Hib Halverson

I've never heard of anyone going from the taper seat back to the flat seat plug but I believe the LT5 plug seats were designed to support both.

Crusin

Thanks for Info, I agree spark plugs are mostly a marketing ploy and changing from the original A/C Delco Plugs to fancy plugs would provide very little in regards to extra h/p.

fake

My 77 L-82 only runs on iridium .Runs like **** on ac. Gap never changes but with HEI you have the spark to fire an oil soaked plug. Just my thought!

Paul Workman

Well, not so fast... I would sooner think the difference might be the heat range or presentation differences maybe? The L82 is a moderate performer, sharing the same cam as the low compression L48. But, the L82 had 4-bolt mains, better intake plenum, "2.02" valve heads and compression that ranged from 9:1 in 1976 to 10:1 in 1979.

Point is, there is nothing special about that engine that would make it perform better with "rare earth" plugs that couldn't also be duplicated with plain ol' copper core plugs OF THE CORRECT HEAT RANGE.

The main reason for using Iridium (or the like) plugs over less exotic plugs is the extended life advantage of the pricy plugs. But, this too is a double-edge sword: Their performance curve from new to replacement is longer, yes. But, plug deterioration is gradual over their life expectancy, and therefore performance is less than ideal over a longer period of (miles) until they clearly reach their life expectancy.

Such is not the case with the (copper) plugs. OK, their life expectancy is significantly shorter, but so is that margin of lesser performance prior to requiring replacement. Plus, being ~ 1/5th the price of rare earth plugs (maybe $2-3 ea., vs. $8-10+ ea), one can afford to have fresh plugs in their car every season or two and thus always having plugs that are in the prime of their life.

Course I understand that if changing plugs presents access difficulty, longer life plugs have their appeal. Just don't try to wring out the last mile before changing plugs, plugs way past their prime...is the point!

.

fake

Thanks makes a lot of sense!