Bosch Spark Plugs

[Keith V]

Has anyone had any experience with the new Bosch multiple electrode platinum spark plugs in their 914?

[Dave at Pelican Parts]

No experience myself. However, one of the local time-trialers has an all-out race motor (200+ HP out of 2.01 liters). He uses an older-design multiple-electrode Bosch Platium plug. I think it was originally spec'ed for 911 turbos and 944 turbos.

I haven't seen the new ones, but the older ones are VERY expensive!

--DD

[nineonefour]

I was discussing this with my uncle who was a drag car mechanic now senior Vp for a banking software company. He says that depending upon they type of engine the multi electrode design actually might depleat HP rather than increasing it. this is partially due to where the spark is located in the cylendar. if the spark plug is on an angle or off set to one side the extra prongs on the bosch +4 may block ignition of some of the fuel and air.
He gave me another reason but I forget what it was I will post it when I ask him tomorrow.

I would avoid these plugs and stick to just regular single tip bosch platnums.

The position of the spark plug electrode can be adjusted by the use of shims. This is an old racer trick. More effecient combustion of the fuel mix can be obtained by the repositioning the electrode.

I have not tried this but heard about it on "Speed Vision". Someone who is more knowledeable can pick up the thread on this I hope.

[Dave at Pelican Parts]

I have seen the new +4s, and they look just like the old cheap Bosch Platinum plugs, just with three extra electrodes. Imagine taking 3 extra outer electrodes and welding them onto the plug every 90 degrees. That's what the new ones look like.

There's a very limited amount of adjustment you could do to try and get the electrode out of the path of the air:fuel charge if it were actually in the way. Too many electrodes.

Furthermore, they appear to be constructed almost identically to the cheap Bosch Pt plugs. And I would say that makes them junk. The QC on the previous generation of plugs was less than stellar, and my mechanic found quite a number of them that would not spark at all. Or where the speck of Pt slid out of the center electrode and bridged the gap. No gap, no spark.

He also said that they fouled much more easily than the Bosch Copper plugs. He thought they might work OK on cars with a modern closed-loop FI, but not on carbed cars or cars with early open-loop FI systems. That's us, folks.

A 914 Rennlister http://www.rennlist.org recently chimed in about the +4s, he said that they fouled out very quickly. He went back to copper and hasn't had any problems since.

This is my opinion, and the reasons behind it.

If you really have the multiple-electrode bug, you might try the older MUY EXPENSIVO Bosch Platinums, or the NGK triple-electrode plugs. I hear NGK generally makes quality stuff.

--DD