Submitted with thanks by Nosmonkey.

Hey guys, I’ve been gathering info on 16VT’s for a while now so thought I’d do a quick write up on some of the stuff I’ve picked up from the internet over the past few months.  It’s not a guide on how to carry things out, more of just a guide of what can be done for anyone looking to do this conversion.  The VW 16V engine is knocking on for it’s 30 birthday soon, but it is still a fabulous engine to work with and it’s interchangability with parts from different models has given it quite a following with silly power being extracted from them even today (1000hp 1.8 16VT anyone?)

Bottom end

There are a few different variants of the 16V engine, each with different specs so there are quite a few ways to go about turbo’ing your 16v.
You have;
-          Tall block (236mm) 2.0 16V (ABF), as found in Mk3 GTi 16V’s. 159mm long conrods, with 60-2 trigger wheels on the crank
-          Standard height block (220mm) 1.8 16V (KR/PL) and 2.0 16V (6A/9A)
Standard internals can handle a fair bit, conrods will be the first to go unless you get detonation, in which case pistons will probably melt due to being cast. As standard 16v’s have a relatively high CR (around 10-11:1) so you would only be able to get away with about 5psi of boost at the most (~40bhp increase in power). In order to drop the CR there are a few methods to go, each obviously with their own benefits, drawbacks and costs.
-          Stacked gaskets and stock internals, not really the best way to go but certainly the cheapest! Stacking 2 gaskets will drop the CR by around 1.
-          For KR/PL engines (81mm bore), installing 81mm 3B/AAN/ABY/ADU/RR pistons (from the Audi S2), dished surface will drop the CR to around 9:1. Pistons are also forged and can take a fair bit of abuse before failure. RS2 conrods will also fit in.
-          2.0 8V pistons (engine codes 2E,ABA,ABT,AGG) will drop into ABF’s and can drop the CR down to around 8:1 or so due to having a large dished surface. Valve clearance may be required. Another option would be to use 6A/9A pistons in an ABF. 9A’s utilise 20mm Gudgeon pins as opposed to ABF’s which use 21mm pins so bushings will need to be fabricated. This method will produce a CR of about 9:1 and will yield a good squish compared with the 8V method.
-          Finally, you could go for forged rods and pistons from the likes of Wössner. Blocks can be bored up to 85mm if in good condition but for forced induction anything more than 84mm may cause problems.

Some things to note
ABF/9A/6A oil pumps flow better than the KR/PL items, so it is advisable to replace the 1.8 units with one from a 2.0.
Only the ABF engines have trigger wheels! If you require trigger wheels for your ignition system on another engine than the set up will have to be fabricated.

Top end

Any head is suitable for this conversion, 2.0’s had smaller ports whilst the 1.8’s had big port heads. Valvers respond well to porting and polishing so it is recommendable to do so.  High lift cams and vernier pulleys to change the powerband to suit your needs is a good idea.
 No point fitting very aggressive cams which only come on around 5000rpm if your looking to have a motorway cruiser, and vice versa mild cams on a trackday beast will be wasted.

Couple of things to consider if you’re rebuilding the heads.
-          Lightweight followers can be had from most new VAG cars. Look for part no. 050 109 309H (previously  050 109 309J). A full set of new genuine cam followers will set you back around £100, and are about 10g lighter each then the standard items. 10gx16 = 160g less valve train weight, pretty useful when you consider that the 16v’s loved to be revved.
-          Stiffer/double valve springs are a good idea when building a turbo engine. They’ll allow your engine to rev higher with less chance of snapping something vital in the top end or letting your valves float about. Available from your favourite VAG tuner, most kits seem to be going for around £100 from ‘Murica, double that if you want some Schricks ones!
-          ABF valve guides are 3mm shorter than KR/PL ones. Less metal taking up room = less restriction = MOAR POWAH!
-          Lightweight valve spring retainers, again these will save a fair bit of weight in your valvetrain and let your engine rev a bit easier. They aren’t cheap, a set of Schrick’s will set you back around £250 odd

Fitting the two together

Standard VW gaskets can be used if the bore diameter is less than 83mm ( 050 103 383A). ARP head studs can be used in conjunction with this, torqued to around 80lb/ft. (ARP-204-4205/ARP-204-4702). ARP bolts for the conrods are another good idea. Torque them to 35ft/lb, ARP-154-6002 are the ones you want. For both the studs and bolts, use some ARP lube (no, your bottle of  durex play won’t work for this!)

