Resizing rod big ends [also known as 'close & hone'] is a standard reconditioning procedure, & has been since the invention of the slipper big end bearing about 100 years ago.
It assures that the rod big end is perfectly round & at a true 90 degrees to the vertical centerline of the rod when in the state in which it will be used, that being, clamped up to the rated torque.

It is commonly done to rods where the bearing has spun in the rod & as long as the rod is otherwise undamaged, it is an economical way to restore a rod to service.
This procedure is sometimes used to ensure that all rods are exactly the same length, C to C, in a blueprinted race engine.

It is not some black art practiced by highly paid engine scientists in the deep recesses of a secret race engine laboratory belonging to some multi million dollar factory backed race team.

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Thats what I thought untill I tried to fit mine. They had to be carefully driven it. (I didn't have a press handy at the time) The old bolts were a free and easy finger tight slide in fit. (Actually they were free-er that I would have ideally liked) So It wasn't just that the rod bolt holes in my rods were tight.
The instructions that came with the bolts (albiet that they are most likley a generic instruction) said after fitting new bolts, the end of the rod would need to be resized.

ARP often use a lower torque value than stock because the thread is finer (which still means it can actualy have a higher clamp load)

Think of a con rod and how the big end cap bolts to the rod, the more clamping force you give it the more out of round the circle will become and thus you need to then resize the rod. What I said is the A-series rods are quite resiliant to going out of round when adding a little extra clamp load by using ARP (some rods can go way out of spec)

Dont know what stock torque specs are but ARP recomend useing the strech method, streching them to .0051 +/- .0002.

But It says if you dont hav a stretch guage to torque to 28ft lbs, then to loosen entirely, repeat then tighten for a third and final time also to 28ft lbs

You guys must please explain to me more about this re-sizing story. I would have thought you just torque and you are done.

Also, I don't understand how the ARP can increase clamping force in the con rod. On the VW site and I think somewhere on this site I read that the ARP bolts have a lower torque setting than standard rod bolts.

ARP A-series rod bolts do not need to be pushed in, they slide in with just finger force just like the stockers.

While resizing is the correct thing to do, I have never needed to resize an A-series rod after fitting ARP's when the ARP's are torqued to the correct settings, all of them have stayed perfectly in spec (unlike SR20 and RB's that can put the big end way out of round) Either way you need to measure as every motor is slightly different.

Because the ARP rod bolt exerts more clamping force on the rod, the shape of the big end hole min the rod may change. Also Factory A series bolts are a finger tight push in, where as the ARP need to be pressed in. The force of pressing them in can also alter the shape. it's not a huge expense to have an engine shop resize them for you. Having your rods resized is part of a sound performance engine build anyway.

Read any good performance engine book you will know about the modifications you can do to increase oiling, cooling, rpm, strength etc. As Jmac said the ARP Bolts will clamp more meaning clearances will be wrong... its simple, bolt the rod together, torque, and resize big end to spec, all do-able by a competent machinist. As for stretch well some bolts can stretch more than others so if you torque them all the same they might stretch differently so will not be equally as *tight*. Well thats my understanding on the matter, which I can't say i've completely got my head around yet, but im getting there.

Resizing rod ends, playing with different bearing clearances, balancing etc. all these checks and triple checks are steps towards building a motor that MAY give a horsepower/rpm increase, when your chasing a tenth of a second these things count.

I do not believe its worth spending the time or money on a streeter motor, all these things do add up but bottom line is it all worth it when for $50-$0 you can have another 2nd hand bottom end throw some rings and bearings at it and it might live for another couple years. If your building a motor worth chucking ARP products at then your not building a garden variety stocker for the missus to putt down to the shoe store with.

The bottom end I have been building has about 50 hours time spent on it and its not even close to being together, the whole inside of the block is smooth, decked, bored to 87mm, acid cleaned, rods have been resized and balanced, pistons balanced, crank linished and bearings have been selected, using two different sets of bearings both have the oiling hole and groove to reduce drag but will reduce life too. I spent 4 hours redrilling oiling holes in the rods and crank... rotating parts still have to be balanced as a whole. But most of this is just making sure it holds together, power is mostly in the head.

@jmac
Please tell us more about this as this is the first time I have read about this.

What's the reasoning behind this suggestion? Is it just to blueprint the bearing clearance to minumum spec? Or is there some problem with the original design of the A-series rods?