Yes come to think of that.There are two lengths.I have a/m alloy heads and swapped the plugs over & had a low speed miss, [cold] even done a dyno run through the xr club.Found out that they are the wrong lenghth way too short,I needed the plugs for sprint, way better performance and economy.. ngk's. forget what part # is..platnum ?? $$$
In response to your plugs for ya EL XR8, best on the market in terms of mileage, spark, and resistance to temp (from fanging) is NGK BPR5FS-15. Gap them to 1.4mm. They are a V grooved type plug. Happy revving
Come to think of it I've got a slight miss at idle on my 250. I know the EFI plugs are different, as they penetrate more into the combustion chamber.. Would it be worth maying more $$$ in the hope that it *might* get rid of the miss? Its a next-to-new Veale motor btw..
I did have NGK plugs in it that were only a few weeks and i changed them with motorcraft ones and the miss got worse. A bit more investigation found the connection on coil where the lead goes on was corroded and the resistance on that lead after cleaning it was too high (the leads where top gun 8mm cost $90) and all the other leads are stuffed. You can touch them with your hand and see sparks but it doesn't zap you. Having to much resistance in my coil lead and the spark needing to go somewhere broke down to coil stuffed it (you could only see the sparks coming out it was completely dark. So i know have a new plugs, leads and coil and it run sweet.
Anyone with a pre AU V8 and needs a coil be prepared for their jaw dropping price!!! They retail at about $260......good thing i get dealer price from Ford!!!!
svo 302:: checkout the length of your plug.Plug is too short.Compared to std iron heads by about 10mm.I'v recently had my heads off to cc the chambers etc.Check it out..First..Twisted Wedge reqire longer plugs ,should bring compression back ..