After a few recent GTti items i have spotted being sold on Ebay, some fetching silly over the top money, I thought it's worth a quick guide to help you decide what hot and what's not when it comes to Tuning up GTti's.

These cars are easy and cheap to tune-up, but because knowledge is often fairly limited and performance parts are scarce, people tend to get carried away when a unusual item appears on Ebay...often claimng big power increases.

First of all,

Throttle body. Recently there was one being sold which had been mirror polished up inside, and it claimed a power increase of 3-6bhp!  The only way you will gain worthwhile power increase is if the throttle body is bored out to it's max size of 39mm, and a new butterfly is made to fit. Just polishing alone would hardly do anything and certainly you wont notice any real gain.

You may have heard of some people using a throttle body from another car (Toyota MR2 Mk1 is similar looking but much bigger). This wont work very well using the standard ECU, the airflow into the engine will be so different to standard. But its something to consider doing if you change the ECU to a programmable one (or a piggyback such as E-manage)

DRS Ecu's....

These appear every so often, and I sold mine last year for a fantastic price. Be aware that every DRS i know of (apart from the one i had) is a 1 bar / 15psi  DRS, In other words it is mapped to run about 15 psi boost pressure, many will still have a safety fuel cut but set at just over 15 psi instead of the standard ecu's 12.5psi.

These offer about 30-40bhp gain over a standard GTti, and they simply plug in just like standard ECU. However you won't really be able to re-tune it easily for even more power as there is no software or computer hook-up cable available to remap them. The chips inside could be removed and read by a chip EPROM reader/Writer, but this means you cannot tune the DRS whilst car is running on a dyno. So it would be a longwinded process.

Also, you can get just the same amount of power for very little money by raising the boost to 14/15psi, and using a Fuel cut defender to defeat the standard ecu safety cutout. These are often hated as its seen as a bit of a bodge..but in reality if the car is setup well it should be perfectly OK if you can set the boost to 14/15psi and not be tempted to raise it up further!

The DRS i had was a little different in that it was mapped to suit more boost (18psi), and also came setup to run with a new uprated MAP sensor. This gave it about 50-60bhp gain over a standard car.

DAD ecu's (Dawson Auto Developments)

These are a UK modified standard ECU used on the old Uk rally GTti's, similar to the DRS but they seem a little more crude.  They tend to be setup to run very rich fuel mixtures (for engine safety) so i would not suggest running one for everyday road use. Heavy fuel consumption and even black smoke is likely.   

The Greddy e-Manage piggyback (blue version) is a great easy way for proper tuning, and once installed will have far greater scope for tuning than a DRS or DAD ecu, and for much less money. 

You can adjust fuelling and ignition timing via a laptop and installation is really easy, about 8-10 wires T's into the standard ECU harness and its ready to go! The car will start and run identical to standard until you start to play about with the setting of the e-manage, so there is no problem driving the car to a tuners/rolling road to be setup. 

Air filters / Induction kits...for max power the golden rule with a turbo engine is to fit the biggest free flowing air filter you can manage to fit under the bonnet! There is so many brands / shapes and sizes out there but you dont need to spend a fortune. A simple 90 degree downwards pointing silicone hose straight off the turbo and then hang a good size cone filter off it is all thats needed.

Generally the stainless steel mesh filters flow the best, but filtration quality is not quite as good as cotton or paper,

K&N or other brand cotton style filters are good all rounders and filter and flow OK.

Foam type air filters im not a fan of, They are messy to clean and re-oil and the flow and filtration levels are nothing special.

Boost Controllers  - Conventional bleed valves work OK to raise boost, but best to use a manual boost controller (MBC) aka Dawes Device / Ball and Spring controller. These simple little valves stay closed until you reach your desired boost level, this makes the turbo spin up sooner and harder because the wastegate actuator stays shut for longer. Electronic controllers are a nice addition so you can adjust the boost pressure whilst driving, but to be honest, from the testing i have done a good ball and spring type manual controller are just as effective at keeping boost steady.

Turbo's

Another popular modification is the hybrid turbo. Whilst these offer great top end power, remember that the mid-range power will suffer considerably. They only tend to get boosting properly at 4000 rpm onwards.

So if you love the way your GTti drives and accelerates on standard turbo, dont swap to a hybrid!  Consider sticking with the standard turbo but just a bit more boost!   

To spot a hybrid for sale, look into the compressor inlet (air filter side), the compressor wheel will fill the size of the inlet hole fully, on a standard GTti turbo the wheel is noticably smaller.

Fuel pump

Dont waste your money uprating the fuel pump unless your pump is faulty and needs replacing, then you may as well fit one. Standard pump in good working order can certanly handle 170-180bhp.

Injectors

You only really need to think about swapping injectors once you are 170+ bhp, and by then you are going to be using a different ECU or piggyback to control things so swapping injectors will be quite easy.

Do not try to run bigger injectors with just the standard ECU, its likely the car will start / idle / run like poo.

Clutches

Ignore the +30% and +50% ratings....these are confusing. Its not refering to the amount of power they will handle, but the  clamp increase of the clutch cover. A good standard GTti clutch will just about hold 14/15psi boost (about 130bhp).

The 50% uprated clutch will hold a little more power, but not 50% more than a standard clutch, 150+bhp and if boost comes in hard it will still slip.

For serious power im afraid the only option currently available to avoid clutch slip is to go a paddle style racing clutch plate.

The problem is simply the size of the clutch, 180mm is not very big for the amount of power these cars can develop.   

Dump Valves

These will not make any extra power or performance, they are only worth considering if you run high boost (15+ psi) and even then the debate is out as to whether they really help prolong turbo life.

Of course if you like the dumping air noise then fine, personal choice.

I much prefer the compressor wheel flutter noise (air passing back through the compressor wheel) you get when no dump valve is fitted (large air filter needed to hear it). Like mentioned above, the flutter noise is of no concern (despite what some may say) unless you start using high boost.

A final note.....

I get many emails from people expecting or planning on making 200bhp with their cars. This is unrealistic for everyday road use and you run into all sorts of problems, such as gearbox, clutch, engine mounts and of course engine reliability.  Whilst 200bhp is certainly possible i would personally aim for a healthy 150-170bhp with a wide spread of torque. The car will still be staggeringly quick (the GTti is all about power to weight ratio and low gearing) and you won't be rebuilding things every month if it's done properly! 

Most GTti's that have the common bolt on mods (air filter/exhaust/ bit of extra boost) make about 130bhp once on the rolling road. With a bit of extra effort so you can safely run higher boost (ECU or e-Manage to do this) you will hit 150-170bhp quite easily.

Contact me if you have any GTti questions