13-02-2012, 02:35 PM
tomw1123 Wrote:Buuuuuuuuuut then he started banging on about i'll loose power and that i need back pressure and theres no point and it'll fail mot for emissions i was like no its just smoke for diesel buuuut no no its emissions aswell
Guy is a retard.
Turbocharged Diesels don't need backpressure anything like Petrols do, they don't have a massive amount of valve overlap due to the fact they have positive pressure in the cylinder, so it'll just blow all of it out the exhaust as soon as the mani pressure rises if they had overlap. You want the least backpressure down the exhaust to expel the gasses as quickly as possible, otherwise you suffer from excessive EGTs, and melt things - put a petrol exhaust on a Diesel and see what happens, you'll probably melt something if it's remotely tuned.
Emissions - another load of bullshit, the Cat that they are fitted with as standard won't reduce Particulate Matter when cold, only once they are red hot (i.e. on the motorway...) will they become effective, so in your average MOT test, they won't do anything... And besides, it's JUST Particulate Matter, so just turn down the pump, both me and Darren have passed with flying colours every year... I've never failed due to smoke. Oh and Diesels don't need a Cat for an MOT. Just need one silencer in the exhaust - but that might be more popo regulations than MOT...
So basically, tell him to shut up and start welding, but make sure he puts at least one box in... I've been done for just having a piece of pipe as an exhaust...
Standard is 2 1/4" to the cat and then 2" thereafter, I think on some models it's 1 3/4" to the backbox from the midbox.. 2 1/4" is about right if you keep it the same the entire way down... Darren and I have 2 1/4" pipes - Darren's car made 213hp on a 2 1/4" pipe, so I wouldn't worry about it restricting...