Inlet Manifold

For sucking in your nice, pressurised air from your big shiny intercooler (You are using an intercooler, right?), you could simply use your existing manifold from your KR/PL K-jet  system and use an EFi fuel rail.
If you’ve got an ABF manifold, you can swap out your existing 225cc injectors for some 279cc ones from a Nissan Primera (0 280 155 607 / 0 280 155 611) if you’re on a budget and not looking to run much boost, more on injectors later. A cut down Audi S2 manifold with a 1.8T fuel rail can also be used.
If you’re wanting something more special, a custom inlet manifold could be made, 1.8T fuel rail can be fitted up. If you’re using the stock flange, G60 injector seats will be to be swapped in (037 133 555A).

Exhaust Manifold

To get rid of all your nasty gases and make your turbo go BWAAAAAH (and actually have somewhere to fit it) , you’re gonna need a new manifold. Same as the inlet really, you can either adapt your existing ones, make one fit by butchering it or make up a special tubular jobby.
So you could just cut off the flange from your original flange and weld on a turbo flange, but this will place your turbo lower than a smackheads morals.
As with the inlet, an Audi S2 manifold can be cut down to fit, or a 20VT with an adaptor plate.
You can also go with a custom tubular jobbie, as well as going for some off the shelf 16V turbo manifolds (not entirely sure on what to go for, I’m sure that somebody will add their 2p into this thread as to what to get)

Turbo

Obviously everyone will have their own opinion as to what to run on a 16VT. There are a lot of choices to go through, and as I said earlier, it is paramount you choose a turbo that will be matched not only to the engine, but what you will be asking of the car and how it will be driven. Flow rates, CFM etc. will all play a part but in general look for something suitable for a 2.0 16V that will be revving relatively high. A good overall starting point would be a .48AR Garrett T3/4. Ideal for low end response with decent top end as well. Next up would be something like a 50 trim hybrid .63.
Don’t be afraid to ask around and see what would be best suited for you.

If you’re going with a second hand unit, it’s best to actually physically see and hold the turbo. Side to side play in a brass bushing turbo is not the end of the world as they rely on a cushion of oil between the shaft and bushings to keep it lubricated which take up most of the play, but do check that the turbine and compressor blades haven’t been hitting the housings. In and out play on a turbo is not a good sign and a good indication that something is amiss in the turbo. Rebuild kits can be had for around £70 on eBay for a half decent kit. Rebuilding a turbo is not that big of a job (Despite what some may tell you), but it is vital that any parts which have been lightened as a set go back in the same position that they were in before. A T3 CHRA is easy to rebuild for anyone with basic mechanical knowledge, three circlips hold the two bushings, take the two out either side, out pop the bushings, take the third circlip in the middle out and refit new parts using a touch of engine oil / assembly lube.

Ignition

Not really much to say here, with a turbo’d car you’ll be wanting to run colder plugs. NGK 7’s gapped to .7/.8mm will be fine for most applications, you might want to go up to NGK8’s for higher boost. Might as well get some new HT leads as standard ones might be deteriorated, Magnecors and the like are always a safe bet, remember, buy cheap and buy twice!

Fuelling

Ok, so we all know that more air equals a need for more fuel, if you don’t add that into the engine, things will get lean and you’ll end up detonating. So some big(ger) injectors are gonna be needed. 300cc/min will do but if you can get your hands on something around 400cc/min or preferably even higher it’ll give you a bit of room for more boost (which after a few months of driving the car, you WILL be wanting!). To manage all this you can go the mega squirt/omex/emerald route, or just use a G60 ECU and loom to control it all. Standard pumps in good nick are good for 250bhp, An inline Bosch or a Walbro is needed for anything more than that.

Cooling

Right, so as some of you may know, the cooler air is, the denser it is. Denser air means more oxygen, more oxygen getting into our engine means…yep….more power! That’s why people run CAI’s and inter/chargecoolers. A decent sized front mounted intercooler (FMIC) will help cool all that hot air coming from your turbo before it enters your engine. Besides cooling air, your oil will also be getting hotter than a standard 16v, not just because all that extra stuff happening in the engine, but also don’t forget that your turbo NEEDS oil. If it doesn’t get oil, in a few seconds in will die. Not “might die”, it WILL die.  An oil cooler is a good idea. One from the likes of Mocal or Setrab will do your engine a world of good. If your turbo is watercooled (which most these days are), a good alloy radiator and high flow fans are also going to be playing a big part in helping to keep your engine cool.

