[TransAm 474]

Originally Posted by Cliff R

I use and prefer NGK's, and have had perfect success with them to date. I will even use the same plugs over and over as I have in my own engine(s) for decades. I just periodically run them to the bead blaster and knock off all the carbon, check the gap and back in they go.

For several decades I ran the same set in a 400, then two 428's, then a 455. I only replaced them because they would fit the new KRE heads.......Cliff

Thanks Cliff, what is the number of the NGK that we should run in this?

[Cliff R]

There is a nice cross-reference chart via a Google Search.

I just used it couple of days ago to locate NGK's for a John Deere model 60 I'm working on. The "go to" plug for those is an Autolite, but we've had two in a row defective right out of the box, so switched to NGK's. So far so good......Cliff

[Cliff R]

https://www.ngkpartfinder.co.uk/cros...act=AC%20DELCO

I used this the other day to locate plugs for a John Deere model 60 I'm working on. The "go to" plug for those are Autolites, had two in a row defective right out of the box. Switched to NGK's and good to go so far......Cliff

[TransAm 474]

Thanks Cliff, using the cross reference chart, it shows the AC R44S plug crosses to a NGK BP5S plug. Oreillys website shows a NGK XR4 plug for a 1970 RA III Trans Am. These are stock Heat Range I suppose, is the stock Heat Range fine for high compression, pump gas engine, or is it better to run a plug a step colder? Now, I have to find out what the difference is between the NGK BP5S and the XR4.

[Cliff R]

Plug heat range is something I never worry much about or have noticed any improvements messing around with it. I just run what is recommended in most cases......Cliff

[Jay S]

Originally Posted by TransAm 474

Thanks Cliff, using the cross reference chart, it shows the AC R44S plug crosses to a NGK BP5S plug. Oreillys website shows a NGK XR4 plug for a 1970 RA III Trans Am. These are stock Heat Range I suppose, is the stock Heat Range fine for high compression, pump gas engine, or is it better to run a plug a step colder? Now, I have to find out what the difference is between the NGK BP5S and the XR4.

XR4 would be a vpower plug. Bp5s is a standard plug.

There is some overlap on heat ranges jumping from one company to the other. The bp5s falls from a cold side of a 46 to the high end of a 44 a/c plug. It is probably closes to a 45. A 6 starts at 44 and goes as cold as a 43.

A 6 would give the engine more thermal buffer. Thermal buffer is why we like to run on the colder side when it comes to plugs on performance engine with good compression. The 5 is more than likely ok, it is the non ok conditions like over heating or bad gas with high compression that your better off with the 6. If the engine never gets hot or some bad gas the 5 may never bother anything. Brisk has a pretty good explanation of heat ranges. Scroll down on the link and you can see that chart that shows a good depiction of thermal buffer and proper heat range.

https://www.briskusa.com/spark_plug_...at_range_chart

[Pete D]

One my last rebuild I took out the cam advance key, 2 degrees I think. I had originally installed it to build a little more bottom end. Before the engine would ping going up the hill to my house under part throttle. After driving it to my house from the shop where I work on it I did not notice the ping anymore. Yay! This is a 421 60 over with +5 thou deck and slightly ported 670 heads running 1:1.65 rockers and Crower's 041 clone cam.