[ScumOne]

I put some new plugs in the 69 FB. Motor is a 400 / 4 bbl with #62 heads, bored .030 over with Rochester Q-Jet, and Pontiac HEI distributor. Some friends are saying the Iridium plugs aren't optimal for the engine, and to switch back to copper plugs.

I've had the iridium plugs in for six weeks, no noticeable change in idle, acceleration but it does seem to have less smoke on startup (previous plugs were 10 years old with 8000 miles on them, though).

Has anyone had any negative experiences or issues with Iridium plugs in their old 400 motors?

Thanks in advance!

Jim

[unruhjonny]

personally, I wouldn't run anything other than a standard copper core plug on that car.
I have had good results from the Autolite 85 in the absence of Delco R44S plugs - but I have also received some flack here for running a "ford" plug
What type of distributor are you running?

Your comment about smoke on start up should have absolutely nothing to do with plug type used - I believe that it would either be evidence of a leaking carb, or oil getting past rings/seals...

[ScumOne]

Sorry, Pontiac HEI distributor added, gapped the plugs at .045. The beast is going to Sean Murphy Induction next Tuesday because the Q-Jet is suspect, as well as the electric choke kit add on which is not staying in adjustment. Looking at a Stage 2 upgrade on it. Had the Autolite copper core plugs in it before, but there's been no change going to iridium versions performance-wise.

[steve25]

I have run Autolite's for years and never had any issues or bad ones!

[Formulas]

When someone gives me their opinion I always ask myself ok and what is this opinion based on and ask a follow up question or not and if the next answer is not based on any facts from experience
I give that opinion almost zero weight

Not optimum? Based on what a discussion at the water cooler or a dyno experiment with egt. gauge's and scientific fuel consumption monitoring or something in the middle



Iridium plugs are engineered to make a spark and go the distance

If they have the reach, acceptable heat range and a gap that works with ignition and compression they should work fine be interesting to see if they possibly have more resistance due to computer usage in new cars
And that's worth what you paid for it

I have some iridium's that are take outs from my old Honda that physically fit my Edelbrock heads I will be experimenting with them someday.

.

[Formulajones]

Stick with the copper core and save yourself some money. Nothing wrong with the copper core, and it's said copper is a better conductor of electricity anyway.

As far as the Autolite, AC, or NGK debate, I switched to Autolite for all the GM cars here many many years ago back when AC Delco started dropping heat ranges and combining stock.
(Don't worry about the brand specific people Jonny, they are very narrow minded )

NGK's are good plugs, just erks me that they run their heat ranges backwards from conventional thinking (Japanese thinking process I guess)

[ScumOne]

My bad, I put iridium plugs in the Chrysler 300C, I put platinum AP 86 Autolite plugs in the Firebird. Too many orders to verify from Rock Auto when you have six cars.

Can't seem to edit the title now, so any issues with Autolite AP86 platinum plugs in a 400?

[unruhjonny]

the Autolite 86 is (iirc) equivalent to a Delco R45S - so you should be perfectly fine.
I believe the OE plug for a 1969 400/4bbl w/62 heads is a R45S.

[Formulas]

I was wondering where you got short iridium's but didn't ask ... Because they basically go hand in hand with OE. aluminum heads and are long.

Not a thing wrong with a platinum plug as long as it meets basic specs they may actually live longer than a regular plug

.

[ScumOne]

Originally Posted by Formulas

I was wondering where you got short iridium's but didn't ask ... Because they basically go hand in hand with OE. aluminum heads and are long.

Not a thing wrong with a platinum plug as long as it meets basic specs they may actually live longer than a regular plug

.

This was what I came up with, too, when I bought them. And since it was only 60 cents more per plug, the $5 extra cost seemed paltry compared to the benefits.

[64speed]

MSD has a line of plugs out now that are supposed to work perfectly in harmony with your MSD wires and CDI box if you have one. After I put a few thousand on these NGK I am gonna switch

[jonmachota78]

I'm certainly no expert in the matter but my inderstanding was that those tiny pieces if platinum or iridium that last forever can get Hot. Making them not a good choice for these engines if you have any concern about preignition. Safer to stay with cenventional plugs. I'll stay with NGK for now

[shaker455]

I always recommend copper core plugs for carbureted engines.
high end plugs are designed for precise metering of FI.

[Formulajones]

Originally Posted by jonmachota78

I'm certainly no expert in the matter but my inderstanding was that those tiny pieces if platinum or iridium that last forever can get Hot. Making them not a good choice for these engines if you have any concern about preignition. Safer to stay with cenventional plugs. I'll stay with NGK for now

Those little pieces have also been known to fall off. I've found them stuck to the tops of pistons on some engines I've torn down.

[Formulas]

Enough abuse anything can fail, the number of things that can fail is nearly endless.
I don't think anyone here is selling plugs

[tom s]

Jim,I was at SMI yesterday and he had a carb with a elect choke sitting along side his pontiac,was that yours?Tom

["QUICK-SILVER"]

Originally Posted by unruhjonny

the Autolite 86 is (iirc) equivalent to a Delco R45S - so you should be perfectly fine.
I believe the OE plug for a 1969 400/4bbl w/62 heads is a R45S.

Autolite shows 86 replaces AC R46S. And shows 85 for AC R44S that factory listed for "normal" driving. R43S for trailer towing and severe service. So the OP needs to listen close for pre-ignition if he plays hard with it.

And how long has it been since ford used autolite plugs? Ford has been using motorcraft plugs for many years. Really can't remember when ford and autolite went their seperate ways.

Clay

[Formulajones]

Originally Posted by Formulas

Enough abuse anything can fail, the number of things that can fail is nearly endless.
I don't think anyone here is selling plugs

Fail is one thing, but pieces falling off and running through your engine is another deal entirely. Never had pieces fall off a standard copper core plug in 40+ years of my existence playing with cars.

Those little platinum or iridium buttons attached to the ground straps however do fall off, with normal use. I've even knocked them off trying to gap the plugs. Anytime pulling those plugs out of an engine the first thing I look at is if the button is in place. If it's missing, and I usually find a couple that are, just hope it ended up somewhere it isn't causing harm instead of scarring up the cylinder wall or valve seat. I've seen too much of that to even want to consider using those plugs anymore.

[Formulajones]

Originally Posted by "QUICK-SILVER"

And how long has it been since ford used autolite plugs? Ford has been using motorcraft plugs for many years. Really can't remember when ford and autolite went their seperate ways.

Clay

Early 70's

[geeteeohguy]

Iridium plugs are used by the oems so that the vehicles make it through the warranty period passing emissions. They last longer because they erode less. They don't give a better spark all else being equal. For our older cars, copper core plugs are just as good and a lot cheaper. There is no performance gain by going iridium. We change our plugs more often than every 120,000 miles.