Having a Phat exhaust -

Caporegime
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So, i wondered as many people do, what exactly are the benefits of a fatter, wider, straighter exhaust?

Does having a big phat pipe sticking out the tail end make a tangible difference compared to a smaller peashooter that winds its way around the back side of the car?

Yes.

My car hasd a JDM Apexi Hayabusa which is a single exit with pipework at 76mm increasing to the tail.

I also have an exhaust bung and a boost controller with which to test the setup.

being MOT day, i popped the bung into the exhaust and tried a run on the motorway. The acceleration seemed much more pedestrial than usual, and boost peakes at about 0.72 bar (Blitz DBSC).

Finish MOT, remove bung, drive home and voila, same piece of road etc same conditions, car now gets to 0.84 bar with no alterations or tweaks. Same EBC settings.

So what does this mean?

Exhaust bungs are bad. its official. MOT testing Yes, performance, No.

Fatter, straighter exhauists will help you to produce more power by reducing the pressure on the exhaust gas outflow, IF the existing diameter or smallest diameter is actually blocking or inhibiting the boost escaping quickly enough.

Sounds simple, but i was actually shocked at just how much the bung reduced the forward accel of the car itself.
 
Associate
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Yes, but you have a (probably modified) turbo car. The Barryboys who fit the proverbial dustbin to a standard Saxo don't usually see that a bigger exhaust will usually slow down the flow of exhaust gasses from a small NA engine.

Think of a garden hosepipe that has water running through it, with someone putting their finger on & off the end of it. Doesn't the water actually come out quicker if you "restrict" the flow a bit?
 
Associate
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In general with a turbocharged car if you free up the exhaust, you will make a bit of peak hp.

You will however lose torque at a lower rpm. If you drive about on normal roads the OEM systems are (usually) a good compromise.

Also the method by which your Blitz boost controller actually controls boost is critical in
your testing - does it use feedback?
 
Permabanned
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I wouldn't be very suprised that blocking the exhaust partially is going to have a corresponding effect on power production.
 
Permabanned
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Having a bit pipe sticking out of the back just makes noise and nothing else really if the rest of the system (Pipes, cat, downpipe/manifold) are all standard.

Edit: I made a thread on PH a while ago asking about exhaust back pressure etc, worth a read: http://www.pistonheads.com/gassing/...+someone+explain+exhaust+back+pressure+to+me?

Not really, try running a straight through pipe with no back box and say it just makes noise, a backbox reduces noise and turns it into a nicer note. Most of the time.
 
Soldato
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Yeah on most engines (this side of maybe a v8 anyway) if you remove the exhaust at the downpipe it sounds frankly horrible
 
Soldato
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Yes, but you have a (probably modified) turbo car. The Barryboys who fit the proverbial dustbin to a standard Saxo don't usually see that a bigger exhaust will usually slow down the flow of exhaust gasses from a small NA engine.

Never heard them called barryboys...i must remember that next time lol

I love the pops and bangs of my Milltek decat tbh, open it right up and after about 4k it sounds raspy like a rally car :p

I have never heard a rally car with that sound lol :p
 
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Soldato
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I'm guilty for having a phat exhuast, get no end of ribbing from the guys at work.

Japspeed cat-back on a 1.3 Starlet turbo, innit blad.

EDIT: To be fair, when I first got it I thought it looked a bit too big, but hey, it was a brand new system practically for 100 notes, and I needed some form of exhaust to get it on the road!
 
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Soldato
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To add to the Chavvometre!


If i had known at the time i decided to sell her, that i was getting a house with 2 big drives i would of kept the ST for the mrs to run and for some track day fun for me! Was a awesome car and sounded awesome!
 
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Caporegime
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I'm guilty for having a phat exhuast, get no end of ribbing from the guys at work.

Japspeed cat-back on a 1.3 Starlet turbo, innit blad.

EDIT: To be fair, when I first got it I thought it looked a bit too big, but hey, it was a brand new system practically for 100 notes, and I needed some form of exhaust to get it on the road!

Hmm at work they all tell me my exhausts getting louder. It's not, it's the solid mounts blud.


But yes of course not every car can benefit, but definitely those pushing a lot of fumes out the back.

it eases the restriction on the turbo and allows it to work more easily to produce the same, or more power.

Piping like this
 
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Associate
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Having a straight exhaust has it's benefits.

http://vimeo.com/47179122 this has straight pipes and makes the most glorious V8 sound I've ever heard, definitely the best car I've had the pleasure of driving.
 
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