Which Brand of Spark plug do you run??

[Hib Halverson]

Originally Posted by XfireZ51

Hib,

Do you know why the 375hp motor has a recommend of a .035? plug gap, while the 405hp motors were spec?d for .050?? Am I correct, and if so, what change made that possible?

I don't know what change made that possible.



As to why the bigger gap, I bet Behan probably knows for sure, but I bet it was to improve idle stability and idle emissions.

[Hib Halverson]

Originally Posted by 32valvesftw

NGK BKR5E plugs gapped at .042-.045, per Corey.

Sheesh that's a hot spark plug. I wonder why he recommends that?

[Matt B]

Originally Posted by XfireZ51

Hib,

Do you know why the 375hp motor has a recommend of a .035? plug gap, while the 405hp motors were spec?d for .050?? Am I correct, and if so, what change made that possible?

I read that 405 engines used better plugs from the factory which were less prone to wear than what was used in early engines. So they could be gapped already wider without loss of lifespan.
Not sure if I remember correctly with that but it sort of makes sense.

Can anyone confirm? Or am I wrong?

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[ImpalaDave]

Just installed Denso IT20TT plugs as per a recommendation by Marc I found on the forums. Gap 0.045". I was aiming for an NGK 6 heat range equivalent plug as I'm mostly street driving with an occasional pull. They're an iridium/platinum electrode plug - supposedly ideal for wasted spark ignitions. This was my first plug change since acquiring my Z this year - the AC Delco 41-963's were crusty (due to moisture?) and had worn to about 0.053" except one, which was about 0.037" (dropped before install?). Runs noticeably better now.

Plug 8 was much easier to get at than I expected - below is the combination of tools I used to get at the plug. The aluminum welding wire was used to separate the plug socket from the short extension, magnet used to remove the socket and extensions from the hole.

[max76]

Bosch FR7DC+ 0.9gap

I'm in Italy

[Hib Halverson]

Originally Posted by ImpalaDave

Just installed Denso IT20TT plugs as per a recommendation by Marc I found on the forums. Gap 0.045". (snip).

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?

[XfireZ51]

Originally Posted by 32valvesftw

NGK BKR5E plugs gapped at .042-.045, per Corey.

I am using same only gapped at .035?. I did try the
NGK BKR5E-11 which come gapped at .044? but motor seems to operate smoother at .035?. My LT5 has had porting by Pete along w his Stage 2 cams.
FYI, no knock retard to speak of.

[lfalzarano]

De so IT20TT gapped at .45


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