What's the right spark plug to use in a 2.7RS?

[JimR]

I'm nearing completion of my 2.7RS engine and I'd like to find out what are the correct spark plugs to use on this engine. Thanks for your advice.

Regards,

[ttweed]

I would start with the NGK BP8ES, Jim. If you find they are fouling easily, move up to a 7.

Or you could wait until Steve Weiner finds this post and tells you the real answer. I think the right choice involves what induction you are using (stock MFI?), if the compression ratio is stock RS (8.5:1?), and what the prevailing operating conditions will be for the car (hot/cold, street/track). The important thing is to not use too hot a plug, to avoid detonation. Start colder in the heat range and move up as necessary.

[JimR]

Great reply Tom. Just to fill in some of the details, the engine uses MFI, the compression ratio is bumped slightly to ~9.0:1, and although the heads have provisions for twin-plug operation, it will run single plug for the forseeable future. It will see use both on the street and on the track (Driver's Ed.), from March to October (ambient temp swing of low 40's to upper 90's). Thanks for your comments!

[rs911t]

Jim,

I tried BP8ES on the "T" when it had carbs. Fouled badly, even with the MSD unit. I think I'm running Bosch W5xxx series at the moment. The NGK and Bosch heat scales are reversed, but I think the Bosch 5 is mid-range.

FWIW

[Steve@Rennsport]

Jim:

NGK 8's are too cold for anything but racing.

I would use either Bosch 5's (I like the W5DS Silver's) or NGK 7's to start.

Remember, the comparable heat range selections between these two manufacturers are not precise so you might need to make some changes, depending on what you decide to use.

We use the Bosch ones for their consistency and overall performance.

[Shuie]

How much of a role does the climate play in plug choice? My old low compression, low horsepower 2.4MFI T engine pinged when I installed BPR6ES plugs. I thought about going to a BPR7ES, but went with a BPR8ES instead. The car ran great with those plugs. Part of my decision was based on the fact that the Summers can be brutally hot here and make the car even more prone to detonation. Should this be a concern?

[Steve@Rennsport]

Climate does play a role.

High temps lower the threshold of detonation and hot plugs can trigger pre-ignition when cylinder head temps get too hot.

The objective is to use a plug thats cold enough to supress detonation/pre-ignition while staying hot enough to burn off deposits that can foul.

Temperatures (ambient & engine), ignition timing, compression ratio, air-fuel mixture, octane grade, and camshaft profile are all factors in determining the right plug for your engine.

[pwd72s]

Just to add to the spark plug confusion...

http://forums.pelicanparts.com/showt...threadid=77219

[Steve@Rennsport]

Hi Paul:

LOL,..Its not confusing to me,.......

I've simply relied on long-term experience with these things to know what works and what doesn't.

I have spark plug catalogs & charts going back to 1965 and every few years, all the manufacturers change their product lineups and recommendations. Its a shell game that creates a LOT of confusion and misinformation.

Plugs, ignitions, and fuel formulations have really changed over the years and its not a one-size-fits all. Many past successful combinations are no longer valid due to the state of pump gasolines. Now, the only way one knows is by trying all pertinent plugs, ignition systems and varying plug gaps to figure it all out.

[ttweed]

I've simply relied on long-term experience with these things to know what works and what doesn't.

Thanks for jumping in and straightening us out on this, Steve. There is no substitute for real-world experience. You da MAN!

Thx,
TT