with OE HT wires. The OE wires had a resistance of about 6.6 kohms. If used with WR plugs, this would increase loss to close to 1Kv instead of 0.4Kv. Or about 20% of what is required at idle - not insignificant. With other losses in an old car, such as worn distributor with varying air gaps, this could perhaps be enough to cause uneven idle.

Mark also uses a "typical" figure of 80mA for the current. This could be different for our old cars with the typical Blue coil. No way I know of accessing this number unless Bosch has it their archives.

I did write to Mark pointing out the above.

Personally, I have no problems with WR plugs, but I have new Bosch HT wires without resistors.

Thanks for pursuing this

[Jack M]

Thanks Jack. I appreciate it.

Actually, most of the emails have been positive and more of an inquiring nature. See my response to one from this morning below. You may find it interesting and useful as well.

Dear Mr.

I appreciate the feedback and question. Unfortunately, I don't have the original design specs of the ignition system you mentioned. However, in general a typical range for current is between 80 - 120 milliamps. There are some systems that run slightly lower and some slightly higher, but nothing substantial enough to make a big impact on demand voltage which would ever come close to the kv limits of the ignition system.

In looking at the scenario you mentioned, we would really only be concerned with the delta between the system as originally designed vs. that addition of the resistor plug. The reason being is that the typical demand voltage I noted of between 5-6kv at idle to 10-12kv under load assumes there is some resistor built into the system...either in the plug or the spark plug wires. For the Mercedes vehicle noted, it is safe to assume that the system was designed to supply in well in excess of 20kv. Even if we assumed the current flow is at the upper end of the range, meaning 120 milliamps, the incremental demand voltage would only be approximately 600 volts or 0.6kv. If we add this to the typical demand voltages noted above, we are talking about a range of between 5.6kv and 12.6kv. Assuming that the system is only capable of putting out 20kv (I am confident it is higher), we are talking about an operating range that only demands a maximum of about 63% of what the system is capable of outputting.

There are some other things to consider besides demand voltage when we talk about sparking events. These include things like engine temperature, the presence of an accelerant (meaning fuel), engine speed, and spark plug gap. If we were to rank ignition conditions from most difficult to occur to easiest, it would generally look like this:

1. Cold Crank with no fuel (most difficult ignition condition)
2. Start up: meaning engine cold, but with fuel
3. Engine at idle
4. Wide open throttle or WOT (best ignition conditions)

The biggest single issue we see when it comes to ignition and sparking events, assuming all components are in good operating condition, is spark plug gap. We recommend that if you are having issues, start here. We DO NOT recommend using a ring type gapping tool (round tool with various thicknesses of U-shaped wires extending out). We have seen significant gapping errors when using this type of spark plug gapping tool We would recommend a pin style gapping tool. See below:


I hope this information is helpful.

Feel free to share it with others. I only request that you NOT POST MY EMAIL ADDRESS. We have a website where communications can be sent and will be forwarded. This helps me to address multiple people / questions in one email rather than one person. As the Senior Product Manager for spark plugs in North America, I take seriously my responsibility as it pertains to responding to customers. I just want to do it as efficiently as possible.

Thank you for your time and inquiry.

Mit freundlichen Grüßen / Best regards,

Mark Wilkinson
Robert Bosch LLC

Sent: Friday, August 13, 2010 8:39 AM
Subject: Resistor plugs on old Mercedes
Good Morning!

I have copied an email you sent to a fellow Mercedes owner below. We really appreciate you taking the time to explain this. It is an on-going debate amongst owners of old Mercedes. Some insist that the Resistor plugs cause problems with their cars.

One factor that you did not mention, is the affect of using original spark plug wires with resistor plugs. The original wires on my 1972 Mercedes 350SL had integral resistors at each end. The one at the plug end was 5kohms and the other one about 1.6kohms, according to a rough measurement. If we add a 5kohm plug to that wire, we have about 11.6 kohms. You mentioned that the current would typically be 80 milliamps - Perhaps that number is different for these old cars? That would make a difference if it is actually higher. Perhaps Bosch has the original design figures? I do know they used non-standard Bosch coils. But even at 80Ma, the voltage loss would be closer to 1Kv or about 20% of what is required at idle. Other losses in the distributor and wiring could perhaps affect performance at idle.

On my own car, I installed new Bosch HT wires that have no resistors at either end. They appear to work well with resistor plugs. My interest is just technical - no complaints with WR plugs!

Regards




Mit freundlichen Grüßen / Best regards,

[mgburg]

Graham:

As you pointed out, ALL the components, from the coil all the way to the plugs' tips, need to be in the complete circuit to determine TOTAL losses of of the sparkplugs' E & I. (E = Voltage, I = Current)

And, the really, only proper way to test all situations would be on a dynometer. "+ plug" vs. "non-+ plug" - resistive wires vs. non-resistive wires, used (20K+ mileaged) distributor vs. new distributor.

THEN, you can see the cumulative effect of trying to throw a few new parts at a problem without considering the system as a whole. Change the plugs only or plugs, wires, cap, rotor, coil...where does it stop? Or better yet, where should you start and is there a point (or points) along the way that you can say, change only the plugs, then after a certain mileage, change the wires, then the cap...etc.?

