<VV> Re: What plugs for my 140?

Bill Elliott Bill Elliott" <Corvair@fnader.com
Tue, 14 Dec 2004 19:55:17 -0500


Okay, I'll try....

I'm a huge Bosch fan, so my issues with the Platinum plugs are nothing against the company...only against that specific product.  I think that for the most 
part, they are more of a marketing ploy than a great product, but they do work well in some applications.

First, when the Platinums first came out, I actually did use them in my Little British Cars. Even with a stock ignition (though I routinely added a higher voltage 
Bosch Blue coil) they did not seem to foul as badly as the standard Coppers (as the Supers were them called) on engines that ran rich and/or burned oil.  

However, when I added them to my '86 Chrysler 2.5 normally asiprated 4, they immediately badly misfired. My local garage (real mechanic, not parts 
exchanger) told me that "some cars just didn't work well with them" and that the MOPAR 2.2/2.5 was one of those.

Now jump forward a couple of years. I'm now driving Corvairs (same car I have again today) and first tried a set of Plats in the Corsa. With no other 
changed the car would not even idle. Was told by the local Corvair guys "Corvair just don't like the Platinums".  When I worked at the Corvair-only resto 
shop in the early 90's, we w ould have customer after customer come in complaining that they (or a neighbor) had "just done a tuneup" and screwed up 
the car. Well over 9 times out of 10, we found Platinums in there. Replaced them with a set of Supers, syched the carbs (90% were done wrong as well) 
and the car ran perfectly with no other changes. Often a customer would come in and request Plats for his tune up and resist when we put in Supers... we 
always told people if they were dissatisifed with the Supers we'd replace them for free... nobody ever requested replacement.

However, some Corvairs run perfectly well with them, which was always a mystery. I should mention that I did an engine change in my Corsa and again 
tried platinums... and they ran just as poorly with the new engine as they did the old one.... so it does not seem engine specific.


Now jump forward a few more years. I had an Audi Quattro Turbo Coupe with a hot engine, hot cam, running over 15psi of boost. The guy sold it because 
it would not run well under boost, but ran fine otherwise. Sure enough, Bosch platinums. So I put in a set of Supers... better, but still some bucking once the 
boost got over about 9 psi. At the advice of the Audi guys, I added a set of Bosch DTC's...essentially Bosch Supers with three electrodes. 

Promoted basically to make the plugs last longer, they also completely solved my running under boost problems. However, they would only last 10,000 
miles. After that, while still looking perfect, they would start misfiring. So (again at the advice of the Audi guys) I bought a set of Platins ($25 ea) which were 
specified for Porsches, Jags, and the new 20valve Audi turbo. These are a pure platinum electrodes (like the Platinums) but have a large diameter 
electrode like the Supers. Now while the throttle response was not quite as good as the DTCs (leading me to think there was an effective heat range 
difference though both plugs were rated the same) but they pulled strongly to redline under full boost and were still going strong when I sold the car 30,000 
miles later. 

Strangely, the standard Bosch platinum was the plug of choice for normally aspirated Audis, with the Supers dulling throttle response and the DTCs 
providing no advantage over the platinums... so I ran Bosch Platinums in all of my non-turbo Audis. Ignition systems are the same in the turbo and non turbo 
cars... and both cars used the same Bosch K-Jetronic CIS (not EFI) which always tended to run a little rich...

So what does all this evidence suggest to me about the plugs?

1. Platinums require more power to fire without misfiring
2. Platinums in a forced induction engine require even more power to fire
3. The platinum electrode does a great job of selfcleaning and this may make it run better in some cars.
4 The platinums seem to last longer. IF the car would run okay with them, they were typically the last set of plugs I had to put in that car. (Not sure if this 
translates to Corvairs)
5. The smaller diameter of the platinum seems to be the main reason that it misfires since the larger diameter Platin is superior in every way to the Platinums
6. Platinum as the center electrode is superior to Copper since the Platin is superior in every way to the Supers.
7. Whether the Platinum is superior to the Copper is application-dependent
8. Platins are pretty much the ultimate plug (and should be at $25 each). 

Now to the Corvair question...

One more set of evidence... Ignitors. Some Corvairs seem to run "okay" with Ignitors hooked to the coil while others (including mine) will misfire at the mid-
rpm range when hooked up that way...but run perfectly when hooked to a pure 12V source.  (And over 90% of the reported Ignitor failures are wired to the 
coils with virtually no failures when wired to 12v)   And those Corvairs that seem to run fine with the Ignitors hooked up to the coil also seem to be in the 
same group that seems to be able to run Platinums okay. Hmm...

So my guess? The ignition system in some cars gets more power than others. That on some cars (potentially like mine) the voltage drops to unacceptable 
levels under periods of greatest current draw and that this could be due to corrosion in the wiring harness or a breakdown of the resistor wire in the 
harness. So we really should be addressing THAT problem instead of the plugs. Or should we since the cars run great with the right plugs...

So back to the plugs. In Corvairs, I have tried Platinums, Supers, and DTCs... and the Supers and the DTCs seem to be about equal in performance while 
the Platinum only works in some cars. And no one (until today) has suggested that a Platinum works better than a Super EVEN IN a Corvair that runs fine 
with them.

So again, what does this suggest?

1. You don't need to spend more than 99 cents a plug because you can't buy better performance (though I would like to try a set of Platins sometime...)
2. Even if your car runs fine on Platinums, why would you run them since they cost more and give you a lower margin of reliability should the ignition system 
develop a fault? 
3. Why would you wire your Ignitor to the coil and risk it when you can feed it pure 12v and have the situation completely covered?

Is all this scientific? Not exactly. But they are my observations based on years of dealing with plugs in a variety of applications and dealing with a large 
group of Corvair owners. .

I currently run Bosch Supers in all of my Corvairs and some of my LBCs, NGK's in a few of my LBCs, and AC Delco Platinums in my Northstar and 
Suburban. And it works for me. YMMV

Bill Elliott


--Original Message Text---
From: RoboMan91324@aol.com
Date: Tue, 14 Dec 2004 19:00:05 EST

Hi Bill,

I agree that sometimes the "better" and more expensive model of something isn't 
necessarily better and is sometimes worse.  However, I am curious as to why in this 
case.  Can you tell us how Bosch markets the platinum plugs as worth the additional 
price, what the symptoms of the inferior performance are that you have experienced 
and what you think may be the cause of these symptoms?  Is it an idiosyncrasy of the 
Corvair that contributes to this issue while other cars actually benefit from the platinum 
plug?  I think that Bosch is a fairly respectable outfit and am surprised that they would 
market a clearly inferior product for more money.  

Please note that I am not questioning your conclusions.  Inquiring minds want to know.

Doc