L78 Plugs Color Of Combustion Residue

[Daniel K.]

Re: L78 Plugs Color Of Combustion Residue

Duke,

Back to you on plug heat range for the L-78:

AC Commercial Plugs

C43N

Thanks for your help.

Dan K.

[Clem Z.]

Re: L78 Plugs Color Of Combustion Residue

unless you are doing track days i would use AC R-45 XLS plugs for everyday driving.

[Duke W.]

Re: L78 Plugs Color Of Combustion Residue

What Clem said...

Regardless of what the owner's manuals say, there's a vast agreement that regardless of diplacement or power rating, the best road use heat range for production Corvette engines is AC "5" or equivalent in another brand.

Colder plugs won't burn off deposits in normal road use.

Duke

[Clem Z.]

Re: L78 Plugs Color Of Combustion Residue

also to prevent the "bake on" of deposits after around town driving take the engine up in RPMs but not at full throttle which will cause the problem of plug glazing causing a high RPM miss. take it up in RPM using just part throttle as this will "clean" the plugs without overheating them

[Daniel K.]

Re: L78 Plugs Color Of Combustion Residue

Back to this topic on spark plugs as recommended by Duke, the AC #5.

Looks like the plugs I purchased have a little longer thread and the electrode extends a bit farther. Also, the ceramic part of the plug is smaller in diameter than the C43's and is shorter as well. Want to make sure internal clearances will be OK with these plugs in the L78. Gap these new plugs @ .035?

Thanks.

Dan K.

[Clem Z.]

Re: L78 Plugs Color Of Combustion Residue

Back to this topic on spark plugs as recommended by Duke, the AC #5.

Looks like the plugs I purchased have a little longer thread and the electrode extends a bit farther. Also, the ceramic part of the plug is smaller in diameter than the C43's and is shorter as well. Want to make sure internal clearances will be OK with these plugs in the L78. Gap these new plugs @ .035?

Thanks.

Dan K.

looks like you are using never seize on your plugs threads and that is not necessary unless you have aluminum heads. the new plugs you bought will work fine if they are equal to R-45XLS

[John H.]

Re: L78 Plugs Color Of Combustion Residue

Back to this topic on spark plugs as recommended by Duke, the AC #5.

Looks like the plugs I purchased have a little longer thread and the electrode extends a bit farther. Also, the ceramic part of the plug is smaller in diameter than the C43's and is shorter as well. Want to make sure internal clearances will be OK with these plugs in the L78. Gap these new plugs @ .035?

Thanks.

Dan K.

Dan -

What's that "5" plug - a Rapidfire or something? When Duke said "5", he meant "45" heat range (vs. 43, 44, etc.). As Clem noted earlier in the thread, you should have AC R45XLS plugs.

[Duke W.]

Re: L78 Plugs Color Of Combustion Residue

Ditto what Clem and John said - R45XLS, .035" gap is fine.

Do not even attempt to install those plugs at the bottom of the photo. Exchange them for R45XLS.

In the traditional AC number system, the "4" means a 14MM thread, and the second digit is the heat range, and a higher number is a hotter plug.

For the way we can reasonably drive our cars on the road - very little time at high load and revs - a hotter than OE plug is best to keep them clean. Heat range 3 or 2 would be okay for hot lapping race tracks, and 4 would be okay if most of your driving was sustained high speed freeway cruising or if you drove up Loveland Pass from Denver every day and coasted back down with the engine off.

Duke

[Daniel K.]

Re: L78 Plugs Color Of Combustion Residue

OK, got it. Thanks guys.