NGK XR4?

[Ghoste]

New to the NGK plugs and their rating system, is XR4 a colder plug or hotter or neither?

[firefighter3931]

The XR4 is hotter than the XR5....smaller the number, the hotter the heat range. 

I wouldn't consider an XR4 unless the engine was under 9:1 


Ron

[Ghoste]

Just found that info on another site, thanks Ron.  I have some XR5's and I pulled the first plug and it was an XR4 in the car.  Might explain some of my other issues huh?

[firefighter3931]

Might explain some of my other issues huh?

Yep, a 4 series plug will put too much heat in the chamber (in a build like yours) and idle quality will suffer. Under load it will push the detonation envelope as well....and throttle response will suffer 
 
How did the plugs look ?

Try grounding the #1 ignition wire and turn the engine over....you should see a blue/white spark 



Ron

[Ghoste]

Actually the plugs look good but I just ran two tanks of leaded fuel through it.  Next week it would have been back to exactly the conditions you mentioned.

[Brass]

The XR4 is hotter than the XR5....smaller the number, the hotter the heat range.  

I wouldn't consider an XR4 unless the engine was under 9:1  


Ron

I've been thinking about this.  Just out of curiosity, why would you consider a hotter plug in a lower compression engine?  Are there advantages to a hotter plug in that application or would it be a wash?  Also, could less resistance of a hotter plug contribute to higher engine temps?  Thanks!

[firefighter3931]

The XR4 is hotter than the XR5....smaller the number, the hotter the heat range.  

I wouldn't consider an XR4 unless the engine was under 9:1  


Ron

I've been thinking about this.  Just out of curiosity, why would you consider a hotter plug in a lower compression engine?  Are there advantages to a hotter plug in that application or would it be a wash?  Also, could less resistance of a hotter plug contribute to higher engine temps?  Thanks!

It's all about balance   

You need heat in the chamber to make power. Too cold of a plug and it won't make enough heat and the plugs will foul. Too hot of a plug will create too much heat and detonate. Balancing heat range with compression becomes important in the tuning/performance arena. 

A plug that is too hot increasing chamber temps will also make the engine run hotter 



Ron

[BananaDan]

Ron,
I currently have NGK-XR5's in my engine and as I've mentioned elsewhere on hot days or climbing a grade on the highway she detonates a bit.  Mike recommended the NGK-2746 V-Power Racing HR6 plug to me but I haven't bought them yet.  I also recall reading something about the racing plugs could cause some sort of electrical interference with the radio?  Can you shed any light on this subject?  Is there an XR6 that would have the same temp rating as the one Mike recommended but wouldn't have the interference issue?

[firefighter3931]

Hi Dan,

The plug Mike recommended is a racing plug and not available with a resistor. NGK does not make a 6 series resistor plug that fits the old factory heads....unfortunately. 

The BCPR-6ES is available but that plug fits the aftermarket aluminum heads like the Eddy RPM and is a resistor plug. I ran those in the old 446 with great results on a pump gas build with 10.4:1 compression. 


Ron

[BananaDan]

I have 906 heads currently, will that plug you mentioned work for me?  What does the lack of a resistor on the racing plugs mean?  What could I expect to experience with the racing plugs?

[firefighter3931]

The plug I listed above for the Edelbrock head will not work with a 906....the reach is too long. 

Resistor is just a noise suppressor....nothing more.

Your only option for a colder plug is the one Mike recommended. It's a non resistor plug and may cause radio noise.

Depending on where your timing is set you may be able to make some adjustments. That's why I was asking you to map out the timing curve. 


Ron

[Ghoste]

Do non resistor plugs interfere with any of the other engine electronics?  I know obviously not all of them but are there some?

[firefighter3931]

Do non resistor plugs interfere with any of the other engine electronics? 

Not from my experience but then again i've used only analog boxes.

The digital electronics are very sensetive to EMI/RFI and those guys all run non-resistor plugs with zero issues. With the digital stuff it is highly recommended to route wiring away from the alternator and shielding the wiring seems to be the answer. A lot of the race guys just run w/o an alternator and charge their batteries between rounds so that would eliminate the alternator issue. 

Ignition wires can also be an issue with some brands causing problems. A lot of pro teams are running the FireCore wires and swear by them. Those guys have sensitive electronics and the Firecore's are properly shielded to suppress the EMI that reaks havoc with those complex electronics.


Ron

[Ghoste]

I suppose it would be foolish to make a digital ignition box that could fail because of ignition generated interference.