I've done so much now, I though I might list all the things I had done and told you if it made a difference or not.
1) Power flow exhaust from the centre scilencer back
Origionaly from the CAT back but the car kept stopping and going into limp home mode due to the pressure sensor presumably. I tried blocking two of the quad pipes on some runs and the result was slightly less peek torque and bhp but just after peek torque that of the run with blocked exits became higher because it did not fall as fast. This ment that with restricted flow the bhp was higher for about 1500rpm. The torque then falls off quicker on the restricted run and the free flowing exhaust reaches higher max bhp. So the best exhaust would have to vary it's flow characteristics dependant on rpm. Now that is very achieveable but somewhat complicated and expensive. I think I have a reasonable balance though with an unrestricted exhaust from the centre scilencer back.
Agree? Disagree? Constructive coments please.
2) Air box mods (K&N panel filter, two cold air feeds, additional cone filter)
Now I don't know how much difference exactly these air box mods have made but I did do some runs specifically to see wheather or not better air flow would improve performance. I found that a foam mushroom filter with unrestricted cold air flow (it was actually stuck up in the air away from the engine) gave better performance than a paper panel filter in a standard box. So improving air flow will give you better performance.
3) Second intercooler
Well this was a strange one, I though by hooking up both intercoolers I would possibly get a bit more lag but the air would move more slowly through the matrixies because of the larger volume and so shed more heat. Running on just the VXR map, there was no noticable difference in performance, one or two bhp which is easily attributable to variation in readings. With the box ontop of the map though there was an aparent increase of about 6.5bhp and 10lbft. Now that is enough to suggest a real benifit but not much concidering the cost. I paid just under £100 for the inter cooler (which doesn't fit behind the bumper properly), then about £40 for all the hoses and clamps.
4) Remap and Tuning box
Now the VXR remap did give a noticable increase in power and torque over the standard map, however, better results have been gained from a tuning box alone just altering fueling. With both a box and the VXR remap, good figures can be gained but still only just over the 200bhp. What gets me is that the torque can be increased so much without any over fueling, I'm seeing 303lbft at the road wheel now and without over fueling. Admitedly, at the top end it is a BIT smokey but (sorry Harry) to be honnest Harry's remaped 3ltr was just as if not more smokey at top end than mine with the box on max.
So what can you do to get more out of you 1.9CDTI?
Definatly get yourself a custom exhaust with less restriction; if you go from the centre back it won't be loud and you'll see an improvement in performance.
Get yourself a K&N panel filter and take out the ducting in the lower half of the air box, alternatively get an enclosed induction system (not just a cone, one of the carbon fiber cylinders with a cone inside and a cold air feed). Anyone who says "what about the extra particle getting through", concider this; all diesels now operate EGR systems, which dump dirty soot filled exhaust gasses back into the intake manifold. My five year old 2.0 DTI had half an inch of carbon built up, over the whole of the inside of the inlet mainfold. What difference do you thing a few micro sizes particulates are going to make to that?
Remap it? obviously this is a better idea than a tuning box because you know the ECU is in control and you aren't damaging your CAT through over fueling. Don't go for a VXR or Regal remap though, they don't customise it to your vehicle and what works great for one, may just be okay for another. Go to a companey that puts in a map, tests it and modifies as necessary. Last time I spoke to Celtic tuning they said they would not give me more than 180bhp but they are now advertising 205bhp on their site. They claim they write their own maps, here not get one sent from Germany by someone who has only seen Britain on a map let alone seen your car. They turn up at your house, with a laptop and alter the map to suit you. Well that's what they and they testimonies on the site say... I'll speak to them tomorrow and we'll see. That's what you need though, otherwise your just not getting your moneys worth. What's more, in the good old days you would mod your car and then get it remaped to make the most of your hard work. A one map fits all job does not take advantage of any of your expensive hard work and you'll only see a minimal increase as shown by my second intercooler. With just the remap there was no benifit from the intercooler but with the box aswell, it was up by a reasonable amount throught the rev range, not just at the top end (6.5bhp and 10+lbft at the road wheel).
The next thing to think about is how that increase power and torque is going to hit the road. The 1.9 is not as good at putting down the torque as the 3ltr because it is not as front heavy so when you accelerate the back end drops and the wheels just spin. So you'll need good suspension to stop the back droping. Springs that lower the front more than the back will also help. I've tried just wider, higher quality tyres (Toyo 888 235/45 R17) but in the end it can only do so much and they still spin in 3rd on occasion.