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So I went to replace my plugs because I hadn't yet and found that all the plugs were barely tightened. I had never checked them because I thought....Everyone can replace plugs. Gap, Insert and tighten to specs (WSM). I actually applied no pressure to the plug wrench. So what I found was Bosch 4510 Platinum Fusions. I had bought the WR7DC plugs to replace. Any thought on what was in there. Here are some pics.
So the WR7DC plugs I purchased are a single prong plug. I thought they were the preferred plug for the application. Are the 4 prong plug a more acceptable plug? Are there benefits to either?
So the WR7DC plugs I purchased are a single prong plug. I thought they were the preferred plug for the application. Are the 4 prong plug a more acceptable plug? Are there benefits to either?
I wouldn't bother with the 4-prong plugs, especially since you already have the correct plug.
But I would definitely make sure to use a torque wrench when installing them.
So the WR7DC plugs I purchased are a single prong plug. I thought they were the preferred plug for the application. Are the 4 prong plug a more acceptable plug?
The 1-prong copper was the OE-type plug. From what I can tell it is no longer being produced and once stock is depleted at any particular distributor it will get replaced with the 4–prong under the same part number.
Are there benefits to either?
I don’t think the number of prongs matters at all. It’s the copper vs. platinum vs. unobtainum that matters. Lore is that the 928 runs best on the ‘cheap’ copper plugs. I don’t recall anyone offering an engineering-based explanation for this.
Copper has higher conductivity, so it's generally better for lower voltage systems. Although the plugs I pulled out of mine were platinum, and I can't say I noticed any missing or any improvement with copper.
Copper has higher conductivity, so it's generally better for lower voltage systems. Although the plugs I pulled out of mine were platinum, and I can't say I noticed any missing or any improvement with copper.
Platinum & Iridium are harder and last longer. That's a factor for cars that have plugs that are very hard to access.
Like 'loosen the motor mounts and raise the engine a couple inches' hard.
Copper actually makes for a better plug. Cheaper too.
However, the reality is that the difference is insignificant enough that your 'butt dyno' won't be able to tell the difference.
At least not if you don't know which is which.
How interesting. When I checked my plugs every one of them was finger tight. Strangest thing I have seen, all are torqued down now but I wonder: Was this a fad or something?
I ran the WR7DC Bosch plugs in my 87 s4. The 89 I have now had the 3 prong plugs in it when I bought it, and I've never changed them. I do have a set of the copper plugs new in the box, only one number colder, cause I'm running the supercharger on it now. I'll swap plugs, caps, and wires when I do the head gaskets, and top end refresh later this year after 3rd coast. Car runs awesome, and my theory is if it ain't broke, don't fix it!
They're silver so they are both harder and conduct better than the copper variety, but they are a fair bit more expensive costing around $8 a plug. Over double that of a comparable copper plug.
Not sure why you'd go up one heat range from original.
The exotic metal options started with 911 engines that had trouble with plug fouling if not driven "briskly". Early 911 owners fondly remember how the cars would run rough, buck and miss if driven for any length of time at low loads and low RPM's. There's lore that suggests that the need for higher RPM's was something mechanical, but in fact it was a ploy to keep the plugs clean especially in carbureted engines.
Fast-forward to your water-cooled 928. Combustion temperatures are much more stable than they were in the air-cooled cars. We no longer need a hot plug for anti-fouling when just driving around, and a colder plug for high-load operation. The exotic metals like silver were intended to allow an extended tip to stay hot enough to be somewhat self-cleaning but not have hot-spots that would risk detonation at high loads. Not needed at all in the 928.
Fast forward again to the 1990's, when US regulations said that manufacturers had to warranty emission-related components for 100k miles. Spark plug durability was an obvious issue, as no manufacturer wanted to have every car come back to the service bay for a "free" plug change every 25k miles. Enter the multi-electrode plug with the exotic electrodes. All are intended to allow the plug to perform adequately for those extended miles required.
Meanwhile... I was looking at the plugs in the car every couple years when we were in SoCal, part of the prep for the bi-annual emissions testing. It's a chance to look at color for combustion faults before the tailpipe sniffer detected them. Plugs are really cheap, so new ones would go in as a matter of course. The first time I tried platinum plugs, I got higher NOx readings at the test, so for the next test I went back to copper plugs and the NOx settled down again. Hot spot in the platinum tip? Hard to tell, since the color was fine when I took them out. Since no other changes were made to the engine between tests, the one obvious variable and the obvious change in test results pushed me back to the original copper-electrode plugs.
Anecdotal: While racing some interesting engines a long time ago, the tuners were finding that the electrode alignment with the valves made a difference in how much power was available. Point the open end of the electrode towards the intake valve, and get more power. It was part of some flame-front and turbulence theory. Anyway, heads would be fitted with plugs cylinder by cylinder before they were installed, so that each cylinder had specific plugs assigned to it for later use. Buying cases of new plugs and testing them one by one was a necessary exercise. How does that relate to the 928 question? Multi-electrode plugs offer a partially shrouded end in all directions except off the end. Plus historically, the multi-electrode plugs with the exotic metals are multiples expensive compared with the copper single electrode plugs. Look at multi-electrode double-Irridium plugs for a modern car, and you'll be happy they don't get changed often. Is there a frowny emoticon with dollar signs in it?
Reality for almost all of us is that the plain copper plugs are fine. We find other reasons to pull plugs, like making it easier to rotate the engine during a timing belt change every so many years. I drive the car gently, just rumbling around at fractional load even while out touring briskly in the local scenic drives. I'll never get near the worry that I have a shrouded plug and a flame front moving from the wrong side for max power. I guess if I need to spend up on the supercession plugs I will. After I get through the several boxes of old-style plugs sitting in the parts drawer.
I guess if I need to spend up on the supercession plugs I will. After I get through the several boxes of old-style plugs sitting in the parts drawer.
The multi-electrode copper plugs are still <$3 each when purchased in quantity.
Heck even the platinum 4-prong plugs used in modern Porsches are about $4 when purchased in quantity (even though the dealer charges $34 each (for the Porsche label on the other side of the plug from the Bosch label.))
03-30-2019, 10:02 PM
Bosch 4510 Platinum Fusion
