AUJ

So, Audi stayed with the claimed superior HP-2s until what model year 4.2 top of the line A6? Can I get them on a 2012?


Could be a lot of things; conjecture does not grade anywhere in the evidence base, though. Best not to assume and to do the math to support one's claims. Ability to apply clamping force is definitive in comparing calipers as to the OP's question. Whichever caliper produces more via the measurement of sum of piston surface area is the winner on white paper. Everything else is unverified speculation. Nothing wrong with a logical discourse.

isleblue65

I could not find any instances on the internet where people were swapping ATE for HP2 and providing any real evidence of performance gains, etc. All speculation.

I can measure the HP2 pistons now and my ATE pistons when I have them out next, but it sounds like piston diameter is not necessarily the decide-all factor.

As I mentioned, I don't mind doing the swap while I'm in there doing other stuff (like my inner and outer CV Boots in the next few weekends), but I won't waste my time for no improvement.

AUJ

Actually, it is sum of piston(s)surface area per caliper and the equation is A = Pi times r squared. You are correct that clamping force potential is not the decide all factor. However, what is verifiable on white paper may be enough inspiration to do the work for the swap, or not.

AUJ

Perhaps. For ***** and giggles, can anyone name the vehicle Audi replaced HP-2s with ATE's for production?

Just Me

that's the equation for clamping force, given identical other factors (rigidity, applied hydraulic force...).

Point is, its not terribly important in terms of improving a real world car's stopping power. Brake pad material and tires are vastly more important, because they are limiting factors - it depends when.

There's probably no car in production at any price that cannot lock its wheels - abs aside, and until such time as repeated use overheats something. Which is why brake pad material is really a much more important issue if you are in fact experiencing fade.

Just because we *can* calculate it does not mean its actually significant to practical issues. You must find the weak links and address them. I seriously doubt clamping force is one.

I'm not saying its wrong. I'm simply pointing out that in the overall system it doesn't really matter.

G

mithrilG60

I said model run, in this context that means C5. It's a simple fact that the C5 4.2L and S6 used the HP-2a through out their entire production run. So did the D2 A8. I also never made any claim as to whether the 2 piston caliper is superior to the single piston calipers or not. I merely said they probably discontinued them on the C5 2.7T because the model that specific A6 shared the part from (ie the B5 S4) was itself discontinued. Ultimately I neither know, nor really care, why Audi chose to use a different caliper on the facelift 2.7T. Quite frankly it's just not important enough.

God I love people who feel the need to wave their ePenis' around and try to prove how smart they can sound

AUJ

I love how people who argue on speculation resort to insults when their method of argument is proven inadequate. At least my ePenis is functional and solid. Sorry about the limp basis of your argument, but it is all on you.

Perhaps Audi used the HP-2s that were left over for production on the precise volume models because they had just enough left overs for those manufactured planned units. The 2002 Audi's have 2 button and 3 button remotes without discretion. Audi always uses its leftovers in the name of German efficiency.

See, that is speculation based on fact. My speculation is bigger than yours.

AUJ

The Audi production calipers pictured above were manufactured by ATE and replaced by engineer's discretion at Quattro Gmbh because the HP-2s on the B5 S4 was deemed inadequate for the higher performance of the B5 RS4; since there were no takers on the picture challenge.

Audi passed on HP-2s, but used all the leftovers on end run units of the C5 line. B6 came out before C6. My point is that everything in this thread is speculation and opinion and that the only truly measurable difference between the calipers in question is clamping force potential. If HP-2s have more clamping force, it may be worthwhile to do the work. The only variables that matter are those supported by logic. No ePenis needed when facts are adhered to. Personally, I have no horse in this race. Pun intended.