So this has been coming up more often lately, and as time wears on it will only get more common. In addition most of the threads end up repeating the same stuff, which unfortunatley never seems to get the point across to the orignal poster because they are usually looking for a step by step pictoral with pictures. So I though it was time for this,
as in general these threads anger me.
Swapping in a MKIV engine. (2.0 to 1.8t, 12v to 24v, 2.0 to tdi, 1.8t to 2.0, 2.8 to 3.2, etc, so forth and so on)
MKIV engine swaps come down to two basic things.
1. All of it is bolt in.
2. If you need to ask how, you probably aren't ready to do it. So without being too much of an ass, don't waste our time.
Lets start at the beginning. It doesn't matter what your donor car is and what your recipient is, any MKIV engine can be successfully swapped into an MKIV chassis car. Yes this includes TT's and New Beetles. From the very beginning VW's have been built like tinker toys, which is why so many people do engine swaps. Even though a specific engine may have never been available from the factory in a certain body style, platform sharing and the transition of subsytems and engines between generations and bodystyles means that in most cases a swap can be done, you just need to find the right interfacing parts that join the two disparate systems. This is why MKIV rear brakes can be bolted on a rabbit, why a 16v out of an A2 GTI or a crossflow out of a 1999 Jetta can be bolted into a rabbit, why a VR6 from a Passat can be bolted into an A2 with the help of a Corrado.
Now that I have elaborated on how easy it is in general to create hybrid VW's, let me tell you why the introduction of the MKIV made it so much more diffcult. For one, VW four cylinder engines since the early 70's had all been based off of a common design. Even though the A1's, A2's and A3's did not share motor mounts the motor mounts were not an integral part of the engine and transmission. Because of the common block design the way the mounts bolted to the engine/transmission did not really change, so in order to put a crossflow in Rabbit all you had to do was bolt the Rabbit's motor mounts to the bolt and toss it in a willing bunny. The same thing applied to transmissions. Since all vw 4 cylinder transmissions were interchangeable, you could use the orignal tranny or the newer one, you just needed the linkage from the original car. MkIV's went to a much different mounting system then previous generations, and this combined with several other factors including new engine management designs, crashworthiness and the like made it so you couldn't just bolt MKII mounts to a 1.8t and call it a day. The same thing applied to the mounts and linkages/interfaces for the hydraulic/cable shift transmissions. The GOOD thing is, since you are swapping from a MKIV to a MKIV, you don't have to worry about this at all!
You DO have to worry about the next big obstacle that presented itself with the advent of the MKIVs. Intelligent cars and whole-car integration. The MKIV was the first real "self aware" generation. Everything is integrated into the ecu, and while that makes it nice for troubleshooting, it makes it a bear if one thing isn't working right, or more importantly, missing altogether. The issues come down to two big things, drive by wire (electronic throttle) and the immobilizer. Now if the donor car and the recipient both have drive by wire you are good to go (this is the majority of MKIV's), but remember that all 2.0's into 2000+ were drive by cable, and as such will need the pedal cluster from the dnor car (or just the throttle pedal and it's potientiometer). Since the immobilizer is integrated into the instrument cluster on the car, and talks to the ecu, which is tied to the engine (this is a must have btw), you will have issues with the communicating if they are not coded to each other, which VW has made much more diffcult in recent years. I am not even sure you can get an SKC from the dealer at all anymore, and there are many better vag com people out there then me that can elaborate on compatibility between the different immobilizer versions and all that, but if you just get the cluster from the donor car, it won't even matter. Once you get the whole immobilizer/ecu thing worked out, it's pretty much plug and play.
This shift to eletrical integration has shifted the definition of a succeseful "swapper" from someone who can weld and use a hammer, to someone who has mastered the use of electronic tools like vag-com and in house VW information systems. AS stated, some of these are easier to get access to than others.
