Exhaust Options - 300 Tdi

**Jock The Rock** · 25th January 2010, 05:57 PM

Gday

After fitting this new turbo I want to fit a larger exhaust. The kit came with a 2.5" dump pipe (ends just near the bellhousing) and a 2.5" extension to connect up to the join below the transfer box (normal bends)

Originally I was going to go a 2.5" with straight through muffler. That was not mandrel bent. I was quoted $375 to finish off the exhaust in 2.5"

Now I've been thinking and talking to a few others, it seems 3" is a better option.

I went back to the exhaust place and was quoted $995 for a fully mandrel bent 3" system with straight through muffler; which will join onto the 2.5" dump pipe

What are your thoughts?

I've pretty much committed to the 3" system but I just thought I'd see what you all have to say

Thanks

**Bush65** · 25th January 2010, 06:16 PM

I cut the flange from the 2-1/2" dump pipe and welded it to modified a 3" mandrel bend when I did this in my rangie.

**triso** · 25th January 2010, 06:36 PM

Yeah the price sound about right, I got quoated a grand for 3" mandrel bent, have put a mid-muf replacement on in the mean time.

**Jock The Rock** · 25th January 2010, 09:10 PM

Thanks for the replies

Seems as though I'm heading the right way

**C H T** · 26th January 2010, 06:10 AM

Just a quick note - don't be tempted to for too large an exhaust - if the diameter is too large for the engine total gas velocity will be reduced and therefore negatively affect engine performance. i have been advised that optimum for a 300Tdi is 2.5 inch mandrel bent. (if you use an exhaust with ordinary bends that crimp the pipe you might want to try 2.75 inch diameter pipe. When Beaudesert exhaust built the system on my 3.9 Isuzu turbo Defender they specified 2.75 inch, which has worked brilliantly. (Beaudesert explained that if the pipe is too big for the engine the effect is akin to passing the gas through a 44 gallon drum gas in = gas out but without any scavenge effect and at recduced velocity)

C H T

**dullbird** · 26th January 2010, 09:53 AM

I was told that you cant over exhaust a tdi.....

**spudboy** · 26th January 2010, 11:35 AM

Hi Jock - do a search here on some old posts by Tombie2 as he had definite thoughts that 2.5 was far preferable to 3" for some reason. He does a lot of stuff tuning TD5s, so maybe not applicable to a 300TDi, but worth a search.

HTH
David

**goldrover** · 26th January 2010, 08:39 PM

I have a mandrel bent 2.5 on my 300 with just a rear straight thru very small oval muffler & no centre muffler. This complements a vvt with a larger intercooler & tweaked pump. I am very happy with the low down pull which is what I was aiming for. Punts the 35's very nicely.

I was advised not to go too big with the exhaust, something to do with gas velocity.

cheers
Philip

**saiken** · 26th January 2010, 09:12 PM

I'd recommend sticking with a 2.5" exhaust system as you don't want to go any bigger than 10% over the size of the turbo outlet.
By using a larger pipe diameter you reduce the velocity of the exhaust gases and can increase the retained heat at the turbo and detrimentally effect the turbo and manifold. This can also reduce the back pressure on the turbo enough to cause turbo overspeed which will decrease the lifespan of the turbo greatly.

**please excuse any bad english or spelling as i've been drinking to celebrate the best day of the year!!!! [australia day]**

**C H T** · 27th January 2010, 02:20 PM

Originally Posted by C H T

Just a quick note - don't be tempted to for too large an exhaust - if the diameter is too large for the engine total gas velocity will be reduced and therefore negatively affect engine performance. i have been advised that optimum for a 300Tdi is 2.5 inch mandrel bent. (if you use an exhaust with ordinary bends that crimp the pipe you might want to try 2.75 inch diameter pipe. When Beaudesert exhaust built the system on my 3.9 Isuzu turbo Defender they specified 2.75 inch, which has worked brilliantly. (Beaudesert explained that if the pipe is too big for the engine the effect is akin to passing the gas through a 44 gallon drum gas in = gas out but without any scavenge effect and at recduced velocity)

C H T

Further to what I said above - and confirming what has been said in couple of later posts in this thread - it is important not to go too large in exhaust diameter. I recall talkig to someone some years ago (I think form Beaudesert Exhausts) that had done some serious investigation into 300Tdi exhaust diameters - they found that with a 3 inch exhaust the engine produced less torque than it did with the standard exhaust, and that, as far as I can recall, the best results were obtained with a 2.5 inch free flowing system

C H T

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