gregh

What kind of pros/cons are there in doing this?

I'm assuming better breathing therefore better pickup as a pro, but the downside is it will fail the MOT.

Any other things to consider?

cheers,

greg

john banks

You might need to sort out the overboost by altering restrictor size, but it will add substantial throttle response, boost threshold will reduce and it will just generally be nicer to drive. If you stick with the PPP BB not too loud either. You can borrow beefy centre cats for the MOT from a few specialists.

SoreHead

What's this about overboost??? I'm getting the PPP next month and had planned to fit a DP also. How do I find out if this will be a problem? I thought the wastegate and ECU handled the boost??

john banks

The wastegate and ECU do control the boost, but they also use a 1.2mm restrictor orifice inside the pipe off the turbo outlet. When you switch to a decat exhaust the turbo spools much quicker, and can overshoot the 15.7 PSI target in the MY99/00 PPP. If it goes too far the ECU drops the duty cycle and the boost undershoots before stabilising. Sometimes PPP even does this as standard. In worse cases like on my car it oscillates the boost from 18 to 14 PSI as you are on full throttle - not fun. The solution is to adjust the size of the restrictor, and it can be a big faff to end up with it about right in all weathers. The 15.7 PSI target is just too low for the sort of duty cycles the PPP runs - it was not designed around a downpipe and it shows when you put one on. It can be made to work by changing the restrictor, but you end up strangling your boost levels. I ended up using a Dawes to control the boost much more effectively, and eventually sold the PPP as it was just too tame.

gregh

Hi John,

Do I get overboost dependent on the make of downpipe I choose, or does it not matter?

If I do get it how do I know what size restrictor to then go with?

sorry for the dumb questions!

cheers,

Greg

john banks

Some people say the make of downpipe does matter. You need a boost gauge - if it overboosts then undershoots then stabilises and you don't like that (I didn't - depends how bad it is) then you need a 0.1mm increment in restrictor size from 1.2mm to 1.3mm which should fix it. I had to go to 1.35mm.