Finished that stubby exhaust

[X64v]

So I ended up making that short exhaust after all. What I was using was just too quiet.

 

All I used was the flange off a stock downpipe, a little over 45 degrees of 2.5" mandrel bent pipe, and a 2.5" Dynomax Bullet Muffler. It's listed as a muffler, but it's really just a resonator.

 

 

 

 

 

 

I made it the way I did for two reasons. One was sound, as my full length exhaust with the MSA turbo muffler was just too quiet on a turbo motor. The second was ground clearance, as I was tired of scraping all the time on steep driveways and speed bumps. I would have thrown an o2 bung in the elbow, but didn't have a step drill bit handy. It's an easy fix, as the whole thing comes out in as long as it takes you to remove the four nuts.

 

I drove it to school and back today, and I can say that the noise is totally reasonable. I can hear my radio at it's initial volume at idle, and can hear it while reasonably low at cruise. A 15 minute drive did not cause me any discomfort or annoyance whatsoever. I doubt it's loud enough to draw the attention of the cops, as Harleys and crotch rockets are quite a bit louder.

 

The Dynomax website lists the bullet muffler as giving a 2-4dB reduction in sound, and I would say that sounds about right. It's a tad bit quieter than when I started the car with no downpipe. The main reason for using it though was the exaust note. It pretty much eliminates the higher pitched overtones that L series engines tend to have through open or semi-open pipes. It also softens the turbo spool noise, as that's high pitched. You can still here it very clearly, but it's not overbearing in any way.

 

I've also gained almost two inches of ground clearance, as the bottom of the pipe is about even with the frame rails, so it's not ever going to touch anything. It does extend low enough, however, to keep the exhaust gas out of the engine compartment at idle, and you can just faintly smell it at a stop light. I get no fume smell during cruise.

 

The hardest part was getting it to fit between the tranny and the frame rails. The outside diameter of the resonator case is 4", so it's a tight fit. I have about 2mm between it and the tranny (which is fine because the engine and tranny rotate together), and about 5-7mm between it and the frame rail, which seems to be enough to keep it from hitting as the engine moves on its mounts.

 

If I end up happy with it, I'll send it off to be ceramic coated. I'm happy with it so far, but we'll see with time if I get tired of it or if it causes any unforeseen problems. I'll post a vid of it later today so everyone can get an idea of what it sounds like.

[palauoriginal]

that's awesome. cant wait to see the vid

[mario_82_ZXT]

Pfff who cares about the vid you're gonna have to take me on a ride in it

 

BTW I popped another headgasket (after I fixed the smoke issue )

Mario

[X64v]

Ha, good one. How much boost are (were) you running?

 

and what was causing the smoke that you fixed?

 

(vids to come after I get out of chem class so I can reduce them to a manageable size)

[mario_82_ZXT]

Stock boost. Smoke was caused by washed cylinder walls in 3-4 (injectors stuck open). After I replaced those 2 the car was running awesome.

 

Sadly a few hours later, injector 4 started coming apart (huge fuel leak between injector plastic and metal body). Went lean on a 3rd gear pull and seemed to have blown it between 5-6 (both cylinders are dead). I'll know for sure tomorrow after a compression test. At least the car didn't go up in flames...

 

The easiest thing for vids is to just throw them up on Youtube or Google Video.

 

Mario

[big-phil]

when I had my "dump" pipe it was really cool. Loud, you could hear the turbo real good. I bet that sounds awesome!

[X64v]

Ha, that's just your luck, Mario. Thankfully you're car isn't a barbecue..

 

And yeah Phil, it sounds quite awesome. Even off boost I can hear the turbo spool up and down, like a little jet engine on my engine.

 

This first vid is a cold start and normal paced drive around a few streets on the way to school. Pretty uneventful, but you can hear what it sounds like around town.

