I posted this message yesterday, and it did not seem to stick. Here goes again: Does anybody want to address spark plug indexing. Mike, I know you have good experience with this. Dan, you were the one that told me to leave the gasket off the plug. What can you add to this. What kind of extension into the chamber is looked for here, and in what direction should the electrode point relative to the valves?

Did anybody see the first post? It came back on my screen as saved, and I viewed it from there, but never showed up as a thread in the list. I left things alone at that point, as I have double posted in the past by following up with another attempt. Thanks,
Sam

PS, Pray for warm weather I am going crazy waiting in this cold for some car time.

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I think you might be confusing two different issues: Plug nose projection into the combustion chamber, and presence/absence of ring washers.

The projection issue has to do with which spark plugs you choose. I like to use the NGK ZFR5N because its extended-nose construction moves the spark point away from quenchout areas and closer to the centre of the combustion chamber. Picture of the difference is here.

Presence/absence of ring washers: See here.
The '63-up heads have a redesigned counterbore at the top of the spark plug hole; the spark plug tube itself seals the plug, and if you use the washer it interferes with heat transfer from the plug to the head. The '60-'62 heads don't have the special counterbore and need to use the plug gaskets. This is factory info; following it has always produced best results for me. The idea is to prevent the plug from running too hot; following factory procedure and going without the ring washer means you can dial in just a tetch more timing 'cause your engine is just a tetch less prone to pinging, well, you're that much ahead.

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The orientation of the plugs electrode depends on the individual combustion chamber....

Some may like it towards the intake valve, others exhaust, others towards the north pole.....

My opinion on the slant 6 chamber is that the electrode should be in the top half of the chamber away from the piston (i.e. the opening is towards the piston). This goes with having the extended tip plugs putting the spark deeper in the chamber.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

A slite side question on this topic in regards to the NGK ZFR5N plug. I installed them and now I am noticing the spark knock rattle. Should the timing be retarded some with the use of these plugs? They look like a really hot plug also.

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67Cuda,FAST EZEFI,340cu,CR=10.25,RollerCam&Rocker (XR268HR,#20-810-9)(#1622-16)(EddyRPM#60779,#7576), (MSD6AL,#6425) A904, GearVendorsOD, 8 1/4,3.55:1, ClassicAir

The "5" is a colder plug, a ZFRN-4 is a hotter plug... I would check the timing and your mix...this happened when I installed the Autolite 985 in the '67 Beater Valiant, plugs were on the "too clean/lean" side, so I changed the jet and bumped the idle mix screw on the Holley 1920, until I got a nice light tan look on the plugs...I also adjusted the timing for a bit less initial (5 BTDC with a 1973 EI distributor), works OK for a '67...

-D.Idiot

This is something I have done regularly on my highest performance Jetskis. The concept is the same on any engine. I buy plugs by the box, put a pen mark on them and use the ones that line up. The ones that don't line up go in the rest of the fleet. It is not that hard to get them lined up with only two cylinders. Dyno tests by some of the top builders (real engineers) seem to show 1 - 2 % increase in peak power. It is a small increase and hard to verify but free. It also helps keep the plugs a little cleaner when idling or at low rpm. Keep in mind these engines rev higher than just about any slant and are fairly high strung, 46 cubic inches making well over 100 horsepower on 108 octane. They are indexed with the open gap toward the exhaust so the center electrode is shielded from the blast of fuel/air mixture coming in on the intake cycle. This is what helps keep the plugs cleaner, less raw, uncompressed fuel mixture hitting the insides of the electrodes. Or maybe the blast cools them less, I don't know. On a four stroke I have always heard to index the opening toward the exhaust. This shields the gap the same way from the intake charge and leaves the gap open to the mixture when it is time to fire. I have heard arguments that it should be open toward the intake to expose the mixture to the spark better, but we all know it is not firing on the intake stroke. The larger area of the chamber is also the intake side on a four stroke. I believe there is a small gain to be had. It is mostly something to do on a max effort setup, or a good trick to use in stock or limited types of racing where you can't do much else and every little detail counts. I have not bothered with my cars, too many other things to work on and they always run better with new plugs anyway. On the Jetskis, I noticed a slight improvement in throttle response which is directly related to handling, so worth it to me. On a six or eight it takes some time and a bunch of plugs or a set of index washers. It cannot hurt to do it with new plugs on race day, I would not bother for day to day.

I made a little tool to line up the plugs..........



I marked the top of the installed plug, took it out and screwed it in my tool.

I then made a mark on the tool that corresponded to the mark on the plug. Thus the mark on the tool would be where the top of the combustion chamber is for the various cylinders.

You then thread various plugs into the tool to see how the ground electrode lines up with the top of the chamber. You can use any scheme you want for alignment, but it's alot easier than threading the plug into the cylinder head to see what's going on...........

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

You are right Dan, I did misunderstand. I thought leaving the washer out was related to how far the tip extended into the chamber. Since I am dealing with a preignition problem here, can you recommend a plug tht is more resistant to spark knock? If I recall right, a cooler plug should be better, but the theory on things like that change with time. If leaving the washer off helps keep the plug cooler, maybe that is a good start.
Sam

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Sam, perhaps a bit late, but here is a link on indexing (with another trick):

http://fueleconomytips.com/2005/10/28/spark-plug-magic/

Mike

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Recognized by US Federal Courts as a Fuel Economy Expert!

This is a turbo charged engine? On my GN, as well as countless others, going from the stock 44 heat range AC plug to a 43 heat range made a huge difference. It's a tried and true part of setting up one of those cars. With those cars up to about 17 psi works well with the 43 heat range. Above that 42s. Sure the chambers are different, but the pre-ignition situation that this can help is caused by the plugs being too hot. If it does not help then something else is causing it. You would have to cross reference those numbers to run NGKs or something else. Likely they overlap two ranges when you switch manufacturers. I would try colder plugs first and see if they help and stay clean. I never had a problem with them staying clean. If you happen to ever swap to the peanut plug style head, the AC CR43ts would work well. The "C" is for commercial, it is a truck plug that has heavier electrodes than the normal R43ts. They hold up really well with a turbo and cost the same as the normal plugs. They come in a 42 as well but no 44s or hotter. They may make a commercial version that fits the old style head, but I don't have any references to check.

Thank you all. It is amazing how little things can add up. I can;t wait to get back to the car once the weather warms up. Have I mentioned the cold before? I have printed this thread, and put it in my book.
Sam

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