Are Bosch Platinums the Worst?

[Dyno247365]

If they're not the worst, are they still really really bad? I bought a new set of Bosch Platinums(normal, no pluses) from autozone and I got 6 into my 305 already. I'm selling it but I want to make a good impression on the person buying it.

Some other AF members have mentioned that these plugs cause the engine to operate poorly. It all started with me getting antiseize compound on one of the plugs and needing to replace it(1). They're telling me to use AC Delco or NGKs instead. Does anyone agree? Do you have horror stories of these platinum plugs?

[TheSilentChamber]

bosch platnums are very good plugs. There is some problems associated with them (and other platnum and multiground plugs) when used on waisted spark spark iggnition setups.

[Dyno247365]

wasted spark ignition setups? you mean messing up the gapping?

[TheSilentChamber]

Wasted spark as in ignition systems that have a coil per every two cylinders, while one is firing on power the other is fireing on exhaust on a differnt cylinder. Thus the one fireing on the exhaust stroke is a wasted spark.

[boarder_punk]

I've only had good experience with them. But the +2/+4 will just hurt the airflow inside of the combustion chamber, thus decreasing performance, although they will last a lot longer than normal plugs (which last plenty long already). The best route when it comes to plugs (if your engine is stock) is to stick with OE.

[Dyno247365]

Why do they have a different shielding compared to AC delco plugs?

[TheSilentChamber]

Originally Posted by boarder_punk

I've only had good experience with them. But the +2/+4 will just hurt the airflow inside of the combustion chamber, thus decreasing performance, although they will last a lot longer than normal plugs (which last plenty long already). The best route when it comes to plugs (if your engine is stock) is to stick with OE.

Is that why its dyno proven that the +4's make more power?

[Dyno247365]

Originally Posted by TheSilentChamber

Is that why its dyno proven that the +4's make more power?

I hear they spread the spark too much

[curtis73]

Not that this is on the topic, but the best spark is the most consistent spark. With multiple points on the plug you have one of two scenarios; Either one gap will be smaller than the rest and it will always get the spark, or you'll get sparks at all different places every time. The first way you're getting a pretty consistent spark which defeats the purpose of getting multiple gaps in the first place. The second way you're not getting a consistent spark.

Plain old single point plugs are fine and dandy. Platinums are good plugs, especially in higher compression. They don't do so well with older engines where blowby may be excessive, or where compression is low.

[NA_Vogue]

Another thing I hear is that the extra points on the plug can act as a heat sink. So in theory this increased cylinder temperature supposedly can contribute in causing preignition. Trippy, but this is what i was told by my instructor in engine performance class.

[alkemist]

Originally Posted by curtis73

They don't do so well with older engines where blowby may be excessive, or where compression is low.

What would be the recommendation for older engines with low compression? I am currently running Bosch supers on 96 riviera with almost 100k.

[UncleBob]

I do car runnability diagnostics for a living. When a car comes in for a misfire, know what the first thing I check is?

Does it have Bosch plugs.

I have seen it so many times I couldn't even count. They are highly prone to misfire issues. I have theories on why, but I wouldn't want to suggest they aren't a great plug like everyone else

[SR Racing]

Originally Posted by UncleBob

I do car runnability diagnostics for a living. When a car comes in for a misfire, know what the first thing I check is?

Does it have Bosch plugs.

I have seen it so many times I couldn't even count. They are highly prone to misfire issues. I have theories on why, but I wouldn't want to suggest they aren't a great plug like everyone else

I too make my living building and maintain race engines. (and some hypo street engines.) Frankly, in dyno tests (engine and chassis) I have not seen any plug manufacturer that is any better than any others when using the same replacement plug. Bosch is no better or worse than any other.
So what is your theory for your thoughts?

Jim
SR Racing

[UncleBob]

the particular type of bosch I'm talking about are the +3, +4 type platinums. They have very very small platinum electrodes seated in a cavity in the porcelin. Due to this, there is very little electrode exposed. They are very very very sensitive to carbon fouling, even a hint of carbon and they won't fire.

These aren't the only style of bosch, of course, but these are the popular aftermarket cheap plugs they sell in large quanities at the big auto part chain stores.

If you have a high mileage engine that is burning oil, for example, they can "foul" (although there will be no obvious fouling signitures) in a VERY short amount of time.

The other problem is the screw-on caps. They are not torqued out of the box, and almost nobody ever torques them when installing. They like building up resistance, sometimes very quickly.

Like I said, I see it all the time, and every diagnostic mechanic I know, sees it all the time.

[SR Racing]

Originally Posted by UncleBob

the particular type of bosch I'm talking about are the +3, +4 type platinums. They have very very small platinum electrodes seated in a cavity in the porcelin. Due to this, there is very little electrode exposed. They are very very very sensitive to carbon fouling, even a hint of carbon and they won't fire.

If you have a high mileage engine that is burning oil, for example, they can "foul" (although there will be no obvious fouling signitures) in a VERY short amount of time.

The other problem is the screw-on caps. They are not torqued out of the box, and almost nobody ever torques them when installing. They like building up resistance, sometimes very quickly.

Like I said, I see it all the time, and every diagnostic mechanic I know, sees it all the time.

Fouling is most often when carbon (or whatever) shorts across the electrode in sufficient amount to eliminate or shroud the spark. In itself, carbon doesn't interfere with the spark since it is a great conductor of current. Of course, a carbon deposit can get hot and cause pre-ignition, but this is more of a problem with standard plugs.

In regards to the resistance build-up on plugs at the screw on cap... Old wife's (mechanics?) tale.

The resistance at that point (of even several thousand ohms) has zero effect. It is at ambient pressures at that point and the resistance MIGHT drop 500 to 1000 volts at WORST. Whereas the avalanch voltage is in the 40K range. You would literally have to have a .010 to .020 inch air gap. (at normal pressures). Try this on your distributor tester.

In any case, the caps are not torqued so that the installer can remove them when installing on those few cars where they are not used. We tighten them up, but it ain't an issue.

Jim
SR Racing