 

http://smg.photobucket.com/albums/v472/X64v/?action=view&current=P1020376-MPEG-4.flv

 

The second is a 1st/2nd wot run. It takes a while in first because I didn't launch, just let the clutch out and floor it and let boost build. Thanks to my trusty cameraman/roommate, all you can see is the dash.

 

http://smg.photobucket.com/albums/v472/X64v/?action=view&current=P1020378-MPEG-4.flv

 

The third is obvious.

 

http://smg.photobucket.com/albums/v472/X64v/?action=view&current=P1020379-MPEG-4.flv

[palauoriginal]

nice. i like the sound alot even tho its just a pipe then a resonator/muffler. its sick.

+1

[mario_82_ZXT]

Sounds really nice! It's not as raspy as my straight pipe.

 

Mario

[Daeron]

sounds great, I LOVE the Pepsi product placement in the first video

 

might there be room for a small "hood" on the outlet? I am picturing a slight angle cut in a piece of pipe, not enough to form a complete ring but something to be centered on the bit of the pipe most exposed to the engine bay, to "persuade" the exhaust gases to go down under the vehicle rather than anywhere else. Just a thought for possible (possibly un needed, for all I know) improvement.

[Tony D]

It's listed as a muffler, but it's really just a resonator.

 

How's that again?

The thing is a muffler, especially in the application you use it.

The difference between a 'muffler' and a 'resonator' is purely in their position in the exhaust stream and their designed function at that position.

 

Because something is straight through does not immediately make it a 'resonator'. Putting it at a point in the exhaust system where it takes out a specific exhaust system resonance frequency (this could be before or after another 'muffler') is what dictates it's nomenclature.

 

A Muffler knocks down all frequencies, whereas a resonator knocks down a specific frequency or set of frequencies.

 

So as you are using it, indeed it IS a muffler. Were you to have two of them, placed traditionally they could both be considered mufflers. But if you started playing with positioning of the front end unit to take out resonance in a specific rpm range (like the boomy 2500 rpm cruise range, usually knocked out placing it under the tranny) then the front one could be the Resonator. But if you put it in a generic under-tranny placement position, and then sized the rear unit for removing turbine whine specifically, the rear one would be the resonator.

 

Generally mufflers will have a chambered construction, but not always.

 

This is like "Freeze Plug" with BRAAP. It bugs me when people think because it's a straight through design that 'it's not a muffler, it's a resonator'....

 

My weakness is revealed...

 

This setup looks good though, I'd not considered a stainless muffler AS the downpipe... I have a setup where the chambered muffler is under my seat in a box, exiting out the side. This may make it more friendly with smaller units in two places. I'm going to have to redesign now...

[Tony D]

I am picturing a slight angle cut in a piece of pipe, not enough to form a complete ring but something to be centered on the bit of the pipe most exposed to the engine bay, to "persuade" the exhaust gases to go down under the vehicle rather than anywhere else. Just a thought for possible (possibly un needed, for all I know) improvement.

 

Actually this would be a highly recomended modification. A "Baloney Cut End" is almost required in this case...not so much for the direction of flow (which it would do, especially if you placed the longest point forward, opening to the rear) but for decrease of the pressure where the gasses exit the piping. A baloney cut increases the surface area of the pipe making the flow exiting the pipe to drastically decrease it's speed...it's like discharging into a much larger pipe. It not only decreases exhaust velocity, but it also increases scavenging effects.

 

It's a highly recomended addition. Watch industrial stacks for process flow, and you will ALWAYS see them angle-cut. A straight pipe will make more of a 'pop' for each pulse that comes out, and angle cut pipe will more 'woosh' for each pulse.

[X64v]

Ah, well you learn something new every day.

 

I wasn't calling it a resonator for the straight through design, as I know there are straight through mufflers that do quiet the exhaust down quite a bit. I had always thought the difference between a muffler and a resonator was it's size and decibel reduction. Since this had such a small volume and just changed the tone instead of reducing the decibel volume of the exhaust that it was just a resonator.

