new exhaust

PinkBitz · petrol head Joined: 13 Apr 2002 Posts: 1594

i am plannin on puttin a sweet exhaust on my second tf and i was wanting to know if a 2.5 inch exhaust wit extractors and one muff is 2 big for my stocko g161. caus i am planning for it to be loud as! but not lose too much backpressure.

goons hired goons · petrol head Joined: 04 Jul 2002 Posts: 3268

isnt that a bit big for a n/a engine?

Gemin8 · newbie Joined: 15 Sep 2002 Posts: 1

The idea of getting a big exhaust is too lose the backpressure.

goons hired goons · petrol head Joined: 04 Jul 2002 Posts: 3268

i thought that it had a detrimental effect on engine power ie it chokes it.

peteymate · tinkerer Joined: 15 Aug 2002 Posts: 306

the more backpressure the exhaust produces, the harder the the engine has to work to push the exhuast fumes out. So when you get a bigger ie. wider exhuast, the engine doesnt have to work as hard and can produce more power. 2.5" probably would be a bit too big. Go for a 2" or at the most 2 1/4"

PinkBitz · petrol head Joined: 13 Apr 2002 Posts: 1594

yeah, i was going to opt for a 2 1/4. what i meant is would a 2.5 lose compression.

Neslo · tinkerer Joined: 21 Oct 2001 Posts: 133

could this be the problem with my car? I'm running a stoko engine with a 2.5" exaust...and it seems really...sluggish. its pissing me off.

Andrew65 · tinkerer Joined: 23 Feb 2002 Posts: 303

A pipe of this size would be ok but only at high revs,benifits would be seen from a head job and cam to go with the big pipe.

macca_loto · tinkerer Joined: 30 Jul 2002 Posts: 168

If you lose too much back pressure then you start to lose power and if you have the exhaust too big with only one muffler depending on where it is the exhaust note will just drum in the pipe.

Ben Wight · backyard mechanic Joined: 04 Oct 2001 Posts: 946

Putting the way an engine works and breathes into a common analogy, the human body, you should understand this no worries.

Exhaust flow of an engine is how it breahtes, just like how a human breathes. If we are sitting down, we could probably breath comfortably through a drinking straw 5mm in diamter. This would be the same with an engine, trying to idle or at low revs.

As soon as we start to walk around, that 5mm straw will probably be restricting our breathing, as you try to breathe out harder through the straw, you actually create pressure within the straw, this is the same as engine exhaust back pressure. Imagine how much easier it would be to breathe if we now had a 10mm straw. Well its the same with your engine, at human walking or jogging pace, it would probably be comfortable to breath through a 10mm diameter straw, this would be equivalent to say medium rpm of your engine.

Now try and break into a sprint with that 10mm straw in your mouth, you will run out of breath real quick, same with your engine at max rpm, but if we had a 20mm diamter pipe, things would be fine.

so basically, for a human, the bigger the pipe, the better, and its the same for and engine, because of the huge amount of air they breathe, and engine at max rpm needs a pretty big pipe for max power. This is all fine except for one detail. If a max rpm pipe diameter is used whilst at low rpm, because of the way air flows out of the engine in a laminer form, it then enters this large pipe, and spreads out to fill the pipe volume. This causes air turbulence, and hence literally slows down the airflow at low rpm with a big pipe.

So in effect, all forms of back pressure are bad, but going to a large pipe can reduce low rpm performance due to turbulence. You have to pick a compromise between max power and low rpm power. I have no idea what engine and specs you have, but for a decent 1600, I have had good results with extractors into a 2.25" pipe, with a straight through muffler in the standard position (no baffles or chambers in the muffler at all, just a straight perforated tube), and a straight through resonator at the rear under the boot floorpan (hot dog).

As far as the exhaust being so big that your engine loses compression, this cant really happen, back to the human analogy, compression is like strength in your muscles, if you go from the 5mm straw to the 20mm pipe, you still have the same amount of muscle strength, but with the larger pipe, you can use it all, whereas the smaller pipe was choking you and you couldn't run as hard.

Now go and buy an exhaust system, should cost about $450 all fitted. But dont come back with some crappy super turbo muffler with bends or baffles or something, because the exhasut guy reckons it will work well. Ask if they have what you want, if not, go somewhere else.

Ben Wight

PinkBitz · petrol head Joined: 13 Apr 2002 Posts: 1594

yeah thanx ben. its a stocko 1600. i am opting for a 2 1/4, possibly 2 inch. all i am puttin is 1 straight perforated muffler in normal pos. wit extractors. what ya reckon?

cheers.

Ben Wight · backyard mechanic Joined: 04 Oct 2001 Posts: 946

Just a straight through with 2 1/4 pipe will be loud, most definitely illegally loud.

martin · backyard mechanic Joined: 04 Oct 2001 Posts: 900

does anyone else just click straight onto ben wights posts without reading the ones surrounding it in the thread?

Ben Wight · backyard mechanic Joined: 04 Oct 2001 Posts: 946

I have to go now, my head just exploded!

later

Adam · Site Admin Joined: 04 Oct 2001 Posts: 682

It isn't *just* ben's posts, there are a few regulars whose posts I will take the time and effort to read even if I'm not the least bit interested in the thread itself...