exhaust size

gday just a quick ?... what size exhaust do ppl recommend 2.5in or 3in? also is there much difference...
cheers

if its the d22 your talking about, most people (exhaust shops) recommend the 2.5". i had to tell them i wanted mine in 3". i think the 3" is a bit less restrictive than the 2.5" thus allowing the turbo to spool up a bit quicker and at lower rpm. but from what ive heard there is not to much difference the 3" and the 2.5 cos really its only another 12mm. guess it just comes down to personal preference

2.5" is quiet, if you want noise go 3"

My 3 inch exhaust when the free flowing muffler is in is quiter than it was stock, without the muffler is a bit louder.

Matty there is a big difference in area between the two:

3 inch = 17.9cm3

2.5 inch =12.4cm3

A touch more than 40% more volume in the 3 inch.

I really don't think a 2.5L engine needs a 3 inch exhaust though. I would just get 2.5 if I had my time over.

I am in two minds as I plan to build my own for my ZD30 D22. 2.5" is probably fine and would make the dump pipe a bit easire to fabricate. Open to someone to convince me that 3" provides a real benefit though.

When experimenting I found that the biggest difference was removing the rear muffler, everything else was pretty insignificant in comparison.

i found much the same. main muffler made the biggest change, replacing the cat with 3" dump didn't make as a difference.

Matt76 said:

My 3 inch exhaust when the free flowing muffler is in is quiter than it was stock, without the muffler is a bit louder.

Matty there is a big difference in area between the two:

3 inch = 17.9cm3

2.5 inch =12.4cm3

A touch more than 40% more volume in the 3 inch.

I really don't think a 2.5L engine needs a 3 inch exhaust though. I would just get 2.5 if I had my time over.

Click to expand...

matt, dont know how you done those calculations but put that way i guess there is quite a in difference

matty said:

matt, dont know how you done those calculations but put that way i guess there is quite a in difference

Click to expand...

I just worked out the area for each of the pipes to compare them. I'd love to say I remembered how to do it from school, but I had to google it I have had far too many beers between then and now.

G'Day tuffnav,
I went with the 3" full system with dump pipe on my jap built 09 model D22, its a fully manufactured and designed system from Taipan Exhausts.......there must be a reason they go with the 3" systems or they wouldnt do it I guess, mine isnt really any louder than stock only marginally, might get a little louder over a bit more time. It definetely made a noticable difference over the standard system though. As for a 2.5" or 2.75" system I havent driven a Nav with one so cannot compare but I am more than happy with my setup.
Cheers Matt

Matt76 said:

I just worked out the area for each of the pipes to compare them. I'd love to say I remembered how to do it from school, but I had to google it I have had far too many beers between then and now.

Click to expand...

I'd done the calcs as well just out of curiosity.

The formula is simple: pi x radius x radius

In the 2.5" pipe (63mm) the radius = 31.5mm so area = 3.1415926536 * 31.5 * 31.5 = 3117 square mm

In a 3" pipe (75mm) the radius = 37.5mm so area = 3.1415926536 * 37.5 * 37.5 = 4417 square mm.

It's a big difference, for not a lot more pipe. If you've dabbled in fluid dynamics (and air is considered to be like a fluid when working out flows), the air near the wall of the pipe moves much slower than the air further way. This compounds the effect with a larger exhaust - so just half an inch gives a far greater flow.

The real question is: does the Navara *need* that? I don't know, mine's only just coming up to 4 months of age and still sports its original diaper.

Hello all - My 3" with 3" dump and Hi Flow cat and Resonator - is barely any louder than Std - ( Im 51yrs old and wish it was louder!!!!!!!!!!!!!!!!!!!!! ) but the turbo whistle is tops thru the gears - and not NEEDING to go over 2500RPM - 09 STr 2:5ltr

i,ve got a d21 with a off it face petrol non turbo motor with a 3" exhaust and it bloody loud