I wanted to know if anyone had any thoughts on running a slightly hotter plug in the Jalpa. I called Bosch customer service and they recommended running a W6 Bosch as opposed to a W5 (W5 is an exact cross over to the original W235 P21 plug). The rep thought the slightly hotter plug would be advantageous and not enough of a heat range jump to cause any harm.

He also recommended staying away from the Platinum’s as this is an older carbureted car (WR5DS or WR6DS). I agree with that philosophy as I run Bosch Silvers in my old Maserati. Silvers have a much larger tip and better conductivity characteristics than the Platinum’s which were designed for emissions/fuel economy. The rep did say that they offered a W_DP0 Platinums (the "0" stands for a larger oversize tip), but felt in general the Silvers would work better in a carburetated car such as this.

At any rate, I do know the old adage try it and see, but it is winter here and I thought I would find out what others are using and/or recommend.

Thanks, John

My post reads incorrectly:

W_ _ Ss are Bosch Silvers

and

W_ _Ps are Bosch Platinums

I realise that the std coppers work just fine, but for the extra $1 a plug it seems worth while to upgrade. -John

Just a follow-up for those who might be interested...

I work at DaimlerChrysler and talked with the engine lab tech guys on spark plugs.

Platinum and Iridum:
What I learned was that irregardless of the manufacturer, Platinum and Iridium plugs are designed to meet modern OEM 100,000 Mile Service Requirements. The primary reason is due to their excellent anti-corrosion properties.

These types of spark plugs were designed with extremely fine tips to maximize emissions/fuel economy in modern injected engines where the gas/fuel mixture is optimized.

In general, these type of spark plugs perform poorly in carbureted cars... especially those that are running rich.

Silver:
Irregardless of the spark plug manufaturer, Silver plugs have much better a significantly larger tip and better conductivity characteristics than Iridium and Platinum. Consequently Silver Plugs will always out perform Platinum or Iridium in carbureted cars... again especially as these cars tend to perform better when running slightly rich. The disadvantage to Silver is Life Cycle... they do not have as good corrosion properties and will need to be replaced more often... also tend to cost a bit more.

At any rate, as an engineer I thought this was fairly interesting.
Hope others find this helpful, John

Forgot to include...

The lab guys also mentioned that standard Copper plugs are the most economical and would also be superior to the fine tip Platinum and Iridium plugs for carburated appliactions. Silver is a little better as far as conductivity, but does cost more.

-John

I will have to remeber that, thanks!

I had bought a set of plugs not knowing the difference and the car went from running amazing to being a dud. I then realized that the plugs were wrong and the goofy mechanic didn't get all the plug wires connected.
Went back to the old school plugs and they worked very well.

__________________
Had Enzo been a gentleman...The greatest cars on the planet would have never existed.

Jalpa FLA12194
Countach ELA12667