I used Bosch Platinums in my XK8 but read something about cold start flooding. I never had any problem with that before; wondering which plug people prefer for the XKR. There are several varieties of Platinum/Iridium plugs from NGK and Bosch - a penny for your thoughts.

Also if you know which part number that's a big help - I don't trust Amazon's judgment over what fits this car.

 

FWIW, I've used the autolite XP's for the last 23k miles... no problems, no complaints.
Just recently, I replaced them with bosch fusion #4501 spark plugs. These are a 4 ground electrode design with an open center electrode design and its a mixture of iridium and some other high wear material. Although its only been about 1k since I've installed them, I like them!.. great starts, smooth idle, OA just seems to run better.

 

Thanks, I'm going to give the Bosch iridium (part number 9603) a try; got a good price on 8 of them and (supposedly at least) they last longer than a regular platinum plug. They did not have Autolites or NGK in stock, and I held back at the Champions based on past experience - though who knows, their iridium plug might be ok nowadays.

Will see what happens!

 

I have used NGK iridium plugs in several supercharged cars with good results. For the twin screw I opted for a step colder than stock.

50k miles in a Mini with an overdrive pulley and 10k in the XKR. No problems.

 

My experience is that NGK and Denso are the top two iridium spark plugs in the market. Go with either one and you'll be set for 100,000 miles and more....

 

I've been a professional motorcycle tech for 36 yrs. I've also attended numerous manufacturers trade shows. I must say, the Reps. from AUTOLITE were the MOST helpful and KNOWLEDGEABLE of all the spark plug manufacturers. These Reps were the guys who DID all the testing on their products... they taught me ALOT! While NGK has always had a stellar reputation and, Champion has since the 70's had ... well.. a less stellar reputation, Champion's have indeed improved and I'm sure a fine product today. Even though I am currently experimenting w/ the Bosch Fusion and, I am pleased, I assure you won't go wrong using Autolite plugs. I have used all the major brand spark plugs and I've never had failure using Autolite plugs. Giving credit where it's due, the Reps. from Autolite were indeed the most credible and knowledgeable and they believe in their products 100%.

 

If 4.2 XKR then same as STR: NGK IFR5N10. Good for 100K miles.

 

With plugs, buy for service life. Any quality brand name plug that fits and has the right heat range works the same, they just last differently. The standard plugs need replacing more often, the iridium last the longest, saving a lot of time. None give more power or save fuel, buy for time.

 

What brand did /does Jag put in from the factory or from the dealer. For Plugs, Batteries, etc I sway toward OEM. Since I own 6 Lincolns and 3 Fords besides the Jag its always been Motorcraft.........with good results

 

Mine were NGK as above. You can buy 'em cheap from parts places or pay a bit more for Motorcraft. (Even more from a Jaguar franchise.)

 

I think they use NGKs; they're a popular choice in any case.

Thanks for the input; I found a set of Bosch Iridiums locally for a good price. I agree to buy for longevity and time saved on replacement versus perceived power and fuel economy. You may get a smidgeon more with copper but they just will not last as long.

 

Bosch is not a problem I used them in both my cars for years.

 

I've had good very good experiences with Bosch and Autolite Iridiums in "blown" engines. My default preferences are still ND and NGK though (from my BMW days), but I have to agree with everyone else that leans toward the Iridiums for longevity and smoothness.