Thread: 300tdi 3inch exhaust required

theres an exhaust shop near here that will make up what you want custom to your vehicle and not charge you umpty million dollars for the privilege of doing so.

Havent had a complaint about them yet.

A 300Tdi,unless you are doing something outlandish to it,doesn't require anything more than 2 1/2" exhaust.And that will save you a considerable amount.

you could always just put a 3" tip on it!

i had my 2.5 fitted normal bend at redcliffe, straight through no exhaust with flexi joint for $200 from memory

-With out starting an arguement those that i have spoken to with the 3in exhaust all reccomended it, my defender runs a full front allard intercooler and a water cooled MTQ mitsubishi turbo, i dont have a centre muffler but the exhaust is tired and i have been patching up holes around the rear muffler so if i am going to replace now would be the time to upsize

Originally Posted by redrovertdi

-With out starting an arguement those that i have spoken to with the 3in exhaust all reccomended it, my defender runs a full front allard intercooler and a water cooled MTQ mitsubishi turbo, i dont have a centre muffler but the exhaust is tired and i have been patching up holes around the rear muffler so if i am going to replace now would be the time to upsize

Yeah, fair enough, but the question you need to ask yourself is have any of these people produced quantifiable positive results from running a 3" system that have been doccumented and compared to a 2.5" or 2.75" or do they just not know any better? Most opinion is a 3" is too big and can actually cause issues.

What CraigE said is exactly correct.
A 2.5" exhaust will flow over 500 CFM which is approx. what an engine putting out just over 230H.P. will flow.
This is more than enough for a 300Tdi no matter how big the intercooler and size of the turbo,without some serious internal work done to the engine.
There are a number of reasons you don't want to go too large with the exhaust,such as loss of scavenging and accoustic resonance.There is a lot more involved than just picking a big pipe.Just look at the doof doof brigade,all noise and no go,but they usually have a nice big pipe and chrome resonator.

Originally Posted by CraigE

Yeah, fair enough, but the question you need to ask yourself is have any of these people produced quantifiable positive results from running a 3" system that have been doccumented and compared to a 2.5" or 2.75" or do they just not know any better? Most opinion is a 3" is too big and can actually cause issues.

IMO 2.75" would be about ideal, but there's no problem with a 3" system, plenty of us use them and have done for a very long time now without any known overspeed issues.

When I built my system (too many years ago now) 2.75" tube was prohibitively expensive here in Australia and for the overall length of a 130 system I couldn't see any sense in 'just' going to 2.5" tube, although in hindsight it probably would have been fine.

In comparison the standard OE exhaust is 60mm OD, (2.375") all bends are mandrel bent with the main muffler and resonator straight through perforated tube, so it is nicely made.

Before making the big pipe system I had ground out the large mig weld bead inside the throat of the dump pipe, it encroached into the pipe by a large amount, (close to 5mm all the way around) but my sensitive bum dyno couldn't feel any improvement, nor was there on my test roads and hills.
Having noted that, I still ground out/throated and matched the cast dump section to the flange and pipe and made sure the transition to 3" was at a 15* taper to minimise turbulence....

Going to a 3" exhaust several things were immediately apparent.

Maximum EGT's dropped by about 25*C.

The rev range through the gears was extended significantly.

With the OE system 3rd gear was good for about 75km/h, then the engine just stopped accelerating, it hit a wall so you had to change gears. (255/85-16's)
With the big pipe 95km/h was easily within reach, and the first test run I hit 100km/h in third.
The engine has done 300,000km now and the improvement there is still useful, I hit about 95km/h in third yesterday overtaking a car, so nothing untoward has happened to the turbo or the engine over all those years either.

Apart from that, the performance increase was pretty minor (no pump fuel adjustments had been made, everything else was stock)

I have no doubt a 2.75" pipe would have enabled exactly the same improvements, although I'm not sure a 2.5" pipe would, taking into account the length of a 130 system. A 90 or 100" (RRC/Disco) could probably utilise a 2.5" system well but I think a 110 could leave something on the table, but we'll never know unless someone does a back to back dyno run and it's only a 300Tdi on a Landy, so why would you ?

One thing I must point out, the noise increase, drone and resonance was terrible. (and I'm an ex-racer)

Don't listen to anyone that says a turbo alone muffles an exhaust adequately, a muffler and particularly a resonator is a must with a 3" pipe.