Considerations
The 1.8T engines are known for their reliability and tuning capabilities, however certain considerations need to be made when aiming for power over a certain level. While no internal engine work usually needs done when going down to the typical Stage 1/Stage 2 route with bolt on mods, this isn’t the case with upgraded turbos.
Generally speaking, the initial common weak point in these engines is the connecting rods. Regardless of what model/year your MK1 TT is, you will want to upgrade the rods if you are aiming for power at over 300ft/lbs torque.
Of course this doesn’t mean to say that the second your car goes to 301ft/lbs, your engine is going to blow up. This is just the generally accepted safe threshold within the 1.8T community. It’s also worth noting that there has been many cases of these engines bending rods before 300ft/lbs too. A lot of it comes down to the power delivery of the torque. Sudden boost spikes and lots of torque low down is what bends the rods the most. A good tuner should be able to work around this.
Supporting Mods
It should come as no surprise that when you upgrade your turbo to run higher power levels, then you will also need to upgrade other components of your TT. This isn’t necessarily wear and tear components like the brakes and the clutch. Instead, these are components that may limit your power potential or fail under the new increased power output. In some cases this can be catastrophic to your engine so you need to ensure you have the supporting mods planned out before diving head first into a turbo upgrade.
The supporting mods required will depend on how much power output you are looking for and the type of turbo you are upgrading to. The requirements for 300bhp will be different to that of a TT running 500+bhp.
Lets start with the basic upgrades that will be required regardless of what type of turbo you go for.
- Front Mount Intercooler (FMIC)
- Free flowing air intake and turbo intake pipe (ideally 3 inch)
- Free flowing exhaust with a 3 inch downpipe and sports cats/decat and cat-back
- Bespoke remap (this should be done after all the physical mods have been put in place)
This is the very minimum and won’t reliably see you over 290-300bhp.
As touched on at the start of this article, the rods are a weaker point of these engines when it comes to tuning for high power. If you are going for a hybrid turbo/big turbo then it is imperative that internal engine upgrades are done. The last thing you want is your engine going kaput and throwing a rod after all the work and money that goes into a turbo upgrade.
For over 300bhp + /300ft/lbs torque, then you will need to do further upgrades to the internals.
- Forged connecting rods for durability (stock ones are prone to bending)
- Exhaust valves (can become an issue when you get into the mid 300’s bhp)
If you are going big turbo and looking at power levels over 400bhp then you are likely going to need to further engine internal upgrading to ensure the block and the components can reliably handle it. Budget for cams, pistons, head studs and more.
As you increase the power, you will also need to upgrade the fuelling system on your TT to cope with the demand. Bigger injectors, an uprated fuel pump and 4 bar fuel pressure regulator is recommended.
In terms of air flow, you want your engine to be as free flowing as possible in both the intake side and exhaust side. A free flowing intake manifold can be beneficial at higher power levels. The same can be said with a free flowing exhaust manifold and downpipe to relieve any back pressure on the turbo. Porting the head is another recommended mod, but this should only be done by a professional.
Hybrid/Small Frame Turbo
Hybrid turbos utilise the standard turbo and upgrade/enhance it by strengthening the internals and upgrading the components for a larger reliable power output. There are various companies that sell hybrid K03 and K04 turbochargers for the TT MK1. If you are looking for a fair amount of power, you are best looking at a K04 hybrid variant which produce more power than the K03’s.
One of the best options you can go for is the AET K04-380 that Badger5 sells. This comes as a kit with a larger turbo intake pipe and actuator. You can check it out here for more information.
This turbo has been proven to make 418bhp on a dyno which is extremely impressive for a hybrid K04.
For this, upgraded internals is a must as the hybrid turbos increase the torque down low which is known for bending rods. In addition to the forged internals, you will also need other mods to support additional airflow, fuel and a bespoke remap to bring it all together. Ensure you go with a mapper who knows the 1.8T engines well. If you are UK based, Badger 5 are often the number 1 choice due to the high reputation and knowledge they have when it comes to these cars and engines.
Large Frame Turbos
If you are looking for a bigger step up than a hybrid turbo, then you are going to want to look at a large frame turbo like a Garrett. These turbos can produce higher power than the hybrids can, but tend to be more expensive and require additional mods and support work.
A common mod is the “stroker motor” when going for big power which increases the displacement of your engine. This allows for more power gains and can help eliminate lag by providing some extra power lower down in the rev range. This isn’t the cheapest of mods but if you are going big turbo then the engine will need to be taken apart and new internals put in anyway.
When you opt for an aftermarket turbo, there is a lot of custom work that has to be done. This can involve a custom downpipe, exhaust manifold, injectors, fuel pump, custom oil feed lines and a fair bit more. That’s not including any internal engine block work.
Don’t cheap out on a turbo when going for high power, do it properly. A cheap poorly designed turbo can cost you a fortune, especially if it ends up damaging any other expensive parts you have purchased for your build.
The turbo you should go for will depend on your desired output and of course your budget. You can’t go wrong with Garrett turbos on these engines, and there are many TT MK1’s running 500-600hp+ on these setups.
Some of the popular options among enthusiasts include the GTX2867R (Gen 2) and G25-660 however there are various other options out there. Speak to your local tuner to see what they recommend if they are the ones who will be completing most of the work for the build.
Finishing Thoughts
We hope you found this article useful and that it helps you make the right choices when planning for a turbo upgrade. There are numerous options out there for reaching big power outputs with different routes to go down depending on if you opt for a large frame Garrett turbo or a hybrid turbo. Whatever route you go down, plan ahead and work out the rough costings and the power figures you are aiming for. You don’t have to do all the mods at the one time, however knowing which route you want to go down will save you a lot of money and hassle.
Happy modding!
