Exhausted Opinions
 

What do you fuckers prefer when it comes to making a cheap exhaust. I'm gonna do a 2.5" all the way back from the downpipe (read: when I get my turbo kit) but what do you guys suggest as far as a muffler goes? Something cheap but doesn't sound like ----. :6


Oh yeah I've been told that turbos cancel out noise... If this is true does that mean the exhaust noise won't sound like a hive of angry metallic bees coming out of my ass anymore?

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Turbos do quiet the exhaust. I had a glass pack and thrush muffler on my hatch with a header, and the put the turbo on and it quited down a lot.

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turbos help get rid of the raspy sound. i just made a 2.5" exhaust out of an intercooler kit from racing solutions. it is 2.5" from the turbo to the muffler with no cats or resinator. i used a $20 stainless ebay muffler and i think it sounds awesome.

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Get a sound clip of that ----...

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2.5 straight pipe with a blown rez and a glass back
no rasp, sounds great and is quit till waste gate opens up

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Nice ;D

Looks like an exhaust is going to be cheaper than I thought.

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i will try over the weekend

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Go big or go home....I'm much loving my 3" exhaust. O0

http://www.miataturbo.net/~web1_brai...ol_exhaust.jpg

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3" is way overkill. im not saying there is anything wrong with it, but it is overkill on pretty much anything built on this site

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may be true, however, the 2.5" system has a cross sectional area of 3.91761 square inches; a 3" is 7.069 Sq"...80% larger.

while it certain may be more than you need, there's no way it will hurt you, and I'd suspect you'd see better spool/ouput all other things being equal.


but yes, to answer the first question, the turbo acts as a muffler, wire your wastegate open and you'll notice the difference right away. a 2.5" system with a muffler alone will not be loud. Make sure to get a straight-through designed muffler to prevent flow restrictions/loss.

fwiw, my 3" exhaust with a small magnaflow muffler is much quiter than the same engine with a header, 2.25" exhaust with an additional resonator and larger muffler.

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yea, im not saying it will cause any negitive problems, just saying its overkill

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summit muffler = 17.95
Flow Tech glas pack = 18.95

and what ever your piping you choose = sound good for cheap.

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how long dose a glass back last before it burns out when your running no cat

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depends on richness, speed of flow, egt's, all of that stuff. i had a dynomax race (aka summit bullet), after about 75 miles it wasn't really getting any louder.

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get a magnaflow or simliar. as nice as the price tag of a summit racing muffler looks, the internal baffles kill flow. I'd expect a loss of spool in the 400-500RPM range in that muffler alone in the same size vs. the magnaflow straight through.

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2.5 is good for like 450hp, 3" over 650.

2.5 is plenty.

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But doesnt a 3'' have more response than a 2.5?

Turbos dont need back pressure, is it not a case the bigger the better?

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you would never notice it.

and back pressure is a myth. its all about velocity

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thats sweet i thought i would have to up grade to 3'' when i went for more hp
now i dont have to do a under axle and can keep my sleeper tip

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i have 3in with high flow cat 20in or so resinator, and a flowmaster muffler, and its not loud when at idle or regular driving, sounds good. But if i get on it or if im on the high way it gets a little loud, ill throw some ear plugs in on long trips.

But when the wastegate opens, the angry bees come back :'(

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at low rpm when you step on it, the exhaust is flowing plenty to offer no restriction to the turbo, and thus a near ideal pressure drop, all this exhaust sizing is done for peak output. response difference would be almost completely zero.

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pressure drop is key. The restrictions of the tailpipe are somewhere around: the cat (60%), the muffler (30%), and the tubes (10%).

High flow cats and zero restriction mufflers are key.

Measure the turbine exhaust housing outlet for diameter. That should be the first 10-15 inches of the downpipe. From there, expand it 1/2 inch, run another 10-15 inches and expand another 1/2 inch. My exhaust starts at the turbo at 2.25" and ends at 3", stepped to 2.5" and 2.75" in between. The difference between that system and my previous 2.25" catback (same downpipe) is almost 1000RPM faster spool....

http://www.bellengineering.net/Image...foreafter1.jpg

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So a 3'' from the turbo will make the car boost 1250rpm earlier?

in my country all the big guns run a 76mm but it cost 2 months wages. so most cheap skates like me run a 63mm which is only a weeks wages.

what performance am i missing out on, now that we have proof less back pressure = more power/faster spool time/more response.

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Just like your intake manifold tapers in to increase the velocity, the exhaust should taper out. A 3" DP on a turbine with a 2" exit will probably cause turbulence and impede flow as the exhaust gases get lost in the mix filling up a large void.

the general rule is simply: Back pressure in an exhaust system is evil.

the difference in 2.5 piping and 3.0" is trivial, however the cross-directional area is 80% larger....

The people working for 2 months with 3" exhaust most likely get paid 1/10 the amount of the people working 1 week.

It's quite possible my 3" catback may or may not give me any extra benefits of a 2.5". The something like $20 difference in the final cost was enough to go bigger.

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What i just upgraded my Tb from a 54mm to a 70mm was that a ---- up?

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no, the individual runners still taper down in diameter as they enter the head. You're simply allowing more airflow volume to enter into the manifold.

