tuning questiion

[XfireZ51]

I can only answer for my motor, but I was originally running the 5s and was chasing KR. I decided to check plugs for specks to confirm. I also examined the ground strap. It was a light gray color down to the plug thread which is indicative of a too hot plug. I went 2 steps colder w 7s and the strap was now dark to the end if the strap. The 6s produced coloring of the strap which transitioned from light to dark at the radius of the strap. That's the indication of a proper heat range. Also did plug cuts.

[Hib Halverson]

Originally Posted by XfireZ51

I can only answer for my motor, but I was originally running the 5s and was chasing KR. I decided to check plugs for specks to confirm. I also examined the ground strap. It was a light gray color down to the plug thread which is indicative of a too hot plug. I went 2 steps colder w 7s and the strap was now dark to the end if the strap. The 6s produced coloring of the strap which transitioned from light to dark at the radius of the strap. That's the indication of a proper heat range. Also did plug cuts.

Typically, spark plug coloring is used as a measure of air/fuel ratio not plug heat range but, with today's fuels having a lot of "exotic" components, the plug coloring you get with modern pump gas is really not even good for that. Today, the real measure of AFR is what you see on a wide-band O2 sensor.

As for how to select a heat range, my rule has been, given an engine which has its AFR at WOT pretty close and is not using ecessive amounts of oil, I go as cold as possible as long as the plugs do not foul during warm-up, idle or light throttle. That's led me to something along the lines of the AC 1, NGK 7 or Denso 22 heat ranges. I'll add that, if detonation is an issue and one things the spark plugs might be a contributing factor in causing it, then you want the coldest plug you can get. My rule has always been to try and take the plug out of the detonation equation but doing just that.

interestingly, during development and validation of the LT5 and its release for production, the plug GM specified for the LT5 was the FR1LS. The AC 1 heat range is about the same as the NGK 7. Just before the car went on sale, to mitigate fears of some inside GM about pre-delivery spark plug fouling on dealer lots, GM changed its mind and went with the FR2LS.

The majority of street-driven LT5s do not see duty like what would cause "pre-delivery fouling" and LT5s which are raced or driven aggressively on the street will never see it.

I've owned my LT5 for 18 years and on the street I've run either NGK 7s or, for the last decade, Denso IT-22s. When I go to the track or the chassis dyno, i put Denso IT-24s in the engine.

[XfireZ51]

Read this article on selecting the right heat range.

http://www.moparmusclemagazine.com/t...s/viewall.html

You start from there then move on to gap and timing.

[Hib Halverson]

That story doesn't say much at all about how to select a heat range but what's there, if anything, confirms what I said earlier about plugs.

But...if the plug originally developed for the engine was an AC 1 heat range, unless the engine is in a trailer queen...why is everyone running such hot plugs?

Do they know more than the engineers who spent years testing plugs?

I'll stick with my Denso 22 heat range.

But I will grant you, for engines which see a lot of starts without warm-ups, are running too rich at idle and part throttle or are using oil, the cold plug is a mistake.

[scottfab]

Originally Posted by XfireZ51

Read this article on selecting the right heat range.

http://www.moparmusclemagazine.com/t...s/viewall.html

You start from there then move on to gap and timing.

Great post. Thanks !

[XfireZ51]

Click in the pics of the various plugs. The one w high miles
but in good condition. Read the material there. It describes how to choose plug heat range using the coloring of the ground strap. This is really well known in performance circles. Nothing new actually. You don't pick heat range based on the color of the ceramic.

[Hib Halverson]

Well I haven't heard that much about using the color of the ground strap to select heat range.

But, heck, maybe I've not been in "performance circles".