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Old 03-20-2006, 12:34 AM   #1
Dauntless
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Question NA exhaust, need opinions!

Lately I've been planning to build a 2.5" side exhaust for my NA 244. My aim is for a very high flowing exhaust, though still be legal in terms of noise levels.

I Went to the exhaust shop today to see what mufflers are available. Some of the options I have:

1 - Single muffler in the space for the cat
2 - Pair of bullet style resonators welded together

Any oval 2.5" straight through mufflers seem to be at least 4.5" in profile, which would leave the muffler hanging too low, in my opinion.

The idea of a pair of bullet style resonators appeals to me, but would they be too loud? Keeping in mind that they are louvered core. (I figure I can get away with louvered core because of the larger pipe size)

Your opinions would be greatly appreciated. Oh and please don't tell me to +T, lol.

Thanks.
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Old 03-20-2006, 12:43 AM   #2
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I think the best bet would be a 2" exhaust. i'm sure you have heard it before but N/A needs some back pressure. Check out either sam steffanson or (damn forgot the companies name) 4 to 2 to 1 manifold hook that up to a 2" straight pipe and you will have the most wicked sounding volvo.
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Old 03-20-2006, 12:50 AM   #3
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Oh sorry, I forgot to say that I already have a good set of headers, and they are 2.5" outlet.

A 2" straight piped exhaust would be incredibly loud. I was running a 2" system with just a stock resonator and that was far too loud.

I have heard that NA's don't need back pressure, but they do need a header of good design. Anyway, I'm definately going with 2.5" if I can, I'm concerned about noise levels, hence this thread is about mufflers.
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Old 03-20-2006, 12:57 AM   #4
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no NA's do need some backpressure unless you want the trade off of off the line torque. I've ran a high flow muffler and glasspack, off the line torque suffered, I could feel it. Maybe if you're running an aftermarket cam it wouldn't be so bad or there wouldn't be a difference though. I would go for an "in between balance" with some flow gain while still having some backpressure.
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Old 03-20-2006, 01:00 AM   #5
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Ahh ok. I'll be running a H cam, so I'm not overly worried about torque. My main concern is noise level.
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Old 03-20-2006, 01:08 AM   #6
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Straight pipe does sound pretty sweet, too bad it gotta be so damn loud. Anyways, a buddy of mine put a DC sports tcs muffler on his high compression pinto, http://www.dcsports.com/productSubCatImages/49_1_f.jpg

It sounds really good, nice tone, and it sounds like its growling when you put more rev's through it.
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Old 03-20-2006, 01:09 AM   #7
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Straight pipe does sound pretty sweet, too bad it gotta be so damn loud. Anyways, a buddy of mine put a DC sports tcs muffler on his high compression pinto,


It looks like a trumpet, but sounds really good, nice tone, and it sounds like its growling when you put more rev's through it.
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Old 03-20-2006, 01:10 AM   #8
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I don't think that's going to fit under the floor of a 240!

Please read the first post thoroughly.
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Old 03-20-2006, 02:37 AM   #9
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F backpressure. You don't need it, you just need to NOT oversize your piping. Anyway, that's not what this topic's about, so let's not BS about that crap.

If a stock resonator with 2" piping was too loud, your double bullet muffler system is also going to be too loud, if you ask me. I can't say for sure, because I don't know the size of the mufflers, but I'm very positive it'll be too loud.

May I ask why you want to have a side exit?
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Old 03-20-2006, 02:52 AM   #10
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the total length of 2 bullet resonators together would be roughly 25"

I would prefer a side exit because it's much less complicated in terms of piping, and saves me buying 5 mandrel bends at $30 each.
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Old 03-20-2006, 04:18 AM   #11
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Quote:
Originally Posted by Dauntless
the total length of 2 bullet resonators together would be roughly 25"

I would prefer a side exit because it's much less complicated in terms of piping, and saves me buying 5 mandrel bends at $30 each.
can't you just do an under-axle on a 240? that would mean you wouldn't need any mandrel bends
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Old 03-20-2006, 04:24 AM   #12
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I once ran 4-1's and then straight pipe on a worked 1.3 Ford escort motor (cause I smashed the rest of the system out driving off road). You could hear me comming from streets away. I used to blow fireballls on decel and the noise was something you wouldn't believe. Really really good fun.


