Plug indexing...am I aiming for the CCtop or the intake valve?

[crazypete]

Hey folks, I am indexing (and side gapping) a set of afr165 plugs with the heads off the car and I have been recieving some conflicting information on how to index them. Up till now, I've faced the strap torwards the top of the chamber so the flamefront can extend downward torwards the pistons.

Some posts say that I should face torwards the intake valve. This confused me since the valve should be shut already during ignition so there is no fuel flow through the valve at that point. Furthermore, the strap would create a shadow on the exhaust valve side. It didnt seem right

Which way would it be?

Thanks for your input

Pete

 

[Michael Yount]

Pete - I think the side gapping is more important than the indexing in a wedge type chamber. If your quench is right, I don't think it matters much where they point -- just try to have them all facing in a similar direction for consistency. I'd turn them so the open gap faces into the chamber.

 

[crazypete]

Excellent! I was aiming them "down" to begin with.

Every few percent efficiency helps.

 

[dirtysohc]

I've always aimed them in the down position as well.

 

[89notchfox]

to index a plug you are supposed to have all the plugs facing the exhaust valve. but as long as you have them all facing the same way you'll be alright, you just won't get a good clean burn, unless they are facing the exhaust valve.

 

[Michael Yount]

A "good clean burn" has a lot more to do with MANY other variables besides which way the plug is pointed. Given the importance of fuel economy and emissions compliance, if indexing the plugs helped significantly - the OEM's would do it. But they don't - because it's not gonna make that much difference. In tightly contested, strict rules class of racing where every 1/2 HP counts, you do every little thing you can to help -- indexing falls into that category. For us just dicking around trying to make things better -- you'll never notice the difference between indexed and not indexed.

In any event - give us the theory behind the necessity of having them 'pointed' at the exhaust valve.

 

[dirtysohc]

Pointing them towards the exhaust valve? I've never heard that one. The exhaust stroke comes after the power stroke so I'd have to disagree on that one. I've heard the theory of facing it towards the intake valve. I don't think in actuality you ever even notice very much HP gain. Many people do it for piston to plug interference when running very close tolerances.

 

[DMAN302]

For us just dicking around trying to make things better -- you'll never notice the difference between indexed and not indexed.

In any event - give us the theory behind the necessity of having them 'pointed' at the exhaust valve.

You just never hear the phrase "just dicking around" as often as you should....Sorry Mike just bored and lookin to stirr it up a bit.

 

[Michael Yount]

Used it just for you DMAN -- I was outside working on my raggedy-ass car. There's another one for you. Straight from about - oh - 1971. Don't ask how I know.

 

[Daggar]

Ahhh... there's nothing like a fine day working on a fine car topped by a fine post from a fine noob to bring out the verbal elegance.

 

[DMAN302]

It's days like this that I enjoy...sharing thoughts...making freinds...and yes even learning..even if just a little. What did I learn you ask? Well today I did learn if you use a lil old dash infront of the word ass then it will not be blocked by the language filter...oh happy day!!!-ass-ass-ass

 

[DMAN302]

ass... DAMN!! guess I've just learned you can type ass all by it'self, I feel shame and am embarrassed, I will go now.

 

[Daggar]

ass... DAMN!! guess I've just learned you can type ass all by it'self, I feel shame and am embarrassed, I will go now.

Well at least you've reinvented the wheel.... ass.

 

[DMAN302]

Thanks Daggar once again you've taken my failure/disapointment, turned it around, and left me feeling well....mediocre and only mildly sad.
Now for the Tech portion..the only thing I am willing to spend time indexing is the lable on my beer while I'm installing plugs, spend your time on bigger and better things..just my opinion.

 

[Michael Yount]

You can index your ass over the toilet....

 

[DMAN302]

I have used my "index" finger to point out funny things I have seen. I have also used the finger next to my index finger to gesture to others.....









ass ass ass.....don't know why I keep doing that but I better stop before Dagger puts up on of his scary.."THIS IS NOT TECH" things in big bold print.

 

[5spd GT]

I've always understood to point it to the exhaust valve. It allows for the spark to escape quicker or something like that so it is "pushed" right out the exhaust. I do believe consistency is important no matter which way you do it.

Now putting it towards the intake valve might not be a bad idea. No suction from the exhaust valve and not upward movement of air from the piston to disrupt the spark.

Since the compression takes place in a closed cylinder I don't think it matters so much on if the gap (pointer) is towards the piston. It sparks in the area and combust.

 

[crazypete]

I dont think we are trying to optimize exhuast efficiency here but rather combustion speed. I dont think aiming it torwards the exhuast valve is better than the random non indexed trim.

I wonder sometimes why the industry has not made deisel like high compression engines that inject and combust right away out of every car. Seems like the better way to do things.

 

[Michael Yount]

Audi just introduced direct injection gasoline efi in Europe - directly injects the fuel into the combustion chamber just before ignition. They've been working on it for years. The system runs at 3000 psig. MUCH more efficient - better emissions - better power and best of all - helps eliminate detonation. Nothing to detonate if the fuel's not there during compression!

Indexing was NEVER about aiming at a valve --- uh, the valves are closed during compression and power stroke -- they're just like any other part of the combustion chamber when they're shut. Indexing was about 1) positioning the plug in a way that the piston doesn't close the gap in engines that run VERY tight clearances and super high compression ratios (buddy's 16:1 big block Chevy will close the gaps if the plugs aren't indexed correctly, or 2) aiming the gap the same way in all 8 cylinders so the flame front/travel/combustion pattern is similar in all 8 cylinders. It's simply not a big deal no matter which way the gap is pointing unless you've got clearance issues.

Great if you want to play with it -- but probably won't accomplish anything at all except eating up some of your time.

 

[5spd GT]

Looking for more thoughts on this: bump