Exhaust system

[Morton]

2 yrs ago I replaced the entire rear muffler that was damaged on a rock & torn open with some piping on my GU, at the time the pipe made to fit cost $60, today I took that off to fit another muffler on (second hand) & out of curiosty started the thing up without anything on the back section, there is no change in noise, not louder at all, why the hell is the muffler there? I was quoted some ungodly amount 2 yrs ago to replace the last section hence the section of pipe for $60, is it needed for back pressure, I cant for the life of me imagin that being the case, it is a 3L diesel

[threedogs]

Lots of turbo diesel 4x4 run straight through systems ,back pressure must be for non turbo and petrol maybe.
But can't have them too loud these days. Exhaust prices are up there around $1000 and up for some

[Morton]

true & this is the reason I swapped the rear section out for a length of pipe, absolutely no change in the note or the noise coming out of the car, I fitted the pipe back in as I would probably only damage the muffler anyways

[threedogs]

keep an eye on your boost and EGTs, they maybe affected by exhaust change

[mudski]

keep an eye on your boost and EGTs, they maybe affected by exhaust change

Funny about this. Everyone says that, but when I went from stock to 3inch Redback, boost and EGT's did not change at all. As for back pressure. You don't see race cars, even turbo charged one using mufflers, the quicker the gas gets out of the exhaust the better the engine will flow. IMO, back pressure is an old wifes tale.

[Winnie]

Funny about this. Everyone says that, but when I went from stock to 3inch Redback, boost and EGT's did not change at all. As for back pressure. You don't see race cars, even turbo charged one using mufflers, the quicker the gas gets out of the exhaust the better the engine will flow. IMO, back pressure is an old wifes tale.

Back pressure is necessary for sure. Not in the form of mufflers but say for example if you have no exhaust at all your car will run like absolute crap

[BigRAWesty]

Back pressure is necessary for sure. Not in the form of mufflers but say for example if you have no exhaust at all your car will run like absolute crap

But this is a tuning issue. Engines are tuned to run with shout to comply with noise and emissions controls. The easier an engine can breath the better they preform as the expel old gasses and draw new fresh gasses easier..

As for mufflers, well it depends on if its turbo or not? If its turbo drop all of your mufflers off and enjoy earlier boost and a bit more power..
If its a NA, you'll need some mufflers to kill the drone but you can still increase power by allowing it to breath with high flow mufflers..

Kallen Westbrook
Owner of
Westy's Accessories (http://www.nissanpatrol.com.au/forums/showthread.php?15134-Westy-s-Accessories.-A-small-back-yard-builder.)

[threedogs]

Don't too short an exhaust burn out valves on petrol, bear in mind I've just taken a handfull of meds, could kick in anytime ,might have already who knows, who cares yeah har , waffle, waffle ,waffle
Mudski a race car is designed to accept a straight through 3-4" system, talking here about changing from std to infinity and beyond ok that was the meds'
Your 4x4 must have shown some type of change with exhaust change, and agree 100% the quicker you get out the air the better, but gotta get it in as quick to suit ie match

[mudski]

What did you wash your meds down with tonight TD? I washed mine down last night with a glass of red. Man I slept good. :) Felt alright this morning too. :)

[Alitis007]

You need back pressure for low to mid range torque unless your motor sits at high rpm ie drag car so the air going out is the same speed going in. Your exhaust size meeds to match your motor capacity or driving style, on my rotary i have a single 3" turbo back to the hollowed out cat then it splits to twin 2.5" pipes thats tuned length that go into a pair of Varex mufflers (they are adjustable) when the mufflers are open (no back pressure) its gutless down low up untill 3500rpm and the turbo hits boost and it takes off, but when they're shut (back pressure) from idle to 4,000rpm it flys and then hits a brick wall. Thats when you feel the motor start to struggle to push the air out! 24672 this is my system before i made the turbo to cat section!

[threedogs]

You've had schooling hey , nice exhaust too ,no Milo can hanging off the back ,
Mudski I'm told Jack Daniel cans are fine to wash down meds, I'll sleep right through but wake way too early, 5.30- 6 always have
There must be a formula or such to work these things out its not just ,whack a 3" system on and alls good, Who wrote the back pressure book??

