what are the best spark plugs for a MPFI KA24E?

[Arizona Hardbody92]

copper or platinum?

[NM50]

The OEM stock NGK is the best IMO.

[Arizona Hardbody92]

Is is worth it to index the plugs when installing?

[NM50]

Very much so on multi valve engines.Straight down works the best on 3 valve heads because of the overlaps scavenging effect.We never got better HP numbers off of it but pulled off better MPG.By the way factory plug wires are the best way to go.M SD is the only thing that even comes close.

[C-Kwik]

For the original question, it depends on the intended usage and which specific plug you use. Platinum has a higher melting point which allows it to resist wear in a spark plug application better than the typical metals used in spark plugs. Platinum does, however, have higher electrical resistance. But this is only part of the picture one needs to consider when choosing a plug.

For a given metal, the resistance between 2 electrodes is higher when the surface area of each electrode in the proximity of the spark is lower. Spark plug manufacturers typically use smaller center electrodes in platinum plugs which indeed reduce the electrical resistance across the plug.

Another nice effect that a smaller electrode provides is reduced quenching. Quenching occurs when the spark energy gets reabsorbed by the metal in the electrodes. With larger electrodes, there is more surface area available near the spark which can absorb heat from the spark. Smaller electrodes reduce this problem.

Considering all these factors, it can be seen how using a precious metal with a high melting point can result in a spark plug design that uses a narrow electrode(s) that can exhibit good wear characteristics.

Manufacturers have also been using iridium which has a much higher melting point than platinum, less resistance and higher strength and hardness to further reduce electrode sizes. Iridium plugs are not as available for a broad range of applications and heat ranges so they may not be a viable option for some. Most are also focused much more on high performance than increased wear resistance as well but will likely last as long as a conventional plug.

Lastly, you need to make sure to choose the right type of platinum or iridium plug if you go this route. For a distributor equipped vehicle, a single platinum iridium plug is alll that is required. For Distributorless ignitions, a double platinum or double iridium plug is recommended as the coil fires 2 sparks (one on the combustion stroke from the center electrode to the ground and the second on the exhaust stroke from the ground to the center electrode) and would wear the ground electrode well before the center electrode wears with a single platinum/iridium plug.

[Arizona Hardbody92]

What do you mean by straight down? Does the gap in plug go tward the intake or tward the exhaust?

[WWJD]

I think it mean tward the combustion chamber

[Arizona Hardbody92]

The plugs electrode is INSIDE the combustion chamber.

Also, check out this article on side-gapping:http://performanceunlimited.co....htmlwould that be a safe thing to do on a KA24E?
Modified by Arizona Hardbody92 at 2:38 PM 9/27/2007

[C-Kwik]

The 3-valve KA's have the plugs entering the combustion chamber at an angle (by contrast, the 4-valve KA has the plug vertically aligned with the combustion chamber). I think what he means here is to have the gap facing the piston, which is straight down from the plug.

[Arizona Hardbody92]

I indexed my plugs and I reccomend it to anyone when changing plugs! It does take more time to do so but I noticed the difference right away. The engine feels more responsive and has a smoother idle without so many 'hiccups' mpg's are better too! Thanks everyone for all your input!

[WWJD]

explane index

[C-Kwik]

explane index

Here is an exerpt from NGK's website:

Quote »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.[/quote]http://www.ngksparkplugs.com/t...n.asp