Any four cylinder MKIV transmission will bolt to any four cylinder MKIV engine (same goes for 6 cylinders) but you can not mix and match four and 6 cylinder trannies. If you choose to use your existing transmission, realize that the gear ratios will be off in terms of the engines powerband and in extreme cases (say a 1.8t with a tdi engine or vice versa), will be bad enough that it makes the car a pain to drive. If you use the tranmission from the donor car, eveything will be plug and play in terms of hydraulic and electrical connections. The exception being the shift linkage, as earlier cars used a different connection style for the shift cables. This is easily dealt with by just putting your existing shift level on the new tranny, or just getting an OEM "short" shifter from a TT in whatever year the recipient car is and bolting that to the new tranny.
Any MKIV suspension will work with any engine. It is NOT imperative that you switch to an aftermarket VR suspension if you swap from a 2.0 to a VR. The car will behave diffentley, but the weight difference is less than your fat girlfriend sitting next to you and you most likely notice her than you will notice the difference in the car.
2.0's and TDI's use the smaller 11.0" front brakes with the integrated carrier spindles. As such they don't work with the 1.8t and VR axles. You can either change to the bigger 11.3" (or 12.3") brake and spindle setup and run the vr/18t axles, or use your existing axles, but you will most likely have to use your existing transmission (or switch the drive shaft flanges on the transmission side). You also have the option of hybrid axles (basically this part is the least of your worries on a MKIV to MKIV swap).
You will need the donor engines wiring, the more you can get of the wiring harness the better. You shouldn't need to change any of the non engine related wiring (lights, hvac, brakes, spped signal, etc), MKIV fuseboxes are MKIV fuseboxes, but again, it's best to get as much of the donor wiring as possible.
You will need the intercooler and boost piping when swapping in a 1.8t, you will need the auxilary radiator and hoses/piping when going to a VR. You will need the downpipe/cat from whatever engine you are swapping too, and it's easiest to get a fully dressed engine will all accesories and pulleys intact. The subframes are the same, as are the actual engine mounts.
So it short, what you need is everything you can possible get from the donor car. The more you have, the easier and faster the swap will be, trust me, I've done two VW engine swaps and having it all if front of you makes it so much faster than piecemealing it and digging through junkyards every weekend. Now as I say this I know that most people, and especially most people who ask "what does it take to swap a 1.8t into my 2.0" are never ever ever going to do it this way, because doing it this way takes money. And for the most part, people here are cheap asses. You can do a swap without taking the "get everything" approach, but it takes intimate familarity with the MKIV chassis, both engines, and as stated earlier, electronics and integration. This adds complexity and time to the swap and troubleshooting an engine swap can easily turn into your worst nightmare. Abandoned projects litter the classifieds of every generation and if this happens to you, its rare you will ever recoup your expenses. You should also be familar with basic automotive repair and disaseembly. I'm not telling you how to get the engine out, because if you don't know how, or can't look at it (with help from Dr. Bentley and a few friends even) you shouldn't even be thinking about doing this yourself. Remember, the MKIV radiator support bolts on. Take it off.
Which brings me to another big thing, doing it yourself vs. having a shop doing it. The people who should be doing this themselves will probably laugh at this whole post. Basically, you know if you're one of the few. Let me make it clear that "a friend who has done a couple honda swaps and even a mustang swap" is not necessarily one of the few. As I stated, the older the car and engine is, the less issues you have to work around, and even though this friend may have some general mechanic and swap experience, a lack of a basic understanding of the difference between two engines and even the subsystems that they share that one could get just be browsing this forum could be a serious hinderance (take for instance the 2.0 vs. 1.8t front brake thing, common knowledge here, but not for Jimmy backyard swapper). Even worse, this people tend to often be overzealous and/or cut corners when working on unfamilar cars, which can lead to things much worse than the engine not starting (fried ecus, blown turbos, broken valves, cracked blcoks, the list goes on). I HIGHLY recommend that if you are going to take this on yourself or with a group of people that you set aside at least three weeks of not being able to use the car. You may finish in 48 hours, but if you are missing a necessary part, or you need to troubleshoot, and you are stuck in the military garage or under your not-car-work-friendly apartment buildings car-port, **** will hit the fan real quickly. It's also highly recommended that you have, or have constant access to another working (aforementioned fat girlfriend could work) vehicle for parts (and tool) runs. Any special tools necessary will become apparent when disassembling the recipient, so give yourself plenty of time and make sure you keep track of where everything goes, as it's pretty much all going back in the same place. Take pictures for yourself if you need to. Taking something apart is the best way to learn how it goes back together.
