Patrol ZD30 what is better 2.5" or 3" exhaust?

On Patrol (Aust.) replied:

gompy
In West Sydney, talk to Total Care 4WD 7 Hills

He has just removed my Cat converter and put in a straight through pipe with instant results in performance & fuel consumption.

This makes me think that my Cat Conv was on the way out, Jason suggested that the conversion really does make a difference.

Try talking to him. Jason. No bull shyte, just good advice.

Total Care 4wd
Un 1/ 13 Bearing Rd Seven Hills 2147
(02) 9838 9779
Colin. Thumbs UpThanks 0

Wayne-o replied:

gompy,
fitted 3" to the 4.2iTD, instant improvement......so much better
beaudesert system. $1000
i fitted it myself, bit of skin off the knuckles but its worth it!
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Leroy replied:

There was an exhaust guy on the outler limits forum and I called him up to have a chat. He recomended a 3" system with a hi flow cat and you didn't necessarily need a muffler. It was mandrel bent and cost around $1100 but that was becasue of the custom made hi flo cat. He has done them but hadn't recieved feed back on performance and I never got around to calling him back as I ended up with a DTronic. He's located in Croydon. I don't know for sure but if the vehicle had a cat then it has to retain it unlike the 4.2 that has no cat to begin with and he was keen and recommended to keep the vehicle legal.

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Member - Bucky (VIC) replied:

Had my Navara opened up with a 2 1/2 " exhaust, into a straight thru hot-dog muffler, and dumped on the ground, beside the spare tyre.

Beautiful

Instant power difference, not so much on the economy, ( bummer )

Cost $ 220

Originally wanted a 3" but Exhaust bloke ( also a mate ) talked me out of it,, something about back presure and turbos ( " 6 cylinder diesel's need 3" ,, 4 cylinder diesel's need 2 1/2" ," ,,was his quote to me )

Great for towing, our camper, no need to try to hard, it just does it easier, and I have ben over the leadfoot thing for 20 years now ( well almost )
There is still a little hoon there I am sure , ( somewhere )

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Member - Bruce and Anne replied:

Firstly my two MUs have 3 inch mandrel bent systems, probably 12% to 15% improvement in power, nothing in economy (foot closer to the floor haha).
Now in the Marine industry boats have huge exhausts, cause they have the room, but an example: a Yanmar 4 cylinder turbo diesel of 3.45 litres water to air intercooler produces 230 hp/171 kw, not bad for a motor of that size and they have been around for some time, but the answer maybe the 6 inch exhaust coming out of the turbo and then 8 inch after that.
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GU3.0 replied:

I had a 2 3/4 mandrel bent exhaust made and fitted by Beaudesert Exhausts. The original cat pipe was removed and a 2 3/4 pipe was fitted inside. The resonator was removed along with the massive factory exhaust. It now has one smaller exhaust. Was advised that for a 3.0 4 cylinder 2 3/4 was more then engouugh. Very happy with the performance. I think the exhaust made more of a difference then the chip.

Cheers
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GU3.0 replied:

Hi,
I paid $860 for the exhaust (fitted) I also have a rapid chip, and with both chip and exhaust my patrol produced 130hp at the wheels on the dyno. I think that to really appreciate the HP difference you have to get both chip and exhaust done. However having said that..... i noticed a better gain from the exhaust. The exhaust alone increased low down torque and i was able to hold 4th gear in soft sand as opposed to ringing the vehicles neck in third.
I also noticed that i was able to drive around corners and round abouts in third as opposed to having to go back to 2nd. I know doing this is probably not the best for the gear box however.... it gives you some indication of power gains from the exhaust system alone. Make sure you get the cat re piped or purchase a high flow version. The pipe inside the original cat is the most restrictive part of the entire system on the 3.0 GU.

I am selling my GU at the moment as i have purchased a ute. If my vehicle does not sell within the next week or so i will be selling the exhaust and chip if annnybody is interested. (i wil need to exchange the system for an original set up)
Cheers
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Chaz replied:

Gompy
If you still intend to run EGR, then 2 3/4” should be more than enough, but if you block the EGR system you can open it out as much as you like, provided you have some boost control installed . EGR needs some restriction in the exhaust, but not too much. The cat is the source of the most restriction and retains a lot of heat, but if it’s removed it will increase turbo spool up and the associated boost spikes. A 2 1/2” flow through system would be next to ideal for a standard car or a chipped car providing a moderate performance improvement. Opening the exhaust up will lower peak torque in the rpm range and lower low rpm EGT’s, but can have a negative affect on boost.
There is a lot more to this than some people realize and the ZD30 is already a sensitive motor, so doing one modification without doing the other can have negative affects. Having said that, they do have plenty of room for improvement.
I use a 2 ¾” dump (no cat) and a 3” flow through system with two 3” resonators that are specifically designed for their applications eg. one for the middle and one for the back. I have no EGR and use a manual boost controller that limits my maximum boost to 18psi at 4000rpm. I don’t use the VNT control solenoid.
Driving around the city, my EGT’s rarely exceed 250C and I still average 11.2L/100.
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