You can do it one of many ways...be as anal as a top-fueler dragster...complete teardown of the engine after 3 runs or all the way the other way and be as sloppy as Joe Sixpax...when it breaks, he either ignores it 'til it completely quits going forward at all or it ends up smogging the neighborhood for mosquitos during the balmy months of December and January...

It all depends on your budget, family situation (You noticed there is NO particular order to THIS list? ), competitive spirit, how presentable you want your ride to be and the level of pride you have in yourself and those around you. And the fact that no one wants to be PUSHING an MB out of the center of an intersection in the middle of RUSH HOUR TRAFFIC. There's the point that pride doesn't exsist anyone...then it's a matter of survival!

The bottom line is: Do you want to follow Mr. Wilkinson's lead or see if there's another, acceptable, cross-referenced plug that can be used in your particular situation?

I'll be watching this with interest.

GL!

[Graham]

Originally Posted by mgburg

The bottom line is: Do you want to follow Mr. Wilkinson's lead or see if there's another, acceptable, cross-referenced plug that can be used in your particular situation?

I'll be watching this with interest.

GL!

I have used both NGK and Bosch Resistor plugs. No noticeable difference. I have a set of non-resistor plugs - may try them sometime with my non resistor wires. Wonder if they could affect anything - Pertronix, Radio is all there really is on a '72 SL other than ECU ?

[Graham]

I received an email from Mark Wilkinson of Bosch offering to check out an early Benz owner's car that owner may feel does not run well with resistor plugs. Any takers?

Mark has also provided some feedback on forum posts. He seems keen to interact with us owners.

My SL runs fine with resistor plugs and new style lower resistance Bosch wires, so I have no beefs. But I know others do. Especially some of the earlier sedan owners including Pontons. But they mostly post elsewhere.

Here is the email:

Hello Graham,

I have been following the discussion on peachparts. I appreciate that you noted you had tried both NGK and resistor type Bosch plugs. I have attached a pdf copy of a page out of the NGK FAQ guide that I thought you might find interesting.

Also, there was a comment regarding measuring all components, "from the coil all the way to the plugs' tips, need to be in the complete circuit to determine TOTAL losses of of the sparkplugs' E & I. (E = Voltage, I = Current)" This would actually measure the total (losses) resistance and voltage in the circuit, not the incremental resistance or demand voltage caused by the addition of a resistor vs. non-resistor plug. This would probably not be a good indicator of issues related specifically to the addition of a resistor plug. However, it might help diagnose other issues within the system...assuming you knew the rest of the system specs, or at least could compare the results before and after the addition of resistor plugs.

There was also mention of using a dyno to test the various combination of components. This would be an indicator of performance results, but probably not a good test of the system. Ideally you would need an oscilloscope to check the system health and read ignition patterns to understand the effects each component has. A dyno would really provide a performance benchmark.

Further, dyno tests tend to be subjective and can vary within the margin of error of the dyno. Anywhere from 2% - 5% could be a realistic margin of error for dynos commonly found in speed shops, etc... This is really pretty good given the cost to close the gap to that of a test cell dyno would come with a price tag in excess of $100k.

Also, all factors must be controlled in order have viable / valid results...meaning: air temp, coolant temp, humidity, using certified fuels (fuel density can change in different environments / temperatures, which has a definite effect on performance. As such, one should use certified fuels in order to control for those errors), engine temp, time and pattern of the runs, etc... If one could only control a few of these variables, I would suggest controlling the times between runs, time of the runs, specs/pattern for the run, and repeating the full set of runs with all iterations in different orders to cover all equipment combinations. This would allow you to get closer to a good reading by averaging the results across each measurement to take out some of the variability of the results caused by uncontrollable factors.

I know a lot of the information I have provided is theory, but we do a full OE application tests for listings in our catalog. This includes finding the hottest cylinder, checking / validating ignition system readings and ionic current measurements.

We take customer complaints and issues very seriously. We are also willing to learn from the market and our customers. In the spirit of learning, if there is a PeachParts contributor / member or blogger in the Chicago or Detroit area that has similar concerns and has a car we can look at, let me know. I could see if we can engage one of our application engineers to explore the issue further.

We would welcome the opportunity to engage with our customers and learn. You, meaning our customers, are what makes Bosch successful.

Also, as I reread my earlier emails, I flipped the typical demand voltage for idle and load. See correction below:

10-12kv at idle to 5-6kv under load is typical, NOT what I originally wrote which was: 5-6kv at idle to 10-12kv under load

In closing, it is not my intention to debate or challenge anyone, but rather to gain and give feedback, and have a dialog with our customers. Bosch can only get better if we listen to our customers and the market. The only limitation is whether it is technically required and if we can provide it at a price our customers will accept. We are open to all possibilities if we can validate the need.

Thanks again for you input and feedback. Please keep it coming.
Mit freundlichen Grüßen / Best regards,

Mark Wilkinson
Robert Bosch LLC
2800 South 25th Avenue
Broadview, IL 60155 USA
www.boschusa.com

[daw_two]

but someone got lucky. I gave away three of them on my new old stock thread:

W9DC Bosch spark plug ............................ 3 ... g .... free

[cth350]

As I recall the wording in the technical manuals, it does say explicitly to check total resistance of the system and that there are specific upper and lower bounds for what is acceptable. Of course, those numbers presume a stock engine and ignition system, so adding a crane, petronix, etc or a flame-thrower coil would imply a whole new set of numbers. -CTH