Hotter Spark Plugs?

Running the engine rich will cause carbon deposits on the valves/pistons. It will provide NOTHING good for the motor, only harm.

After the mixture is correct for the engine, THEN determine if the spark plugs need to be changed to a different heat range. Normally, increasing compression would, if anything, require a colder plug than standard, not hotter. You really should correct the overfueling as quickly as possible.

 

Stay with BP7ES, or even go to BP8ES due to the higher compression. With a stock engine, BP6ES has quite a bit of pre-ignition over 6000rpm. I evened my situation out with BP7ES and beefed up my ignition system. IIRC, you have a black stallion ignition right? Even with my super-zap ignition system I get a bit of carbon build-up if I leave the engine idling too long. If you run WOT through the first few gears and then pull a plug and still have the issue then I would be looking into main jet issues.

 

Go with Iridium plugs I heard they can tolerate rich mixture far better than a non iridium.

 

I run BP5ES in my 77. I find them great for overall driving both city and highway. I am slightly rich at idle but how 0 fouling issues. I started with 7's in the beginning and then went down to 6's but would get some fouling after ideling for a while. Switched to 5's and have had no problems. I had the same set of plugs in for 6 years and when pulled they looked very good. These plugs are cheap so buy/try a set of each and see what works best. I assume it is in the tune but it works for me.

 

+1 l did the exact same thing...and l tried the irridium plug but they fouled as well..and they cost about 12 bucks a plug as oposed to 3 bucks for the normal plug

 

i ran ngkbp5es and bp6es plugs in all of my carb 308s with no issues. two of the cars had Crane ignition systems, the others were stock points. fix and sync your carbs first, then try 7's, 6's, and last 5's as far as heat range. a 5 is very hot. i think a well tuned engine ( not rich) should run clean on 6's. i ran 55, idle, 135 main with 200 a/c and a f34 or f36 e tube.

 

When I dyno tuned my car, I found that BP5ES and BP6ES had big issues with pinging/detonation when correct ignition timing was used at high rpm. The ground straps showed the plugs were way to hot when the car was ran in the upper end. Using BP7ES increased bhp, deleted detonation, the ground strap showed this was the perfect heat range for power, but I would think with points or anything less than a super zap ignition that the idle plug fouling would suffer. Point is, if one runs correct high end ignition timing which is from my dyno tuning experience about 39.5-40 degrees, you are going to have trace to greater than trace detonation with BP6es or 5es. This loses power and is bad for the engine. The way to get rid of it is to back off a plug heat range (best way) or back off ignition timing quite a bit (not the way to go).

 

So what would be recommended spark plug for a 308 GTBi '81 with stock ignition system?