Aircooled VW South Africa

This might be a strange question, BUT, I am sure there are people here in the know about exhaust things, on all that is powerd by the good old internal combustion engines - even oilburners aka diesels.

I have a Nissan 2.7 Tdi. Its got a "progressive" exhaust system - eg its 50mm from the front, and then changes into a 57mm via a flange just before the rear (and only) exhaust box.

So, I have been pondering, and read a bit on the www about bigger downpipes on turbodiesels etc. I have been told by a guy, at an exhaust place, that he thinks the reason for the smaller into bigger system is something to do with windspeed, and assist the turbo to spool up quicker or something like that.

I want a little bit more oompfh from the engine, so I am pondering to have a bigger downpipe eg 57mm fitted from the front and making the whole system then a 57mm throughout. NOW, will this help with performance, or, will this actually reduce powa !

I dunno, please, if anybody here knows this stuff, I will gladly listen to any comments / advice.

to make more power, you need to reduce restriction after the turbo, i.e. get the gas to flow quicker away from the turbo, thus improving the pressure differential across the turbine. This will allow a little more power, sooner and maybe more power up top.
But then again if your primaries are too small and the turbo is too small, making the exh bigger will only make a change to your wallet.

Thanks Tony, so, it would seem that a bigger system straight through will have some benefits, not too big.

But, how do I know or calculate the best size, and why would the manufacturers go through all the trouble to make the front pipe smaller, (50mm) and add a flange, before going into a bigger (57mm) from the rear box - surely a one size pipe without flanges would be cheaper to manufacture?

A friend has a Landrover TD5 with a 2.5L engine. Odly enough it uses the same Garret GT2052 turbo as my Nissan, and he's got a 63mm system. So by logical deduction, I have a 200cc bigger engine, allthough 4cylinders vs his 5 cylinders, so I could actually fit a 63mm system? Just worried abuot the noise factor - dont want it to sound like a massey furgeson

Your best bet is probably to talk to someone who does chip-tuning and diesel-tuning. SAC for example.
Look in the back of the CAR or SPEED AND SOUND magazine

Not to intrude but know of someone who had a Mazda drifter 2.5tdi with a 50mm straight through pipe. Sounded great but performance dipped substantially. Remember one thing "Golfmad" manufacturers spend big $ on development balancing performance and reliability. I'm sure the exhaust setup you have is pretty good. So before you go and change the whole thing to a straight through pipe try first just doing a down pipe. Then maybe later on remove the box. You could also try a different intercooler possibly even turn the boost up a touch. The guys also play a bit with injector timing. Causes the motor to smoke a little but gain are to be seen.

Good luck.