What I would do is find some big second hand (late model) mufflers. Should be able to pick them up cheap from a good shop. Lots of people buy a late model car then get the system done ASAP. Then mount them in the normal places and run full pipe. not what you want but making a short pipe quiet is much harder than a full pipe. You want to cool and slow the gasses. Having a baffle there will also reduce noise. If you go for small mufflers it's going to be restrictive but a decent large one wont be. The other option is finding a wide but shallow muffler or two. They are out there and a decent shop should be able to find them OR you can hunt around and get them to fit it. any restriction should be placed on the last section.
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Old 03-20-2006, 04:25 AM   #13
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That IS under axle. I would need 2 bends to get around the fuel tank, and 3 bends would be necessary to get 2.5" pipe under the axle with sufficient clearance.

So who thinks a pair of bullet mufflers would be too loud, keeping in mind they are louvered core?

Who thinks I should install a small muffler in the space where a cat would go?
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Old 03-20-2006, 04:42 AM   #14
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Quote:
Originally Posted by AJS
The other option is finding a wide but shallow muffler or two. They are out there and a decent shop should be able to find them OR you can hunt around and get them to fit it.

Actually that's what I wanted at first, but apparently what I want (2.5" pipe, 3.5" height, up to 24" length, centre inlet/centre outlet) is not made.

So this is why I am looking at alternatives.
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Old 03-20-2006, 05:41 AM   #15
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Don't listen to people saying you need backpressure. That's rubbish, it comes about as a result of people not knowing what they're talking about; the less backpressure the better.

However - the 'advice' they're giving is still correct. You can get too large an exhaust. It's not because a large exhaust offers less backpressure; it's because the large exhaust doesn't allow the gases to flow in a nice un-turbulent fashion. In fact, a too-large exhaust increases backpressure. Because there's so much space inside the pipe, the gases slow down & start swirling-around rather than travelling backwards. You don't actually lose torque anywhere in the rev-range, you just think you've lost some because you've got more power higher up in the rev-range.

Now, as for muffling; unfortunately I can't answer your question (sorry). However, the longer the pipe is after the rear muffler, the more resonance you're going to get in that pipe. I'd be kinda tempted to have a 2.5" under the axle (if it'll fit & there's not a nasty reason not to do it), retain the two 90-degree bends at the rear, and put a full-sized muffler in the spot for the existing (ie. running behind the tank). If that's too loud, it's really not that expensive to get a smaller one welded-in (maybe a resonator) under-and-in-front-of the drivers footwell. Just use 90-degree bends with as large a diameter as possible. It doesn't look as cool though, IMHO.
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Old 03-20-2006, 05:49 AM   #16
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Thanks for the very informative post!

I would like to do a side exhaust because it's very simple and in terms of putting it together, even if finding the right muffler is not simple.

A nicely done rear exit would be good to have, but it's a lot of work for a bloke who can't weld and won't pay the exhaust shop to do it because they can't really weld either

I've just emailed Lukey and Jetex to see what they have to say (if anything).
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Old 03-20-2006, 08:18 AM   #17
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your cheapest way out would be to just buy a stock 240 turbo exhaust and bolt it up. its bigger, comparatively inexpensive and damn easy when compared to fabrication.


i played with my n/a 740 exhaust (16v) and i can vouch for the "you need backpressure if you want to keep any power you ever had below 4000 rpm" camp. but with an H cam... who cares about that i guess.

and BTW what i did was remove the rear muffler and replace it with straight pipe... sounded like crap and also hurt low end.

clearly not because the pipes were too big.
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Old 03-20-2006, 08:56 AM   #18
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Quote:
Originally Posted by Forg
Don't listen to people saying you need backpressure. That's rubbish, it comes about as a result of people not knowing what they're talking about; the less backpressure the better.