Extras

Now say you’ve built up your dream spec 16VT, you obviously don’t want it to go bang! Having gauges and dials is vital to ensuring that your engine is operating as intended, as a start I would have Oil temperature/pressure, Water temperature, Boost pressure and Air/fuel ratio. Most people I’ve seen only fit boost gauges to their car, it is rare I go and see someone with a fuel pressure or AFR gauge on the dash. It is just as important, if not more, to see your car is getting the fuelling that it needs. Having an AFR kit installed will aid you greatly in making sure your car is running as it should, and enables you to tune your car without worrying about leaning your engine to the point of death. Make sure you get a WIDEBAND lambda kit. I have an Innovate MTX kit installed in my RS Turbo, and for only £150 it provides you with a great piece of mind!
What I’m saying now should also be pretty obvious to anyone with the slightest bit of sense. SERVICE THE ENGINE WHILST YOU ARE BUILDING IT!! Unless you’ve had the engine since it was new, you’re unlikely to know the full history of it. Replacing water and oil pumps, timing belts, filters and the like while the engine is on the bench is a lot easier to do then fitting everything and then realising that there is a bunch of parts to replace. Frequent oil changes using good quality oil is needed, without it your engine will suffer and parts will fail. Oil choices, again, depend on owner preferences, but personally I think you can’t go wrong with 10w/40 Castrol Magnatec semi-synthetic as a start point, although many swear by Syntha silver (I’ve never tried this so I’m in no place to advise for or against it). Depending on mileage and condition, it might be wise to change engine bearings while you’re at it too.Also you will note that I have not included anything about gearboxes/clutches/drivetrain in this guide. Whilst I won’t go into great detail, it should be said that with great power comes great wheelspin, an LSD is a good way to get more power down onto the road, and make sure that your braking system is capable of stopping your car. A1/A2 chassis golfs and their variants have pretty bad brakes, so you’ll be wanting something upgraded! Wider wheels and decent tyres are also a good idea.

Now this is by no means a gospel to all things 16vt, merely a reference for people who are looking to carry out this conversion,  if anyone has any other ideas or what I’ve written is wrong, please post in the thread so I can add/amend anything.

And remember this

Intercoolers

First off, what is an intercooler?
A pretty easy question but one that some members might not know. An intercooler (or aftercooler if you're old ) is essentially an air radiator that is designed to cool the compressed air from the turbo or supercharger fitted to your vehicle. There are a variety of methods to cool the charge air down but the principles are the same. Hot air goes in one pipe, it enters multiple cores which have finned heat sinks between them to increase surface area and thus to increase heat dissipation and cold air comes out of another pipe. This colder air is denser and richer in oxygen then the hot air, and by the laws of internal combustion, the more air you add the more fuel you can add, the greater the combustion of the mixture is and the more power you get! Colder air also decreases the chance of pre-ignition and damaging the engine internals (as does higher octane fuel), allowing you to run greater ignition advance and boost pressure!
Single or twin pass?
Many aftermarket companies make intercoolers that are both single pass and twin pass. Single pass intercoolers, as the name suggests, lets the air pass through it once. Air flows through one end, is cooled via the cores, and then has an exit for the cold air on the opposite side. Most factory fitted intercoolers are single pass
A twin pass intercooler lets the charge air flow through the intercooler twice. Both inlet and outlet pipes are located on the same side, cooling down the charge air twice.
However, it must be considered that with an intercooler there is a trade-off between cooling ability and pressure drop. With a twin pass intercooler, the air has to essentially travel twice the distance than the air in a single pass intercooler. Whilst this results in lower ACTs, there will be a noticeable pressure drop (around 1-2psi) so boost pressure will have to be raised. If your car has a fairly small or standard turbo running low boost a single pass intercooler would be ideal due to the fact that there is a lot less air to cool than a larger turbo. If you're running a large turbo with some pretty big boost a twin pass would be far more efficient, with the pressure drop offset by the increased cooling.
What is a charge cooler?
A charge cooler is the opposite of a radiator. It is basically a water jacketed intercooler. A charge cooler is far more efficient than an intercooler of an equivalent size as water has a thermal conductivity about 3 times that of air and can further lower Air Charge Temperatures. The drawback of this system is that obviously it is far more complex and heavier that a standard intercooler as components such as pipes, lines radiator and a water tank must be installed in the vehicle.
Installing in the vehicle
Most aftermarket intercoolers I've seen (especially in the mk4 golf scene) is just a standard eBay job stuck behind the front bumper. Whilst this might look cool, half the time 40% of the cores and fins of the intercooler are blocked by the bumper or other parts, with little consideration given (if any) to the reduced airflow to the radiator. A front mount intercooler can rapidly raise engine temperatures if you have a defective radiator or cooling system everything can get pretty toasty! When fitting a front mount, ensure that as much intercooler core is exposed to the outside air (drilling holes in bumpers is a common solution or cold air feeds from foglight holes). A slimmer, high flow fan may be required to pull more air into the radiator. Lower temperature thermostats and fan switches are also a good idea!
Anyone with any more info please feel free to add/correct this post, will add some more info later on!
Cheers,

Ahmet