Another spark plug thread …, WR5DC+ plugs in an RS Spec 2.7l 914/6 Options

[Rufus]

I’m having trouble keeping the Bosch WR5DC+ (7992) plugs in my 914/6 from fouling.

The engine is an RS spec 2.7l except with Webers & more aggressive cams w/ faster acceleration ramps.

I’m thinking the operating conditions are causing the problem; frequent moderate to heavy traffic, numerous traffic lights, and 45 mph speed limits half the time.

Despite the CDI ignition, keeping revs @ 2000 at traffic lights, and rpm above 3000 while moving, the plugs foul quickly.

Planning to change to the next step hotter plug … WR6DC+ (7995) and see what happens.

Comments? Anyone have experience w/ a similar engine configuration?

Feeling like even driving on open roads w/ 60 mph speed limits the “5” would be too cold.

[Rufus]

Thanks for your input, guys. Based on that, the Bosch “5” may be a little too cold … the NGK “5” is equivalent to a Bosch “8”, and the NGK “7” that “slivel” raced with equivalent to my Bosch “5’s” on the Bosch cross reference chart. (Bosch and NGK numbering systems run in opposite directions wrt heat range.)

After buying my -6 in 2020, I had it serviced by a well known, highly respected race shop before shipment to North Carolina. The invoice indicates the carbs were synced, and idle speed & mixture adjusted.

Could the Webers already be out of tune? (Not many miles, but 2 years later.)

Subjectively, I’d guess the mixture might be a little rich … there’s a healthy puff of black smoke in the mirror when the throttle’s goosed from idle … more indicative of a desired richness under power than richness at idle or cruise conditions. But although I haven’t measured it, fuel economy seems pretty poor.

I’m interested in checking the idle A/F ratio. Suggestions on a make, model & source of a good meter are welcome.

Regards,
Bob