Spark plug question + advise needed

[Tow Man]

I've always liked the NGK V-Power plugs and used them in my first GN back in 87 with no problems, but I can't remember if they were UR4's or UR5's

I've read on this board to use NGK UR5's but the book calls for UR4's! Which is the correct # ? The UR4's would be a colder plug correct?

The reason I ask is that I'm still getting some detonation with a Thrasher 92. The only thing I haven't tried are different plugs. I'm running the UR5's.

All repairs, replacements, and mods listed below:

100lb valve springs
new GM coil pack
new Taylor 8mm S/P wires
Trasher 92 chip
3" THDP and dump pipe
Walbro 340 + hot wire
New GM fuel filter
Billet FP regulator
FP set at 45 psi
3" ATR dual exhaust
Big Mouth cold air
TPS and IAC set correctly
Flush IC + bypass VC breather
GM Top Engine Cleaner
Stock waste gate actuator and new Y hose assembly.
Checked all vacuum lines

I'm running amoco premium (93) and 3 gals Cam2 114 per tank full. Still get audible knock on hot days. Every time I get a chance to hook up the OTC it's cool out and no knock!

I ran 5 gals of Cam2 114 to 1/4 tank pump gas at the track this past weekend and no knock! Car ran 13.40 @102 on stock tires.

All is well except for the annoying knock on pump gas!

Things I still have to do:

Fix or replace DS header
Replace PCV Valve (kept forgetting to order the damn thing)
Clean injectors

I will be doing more scan tool testing this weekend. Any thoughts or suggestions would be appreciated.

Thanks

 

[Mr URL]

I personally use AC CR43TS plugs gapped at a tight 0.035". Work great.

How much boost are you running and what are your WOT O2's?

 

[Tow Man]

With the stock wastegate I'm getting 17- 18 PSI. Is this in the ballpark for a thrasher 92? The THDP may have affected the wastegate. I have an adjustable that I haven't had a chance to install yet.

I will have scan tool readings this weekend. For the sake of accuracy, I am also installing a new O2 sensor. The car still has it's original! 21K miles.

I noticed a lot of you are running a tight SP gap, some even tighter than .035" What bennefit do you get from this? With my first GN, I experimented with plug gaps and found smoother idle and running with a bigger gap .045! no detonation! This may be old school tech but, a wider gap allows for a bigger spark and more air/fuel molecules within the gap. Less misfire's, smoother running and more power. This was always important in high compression N/A engines as well as the 70's lean burn (dogs)engines which approached gaps of .065"!

Please don't anyone misunderstand, I don't doubt the methods of so many out here. I've learned a great deal from all of you! I'm just wondering what advantages are seen with running a tight SP gap? Does the ground electrode cause knock with a larger gap? The plugs in the car now are gapped at the recommended .035 so this isn't the cause of my problem. I am concerned about the heat range though!

Thanks

 

[TurboTR]

Actually with NGK the higher the number the colder the plug. A -5 is colder than a -4.

TurboTR

 

[Tow Man]

Ah Hah! Ok.

I did notice, the UR5 is still hotter than the original AC plug I took out! That's what led me to think I got the wrong plug. I don't remember what the AC # was. What is the coldest AC plug you guys run? The 43's?