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.

[slivel]

I ran these when it was track only:
Spark Plugs: NGK BPR7ES (5534 large 13/16 base), or BKR7E (4644 small 5/8 base)
But now that the car is occasional drive to car shows or some canyon carving I thought that I'd have to change plugs to a hotter heat range but it seems to be doing well and no fouling with the same plugs that I used for years when racing. It is crankfired twin-plug so maybe that helps keep the plugs clean. I recommend the small base plugs because it makes servicing the lower ones much easier.

Also maybe your idle jets are too large. This is my track configuration:
Induction: Weber IDE46, chokes: 40, main jets: 185, idle jets: 60, air correctors: 155, emulsion tubes: F7
But with mufflers installed and no more open exhaust, I reduced the mains to 160's. I'm probably down 30 horsepower with this.

[Steve]

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.

I ran NGK BP5ES in my 2.7 with webers and my DME 3.2 over 20 years with no problems. Do you have an AFR gauge? Are you running too rich on your carbs?

[john77]

Same as Steve, I've been running NGK BP5ES in my 2.7RS spec 6 for the past couple of years and they seem to be okay.

I decided to try BP7ES last time I replaced the plugs about 9 months ago and it ran so bad I swapped back to the 5s.

[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

[Steve]

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


Innovate wide band AFR's are pretty popular.
https://www.innovatemotorsports.com/products.php

[Rufus]

Excellent! Thanks Steve.