However - the 'advice' they're giving is still correct. You can get too large an exhaust. It's not because a large exhaust offers less backpressure; it's because the large exhaust doesn't allow the gases to flow in a nice un-turbulent fashion. In fact, a too-large exhaust increases backpressure. Because there's so much space inside the pipe, the gases slow down & start swirling-around rather than travelling backwards. You don't actually lose torque anywhere in the rev-range, you just think you've lost some because you've got more power higher up in the rev-range.

Now, as for muffling; unfortunately I can't answer your question (sorry). However, the longer the pipe is after the rear muffler, the more resonance you're going to get in that pipe. I'd be kinda tempted to have a 2.5" under the axle (if it'll fit & there's not a nasty reason not to do it), retain the two 90-degree bends at the rear, and put a full-sized muffler in the spot for the existing (ie. running behind the tank). If that's too loud, it's really not that expensive to get a smaller one welded-in (maybe a resonator) under-and-in-front-of the drivers footwell. Just use 90-degree bends with as large a diameter as possible. It doesn't look as cool though, IMHO.
true
once I removed the exaust from my honda dirtbike (small 4-stroke) and it had very little low rpm torque. With the exhaust on (straight tru 1" with a small absorption muffler, no resistance at all) it runs much better, more torque. So in that case, backpressure isn't the thing thats important, but a certain length of exhaust.

But, backpressure can help even though your exhaust is correctly tuned. Some motorcycles use valves in the downpipe to create more backpressure at low rpm. (see lower posts for info on this, isn't correct)
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Old 03-20-2006, 09:02 AM   #19
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So these two bullet mufflers are louvered core? Are you talking about Moroso Spiral Flow mufflers?

As for fabrication, get some butt end or butt-joint clamps.



I just re-did ( that's some great English there! ) my exhaust over the weekend using these. As a result, I lowered the involvement of the muffler shop dramatically.

Man, I love my angle grinder!

Cheers
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Old 03-20-2006, 09:12 AM   #20
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Quote:
Originally Posted by 740Weapon
your cheapest way out would be to just buy a stock 240 turbo exhaust and bolt it up. its bigger, comparatively inexpensive and damn easy when compared to fabrication.

clearly not because the pipes were too big.

Getting a stock 240T exhaust from over there to here would be extremely expensive, because I would have to source one from USA or Europe.

Quote:
Originally Posted by BDKR
So these two bullet mufflers are louvered core? Are you talking about Moroso Spiral Flow mufflers?

As for fabrication, get some butt end or butt-joint clamps.

http://static.summitracing.com/globa.../wlk-33229.jpg
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The bullet mufflers I referred to earlier are the brand Berklee, they don't have a website with any info or pics. Apparently they're good, but I've never used them before.

Are Moroso Spiral Flow Racing Mufflers worth looking into?
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Old 03-20-2006, 09:13 AM   #21
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Quote:
Originally Posted by JW240
But, backpressure can help even though your exhaust is correctly tuned. Some motorcycles use valves in the downpipe to create more backpressure at low rpm.
Kind of wrong, if you actually find the OEM info on most motorcycle exhaust flow control valves, you will find they state quite clearly they are there to increase gas velocity at low rpm.
By keeping exhaust gas flow high at low rpm, it gives gains in torque, and can help spread out the power balance between low and high rpm, on cars you make a compromise, but it's still not about backpressure.

But realistically if you can't get your head around the dynamics of flow, then by all means keep calling or thinking of it as backpressure, most of the planet still does.
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Old 03-20-2006, 09:18 AM   #22
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Yeah, as I understand it, it's all about gas velocity, not backpressure. Somehow I knew that this would turn into an arguement and I'd still have no idea what to do for a muffler
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Old 03-20-2006, 09:25 AM   #23
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Quote:
Originally Posted by Bishop
Kind of wrong, if you actually find the OEM info on most motorcycle exhaust flow control valves, you will find they state quite clearly they are there to increase gas velocity at low rpm.
By keeping exhaust gas flow high at low rpm, it gives gains in torque, and can help spread out the power balance between low and high rpm, on cars you make a compromise, but it's still not about backpressure.

