View Full Version : TR2/3/3A Which spark lug to use - copper/platinum/iridium

05-26-2018, 11:28 AM
The Hagerty magazine, May/June issue, page 112, had an article about spark plugs for older cars still using contact points for spark generation. It would lead one to believe that our cars cannot produce the correct spark to properly operate, and thus take advantage of, a newer-type platinum or iridium plug. I have used both and my earlier fouling issue was oil ring related, which hopefully is now cured. I only have just over 500 miles on my rebuilt engine, so my data points aren't sufficient to make a guess.
Any thoughts on which plug works the best in our cars?

Geo Hahn
05-26-2018, 01:40 PM
Whatever works. I just use the basic Champions in the modern number that is more or less equivalent to what is stated in the manual.

05-26-2018, 01:59 PM

About 18 years ago I bought a set of Bosch Platinum plugs for my TR3. There was a discussion around then and Ken Kastner had change his mind to positive on the platinum plugs and recommended the Bosch WR7BP plugs. I went looking and had a hard time finding a set until it was found out that the same plug was also model 4232. I found them at Autopart International in Framingham, MA.

I am happy with the platinum plugs they continued to spark even when sooty from running too rich.

Just been checking and find out that Bosch has discontinued the WR7BP plugs. Found some on ebay and other places.

05-26-2018, 03:10 PM
I was talked into trying a set of Bosch Platinum plugs in my TR6 before setting out on a 6,000+ mile trip. Before we were half way I switched back to Champions. Also I have been running a Pertronix for the last 60k miles and have been very happy with it.
I also ran champions in my then new TR4 and my then new GT6. All in all about 200k of happy motoring.

05-26-2018, 03:49 PM
I'm running Champion L87YC in my TR3, which are copper. My engine is warmed over a bit with a cam and an 0.085" shave on the head. I also have 87mm liners & pistons. I have RH needles in the SUs, and tend to run rich at idle. I also run points...Mallory dual point. Never had a problem with plugs fouling or missing.

05-26-2018, 03:55 PM
I also ran the Bosch Platinum plugs for awhile; they worked great for me with everything from points to a MSD.

There might be some plugs that need the faster rise time and higher voltage of modern electronic ignitions, but certainty not all do. Gap is the primary factor, so stay away from anything where you can't set the gap down.

I quit using the Bosch plugs because I was having trouble with the center electrode breaking inside the the plug body. The broken piece would slide down and close up the gap. So I went back to conventional Champion plugs. They don't last as long as the platinum, but seem to work fine otherwise.

Of course, I'm also not running that motor with the ridiculously high compression and MMT in the fuel.

05-26-2018, 04:26 PM
I ran a Mallory coil in my GT6 and it easily could run too the 7k redline. Sounded like a bumble bee going down the road.

05-26-2018, 11:59 PM
I’m just thinking out loud...

Assuming a plug does not foul from poor oil control or mixture, then the life limiting factor would be erosion of the gap (either center electrode or side, depending on the ground being used). Also assuming we are dealing with healthy engines, then mixture control would be very important, to prevent fouling prior to reaching the erosion limit of the plug.

Carbs are, at the very best, a mere compromise to obtain the proper fuel/air mixture. They go rich on acceleration, lean on overrun, and are always compromised to the rich side to provide a safety margin and prevent engine damage.

I am thinking platinum or iridium are designed to limit electrode erosion to allow plugs to go 100k miles maintenance free, on a car with perfect mixture control...or, more specifically, a fuel injected car. A carbed car will build carbon deposits on the plugs long before the 100k mile erosion limit is reached.

So, thinking out loud...I would think a fancy platinum or iridium plug would work fine in our TR’s. However, you would still have to pull them regularly to clear the carbon deposits. If that is the case, then you are likely just as well off going the cheap copper electrode route, and clean and regap them at the same regular intervals.

05-27-2018, 01:45 AM
IMO you should not be getting carbon deposits once the engine has warmed up. Yes, carbs are approximate, but they should always be close enough that any carbon that doesn't make it all the way to CO2, winds up as CO (carbon monoxide), which is still a gas and gets passed out the tailpipe. Carbon with a cold engine is because the fuel doesn't get vaporized fully (which is part of the reason we need the choke).

BTW, they deliberately go rich on acceleration because that produces more power. The best mixture for fuel economy is different than the best mixture for power (and neither one is stoichiometric where the amount of fuel exactly matches the amount of oxygen).

