I don't know for sure, and am happy to be corrected, but its my understanding that APR and Revo deliver the same map on any car? i.e. due to component tolerances in e.g. turbo performance, HPFP, fuel(RON) etc etc one car will make different hp/lbft figures to the next as the tune is based on a car with all these components performing at an average efficiency.
On the other hand, R-Tech seemingly fettle the map they give based on the performance differences of the various components on you car, specifically. So if you have a better or worse performing components due to tolerancing or wear and tear, all of this is taken into account to deliver the best safe power for your specific hardware. This is what I believe is taken to be the meaning of "custom" in this context. If you take a look at R-Tech's facebook they post numerous results for the cars they tune, explaining why that car has performed better or worse than others in terms of the hardware limitations, issues or exceeding expectations. And the differences, even at stage 1, can be fairly significant.
I will point out I'm on R-Tech stage 1 and have never had any experience with a franchised map such as APR or Revo, so don't know if the tuner which applies one of these tunes to you car will make similar considerations and adjustments.
APR and Revo do the same hardware specific tweaking, hence listing requirements such as downpipes, intakes, HPFPs and intercoolers before going Stage 2 and 2+ etc. They have done the dyno development and road testing (in different climates) behind the scenes. The general rule of thumb there is, providing the engine is healthy (good compression) and the turbo and hardware are decent, then you will make the claimed numbers. Simples. All too often, somebody applies a flash to a knackered engine and they immediately blame the vendor.......go 'custom'....cram more boost in to make up for deficiencies elsewhere, and job done.
I think people forget the ECU self adjusts, aka adapts, whether remapped or not. Therefore compensation for wear and atmospheric conditions is automatic. Components tend to work, or not work, so the tuning window for 'wear' is tiny.....unless the engine has bugger all compression left, or the turbo thrust bearings are shot and the blades are rubbing the housings.......then all the tuning in the world isn't going to help that. Overall tolerances from one engine to another running the same hardware is tiny, +/-5% if that. The days of blue printing are over, such is the manufacturing quality these days.
You can make XXX torque on the dyno on that day, but get it on the open road where the engine load varies considerably, as does ambient temp and barometric pressure, you may find the torque reduces or increases.....and then of course we have optimistic dynos, which is a different topic!
As I say, VW have already done 90% of the core mapping. Tuners modify what's already there. I don't class that as a 'one off' custom job unique to that car since all GTIs have the same ECU, same engine, same software and the same hardware in 95% of cases because everyone follows blindly what tuners tell them to in that respect. There is nothing custom about it, imo. It's just like an old radio with a fine tune knob.
Now, if you turned up with a 4" MAF housing, different compression ratio pistons, ported head and bigger cams, bigger throttle body, GT3071R turbo with aftermarket boost control solenoid, different intake manifold, a tubular manifold and a straight thru exhaust........ getting that to run is almost a ground up, start from the beginning approach with completely redone VE tables. THAT is custom, imo
Only a few VAG tuners in the country can cope with that level of hardware change, and the main one is barely known in TFSI circles.
Revo and APR are popular for good reason. They just work and drive superbly well.....consistently well......and certainly in the case of APR, very competitive numbers too. 'Custom' maps can often be patchy, usually on throttle tip in, and need re-tweaks after the dyno session. If they work for you, then great, but I feel a lot of people only go that way because of pub numbers being thrown around on the TFSI group and some kind of misplaced snobbery about 'generic' maps. Every single GTI left the factory with the same 'generic' map
The problem is, no one has the time, the inclination, or the money to try every map on the market......and try each one for a minimum of a year to really scrutinize seasonal behavior, traffic behavior, performance, economy (if anyone cares about that) and reliability. Personally, I'm not the sort of person to buy one thing and think "Yep, this is the best there is, job done". I like to explore the market and really understand what it is I'm buying. I've had several different generic and custom tunes over the years, and each has it's place. One isn't categorically better than the other but even a basic understanding of mapping goes a long way to helping cut through the sales bullsh*t
