Exhaust Size for HDi

[HDiPeter]

Hi guys

What bore pipe is recommended for the HDi for a 'stage 2' exhaust?

I'm thinking 2.5"?

I have a 2.5" downpipe, drove 100miles yesterday for what I was told to be a 2.5" straight through cat-back, Turns out it's actually 2" OD (internal is like 47mmish) This seems far too small to me?

Also where might I get a full proper 2.5" system for the 306?

Thanks!

[Saxblower59]

Hi Peter,

look at a specialist exhaust place or Local supplier / ebay google

I have one look at my Profile

Andrew (Saxblower)

[Eeyore]

2.5" is the largest sensible size. you could go 3" but wouldnt be great on a daily and its pretty noisy. 2.5" should see a decent amount of gains over stock

[MY95]

2.25 is standard, 2.5 is what you want, loads of threads/stickies on this topic....

[welshpug]

standard are tapered along the system, not a single straight bore.

how much power are you making?

[Poodle]

2.5" will be plenty up to 200bhp on these engines.

[welshpug]

enough for 300 bhp tbh, unless its particularly thick walled mild steel.

[Poodle]

Diesels need more airflow than petrols because of the higher afr, plus the heads on these suffer badly with back pressure. You could probably squeeze 250 and be ok, wouldn't want to push it more than that though.

That said, i've yet to see anyone find the exhaust to be a restricting factor at 2.5" simply because no-one tunes them that far lol.

[welshpug]

Diesels need more airflow than petrols because of the higher afr

Nope, afr between diesel and petrol is very close at stoichiometric point, however the calorific value is different.

look at it as an air pump, then fine tune from there.

http://www.exhaustvideos.com/faq/how-to-...31250#easy

interesting numbers there, I haven't gone any further with the calculations, but it should be straightforward to work out what a 2000cc engine at 1 bar boost running up to 5k rpm will be flowing.

[Ruan]

Bullshit.

Go run a diesel at lambda=1 and see what happens.

[Poodle]

Hahahahahha yeah that.

[zx_volcane]

Yeah diesels move a stupid amount of air. Surprising how restrictive air filters and exhausts can be on a turbo diesel. Moving from 2.5 to 3 inch on mine was pretty evident on Darren's dyno


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[Jonny81191]

If you're after a full system, drop us a message and I'll sort a quote for you. I'd agree on going for a 2.5" system, unless you plan to make over 200 bhp.

[toseland]

I want 4...