best plugs for 3.4 twin plug??

[ourv12]

best plugs for 3.4 twin plug??
Which is the best spark plug to use in a 3.4 twin plug engine?

[Walt Fricke]

I prefer to have the heads machined for 12mm plugs. More clearance to the head studs/nuts/fasteners, and fewer CCs removed from the combustion chamber. Others just use the standard 14mm plugs.

There is no such thing as a standard air cooled 3.4, so "best brand/model" plug isn't really a question which can be answered. What else did you do to the motor? Bump compression, hot cam, EFI or carbs?

But I suspect you could start out two or so numbers/letters colder of your favorite plug, and then read it to see how it is working. You probably are going to have higher combustion temperatures in this motor? Better too cold than too hot to start with.

[ourv12]

Originally Posted by Walt Fricke

I prefer to have the heads machined for 12mm plugs. More clearance to the head studs/nuts/fasteners, and fewer CCs removed from the combustion chamber. Others just use the standard 14mm plugs.

There is no such thing as a standard air cooled 3.4, so "best brand/model" plug isn't really a question which can be answered. What else did you do to the motor? Bump compression, hot cam, EFI or carbs?

But I suspect you could start out two or so numbers/letters colder of your favorite plug, and then read it to see how it is working. You probably are going to have higher combustion temperatures in this motor? Better too cold than too hot to start with.

Andial installed the 3.4 Mahle piston/cyl set. Ollies did all the machine work for twin plugs. stock EFI. stock cams. I believe Andial bumped compression a bit for street usability with premium gas. also using Rennsport custom chip for 3.4 twin plug. Right now im running Bosch silver Tips....just curious if there is a better plug for twin plugged 3.4s.

[Walt Fricke]

Favorite plugs is sort of like favorite method of bleeding brakes, or dealing with CV joint fasteners, or favorite tire. There are a fair number of approaches which work just fine, but guys tend to have favorites. I don't think you can go wrong with Bosh or NGK plugs. I don't think twin plugging changes anything, except maybe the heat range. I've always used the same heat range/brand for the upper and lower plugs. I've never formed an opinion about the pros and cons of platinum, silver, copper, thick, or thin electrodes (though the Bosch which has the whole platinum electrode encased in ceramic except for the tip doesn't seem to be looked upon favorably).

Maybe someone has used an engine dyno to show there is a slightly better mousetrap, but nobody has chimed in. If your air fuel ratio is good, and the plugs read about right, I'd be astounded if changing your pretty standard plugs would give you more torque here, or HP there.