When you index a plug, does the electrode aim toward the exhaust valve or the intake valve ??? Thanks, any pictures?

I have never done it...but I would say the intake valve.

Save your time and energy it isn't worth the effort.

I agree, isn't worth the time and effort, unless your running a funny car or a top fueler.

Vince

i have run into some people who say it doesnt mean anything o go through the hassle of indexing your plugs , well on the dyno i have seen horsepower gains not much but two or three horses. so if you are looking for a good qualifying time or you just need that extra push it is there , wether or not you are that perticular or have nothing better to do it does make a differance.

I won't argue that in "some" cases it makes a "slight"difference. I bet those dynoed engines had dome pistone or pop ups. Am I right? With a flat top or a dish piston I doubt you will see any difference at all. One things for sure it doesn;t hurt to try it. You will not see or feel a difference from driving the car (IMO).

Royce

well actually the engines im talking about where flat top pistons.They where circle track motors. Ihave seen bigger gains on domed tight clearence piston to head engines as much as 5 or 6 horses. when your looking for the littlest edge hard work is required always . Its like the guys who use to argue that crasnkcase pressure doesnt rob horsepower now the top nascar teams run vacume pumps . i built a lot of restrictor plate engines where every horsepower counted , stuff like that gives you that edge .

I agree. On your typical street car or street/strip car you are not going to see any difference in performance. 99.9% of them are not running at maximum efficientcy and the time spent indexing plugs could be spent getting the carb spot on or the timing curve right, etc... Now for class racing where the competition is VERY tight then every little things makes a difference from oil weight to plug indexing, no arguement from me on that. I think you have to determine the type of car we are working with and the goals. I am not going to index the plugs on my wifes daily driver, but if I was running a TF dragster I might think about it.

I figured the gains would be larger for dome pistons, but I am shocked you saw that much difference with flat tops.

Royce

Now what was the question? Is it worth the time, or which way do the plugs face? Anyways I haven't tried it YET, however I have read an article on it somewhere and am interested in trying it. IF, I remember right, the article stated that they are pointed toward the center of the cylinder, and not towards either intake or the exhaust valves. But I may/probably am/could be wrong. I'm interested in the answer to the original question also.

"Generally speaking, the idea of indexing is to position the spark plug so that its gap is facing the center of the cylinder, angled slightly toward the exhaust valve—the most common arrangement. (Some engines work better with other gap locations.) This is important because, as the piston approaches TDC, the air/fuel charge is being compressed. The charge or "mixture" is being forced toward the area of the spark plug—and normally, the exhaust valve. The true speed of this force inside the combustion chamber is extremely fast. Some experts speculate that it surpasses supersonic speeds.

Because of this, the spark generated from the plug should be in a "position" to create the best possible flame front. Looking at a typical side-gap spark plug, you'll note that the electrode can actually block the flame process. On the other hand, if the electrode gap faces the on-rushing air/fuel charge, it stands a much better chance of igniting a flame front."

Does that answer the "original" question?

Royce

depending on the heads you have the plug will point whre ever it points in those particular heads.when you inex them you want open side of the plug to face the combustion chamber or where the explosion occurs to get the best bang.you can't change where the plugs point.not easily.

There is not a set "This is the Best" way to index a spark plug. Every engine is going to be a little different. Too many variables, combustion chamber shape, piston style, quench area, flame speed, swirl, etc. Normally you'll want to start out as stated with the open side of the plug towards the open area of the chamber. Then you'd experiment from there. Doubt you will see any "Seat of the Pants" feel, but you may be able to increase your burn rate which can help your fuel economy.

Yes and thank you very much.

Lots of good info so far,, some more thoughts...

Indexing plugs started as a way to keep the domes of pistons from smashing the ground strap off of the plug. Some engines will require you to do this or else, no more plug ends!!!!!

As far as power goes, It's like most everything else in hot-rodding it will depend on the combo if results are seen from indexing... I would start out with the opening facing the exhaust valve....

Keith

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K-Star Automotive
Performance Engines
The crash was easy: rehab is killing me-"John Force"

One more note we've also "indexed" plugs to control their depth. This has been done on some higher end race engines per cylinder to change the burn rate to compensate for richer or leaner cylinders.