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Mouse_GTI wrote:That's not to bad. Suppose you have to combine it with other mods for best effect

Shot peening is a process used to produce a compressive residual stress layer and modify mechanical properties of metals. It entails impacting a surface with shot (round metallic or ceramic particles) with force sufficient to create plastic deformation. It is similar to sandblasting, except that it operates by the mechanism of plasticity rather than abrasion: each particle functions as a ball-peen hammer. In practice, this means that less material is removed by the process, and less dust created.

The weakness on the GTI, as I've said before, is the exhaust side of the head, and it's gas release characteristics, all the way to the backbox.

You can buy a cat back system. May sound nice, may look nice. Does jack for performance gains, on it's own.

You can buy a BMC. It may have a nice big carbon box that the filter sits in. It may make a nice noise. It does jack for performance gains, on it's own.

You can buy spark plug leads. They now come in fancy colours, and bigger sizes. The core is still the same, the coil still delivers the same spark, and the lead still delivers that same potential. Again, does jack for performance. They only reduce interference, if your motor is highly tuned, and likely to be affected by it.

So, to the head. £500 is about the rate for a fully gas flowed, usually big valve, racey spec head, fully rebuilt, and bought on an exchange basis. You don't need that on the Lupo. The intake is fine. It doesn't need bigger valves, as your not likely to run higher revs, or forced induction. Take your head off, have the exhaust side flowed out, and you're probably looking at £150-200 or so. You can expect to see 10-15 horsepower (peak) and a massive gain in torque. The motor will rev quicker, and will run better at higher revs.

So the next stage, the header. The openings, and the pipe itself on the stock header are tiny. ALL the power developed, is TOTALLY dependant on how well THAT header can move exhaust gasses, and still create a vacuum on change over. There are exhaust headers available for the GTI. I seem to remember a group buy at one point. They will increase horsepower, and torque, and therefore, driveability. No doubt, you could probably have a custom one made, for that £300. You can probably expect to see anything from 5-15hp, depending on the header.

Going on, the downpipe. The 4 into 1 collector, and downpipe setup on the GTI is another restriction point. Scrap it totally, and look at running a true 4 branch header setup, as mentioned above.
And and and...

Tuning a motor is a lengthy process. You have to have one part done, before you will ever see any gain from anything else that you do. Fitting a camshaft will do nothing for performance, if the head is still stock. Fitting a custom header will do nothing if the head is still stock. Fitting a cat back system will do nothing if the header is stock...

Are we starting to understand yet...?

As, and when you decide to tune your motor, you tune it as much as you can. Head, headers, exhaust, cams etc. THEN you take it somewhere, and have the fueling mapped to optimise performance and power delivery. Turbo, or forced induction motors CAN benefit from remapping, as generally manufacturer's will restrict it's performance via the fueling. They'll build a motor, turbo it, then typically turn the fueling down, so that you get a reliable peformance level. With Normally Aspirated motors, in the shape of the GTi, is it entirely different. The fueling isn't turned down to any great extent, so without tuning, there is NO POINT in remapping the stock setting.
Also...

With tuning a motor, comes reliability issues. The motor now runs hotter, uses more fuel, and undertakes more stress when running. Something is going to break... it's not a question of IF, but WHEN. If you choose to tune your motor, EXPECT to find that it wont run very well in traffic. It'll be a nightmare on the school run, and it'll generally start to cook itself as it humps and bumps about. You'll find that you can't use any extra power it now has on your journey to work, and you'll end up hating it. The little Lupo that you once loved so much, is now starting to get on your nerves.

Another thing. All this power... what about the drive train? The brakes? The wheels and tyres? Should I go on...?