[Alitis007]

School? No mate, more like the trial and error. Talking to old school racing mechanics helps too! And thats 304ss i like the way it rattles lol

[mudski]

Kinda doesnt make sense there. Air should be going in and out at the same speed regardless of the power range.

I tapped that app...

[Alitis007]

Kinda doesnt make sense there. Air should be going in and out at the same speed regardless of the power range.

I tapped that app...

No intake is cold so its dense, the air particles are closer together air going out is hot so the particles are spread out. Now thick of your exhaust as a garden hose, if its really thin it comes out with heaps of pressure but not that much in volume say like 5mm, if its too big like 20mm it comes out with no pressure but alot comes out BUT in between say 12mm you get good pressure with a good amount of water flowing it from it. Hope that makes sense its alot easier to explain verbally lol

[BearGUST]

Agreed, gasses flow faster when hot. You want to keep them flowing fast and staying hot, too big a pipe allows them to cool down and slow down.
Power up high isn't much good if you're losing bottom end. I made a few sets of headers for an old 4by of mine, first set made high end power, third set lost a tiny bit of top end but made an awesome change to low-mid range torque by having smaller secondary pipes.

[mudski]

Maybe on a N/A engine but ib a turbo charged engine the hot gases are forced out anyhow so bigger pipe wont matter IMHO.
Plus gases do flow faster when hot but not as fast as cool air through the same sized area its flowing through.


I tapped that app...

[BigRAWesty]

It's not the flow that changes. The air flows in and out the same.
It's the expansions of the gasses changes, thus why exhausts are larger than intakes..

Kallen Westbrook
Owner of
Westy's Accessories (http://www.nissanpatrol.com.au/forums/showthread.php?15134-Westy-s-Accessories.-A-small-back-yard-builder.)

[BearGUST]

Sorry, I did mean to mention that. Forced induction cars are a different story.

Exhaust valves are larger for scavenging.

[Alitis007]

Maybe on a N/A engine but ib a turbo charged engine the hot gases are forced out anyhow so bigger pipe wont matter IMHO.
Plus gases do flow faster when hot but not as fast as cool air through the same sized area its flowing through.


I tapped that app...

Induction system doesn't matter still the same principal for a combustion engine " Suck, Squeeze, Bang, Blow" its finding what size exhaust has the right air speed to suit your needs

[Morton]

so the answer to my question I suppose after all that is I dont need it?

[nissannewby]

Yeah mate scrap the muffler no need for it.

[BearGUST]

Haha, yeah things went a little bit off topic!
Agreed, scrap it.

[Bugjuice]

I use to have a suzuki sierra 1.3L with extractors and a 2 3/4 straight through no cat pipe. Wasnt that loud, had a bit of a roar, but not loud. It had pretty much zero back pressure. When taking off from stopped the engine would stall really easily unless the engine was revved enough to create enough exhaust gasses to pressurize. You couldnt just stick the boot into it, you had to give it time to get sorted, however once the revs climbed the pipe allowed the old girl to rev like crazy.

The muffler reduces sound from the engine, if you have a straight through it obviously restricts the gases for a shorter time and usually is louder. My v8 was so restricted with 2 mufflers, one was removed by previous owner to get it to run a bit freer.

In my opinion removing the muffler wouldn't make much difference to overall performance or volume if the exhaust stayed the same length. I think in the case of the 3L its more the diameter and length of the pipe that makes the difference. I bet if you removed the cats it would splutter with no back pressure.

[Clunk]

Got a 4.2 petty, noticed recently that the exhaust fumes now have what is best described as a sickly sweet smell, could this be because the cat has now failed?...... No smoke of any colour, just the sickly sweet smell.

Don't stroke it, TAP it!!!!.....

[Clunk]

Got a 4.2 petty, noticed recently that the exhaust fumes now have what is best described as a sickly sweet smell, could this be because the cat has now failed?...... No smoke of any colour, just the sickly sweet smell.

Don't stroke it, TAP it!!!!.....

Any ideas gladly welcome........ Apart from yours Grunter ;)

Don't stroke it, TAP it!!!!.....

[Morton]

sometimes a sign the cat failed, use to be worse in some of the older unleaded cars