Which spark plug for this engine [pre 74]

[Two Oh]

I've got this engine that doesn't like the platinum or silver Bosch spark plugs.

I've been using a Bosch w5dc which works well but not for long.
I tend to run a little rich.

This might be a good plug, but is there a plug that would work better in my engine?

Which plug would you recommend for the following:

MSD ignition
Magnacore wires
new 40mm Webers set up as BA recommends in the book
2.4 case
2.7 p/c
S heads
Solex cams
factory headers
Sport muffler

Any help would be greatly appreciated.

Thanks...................

[J P Stein]

My set-up is nearly the same as yours (engine wise).

I like NGK plugs. Assuming you have a hot coil to go with the MSD and 8.5 :1 compression, BP5ES to BP7ES (7s are colder) gapped to .045. I run the 7s but I have 9.7:1 compression.

The MSD set up really wakes up the motor. My usable rev range has dropped down to around 2500 rpm. Not a lot of umph down there, but it runs clean. Pulls nicely and comes on the bump bout 4k. Plug color is light grey, so I think it's about right.

[T Bird]

Two Oh
You need a hotter plug to work with those Webers. W5 is much too cold. Bosch platinum WR8DP works well for me.

Good luck.

[Two Oh]

I'll buy both the NGK's and the Bosch Platinums and then compare the two.

Thanks JP

Thanks T-Bird

Your input is much appreciated.

[T Bird]

Two Oh
Bosch Platinum WR8DP works well for engines with compression ratios up to 9.5 to 1. Gap them between .034 and .036. If your compression ratio is over 9.5 to 1, try WR6, which is a cooler plug.

On the NGKs- I have not used them but the popular wisdom is BP7ES for most applications. BP6ES is also an acceptable choice. Really "hot" engines, like the early S engines, usually call for a cooler plug like the BP8ES.

If your plugs are too cold, they will never reach self-cleaning temperatures and will foul. If they are too hot, the ceramic insulator will blister and the plugs will cause pre-ignition and possibly, engine damage.

Good luck.