Porting/Polishing

[Mouse_GTI]

How much extra bhp alone would porting/polishing the cylinder head give you? Does it cost much?

[MaxZ]

I believe it costs in the region of about 400 pounds, as to the power gains not really sure on a GTi

[garnier]

5-10% increase in bhp, roughly...

[Mouse_GTI]

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

[Dee-vub]

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

yeh defo mouse, if i keep her, i'll go down that route also

[tegwin]

dont get me started on polishing your head and intake....

Yes, get the head and intake ported, clean off any casting fins and marks,...this will help... but dont polish them afterwards....the last thing you want is a totaly smooth mirror like finish on your inlet and head...

Its quite a common missconception that a high polished finish is advantageous....amusingly enough it has the opposite effect...


Once you have finished cleaning the casting marks off and porting etc, get it shot peened (SP)...

Sorry...

rant over

[Dee-vub]

shot peened??

[tegwin]

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 theory is that, if you polish any surface (including intake and heads), it will act as a catalyst for condensation.....

So in the instance of an engine intake, the super smooth polished intake would incourage the atmomised fuel and air mixture to condense onto the metal slowing the fuel/air charge down...

If you slightly abrade the surface (shot peen is one method), it increases the turbulance just enough to prevent this condensation occuring...

Just the theory, someone might be interested lol...

[psycho sport]

i was under the impression that the polo gti head was pretty efficent as it is, so no massive gains can be achieved. Was it also not designed by the guys that built the clio williams?

[Mouse_GTI]

From Club Lupo...

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...?

[Mouse_GTI]

Judging by that I'd say porting/header -> manifold -> sport cat -> cams -> BMC -> remap

[mk4 glx 1.6]

For the outlay vs. gains, I really don't see the point. Each to their own though.

[Dee-vub]

Mouse...where the f**k did you get that??? What a complete heap of s**t!!

I cant even be bothered going into it, but how can you possibly say uprated cams on there own wont improve the performance or a full system exhaust wont......that lad seems to know what he is talking about but hes really on another planet!

[Mouse_GTI]

I think the point he is trying to make is that along, the mods won't give you much power considering the price and all. Cams will give you a noticeable increase, but they'd be better combined with other engine mods that sorta thing He got a lot of stick on Club Lupo and left but this guy tuned a GTI engine up to 180 iirc N/A

[Dee-vub]

yeh i can understand where he is coming from but he is being extremely drastic by saving they have jack effect at all! I agree to maximise the potential of mods is to couple them with other mods but but to say they are s**t and dont work unless you do this or that to them is complete s**t!

Not surprised he left.

I dont think i'll see 180 but i hope to see about 160 after remap then i'll stop. Cost dont want to then spend on getting the head done to then get it remapped again