2 1/2inch exhaust

what the biggest diameter exhaust you can fit on a mk1?

may be something for the boys with 20vt conversions?

my mk1 is a 1.6 GTD turbo diesel engine, so the bigger the exhaust I can fit the better, and I'm just wondering if you can fit a 2 1/2 inch system, specifically over the rear axle as it seems to be the tightest place.

cheers :mrgreen:



EDIT: also does anyone know if you have to have a box on the exhaust to pass an MOT? my guess would be if the noise level is acceptable there is no reason I HAVE to have a box in the system?

mk1vdub said

what the biggest diameter exhaust you can fit on a mk1?

may be something for the boys with 20vt conversions?

my mk1 is a 1.6 GTD turbo diesel engine, so the bigger the exhaust I can fit the better, and I'm just wondering if you can fit a 2 1/2 inch system, specifically over the rear axle as it seems to be the tightest place.

cheers :mrgreen:






EDIT: also does anyone know if you have to have a box on the exhaust to pass an MOT? my guess would be if the noise level is acceptable there is no reason I HAVE to have a box in the system?

Is it for looks? Maybe you should get an Evo instead.

:lmao:  :roll:  

no its for power, the bigger the diameter exhaust you can fit on a turbo diesel the better, it won't even be visible as I plan on having a turned down tdi style tail pipe….


thanks for your help though :clap:

2.5 fits fine, mines 2.25 to teh front box and 2.5 from there on.

Of course its all totally pointless, depends on the smallest part of tehe system which is 2.25 at the bottom of the manifold.

Jetex do a storming 2.5" system apparently, its what i plan on getting eventually  :mrgreen:

excellent, just what I wanted to hear mate :y:

how tight is it going over the rear axle?

I actually plan on welding it up myself, as there is nothing that will fit off the shelf, jetex do universal bends in 2.5 so I'll be able to make up a custom downpipe straight through to the tailpipe in 2.5

Pretty tight, I can either have my exhaust knocking on the beam, or knocking on speed bumps, lol.

Let me know how you get on with that, I wouldn't mind a straight through centre section as well.

I believe one of the jetex systems has a straight through centre section anyway, and just one can a the back, the race system I 'think'.   from what i've heard (but havent confirmed) It comes with a connector section at the end to match up with whatever downpipe youre running anyway.

what manifold are you looking to link it to?  I'm running a Ashley 16v conversion 4 branch this 2.25/2.5" system and inbetween had a short custom bit made up with an extra 2.25" flexi joint.

well as its a turbo diesel, it will just be from the turbo outlet, as the engine is from a mk2 the original downpipe doesn't fit as it is in the way of the gear linkage, and finding an original mk1 GTD downpipe I think will be rather hard so I hope to just fab one up to fit, it should look something like these when its done :
the rest should then be easy….









don't ask me why I posted all of these, I think it might be to give myself some inspiration!

how big is the turbo ?

and being a turbo diesel how high do they rev because going up on size on petrol cars is so that the exhaust can flow enough air and not restrict the turbo this is usually when revving quite high which i don't believe diesels do ?

i don't personally think the bigger is better will be true as you may lose some of the response on the turbo as it may not spool up as quick depending on size of the original exhaust it maybe worth going up 1/2" on the diameter.

don't goto jetex go to sdw fabrications in banbury the bends will be cheaper and most likely better quality stainless.

if not milner off road in derbyshire do them pretty cheap too

Stu

Fair call mate!

if you want to be sure speak to some exhaust manufacturers to be sure you get the size right at least.

cheers Stu

the turbo is a kkk k14 so not all that big but will push about 1.2 bar.

I've modified the govenor in my pump so can probably rev safely to about 4500-5000 rpm, but with full fueling all the way

diesels don't work in the same way as petrols so theres not really any point in comparing them…

I've actually done quite a lot of exhaustive (mwahaha do you see what I did there!! ) research on the subject and yes for turbo diesels bigger is better.

if you'd like to find out more about diesels I can highly reccomend this forum:
http://www.vwdiesel.net/phpBB/

the problem is most exhaust places are only familiar working with petrol engines, and just don't really know about modifiying diesels - I've been for a couple of quotes to get a system made up and found that I quite often know more about it than them, as tuning older IDI diesels just isn't very common.

thanks for the reccomendations I'll check those places out.

i know about the diesel cycles (2 adiabatic) one is a constant pressure cycle and the other is a constant volume if we're getting thermodynamic about it but it's still about treating it as a pump and volume of air being pumped.

i'd be interested to know how it works out when you get it done i got a turbo diesel manifold and turbo so i can fit it on my 1600Gti but i'll be using a different turbo like a t2/t25 at some point.

cheers for the link will have a read of it.

Stu