Spark plug interval changes on a 440

[Bob T]

How often or how many miles do you guys do between changes??

68 440 HP2 750 Holley, I've done around 7000 miles and 2 years on these NGK BP5 S and they are well due...performance has been ok but just dropped a little recently and also after I put a new ignition system on.
I've got a dyno tomorrow so its change out time, #8 plug shown

[John_Kunkel]

Unleaded fuel? If they're not fouled by oil/rich mixture they should last a long, long time.

[cudaken]

Back in the day when are cars where fresh, I think it was 30,000 miles.

Just looked at my 68 Road Runner Warranty information and scheduled maintenance. It ends at 36,000 miles and nothing is said about replacing plugs, covers all the other items that need to be replaced.

It all so stated to change the oil every 4000 miles, but filter only every other oil change? 

Seems good old Dad took her in on time, thanks Dad. 

Cuda Ken

[Bob T]

Unleaded fuel? If they're not fouled by oil/rich mixture they should last a long, long time.

Unleaded, yes, its what passes for either 95 or 98 octane here.
Ok, I thought the interval was shorter  , got a set today they were $4 a plug for ngk bp5 s, took it to a car guys funeral today,  will put them in tonight anyhow and examine the old ones

[Fred]

I change mine once a year without fail. Regardless of their condition. Peace of mind.

[Lord Warlock]

When driving it, i'd probably replace plugs every 7500 miles or so, I like fresh plugs and they were fairly easy to change. Only drove it about 33000 miles back then.  its had the same plugs in it now for 20 years and it still runs fine.  NGK is a good brand of plug, they should last at least a year, If using the platinum plugs they're usually good for 50,000 per change, copper 10-15k or once a year should suffice.

I just ordered new plug wires, distributor cap and other motor parts, so I may crawl under and change the plugs out just for sanity's sake.  Everything else will be new, would suck to use old plugs with all new gear. 

[myk]

Because these cars are driven infrequently it's really up to you.  Periodically check your plugs and treat your car accordingly...

[Bob T]

Changed them out, black as and had a few deposits forming.
Forgotten how much fun it was to change them with 2" headers , took a while and left some skin in the engine bay..

Also fitted an inline fuel pressure guage tonight to see what the pump was doing, its running 6 1/2 lbs solid through the rev range so thats one more tick in the box.

So, on with the dyno tomorrow..

[myk]

Good luck!

[tan top]

once you got the plugs out  , IMO you might as well  replace them ,  its difficult enough with castiron manifolds on a 440   , for me   only #1 plug comes out from the top , all the rest come out from the bottom ,

good luck , looking forward to seeing & hearing about the the dyno adventure  

[Bob T]

once you got the plugs out  , IMO you might as well  replace them ,  its difficult enough with castiron manifolds on a 440   , for me   only #1 plug comes out from the top , all the rest come out from the bottom ,

good luck , looking forward to seeing & hearing about the the dyno adventure  

I did have an easy run then Tan, since they all came out topwise, albiet with some skin ha.

Good result with the dyno today, gained an extra 45 horses that had just been asleep in there 
Will put up a new thread tomorrow, its new years eve and I'm having a few 

[myk]

You picked up 45 rwhp from a plug change?

[Ghoste]

I change mine once a year which works out to two or three thousand miles.  Yes, huge overkill but they're cheap and I don't mind doing it.

[Bob T]

You picked up 45 rwhp from a plug change?

Plugs, carb adjustments and also the kickdown linkage was restricting the wide open throttle travel, but yes 45 rwhp, thats a good gain, the BFG's will be taking a hiding now 

[myk]

You picked up 45 rwhp from a plug change?

Plugs, carb adjustments and also the kickdown linkage was restricting the wide open throttle travel, but yes 45 rwhp, thats a good gain, the BFG's will be taking a hiding now 

Wow, that's something else.  I wonder how much power I and the rest of us are leaving on the table without a good tune...

[Bob T]

You picked up 45 rwhp from a plug change?

Plugs, carb adjustments and also the kickdown linkage was restricting the wide open throttle travel, but yes 45 rwhp, thats a good gain, the BFG's will be taking a hiding now 

Wow, that's something else.  I wonder how much power I and the rest of us are leaving on the table without a good tune...

It was definitely worth the spend Myk 

[RECHRGD]

Let's see those numbers Bob!

[Bob T]

Let's see those numbers Bob!

420crank ,280rwhp, 353 Torque, am fairly happy with that too 
Easier to link it I guess, its over in Performance corner with a vid clip  

http://www.dodgecharger.com/forum/index.php/topic,107245.0.html

[RECHRGD]

Bob, how is your Dyno shop figuring 168 hp loss?  That seems excessive to me.....

[firefighter3931]

Based on the plug's appearance the carb was jetted a bit rich. The chassis dyno tuning will help sort out the a/f curve and it looks like you picked up a nice power gain. 

If you can keep the idle mix at 13.5-14.5 it will help keep the plugs cleaner and extend service life 


Ron

[Bob T]

Cheers Ron, we made some jet changes and put a softer spring in the secondary and it came up right on the money, pleased with the result, its a bit more lively now too, was out in it yesterday and let my Daytona driving buddy give it a shoe full, he was fairly impressed how it went