New exhaust system = better fuel economy ??

[1peter]

I was given a quote of $1700 the other day to fit extractors and new exhaust system to the 4.5 GU and was told by the Shop (4x specialists) that he gets about 70 extra km's from both tanks on his personal vehicle with this system fitted ?? Then, i spoke to a muffler shop local to me and he quoted me $700 for the same setup but different brand extractors and said the only difference would be that he bends his own pipes, then he said IHO i would not notice the difference between the two systems ?? Who has had a system fitted and will it improve economy as well as power ?? Any opinions welcome.

[Bigrig]

I was given a quote of $1700 the other day to fit extractors and new exhaust system to the 4.5 GU and was told by the Shop (4x specialists) that he gets about 70 extra km's from both tanks on his personal vehicle with this system fitted ?? Then, i spoke to a muffler shop local to me and he quoted me $700 for the same setup but different brand extractors and said the only difference would be that he bends his own pipes, then he said IHO i would not notice the difference between the two systems ?? Who has had a system fitted and will it improve economy as well as power ?? Any opinions welcome.

Hey mate - I've got a 2.75" system with pacemaker extractors and whilst there is a definite (but slight) increase in power, where I notice it most is in the rev range - seems to hold taller gears better and produce better torque (but that's my perception, not dyno proven). As for 70 k's extra per tank - I doubt quite that much, but you'll definitely notice an improvement - maybe 10% or thereabouts. Others would have their own experience also, so hang tight as I'm sure they'll add some comments to assist also!!

[Gert B Frobe]

Anything that will get your engine breathe and get the exhaust gases out quicker can only be of benefit. Choice of system will ultimately come down to purpose and taste.

Get the most free flowing exhaust you can afford.

[Timbo]

Hi Peter,

TLDR; Go with the $700 system for your 4.5 petrol GU Patrol.


As Gert said, any improvement to your engines breathing is beneficial as a general rule. It should lower Exhaust Gas Temperatures and Improve Performance, especially on Turbo models and it should always bring boost on quicker (lower in the rev range).

You will probably get a few kilowatts extra power on non-turbo engines but nothing that will be hugely noticable. Larger free-flowing exhausts can have a dramatic effect on turbo engines because of the exhaust gases being forced out so quick due to the Turbo, a larger pipe for those gases to escape out into is ideal. I was always told it's the first 4 feet from the Turbo dump pipe that are the most critical. But on my VL commodore, I noticed that having a barrel muffler on my system robbed me of power something shocking! You could really feel the power loss.

Anyway, off track a bit there. As for fuel consumption, lots of people agree that an aftermarket exhaust helps their economy. I guess there's a couple ways to look at it.

1. A larger exhaust allows the engine to breathe a bit easier, gaining a power increase and as an end result, not having to use the "go pedal" as much. (due to the extra power)
1a. Before my 3" exhaust on my 2.8TD, it was pretty much pedal to the metal all the time to get anywhere. They are real slugs. After the exhaust, boost came on quicker and the car moved along nicely. The difference was quite noticable. Since then, I've put on a diesel chip and she goes really well now. I've noticed fuel economy is a bit better due to not having to go flat out everywhere.

2. On the other side of things, you could say fuel economy may be worse because of the extra power, you may tend to drive the car harder.

Depends how you drive obviously. Although with fuel economy, I see many people comparing figures but what they don't include is the weight they are carrying.

How heavy is the driver? How much crap do you have hanging off the car? Bull bar? Spotlights? Roof rack? Big Tyres? Drawers full of gear?

Basically anything that creates wind drag will affect fuel figures. So it's probably not worth getting disheartened if you buy a new exhaust system and find that your fuel economy hasn't increased by 10% because the little extra bit of power gain you got has probably been offset by all the gear we tend to carry around.

Generally, you can't have power and economy at the same time. You can have a 1000kw motor and drive it ever so gingerly and get reasonable fuel economy. As soon as you stamp that loud pedal to the floor, say good bye to your economy. I know for a fact that in my VL commodore, if I drive it normally and make the turbo work throughout the rev range, my economy is crap. But, if I try and drive it in vacuum (don't allow the turbo to work much at all) then my economy is pretty good.

The difference between the two shops you're talking about, in my opinion is;

1. One is a so called 4x4 specialist. EVERYTHING 4WD related is expensive. They know, we know it, yet we pay the money anyway. It's a niche lifestyle we live and we get charged accordingly. He bends his own extractors and I would assume, uses Mandrel bends in his pipe work so that when the pipe is bent, the bend doesn't flatten out. Think of a McDonalds straw. If you bend it, the bend will flatten out. This is a press bend. Now imagine that some straw with the same bend, but the bend has kept it's shape so that the diameter of the pipe is virtually the same from start to finish. Obviously, gasses passing through a Mandrel bent pipe will have an easier time getting from one end to the other than passing through a press bent bent pipe.. and it creates a bottleneck.

2. The other bloke sounds like your run-of-the-mill local exhaust shop who deals mostly with family cars. He has a Mandrel bending machine (or maybe not) but for regular exhaust systems, doesn't need to use it as most cars aren't performance based. If you ask for a Mandrel bent system, he can do it but charges more because he has to use another machine.

The difference between press bends and Mandrel bends on a stock petrol 4.5 GU would be negligible. However, on a Forced Induction car (Turbo/Supercharged) and even hi performance V8's, there's is more of a difference because those motors are working a lot harder. Any press bends in the exhaust will only slow gasses down which is the opposite of what you want to achieve.

Again, get a cup of water and put a NORMAL straw in it. Bend the straw and try sucking water through. You'll find that it's quite hard. Now, get one of those cool FLEXI straws and bend that at the flexi part and voila, water easily gets sucked up. Bit of a weird way of describing press bends vs mandrel bends and performance etc.. but it was the simplest way I could think of!

Anyway, I've completely rambled on.. hope you can get something out of all that.

[1peter]

All good rambling though Timbo, lol, thanks.