which spark plugs?

[Car #4]

I have a 340 with 10.1 compression. Plugs are 12 years old so I thought I'd replace them. Current ones are Bosch Super RO 362. Is there a better option?

 

[moparedtn]

You're going to get a hundred opinions on this.
My suggestion? With a near-stock engine, run what came in them to begin with.

 

[Geoff 2]

NGK '5' heat range, not 6. Yes, I realise the CR is 10:1.

 

[Car #4]

You're going to get a hundred opinions on this.
My suggestion? With a near-stock engine, run what came in them to begin with.

It's not quite stock. Lunati cam, .060 over, 650 Edelbrock, headers.

 

[blue69runner]

Running AC Delco and quite happy with them. Would run the same type that are in the motor. No clearance issues. They worked. Yes, would put new ones in will run better with new plugs.

 

[moparedtn]

It's not quite stock. Lunati cam, .060 over, 650 Edelbrock, headers.

"With a near-stock engine..."
RN12YC then, eh? Good place to start...and if they turn out to be a heat range off one way or the other,
then you didn't spend a fortune on them guessing like you will with anything else.

 

[68 Sport Satellite]

NGK all day.
Please note, the NGK heat range #'s go in the opposite direction of the heat range for most other brands.

 

[Car #4]

NGK '5' heat range, not 6. Yes, I realise the CR is 10:1.

Mine are Bosch W8DC so the same heat range as an NKG 5

 

[Car #4]

These are my plugs. Passenger’s side then driver’s side.

 

[dadsbee]

Put'm back in and keep going!

 

[Car #4]

@dadsbee They've been in 12 years so likely 25-30,000 miles. The car has been hard to start the last couple years after it sits for a few days. I'm wondering if new plugs would help that.

 

[68 Sport Satellite]

@dadsbee They've been in 12 years so likely 25-30,000 miles. The car has been hard to start the last couple years after it sits for a few days. I'm wondering if new plugs would help that.

NGK's definitely improved my cold starting. I first tried Autolite's, then installed NGK's a few months later. It was night and day.

 

[WileERobby]

Back in the day in the garage, we mostly used Champions, some autolites, some AC delco. Myself, I've been using Champions over 50 years. Many different cars, different engines.

 

[Car #4]

NGK's definitely improved my cold starting. I first tried Autolite's, then installed NGK's a few months later. It was night and day.

Have you tried Bosch?

 

[dvw]

These are my plugs. Passenger’s side then driver’s side.

View attachment 1609150

View attachment 1609151

These were not removed after a full throttle shut off pass. You can't get any meaningful information from them.
Doug

 

[gtxrt]

if you don't have a radio a non resister plug will help. i could feel the difference in a 440 with a pertronix 1 ignition.

 

[DPeltz]

I like NGK in aluminum heads simply because they don’t seem to gall up. Were standard in dirt bikes since the 70’s. Iron heads, no real preference.
I know some hate anti seize, but as long as you’re careful and keep it off the electrodes, sure helps with ease of removal. My car sees< 500 miles a year, and is pretty well dialed in so plugs might be in for years.

 

[RJRENTON]

You're going to get a hundred opinions on this.
My suggestion? With a near-stock engine, run what came in them to begin with.

More than likely, you'll receive several hundred of opinions. The OEM plugs on the 340 engine were Champion N-10Y (3/4" reach) or the Mopar equilivant. The die hard NGK boys swear by the brand....not sure why Depending on the engines configuration (cam, compression pistons, use-race only or a combination), spark advance characteristics, will determine the heat range....with reach determined by cylinder head configuration. CHAMPION, AUTOLITE, AC DELCO, BOSCH, NGK ARE ALL GREAAT PLUGS....all with various electrode configurations. Personally, I use CHAMPION UJ--11G OR CHAMPION HO-8A both are non projected center electrode plugs of platinum or Palladian center electrodes......why??? Because the engine likes them and they perform well......I buy them on line plus I've aquired several dozen sets of MOPAR P34P (MADE BY CHAMPION or J-11Y plugs).....btw....NFS. My ignition system is a recurved PRESTOLITE DUAL POINT DISTRIBUTOR AND FACTORY COIL AND 0.5 OHM BALLAST RESISTOR. The engine will go to 6500 RPM without missing a beat.....but this is just my opinion of course....one of the several hundred......
BOB RENTON

 

[68 Sport Satellite]

Have you tried Bosch?

yes, the split tip version. Not that impressed, but I only tried them on my newer car and once on the mopar. I'm no spark plug expert though. I used to run Champion for 25 years on my old 67 chevy. When I got the mopar, I tried Champion, then Autolite, then NGK on the advice of Dennis H here, and for some reason the NGK just made the engine seem to run smoother so I stuck with them.

 

[dadsbee]

Bosch are for chainsaws....