Quote:
Originally Posted by ImpalaDave
Just installed Denso IT20TT plugs as per a recommendation by Marc I found on the forums. Gap 0.045". (snip).
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How times change...
Starting maybe 20 years ago, on the ZR-1 Net mail list and later on this forum, I evangelized the advantages of the Denso IT20, hotter coils and opening up the plug gaps to .045-.050. While I convinced a few folks of the Denso 20 heat range's merits, at the time, not a lot of folks tried that.
Now, even Marc is suggesting the IT20TT which is basically the same plug but with two, rather than just one Iridium tip.
After I had the late Jim Van Dorn's Automasters, build me a 500-hp "Street Skinner" engine, I went yet another range colder to the IT22. That worked very well for just about any driving I did, except for chassis dyno development, when I would install a set of IT24s.
Today, I still use the Denso Iridium Power IT22 in an LS6, an LS7 and the 2G LT5. Denso, at least so far, does not make an IT22TT or I'd use that.
And, yes, the 405-hp engines used a double platinum tipped, conical seat spark plug whereas the 375-hp engines used a conventional-tipped, flat seat spark plug. Interestingly, the plug for most production engines was an AC FR2LS which was a very late change. Originally, the plug was going to be the AC FR1LS, which for the time, was a very cold plug, but some issues with "pre-delivery fouling" with very early 1990 cars, had GM going one range hotter to solve that problem. The AC 1 heat range was about the same as the NGK 6 and Denso 20 heat ranges.
Another interesting tidbit was that all early LT5 heads manufactured by Brimal were machined such that the flat seats for use with spark plugs having sealing washers could be converted to conical seats for plugs with "tapered seats" simply by installing the taper seat plugs with a one-time "over-torque" procedure which cold-formed the conical seats in the head allowing use of taper seat plugs which in most cases provide a more reliable and durable compression seal.
Ain't these look at how it was back in the early days of the C4 ZR-1 hobby just too much freakin' fun?