But realistically if you can't get your head around the dynamics of flow, then by all means keep calling or thinking of it as backpressure, most of the planet still does.
ok. higher velcity in the exhaust.
The high verlocity in the downpipe is created by reducing the cross section of the exhaust at the point of the valve. Wat is the effect of this high speed? (to create the high speed, some backpressure is needed, p=0.5*rho*v^2, or not?). Does the higher speed cause a resonance that allows better breating, or the higher speed makes the gasses 'fly' out of the exhaust?

interesting


I haven't got a lot of knowledge of thermodynamics, bit more than the average person (student ME). I am still learning
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Old 03-20-2006, 09:41 AM   #24
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Quote:
Originally Posted by Dauntless
Yeah, as I understand it, it's all about gas velocity, not backpressure. Somehow I knew that this would turn into an arguement and I'd still have no idea what to do for a muffler

Always does. It's TBricks!

Anyway, look into it in these two threads:
http://forums.turbobricks.com/showthread.php?t=8129
http://forums.turbobricks.com/showthread.php?t=8394

The way I understand it (and this is based on soon-to-be-tested theory gotten from several sources), the header is the most important piece of the NA exhaust. It will be the part that almost exclusively determines your powerband. From what I've read and heard, the catalytic converter will act as a pulse-wave terminator...basically it will end the pulse-tuned section of the exhaust, and from there on out to the tailpipe, the best thing you can do is have a correctly-sized pipe with as little restriction as possible. For 2.3l n/a engines, I believe that this will be either a 2.25" or 2.5" pipe, along with as few mufflers as you can deal with from a noise standpoint.

I'm looking into a KG Trimming header, a 2.25" or 2.5" high-flow catalytic converter, and a couple of glasspack straight-through mufflers in 2.25" (or whatever the stock turbo system is).

Hoping to get a baseline syno run for the car before doing the exhaust so that I have before & after comparison.

Quote:
Originally Posted by Dauntless
Who thinks I should install a small muffler in the space where a cat would go?
I think you should install the cat in the space where a cat would go. Ebay. Catco. Cheap. Effective. Legal. Polite.

Quote:
Originally Posted by Dauntless
So who thinks a pair of bullet mufflers would be too loud, keeping in mind they are louvered core?
I don't think they'd be too loud, but remember that the louvers are going to put in a little more backpressure. Personally, if I were looking to do this, I'd go to the boneyard and pull a stock turbo cat-back system and replace both mufflers w/ glasspacks or the straightest-through mufflers you can handle in terms of sound.

Remember that "too loud" is an opinion unless there's a law that provides you, locally, with a concrete dB level. Parry's open DP wasn't too loud when I was driving behind him in NH, yet Barney got a ticket for noise and open DP in Worcester. (Of course the 'Merican V8 guys don't get crap for running open headers during Nationals...... )
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Old 03-20-2006, 10:00 AM   #25
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Quote:
Originally Posted by Metalgod_Z

The way I understand it (and this is based on soon-to-be-tested theory gotten from several sources), the header is the most important piece of the NA exhaust. It will be the part that almost exclusively determines your powerband.
I have a Hurricane 4-2-1 header.


Quote:
Originally Posted by Metalgod_Z
I think you should install the cat in the space where a cat would go. Ebay. Catco. Cheap. Effective. Legal. Polite.
This is a 1982 244 with a B23E. It came stock without a cat.


Quote:
Originally Posted by Metalgod_Z
I don't think they'd be too loud, but remember that the louvers are going to put in a little more backpressure.
Thanks for the input.


Quote:
Originally Posted by Metalgod_Z
Personally, if I were looking to do this, I'd go to the boneyard and pull a stock turbo cat-back system and replace both mufflers w/ glasspacks or the straightest-through mufflers you can handle in terms of sound.
For obvious reasons I can't do this.


Quote:
Originally Posted by Metalgod_Z
Remember that "too loud" is an opinion unless there's a law that provides you, locally, with a concrete dB level.
Indeed. I don't mind it being loud, but the cops certainly do.
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