 

But now I know; thank you Tony for the enlightenment, as always.

 

 

While I'm at it, I'll post an update. I drove to Phoenix this past weekend, a two hour open highway drive. Cruising at speeds ranging from 75-90 (which correspond to 2500-3000rpm in 5th with my gear ratios), the noise level was just perfect for me. With this exhaust and the windows down, I could still hear my stereo perfectly clearly, and did not have any ringing ears by the end of the trip. However, I could still hear the tone of the engine with the stereo up, in case anything changed. I used to have to pause my cd and listen if I thought the engine had changed pitch.

 

I also have not had a cop give me a second look. So, to wrap it up, I love this exhaust.

[X64v]

Tony: At what angle should this cut be? Obviously, if you're looking to maximize the area of the outlet, as the angle of the cut approaches 90* from normal, the area of the outlet will approach infinity, but in this case, the limiting factor is the ground. In your opinion, how much of a cut will show benefit, while still keeping the beautiful ground clearance I have with this exhaust?

[MrFancypants]

Man Im really surprised how good that sounds. Clever idea!

 

 

 

- Greg -

[Tony D]

Normally 45 degree cuts are considered the minimum, with 30 degrees being more common for exit. If you calculate the cross-sectional area of the ellipse being formed by the angle cut, you can see there is a point where you really don't get a great increase in opening area for a more radical cut. I think it's slightly more than 30 degrees where it simply doesn't open up appreciably. You can see when you take a 2.5" round hole, and then compare it with the surface area available form the 45 Degree cut, you can see the area increased by the cut. Same for 30 degrees.

 

I'm curious, if I could get you a Db Meter, would you be interested in doing some runs and recording the sound pressure level inside the cabin.

 

Reason I'm asking, with the side exhaust, this would really throw a kink in the CHP Mandated Testing Parameter for Roadgoing Vehicles. Their tests require a Db Meter to be placed directly behind the vehicle at a specific distance with the engine at idle and some other throttle opening. I would think your exhaust exiting out the side of the car could be pretty noisy, and free flowing---yet STILL easily pass the CHP Testing standard. If you have ever noticed some of the aftermarket exhausts for the hondas have tailpipes that point up at a 45 degree angle...it's precisely because the sound is directed upwards a way from the CHP noise monitoring devices!

 

But an internal Db Level may be more quantifiable than those sound clips. To me it sounds pretty quiet. Then again, when my friend's mufflers rotted off on his Corvair I thought it 'sounded about right' when taking a ride, so maybe it's time for me to go to more empirical evidence than my own ears! LOL

[X64v]

I'd be delighted to do some Db tests. It's so hard to qualitatively 'tell' how loud/quiet it is, without having numbers.

 

I should have said something earlier, but the sound levels in the videos are deceptively quiet. The tone is right, but the volume is off. They were just taken with a digital still camera on video mode. I can get access to a digital movie camera this weekend, perhaps I'll take some more video and see if I can get some better clips of it.

 

Shoot me a pm and we'll talk.

[e_racer1999]

if you go to your local radioshack you can pick up a digital sound meter for $50 (sku 33.2055) and return it after you're done testing....

[Daeron]

Actually this would be a highly recomended modification. A "Baloney Cut End" is almost required in this case...not so much for the direction of flow (which it would do, especially if you placed the longest point forward, opening to the rear) but for decrease of the pressure where the gasses exit the piping. A baloney cut increases the surface area of the pipe making the flow exiting the pipe to drastically decrease it's speed...it's like discharging into a much larger pipe. It not only decreases exhaust velocity, but it also increases scavenging effects.

 

I knew it dun' me good when mah pappy dropped me on mah head!

 

thanks for the enlightenment as always, and thanks for backing my idea up with more support than I even knew it had!

[Pop N Wood]

While you are at radio shack, pick up a battery powered carbon monoxide meter and install that in your car.

 

There is a reason safety inspections require solid piping all the way out the back of the car.