Piston Rule

I just noticed this in the box stock rules and was wondering...

"Arrow on top of piston must be pointed toward valves/lifters."

What would be the reason for this? Can there be an advantage to rotating the piston in another direction?
No advantage, its just there to make sure everyone is doing the same thing, as some of the motors came with the piston arrow facing the other direction. I had one early this season that was like that.
A piston with the pin significantly offset as it was in some automotive engines to reduce piston / cylinder wall wear, would in some cases show an advantage when the piston was installed in reverse. These pistons have such minor pin offset and short stroke' there in my experience and testing is no advantage to reversing the piston. There is nothing wrong with having the rule as stated, it prevents the snake oil salesman from selling you another one of his secret engine enhancements. Conversations go like this "yea which way is your piston in" Dunno "let me do your engine I will get you to the front"
i have to agree with kart43....just so much whooey that people are trying to sell to the unsuspecting..... I think the rule is more for consistency than for a performance advantage.... if all the pistons are aligned the same way (with the arrows) then folks aren't tempted to monkey with things....
To satisfy your curiosity before you install the rod onto your piston place the pin in it and with calipers measure from the pin to the face of the piston on both sides to see if or how much off set your piston has.
Not sure which 'nail' you're referring to, Don. The offset to reduce wear, yes. Preventing someone selling 'snake oil', not a chance.

From a DIY'er, the rule will cost them more if they want to take advantage of any performance benefit (they'll need to buy several pistons to find the one with a pin offset that's most advantageous). Since it seems most will claim there is no benefit, then why have the rule? Is it so 'everyone is doing the same thing'? Again, if there's no benefit then why should we all do it the same? Should we all have the pull start at the same angle? How bout only a 10 degree motor mount can be used?

I'd prefer measurements than have a rule that something can only be installed one direction 'just cuz'. The rule just seems silly.
I kinda agree with Mike here. Whereas I have never flipped the piston and tested anything, a rule "just to make sure everyone is doing the same thing" can't necessarily be accurate. If there was no benefit, then it wouldn't be a rule. If that was the case, next thing you'll see would be a rule stating that we all have to just use the round walbro fuel pump, just so we are all doing the same thing.
I remember as a kid standing in line with my Father behind 2 or 3 other shoppers at the Safeway grocery store. I asked, "Why are we standing in line?". My dad quickly responded 'Its what people do, simple as that' (not exact quote, but close enough)... I looked at the other open register... still wondering why we were standing in line when there's no line at the other register... we were, after all, following the 'stand in line; wait your turn' rule...

Its not about following or simplicity. We must always ask and, at least, try to understand why.

Perhaps its a safety issue... but I hope it doesn't go there...
What if I tell you that there is not a performance advantage to using the exhaust retainor and the valve rotator on the intake side. Should the rules be written to allow that modification? There is no advantage to using a catch can on a BSP engine and they should not be putting any oil out, should they do away with them also. It is a simple rule to keep the engine in stock form, what would be a reason to change it?
It is a simple rule to keep the engine in stock form

So when we get these motors from a retailer that purchased them from a distributor that got them directly from China, and the Chinese factory put the piston in upside down, would this not be considered "stock", as this is the way it came from the factory? How about those that hone (or even bore) out the carb to exact specs allowed by AKRA or WKA? This is not how the motor came "stock", so why allow any grinding of the part at all? How about the DIYer that buys a clone in box, doesn't know anything about motors other than taking a side cover off and adding a cam? He/she may not pull the head, therefore a factory "stock" error could cost him/her something in tech.

I am not trying to start controversy, honest, as I don't know enough about this stuff to do so, just saying that a rule without a defined reason other than "making sure everyone does the same thing" is a silly rule, especially since we all know that everyone does not indeed do the same things to get their motors race ready.

Listen, I am not saying that I am against any of that, and that I haven't purchased any blueprinted parts, but the term "stock form" is supposed to mean untouched.
If you have got the ability to install a camshaft, we know you have had the valve cover off, lets take 4 more bolts out and lap the factory valves and check the piston. Otherwise you paid somebody. If the piston is installed incorrectly which is the exception it is a mistake not as intended, no it would not be considered stock. The boring and honing has a spec, the same as the installation of the piston is a spec. The removal of material does contravene the rules but not provable unless out of spec.

It is not a controversy it is a specified racing standard, of which a reason should not have to be stated. The controversy only starts when changes are demanded. There is no reason to change this rule, doing so just muddies the "spirit and intent".
Since day one it has been the driver that is responsible for legality, you cannot blame a distributor, retailer or builder, even when the driver is seven years old. Someone in the chain has to assure legality, and sometimes mistakes are made, we learn from them.
I am not blaming anyone, I'm merely stating that the "because I said so" reason works well with my 6 year old daughter to teach her right from wrong, but most of us adults like hard facts of "why". Why not regulate valve lash, or prevent lapping of valves since it does actually change the make up of the valve and head ever so slightly? Both of those activities provide performance gains.

In reference to boring a carb, you state, "The removal of material does contravene the rules but not provable unless out of spec". To me, this statement endorses the breaking of rules as long as it cannot be proven that you did so.

I guess your "why" is because it is not the intended stock of the motor. And to many that is a valid and acceptable answer. I just find it interesting that it is specifically forbidden in the rulebook yet does not enhance performance and/or have safety concerns. Exhaust retainers and catch cans have specific reasons from a safety perspective even if there is no performance gain.

I, myself, know how to and take all my motors apart before I build them and all my motors have the arrow on the piston pointing in the direction it is supposed to. But I was not always as savvy as I am now, even if that is still amateur compared to the pro-builders and those with 20 years under their belt.

Please allow me to complete this post by simply saying that this is healthy debate. I am in no way accusing nor attacking anyone of their interpretations of "Box Stock". I ask for help from all you good people way too often on this site to voluntarily try and tick any of you off. Thanks for letting me rant.
A computer forum should not tick anybody off, if it does don't participate, it is that easy. I have rewritten many rules for many types of organizations, you must be specific and resolute. It is difficult to please all involved, make the rule stand and all will follow. Your 6 year old will be 16 before you know it and who knows what will be acceptable to her 10 years from now, you know what you wiil accept.