Plus, the plugs should be a high enough heat range to burn off any carbon that does accumulate after a cold start.

Deposits can certainly be a problem, but IMO they shouldn't be carbon deposits.

I've lost track of how long I ran those Bosch Platinum plugs, but it was a long time, much longer than conventional plugs. They did accumulate a lot of deposits when I was using MMT as a fuel additive (it makes a strange orange colored deposit) but kept running. I did change them once or twice, when chasing an issue; but the issues always turned out to be something else. (Most recently, I discovered that the lead substitute I was using had failed to fully protect the exhaust seats. The lash hadn't closed up, but some areas were eroded badly enough that they no longer sealed. I tried changing plugs before I took compression readings.)

Of course, for those of you running leaded fuel, you're going to see lead deposits on the plugs. It's illegal here, so I haven't tried that.

05-27-2018, 09:32 AM
Back in the day, our TR engines spent hundreds of hours on the test stand at the factory being tuned for the maximum performance/economy/driveability the engineers were seeking. All done with the Champion plug known today as the L87YC. There may be "better" plugs out there today, but not for me. Having spent a lifetime doing drivability for various marques, learning the hard way, I always replaced spark plugs with the factory recommendation. Older Volvos would not run well on Champions. The same for Chryslers on Bosch. Autolites/Motorcraft belonged in Fords. etc etc. These were the days where you could actually see what was going on with an automotive oscilloscope, not a digital scan tool.

05-27-2018, 09:59 AM
I drive my TR's hard and keep carbon to a minimum too. I have been running my carbed lawn tractor for 25 years with the same copper plugs because it is always running at high load and high RPM. Most drivers idle at lights, forget the choke, take short trips without time to warm up, don't check mixture, timing, and tune all that often and don't run their car that hard. Hence, most carbed cars build carbon at a regular rate. Even the TR manual gives directions on popping the head to clean out the carbon at regular intervals.

EFI keeps mixture nearly perfect under all conditions. Carbs get close, but rarely get it perfect except when wide open. For engine longevity carbs are designed to always err the mixture to the rich side. The platinum and iridium will keep the gap correct for extremely long periods...but they cannot prevent carbon build up. Whatever plug you use, it will stay clean longer if used with EFI.

My basic though above was that...if I plan to pull the plugs annually to clean and gap them anyway, then the cost of a platinum plug is not worth it to me. If I plan to never look at the plugs, like in my modern Escalade with EFI, then platinum are not just a good idea, but essential.

05-27-2018, 10:58 AM
This is not relevant to this thread, but when I purchased my first TR3 in 1960, brand new, It would foul out a Champion plug at between 1000 and 1200 miles. I tried AC's and they were worse. I finally settled on Autolite, and they would run about 1500. The best I ever got was a little over 3000 on a trip to California. It fouled out a plug less then a mile from my house on the way home. I don't remember if it always the same cyl.


05-27-2018, 12:01 PM
Interesting that the TR4 and my Porsche 912 use the same spark plug!

In the P912 world, the Bosch WR7BP platinum plug has quite a following, as it seems to be significantly more resistant to fouling. That's a big issue, as the horizontally opposed engines tend to burn more oil and thus foul the plugs more easily. That said, I use the NGK B6HS, as I have a fairly new engine, about 10,000 miles since it was rebuilt, and I haven't seen any indication of fouling at all. Indeed, I pulled the plugs about a week ago while working on something else, with 7000 miles since they were last removed, and they looked very good. But the car also has an electronic ignition, and I gap the plugs at 34 mils.

If the engine is in good shape, and everything is set up correctly, you really shouldn't have problems with fouling, anyway. If you do, just finding a different plug almost certainly won't fix it. These cars worked when they came from the factory, with ordinary plugs, and it shouldn't require heroic efforts to make them work now.

05-27-2018, 12:07 PM
As I may have posted in another thread, I have about 154K miles on my 2002 Accord V6 and still running the original platinum plugs which have never been out of the heads. Whether they will come out easily if and when they are ever changed is another story.

05-29-2018, 10:26 AM
Thanks for all the first-hand knowledge, hints, and anecdotes. I'll try a comparison and settle somewhere that seems to work best for my engine. I hesitated to ask the question thinking it might be like the "which oil/filter question" that never seems to stop.
Thanks again!