If you are not going to do it yourself, it kind of puts you in a binding situation. We are getting to the point where people saying " just buy the car with the engine you want in it" may not be so pertinent anymore, especially with the MKV's coming out. MKIV parts are getting cheaper, having moved past the "5 year" line. That being said, MKIV parts and paying someone for labor is not getting cheaper, so if you can't swing this yourself, it's probably wiser to buy the car you want instead of paying someone to make it for you. If you do pay someone to do it, get a dedicated VW shop, and you will be rewarded with a well running, quickly done, stock looking swap (and a lighter wallet).
Costs. No matter what you budget, you will go over it. 1.8t's and VRs are going for around 2+ grand fully dressed. There are deals, but the engines can be beat. Looking at http://www.car-part.com and finding a 1.8t to you for 1800 bucks does not mean this is going to happen to your for 2 grand. The price does not usually include the ecu, transmission, downpipe, any auxilary piping, and will sometimes not include a turbo, alternator or even manifolds. You will end up spending money on hardware, gaskets, seals, belts(no matter how new the engine is), tools, bandaids, and beer. Simply put, it's not that cheap. Any I saying it can't be done cheap? No, but again it's along the lines of you know it you're one of the ones, and it's not because you added up prices on a notepad when a friend crashed his VR jetta. Done in a garage, I would imagine that most MKIV-MKIV swaps will currently average close to 5 grand in expenses. Done by a shop it will certainly be more, especially if they supply the parts.
So to rehash the major things you need to work out
-Drive by wire (if drive by cable orignally)
-driveshafts (depends on tranny/spindle setup you decide to run)
In a perfect world what you would need
-A whole MKIV in a rear end accident
To make things as easy as possible
-Engine with all manifolds and accesories
-Turbos/Downpipes/Cats (even for N/A cars, minus the turbo of course)
-All wiring attached to the engine
-Radiator and fans
-External piping for turbo cars
-Heat exchangers/piping/ducting/hosing (intercooler/auz. radiator)
-Engine mounts, brackets and pans
Swapping in something else (4.2l V8, 2.7t, audi 2.8 V6, W8, W16 etc).
Just stop. You are making me want to slap you. Yes anything can be done with the right amount of money, but if you had 50+ grand to throw at a car you wouldn't be hanging out in a compact economy car forum. The biggest reason this swaps won't work is because of engine placement. The VW A4 (mkiv) platform is setup for transverse engines, all the "big" VW and audi engines are derived from audi, and as such they are setup for longitudinal mounting. Beyond requireing totally custom fabrication of mounts and brackets, the V8's and W8's will not physically fit in a MKIV engine bay longitudinally as intended, and that doesn't even begin to deal with where you would put the transmission, let alone what wheels it would drive. There are no tranmissions setup for these engines to run transversely, and while the engine would fit that way, the transmission would be hanging two feet beyond the side of your car.
That's my brain dump for now. It's alot. Hopefully it gives you a highlevel overview of what is needed (and why it's probably not for most people right now). Remember the truth is out there, specific questions have been asked, get used to the technical forums and the search and you can for the most part find what you need to know, just don't come in and say "how do I do this". If you make no effort yourself, not many people will make an effort for you. I know I said tdi's in the beginning and didn't talk about them much, but that is for some other day. Think no fuel tank, pump and lines on top of what was mentioned above (it can be done though).
I would encourage people who have actually swapped or who have researched this topic throughly to provide their experiences and add/subtract/crap on what I have wrote above. The more stuff the better.