Re: '91 #473 Plugs
 

You should look at the ground straps to consider what heat range works for ur motor. I used NGK 7 (too cold), and used NGK 6 for quite a while, but have settled on NGK 5s.

Re: '91 #473 Plugs
 

I'll do so Dominic.. will get it out this weekend..

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Re: '91 #473 Plugs
 

Finally got the car out. Runs great. Might be imagination, but seems smoother. Pulls beautifully throughout the RPM band at WOT. Never skipped a beat. Very happy so far.

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Re: '91 #473 Plugs
 

So which plugs did u settle on?

Re: '91 #473 Plugs
 

Still have the NGK 7's in. Will pull one later today to look at timing..

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Re: '91 #473 Plugs
 

Some pics of #1Attachment 6081Attachment 6082

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Re: '91 #473 Plugs
 

Overall, looks good altho from what I can see of ground strap, I would say to try
The NGK 6s. Looks like it could use a little bit hotter plug. You want the color change on the strap to occur in mid "radius" of the strap. How many miles on the 7s?

Re: '91 #473 Plugs
 

Less than 10 miles..

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Re: '91 #473 Plugs
 

Back in the days when I owned "Barney" (1995 VIN 00140) I did a lot of testing with different NGK and Denso spark plugs.

The NGK 7 heat range works very well for street high-perfomrance. It is not a plug for cars which are never driven hard or are show cars only.

In the early '00s I switched to the Denso IT-22, because, at the time Denso was the only plug out there with an iridium tip and a cut-back side electrode. I ran the IT-22 after that and sold the car with a fresh set of them installed. I also converted all my other engines over to Denso...either the IT-20 or IT-22. Also, in the case of the LS7, I've done a lot of street testing with the IT-24 and it works well but I went back to the -22 on the street because the -22 has a projected tip where as the -24 does not.

For racing and chassis dyno work I used either the NGK 8 heat range or the Denso IT-24.

All LT5 cylinder heads where machined with a "universal spark plug seat" which accepts either flat seat or conical seat spark plugs, however, to use a conical seat plug in a pre-93 cylinder head, you need to do a one-time over torque of each plug to form the conical seat.

Torque to 22-25-lbs ft, then back off the plug and retighten to your normal torque setting.

The factory heat range is way hot for any type of sporting driving. This is because just before the car was released for sale the heat range spec was changed from the AC 1 heat range to the AC 2 heat range because of concerns about pre-delivery plug fouling.