I have a 2000 XK8, and wondering what orientation the open gap of the spark plug electrode should face when inserting spark plugs, e.g. up towards the middle of the engine, towards the front of the car etc.

 

Ideally you want the flame kernal pointed at the incoming air/fuel mix. But really? You been reading racing forums again
i dont even worry about this on the race car anymore.

 

I've read this question a few times trying to see what I've missed so if I've misunderstood, please come back and explain.

What difference do you expect this to make?

They plugs are torqued 25-29 Nm and not a set number of turns so you have no control over which way it's facing once torqued up. Regardless of the way it's offered up to the head, it only starts to screw in when the lead thread on the plug engages with the lead thread in the head.

Graham

 

Some say that orienting the open-end of the gap towards the inlet port gives some tiny increase in power output. Legend has it that there are available washers of variable thickness, to facilitate this sort of twiddling without interfering with the correct spark-plug torque.

Personally I'll give it a skip!

 

It could be useful at Bonneville.

 

It's really astonishing how much bogus hot rod/racing lore is out there that guys think has application to street performance cars. I would add a few cases in point but I didn't sign on to start any trouble.

O God. I can't help myself. How about plug indexing, fancy air cleaners, purple motor oil, $38/qt transmission fluids and miracle fuel/oil additives just to get the ball rolling. Let the games begin. We should start a comprehensive list.

 

I learn something new everyday! For the record I'm not going to worry about indexing except in financial investing.

 

Heh - one of my personal favourites is the Teflon-based oil additive, such as the legendary "Slick 50".

 

Indexing does help in certain apps. most notibly on racing engines trying to get the last ounce of performance. I used to index( you buy washers Grant that come in varying thickness and draw a line up the electrode that corresponds to the ground strap) but dont worry about it anymore. It used to be a bigger issue on turbo, blown and nitrous engines getting the fire blown out. But with high output ignition systems that for the most part is of little issue today as it used to be.

 

Yup- that's it in a nutshell. Complete waste of time with modern HEI.

 

How about $400 after mkt induction air cleaners with $1200 exhaust systems that dump the HP at low rpms and add a hand full of HP over 6 grand at which point the engine blows.
But the sound is marvelous - while it lasts. Hoo Haah! I'm so funny I can't stand it! P.T. Barnum was right.

 

Sooo, what's the optimal alignment for this 5 minute no-cost theoretically possibly slightly beneficial tweak?

 

Theoretically, you should direct the gap toward the incoming charge. Accel used to offer a threaded tool that simulates the cylinder head threads so you can trial fit the various copper washers so the plugs will be "indexed" correctly before actually installing the plugs. It's a lot of fooling around for nothing on a street engine. How about this... Do they offer a multi-electrode plug for our cars? Several manufacturers offer a 2, 3 and even a 4 electrode plug. I don't know if any list one for the Jags.

 

with a 25-29 NM range, any chance washers might not be necessary in addition to the fact you can try different plugs and see which fit betteR? Still wondering what the direction the incoming charge is coming from

 

This is from NGK

4. Indexing
This is for racers only !!
Indexing refers to a process whereby auxiliary washers of varying thickness are placed under the spark plug's shoulder so that when the spark plug is tightened, the gap will point in the desired direction.
However, without running an engine on a dyno, it is impossible to gauge which type of indexing works best in your engine. While most engines like the spark plug's gap open to the intake valve, there are still other combinations that make more power with the gap pointed toward the exhaust valve.
In any case, engines with indexed spark plugs will typically make only a few more horsepower, typically less than 1% of total engine output. For a 500hp engine, you'd be lucky to get 5hp. While there are exceptions, the bottom line is that without a dyno, gauging success will be difficult.

 

I can recall 2 or 3 cases where friends tried indexing on MC engines. Nothing big enough to even make a blip on a Dyno ever came out of it.

 

It might be useful to pass the time while drinking beer in the garage on a dark winters night.

 

I can offer (to Members Only) French Plug Locating Snake Oil


Not only does this permit precise orientation of the plug electrodes it also allows choice of plug insertion depth.
This increases the number of variables to the point where you will NEVER find a satisfactory solution.
Also labour saving since the next set of plugs can be oriented on the workbench in the (required) new cylinder heads.

 

A fella down the pub with a 3-litre Capri told me that alternately facing the gap towards and away from the inlet in every second cylinder is the best way. It's because the resulting flame trajectory causes reverse-pressure waves that travel through the cylinder walls and resonate with each other in such a way that the film of oil under the oil-control rings magnetises and levitates away from the liners.

BUT - this only works within 200 RPM either side of peak torque. Always consult your pharmacist.

 

We must hang out at the same pub! Amazing.