Straight through exhaust/mot regs

[Tom]

Right i went to see my mechanic mate over the road today about him welding up a straight through exhasut for me he said yehyeh no worries you clamp it up and i'll weld it no problem Theres me thinking yes great he'll do it for free aswell
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 :o
So any of this true or should i just tell him to shut up and do the welding?

[4WayDiablo]

Tell him to shut up and start welding :-)

Emissions on diesel is just particulate
Also by law you need one "box" mine is straight through with baffling removed from the one backbox

[Tom]

Yes im just going to decat and a straight pipe in place of the back box thus leaving the midbox so im all legal
Heard a video of a straight pipe and it sounds wicked with the turbo just whistling away... that and i need more POWWAAAA!!

[4WayDiablo]

Yeah mine whistles away too. Remove what little baffling there is in the midbox too :-)

[Jonny b]

Yeah mine whistles away too. Remove what little baffling there is in the midbox too :-)

whisltes like a fucker with no boost hoses connected ha ha

[Tom]

Is it going to be much quicker with this work done? Its more of the sound im after lol not fussed about the speed its fine as is

[4WayDiablo]

Yeah mine whistles away too. Remove what little baffling there is in the midbox too :-)

whisltes like a fucker with no boost hoses connected ha ha

Fyc! Haha

Those days are gone now anyway

[4WayDiablo]

As with most exhaust mods it wont improve performance that much. Only a few bhp BUT it will get you the most out of any other performance mods you do/ have done

[Midnightclub]

On turbo'd cars the less back pressure the better usually, helps the turbo to spool quicker so all that about making it slower is bull lol

[Tom]

Well thats alright then.. Need to get a new metal cutting disk for the angle grinder

Yeh i didnt think he knew his diesels very well lol

[4WayDiablo]

Definatly not lol. But yeah get the grinder out. Cut open the midbox then remove all baffling then get your mate to weld it back up whilst your there

[Tom]

Anyone know what size the standard pipe is?

[4WayDiablo]

2.25 i think
Probably wrong lol
Go for something like 2.5 if you can

[Ruan]

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...

[mark_airey]

Ideal for a turbo engine is 18" of straight pipe............. don't need back pressure, you has a snail

it will free the exit of gasses from the engine which should mean that you get on boost a little bit sooner (though it probably won't even be noticeable)

As far as legalities go, as said already, as long as it has 1 box in then its all legal as far as the police are concerned, as for the MOT, they can fail them on excessive noise but that is down to the testers opinion and nothing else!

Edit:- Ruan has answered everything pretty clearly there I would say

[4WayDiablo]

Ruan is a god lol

Yeah mine got 0.00 emissions on the mot. Turned down the fuel pump ftw :-) \/\/ is what it usually kicks out

[Ruan]

You want to keep gas velocity up, so don't go for like a 4" pipe back on a stock engine as the gasses tend to hang around (imagine blowing down a drainpipe vs blowing down a straw, you want it right for the amount, 2 1/4" is pretty much from from standard up to probably 230hp... Past there you need a bit more area for the expanding gasses...

And yeah, I am a frikkin' god... Get on your knees, bitch before I open up a can o' whoop ass...

[4WayDiablo]

Yes sir :-(

[Jonny b]

Ha ha Ruan quality

[Tom]

I was going to decat and then replace the back box with a straight pipe soo i need to bits of different size pipe lol

[Midnightclub]

Ideal for a turbo engine is 18" of straight pipe............. don't need back pressure, you has a snail

it will free the exit of gasses from the engine which should mean that you get on boost a little bit sooner (though it probably won't even be noticeable)

As far as legalities go, as said already, as long as it has 1 box in then its all legal as far as the police are concerned, as for the MOT, they can fail them on excessive noise but that is down to the testers opinion and nothing else!

Edit:- Ruan has answered everything pretty clearly there I would say

My friends 1.8 vento idles at 85 db's MOT on wednesday reported "Exhaust is slightly louder than normal but who can say what excessive is"? Legend !

[mark_airey]

My friends 1.8 vento idles at 85 db's MOT on wednesday reported "Exhaust is slightly louder than normal but who can say what excessive is"? Legend !

Friendly MOT testers FTW

[Tom]

I know a few mot testers so thats not a problem

[jammapic]

Have you guys read the new MOT guide coming into effect from March / April this year.

Any DIESEL that left the factory with a CAT/DPF now must have one fitted, they will be checking for one. The exhaust must also have 1 box in it, and not be over a certain volume (can't remember it off the top of my head) at fast idle.

There are LOADS of changes, including airbags / seatbelt pretensioners etc etc... deffo worth a read.

JP

[Tom]

Have you guys read the new MOT guide coming into effect from March / April this year.

Any DIESEL that left the factory with a CAT/DPF now must have one fitted, they will be checking for one. The exhaust must also have 1 box in it, and not be over a certain volume (can't remember it off the top of my head) at fast idle.

There are LOADS of changes, including airbags / seatbelt pretensioners etc etc... deffo worth a read.

JP

Shit.... Good thing i was going to start on it tomorrow.. guess i'll have to take the cat off and smash the shit out of it instead :/

[jammapic]

Yep, that's what I would do.

I'm going to get a "sports cat" from the exhaust place and empty it's innards.

[studturbo]

Oh shit my mot due 3rd of march ahaha and i aint no cat aha

[darrenjlobb]

Any ph1 DT and tbh ph2 unless your MOT tester is a proper dick will pass on new MOT with no cat....

Alot of the early ph1's didn't have them as stock anyway, and there is NO way to prove if your car had one or not...so they cant fail it on a lack of cat.... but yes, any car that had one as stock, is now suppose to have one fitted for MOT.

Basically keep a box inline, and your all good

[jammapic]

there is NO way to prove if your car had one or not

The MOT test software now tells them - the only cars it does not know about are imports.

PH1's and early PH2's will probably be ok, if they weren't fitted with one as standard.

The way around it is to say you've fitted an earlier engine, as you only have to conform to the emissions test / standards of the year of the engine.

JP

[studturbo]

i have got a early engine av got a d8a engine in