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thanks homie...

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holy ---- dude keep it up
+ 1 noob of the year ;D

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? are you saying BRAINEACK IS WRONG?

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hell no if you think about it, it makes sense
i dont think a noob has ever contributed such good info

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i was going to put a 2.5 inch dp straight on my 16g
but now im going to redesign the flange/dp

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any change in diameter is a BAD thing. it causes turbulence.

intakes are tapered with velocity stacks because they are at a full vacuum at the inner end and atmos at the outer end.

you are right about cats (what are they? wtf, who has a cat :-p) and mufflers being key though.

stepping the exhaust part way along is a bad thing. if you had simply changed your mufflers, spool would havce increased, stepping up to 3" the whole way down would work better than the stepped system.

stepping up LOSES velocity in the same way that velocity stacks gain it in an intake.

besides which, the air coming from the turbine is rotating rather quickly and as such has a centrifugal force acting on it, and wants to escape outwards as well as backwards. going straight to your final diameter and not changing and not interfering with the flow is best.

your final diameter is length dependent too, just like wiring. if it had to go 6m instead of 3 you would need to upsize the exhaust

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Exactly that was kinda the point, I didn't elaborate, the velocity is dependent of the cross-directional area. The steady increase in flow area causes a steady decrease in velocity. I had a lengthy conversation with Corky Bell about it when he built my downpipe and it's really hard to argue against him. From his engineering standpoint it makes perfect sense, in the real world will it make a huge difference ???

All I know is I'm happy with the end result. Now if I can figure out how to make my head flow like a honda....

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I have little respect for the man. a lot of what he says is outright wrong. i would however love to argue with him. at the least it would be entertaining watching him get frustrated.

one size pipe from end to end is best sized appropriately for acceptable pressure build up at peak power for the given length.

you define acceptable pressure build up.

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Call him up, he loves to chat ;) I respect him, but I don't think he's the final word and/or god, just to be clear.

The goal is flow; you want to keep the exhaust gases moving. A rapid decrease in temperature or rapid expansion and turbulence should cause the gases to slow. Starting with a matching port will keep the temps high and exhaust moving, as the exhaust cools the second it leaves the cylinder. This is also why we don't tend to port the exhaust on the head, but we do port the intake. Again, to keep the exhaust moving. It's really all a compromise. Throwing the 3" pipe on a 2" turbine outlet will cause both turbulence and a rapid decrease in EGTs, slowing the flow. But if you keep the exhaust moving out of the turbo with a matching port size the back pressure should drop more, since the area behind the turbo wants to keep moving rapidly into the stepped exhaust.

you may be right, i may be wrong. I don't see anything wrong with the idea. I'm no engineer or expert, but I do know the difference from my 2.25" to my 3" catback was substantial.

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trouble is, the air exiting the turbo is extremely non laminar in the first place. once the turbulence and twisting settles down the pipe a little bit, thats where you need to care that its dead smooth to the end. the only thing the turbine cares about is having a low pressure zone to dump to. the exhaust is expanding as it goes through the turbine, that is what makes it work. the more freely it can expand as it exits, the better. a dump out the side 6" wide would be nice, but kinda loud. its impossible to get better than that. velocity in exhaust systems is used for scavenging usually. there is only scavenging before the turbo because of the pressure pulses and runner arrangement.

as for porting intakes, intakes are the path that is under suction. when under suction, the restriction causes a larger pressure drop to the end and you get less air in. when under pressure with a piston pushing the gas out, the exhaust can be pretty crap and will still work ok. its forced to leave regardless of how nasty the engine is. improving things there reduces pumping losses (power required to push ex out) and heat because the overall pressure in the exhaust track is on the average, lower.

disclaimer : very tired and very pissed off right now, if i muddled something, dont jump on me too hard. should be pretty on the money though.

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ok time for some ms paint
would there be a big difference in the flow of these 2 down pipes
the turbine is from a 16g (not sure on diameter) and the dp is 2.5''
i already have the flange for #2 so id have to get another one and a step up pipe, i also think id have to make the 90 bend down a bit sharper for space


Attachment 22125

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if the distance is as you say, the difference would be negligible. i personally went for number 2 on mine (hy35 dumping into straight 4 inch and then tapering down to 3 inch over 300mm because 4" muffler parts come from trucks) i would have preferred to use a 3" straight off the exducer, and just use the 4" flange for mounting, but it was easier this way. i certainly would have gone to the trouble of tapering up from the turbine to the pipe.

up to you. we are splitting hairs.

i just wanted to point out that the stepping the exhaust part way down wasnt ideal. thats all.

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I'm not really arguing, it's the only way, when I started talking to Corky, I was really taught. With that said, here's a pic of mine.

2.5" to mathc my turbine, and 2.75" after the swag joint.

http://www.boostedmiata.com/exhaust/...nifold_002.jpg


3" at the testpipe.

http://www.boostedmiata.com/exhaust/exhaust005.jpg


either way will work, without back to back testing, its hard to say which one is best, the difference could easily be none. I'll comprmise and say as long as you do 2.5" mandrel you should be good. how 'bout that?

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ya it will be all mandrel bent
ok ---- it im not going to bother since i got the ---- already