Correct spark plugs or best replacement for 1963 327/300 and 327/340 Corvette.

[Ruud Z.]

Gents, we need some advise on renewing/replacing our old, burned and tired AC spark plugs. The Chilton guide says to use "44"'s which is just an indicator for how hot the plug should be. I believe the AC 44 is no longer available but what is the best avaible replacement. Pls bear in mind that both cars are in Europe and not everything is easily avaible to us. Thanks Ruud

[Bob H.]

Re: Correct spark plugs or best replacement for 1963 327/300 and 327/340 Corvette.

I would step up to an AC45. Should be able to find nos on ebay. With the miles you likely drive, they will last a long time

[Larry M.]

Re: Correct spark plugs or best replacement for 1963 327/300 and 327/340 Corvette.

I would step up to an AC45. Should be able to find nos on ebay. With the miles you likely drive, they will last a long time

I agree. The AC 45 also is being reproduced, so they are also available new from some of the Corvette Suppliers and on Ebay. ACDELCO also sells new R45 and R45S (extended tip) that should also perform well in the engines you stated. However, they do not have the four green rings like originals. If you want DENSO brand equivalent, we can also supply those numbers, and they should also be listed in the archives.

Larry

[Domenic T.]

Re: Correct spark plugs or best replacement for 1963 327/300 and 327/340 Corvette.

If you want to renew a old plug which was done years ago, the electrode and porceline part of the plug needed to be blasted, the best is glass bead. Then the center electrode was filed flat and then gapped after blowing the dust out and wire wheeling the threads.
Aircraft plugs are cleaned and renewed every 100 hours but not filed as the electrode fires to the side not the center.
They renew about 5 times so your plugs should do well a few times. There is a test to see if the plug is good using air pressure. The plug must fire under pressure, but unless something is suspected I skip the test on auto plugs.
I renew regular plugs to save time, not $ on gasoline shop equipment and works great. If you want to keep original plugs this will work. When the plug gets bad it will let you know.

Dom

[Larry M.]

Re: Correct spark plugs or best replacement for 1963 327/300 and 327/340 Corvette.

If you want to renew a old plug which was done years ago, the electrode and porceline part of the plug needed to be blasted, the best is glass bead. Then the center electrode was filed flat and then gapped after blowing the dust out and wire wheeling the threads.
Aircraft plugs are cleaned and renewed every 100 hours but not filed as the electrode fires to the side not the center.
They renew about 5 times so your plugs should do well a few times. There is a test to see if the plug is good using air pressure. The plug must fire under pressure, but unless something is suspected I skip the test on auto plugs.
I renew regular plugs to save time, not $ on gasoline shop equipment and works great. If you want to keep original plugs this will work. When the plug gets bad it will let you know.

Dom

[Duke W.]

Re: Correct spark plugs or best replacement for 1963 327/300 and 327/340 Corvette.

If you insist on AC plugs the best choice today at a reasonable price is R45. AC no longer offers non-resistor plugs that were OE before 1969.

If you don't have to have AC plugs the NGK B4 and Denso W14-U are non-resistor plugs that are equivalent in terms of geometry and heat range to the out-of-production AC 45.

Despite being widely used as OE, AC no longer offers heat range 4, but they were too cold for normal road and highway driving.

I found out years ago that AC 45 gave much better service on my 327/340 than 44 because they were much more fouling resistant. Heat range 4 doesn't get hot enough to burn off deposits in normal driving, so they foul out quickly.

Heat range selection must be based on type or service, not engine horsepower, and since Corvette engines are usually just loafing, they need a plug that will run hot enough in normal driving to burn off deposits.

So I use heat range 5 for normal service and back in the sixties when I hot lapped race tracks, I installed heat range 3 (AC 43), which is colder and won't overheat during sustained WOT operation.

Duke

[Chuck B.]

Re: Correct spark plugs or best replacement for 1963 327/300 and 327/340 Corvette.

What advantage is there with an extended tip plug? What do the green stripe mean on the AC plugs?

[Chuck B.]

Re: Correct spark plugs or best replacement for 1963 327/300 and 327/340 Corvette.

Thanks for the info!