I was looking on Rockauto today for spark plugs. It list 2 densos for the STR but when you click more info its the same page. So does anyone know what the difference between the 3356 and the 5303 are? The only thing it says different is the 3356 is OE. So does anybody know I've been looking on google and havent found anything yet on the differences. I'm not starting a debate on densos vs ngks so lets not get this started into a spark plug war. I'm just curious why they list 2 and what the differences are between the 2 densos besides the price. ie heat ranges etc. Are they right that the 3356 is OEM since I havent pulled mine to see if thats what is in there?

 

Ok a little more searching and on densos website they dont even list the 5303 for the STR. Its listed for the super V8, XJR, and XKR. It says that the 5303 is the Iridium power plug and the 3356 are the Iridium long life. So what the heck does that mean? Looking deeper.

 

Ok dug deeper. I found this on densos website.
So basically my understanding is if I go with the 5303 power plus that it would only last 30000 miles before needing new ones and that the 3356 will get the stock rating of 100000 miles since they are the long lifes. Well I think I may of answered my own question. In case anyone else is wondering they can refer to this post for the differences.

 

1947?

 

LOL I liked that.

I did some digging on the NGK's as well. It looks as if the Iridium IX are the equivelant of the denso powers. So you guys that got the Iridium IX may want to have them checked at around 30000 miles as they most likely wont last for the stock length of 100000 miles. The NGK equivelant to the long lifes are the NGK Premium Iridium. So just to give you guys a heads up.

 

I found a good article on spark plugs a while back, but now I don't know where it is. It had all sorts of info from consumer reports and everything. Basically, in the Consumer Reports study they determined that no spark plug is going to improve your fuel economy or power, provided that you are using the correct plug for your car and it is gapped properly. Some of the fancy plugs, such as the brand that has two or four electrodes (I forget the brand name) actually decreased power and economy. Those plugs cost something like three or four times as much as the standard plugs, but they delivered poorer performance. It was all marketing hype.

The copper/platinum/iridium debate is simple. Platinum is harder than copper and iridium is harder than platinum. The hardness of the tip determines how long it is going to last. As the plug fires hundreds of times per second a little bit of the metal is eroded each time. Over time the shape of the tip changes and the plug might not fire properly. Iridium is the most resistant to this erosion, platinum is next, and copper is last. Manufacturers switched to platinum or iridium plugs because they last longer and the manufacturer can brag about 75,000 or 100,000 between tune ups. If you don't mind changing your plugs every 30K miles then the copper plugs will work just as well as the iridiums as long as you buy plugs that are in the correct heat range for your car. Plugs that run too hot can cause pre-ignition, especially in high compression cars.

Too summarize: Don't believe a plug maker's hype. Just buy the factory recommended plugs for your car and gap them properly.

 

Reverend, you forgot to get an ahmen.


AHMEN brother!!

 

Still wondering what church Reverend Sam heads up in his neck of the woods. I'm guessing it's Our Lady of the Evening....

(Just a little religious humor, Reverend! No offense intended....)

 

I totally agree about just putting in the factory plugs. I had just always heard factory was denso and then saw Rockauto had two different densos so was curious what the difference was. After researching more I found out so I'll be just putting in the factory replacements and calling it a day.

 

Wassup Vance, After a lot resarching and opinions that I have read through I went with the NGK IX iridium plugs and those plugs actually are suppose to be as good or even better than the Denso's. 30,000 miles is nothing if using the NGK's;thats an understatement . Man those plugs are soo good that the new Jag XF's all have them. Jaguar changed over from using Denso's to NGK's now in all their new Jags The NGK's that go on our STR's are the stock# 7866 http://www.sparkplugs.com/results_app.asp?aaia=1410635.

Take it easy & good luck

 

I jsut bought an NGK AFX stand alone WideBand AFR meter, Im going to experiment, and datalog with different heat range plugs if anyone is Interested I make a thread.

I should be getting it in a week or so.

 

I did see in my research that denso recommends for every 75-100hp you should go up once step in a colder plug. Might get to that with a few mods. I wish I had bookmarked it. It said that the 16 in the stock plug number is the heat range and the higher the number the colder the plug. Not sure how the NGK's work but I'm sure its something like that. I'm curious on what your results will be. According to densos site we are at the hottest plug in the heat range. I cant wait for the thread I will be subscribing.

 

+1 Count me in also please! In all the cars I had even in my 4.2L S type which I have now has the IX iridiums from NGK. I remember back then when I changed over from factory Denso's, the car would more quickly hit the red line on the rpm, like my throttle was more sensitive lets just say.

 

But you'll change the IXs at 30K?

Which NGKs are jag using in the new cars - well, which ones in the R versions? Not the IX, right?

 

There must have been some fault with the old plugs for there to honestly be some difference in performance. Contrary to myth, if a plug is the correct configuration and it actually 'fires', the number, type, or material that the electrodes are made of cannot possibly not make any difference in any engine operating characteristic. This goes for high energy HEI or coil type ignition systems too.

A spark is a spark.

 

Umm...why will I change them at 30K? There is no proven docoumentation saying they need to be changed at 30K, I'll change them at 60K more or less

 

As I understood a previous post, they're good for 30K not 60K.

Back to my other question: Which NGKs are jag using in the new cars - well, which ones in the R versions? Not the IX, right?

 

Yeah from the previous post thats not tested nor confirmed that the NGK IX iridiums last for only 30k. To answer your other question my friend has a 10' XFR who works at the Jaguar Parts department, he got a really good deal on lease there,but anyhow he confirmed with me that all the latest Jags are using the NGK long life IX iridiums and even the R's

Cheers!

 

There's a reason some are "long life" IX (and cost more), and others are not long life IX (and cost less), at least that's what I reckon.

 

Hi Jagv8, sorry I was making my point about the long life IX Iridium NGK's the whole time not the regular IX NGK iridiums. For sure the long life cost more for that reason. May I ask have you done your plug replacement yet on your 04 STR?