McMung

Here are some pics from a prototype cutout design I whacked together today.

The intentions for this design are as follows:

• Provide for a cutout at the midpipe for sound (I have Corsa Sport mufflers so I was not concerned with flow).
• Make use of the vacuum actuated plunger(s) that are used by the stock muffler system.

http://tinypic.com/player.php?v=2qvzgjd&s=5





This is the open position:


This is the closed position:


Mounting detail:


Where I ran an extension of one of the vacuum lines that normally operate the butterfly valves (it's the blue/black looking line).


A few notes:

• The degree to which the valve opens can be adjusted with the coupler (yes it's a bolt and yes it looks ghetto as ****... had no hex or square stock on hand that was big enough).
• Yes it seals completely when closed (the pulling force of the plunger is quite strong, enough to make you scream like a little bitch if you just happened to place your finger in the gap and close the valve. Ask me how I know)
• When opened the valve flaps do not present themselves as the lowest part on the car. The tire is the lowest part on the car HAHAH I funny. nah seriously though, the coupler adjustment allows the open position to be set to the same height as the next lowest underside component, which to seems to be the brackets-with-lips on the floor pieces (not sure what else to call these) and all of this is WELL above the front skirt.
• It is fairly easy to route one of the rear vacuum lines (use a barbed close nipple as a coupler) forward to this position without getting near the exhaust or anything else that is remotely hot for that matter.
• The system can be fully (dis)assembled while the midpipe is on the car.
• The only "permanent" modifications to the midpipe are the bearing tabs for the pivot shaft, the bracket for the plunger, and the HOLES.
• The spring hanger bolts for the midpipe can be accessed easily.
• Everything fits in front of the bell housing on the transmission with plenty of room to spare, probably a couple inches clearance.

In terms of loudness when open, it approx 5 dB lower than fully open exhaust at the cats, and approx 15 dB higher than regular Corsa Sport, all figures recorded with an SPL meter at IDLE and from a standing position next to the driver's door. I have not taken it for a drive yet but I'm sure it will be just as loud as any other cutout. When closed, the SPL is exactly the same as regular Corsa Sport; see above about no leaks.

Some things I would do differently next time, or now plan to do after mocking this up today, or am not sure about:

• It rattles a little bit when open at idle: Raise the pivot approx 1mm from the tubes (right now the pivot shaft sits right on the tubes), and use springs on the pivot shaft on the inboard side of the bearing tabs, this is to keep it centered when it opens and eliminate rattle.
• Tack that plunger bracket in a few more places, or fully weld it (not really important to do so, all of the force acting on it is only helping to hold it in place).
• Use a proper turnbuckle as a coupler. Have to get a left hand 5mm/0.8 die first...
• Next time I would not put one of the vacuum plungers on the roof of my truck while I get in to it, forget about it, drive off, and lose it forever. I wonder if these things can be ordered from the manufacturer?
• Not sure how great of an idea facing the flaps forward is. I am guessing at speed the airflow will shift exhaust up and over the components and maybe soot things up a little bit. Will have to check that out after a few hundred miles.
• Use stainless steel or get these bits plated so they don't get all rusty and nasty.

COMMENTS PLZ?

cty33390

Pretty trick! Props for creativity!

SunsetOrangeCreations

Very Cool setup!

I will be looking forward to the updates.

Ben

White Dually

I believe that is a First. Looks very good.

Cobra604

I love it. But, I'm afraid you may get an exhaust "leak" noise. Aside of that, I think it's cool as hell!

And thanks for the pics & description!!!

Edit: "(yes it's a bolt and yes it looks ghetto as ****... " That's funny. Dude, if it works, is reliable and hidden, it's all good.

McMung

Playing around int he garage last night w/ no load on the motor it was not a concern, but under load that's certainly possible.

I am not expecting it but have not gone for a cruise up a hill with the flaps shut to see yet. The pulling force generated by the vacuum is fairly high, so I am certain the flaps will not creak open (especially since there is no flow restriction to speak of in the downstream exhaust), but leakage around the "seal" (which is just metal on metal after all) is certainly possible.

smallblk400

very ingenious! Keep us posted if it work's I'm in for buying one!!!

VetteFish

badass! might have to come to you to fab that up once i get mine soon.

definitely should take some video of it!

gmansbu

I'd love to hear what this sounds like. Might be a stupid question, but would this be louder than B&B bullets?

0SonOfDreams

Nice job on the mod and the post

I wonder how much exhaust comes out of these? I would think with the flaps open, so little or no back pressure, most of the exhaust gas would just zip past and could even create a vacuum and draw air into the openings. Would be cool to see a video on a lift of just how these perform. With the flaps shut I am surprised you don't get an exhaust leak puff puff sound since the seal is poor.

McMung

I don't have a video camera

Then again I could try doing something with my web cam and a laptop... I'll play around with that in an hour or so.

Yes, a lot. B&B at least produces some muffling effect, but the biggest difference is where the sound is emanating (right at your door sills). I ran straight pipes to the rear and also dumps at the rear of the midpipe for a few months and there was a pretty noticeable difference between just those two locations as variables.

One interesting thing is depending on the size of the holes under the flaps and the degree to which the flaps open, the amplitude of the sound can be changed somewhat.

McMung

You know, I was thinking about that, whether at speed air may be sucked into the openings in part by venturi effect in part by the airflow shaped by the flaps... Not sure, it seems possible in theory but not being able to "watch" it happen makes it rather hard to know for sure.

At idle i sat under them and actuated them a few times, there is a little bit of exhaust coming out but nowhere near the full flow.

I'm not sure what you mean by the puff puff sound.. FWIW the seal is actually pretty decent, the flaps are simply 3" tube sectioned down to 1/4 arcs and formed slightly to match the exterior curvature of the stock 3" tubing and there is approx 1/4" overlap around the hole underlying each flap. The force of the vacuum plunger coupled with the leverage of the flap arm makes for a pretty good clamping effect, also. They do not flutter or vibrate at all when closed. When open, on the other hand... (see above for "what I would do differently" w.r.t use of centering springs).

I'll try to make a video in a few...

McMung

Okay I took a video... had to bust out my studio recording gear for the audio as the little mic built into the web cam was having "issues" with the amplitudes involved...

As a result of this, you will need to turn your volume up to reference levels (assuming you have a calibrated speaker/headphone setup and can do this) and you will roughly hear the "real" loudness. The mic was positioned at the RIGHT REAR of the vehicle, not near the camera, equidistant from the rear muffler tips as well as the cutout holes, so there is no distance bias towards one or the other giving you a really good idea of the volume difference.

This is UNEDITED because I dont have any editing software, so its rather long as I tried to fit in a bunch of things to show visually what is going on with exhaust flow. The short blat at the end was up to about 5500rpm.

http://tinypic.com/player.php?v=2qvzgjd&s=5

For whomever it was that was asking: Decent quality audio only near the end is @ http://uploading.com/files/2NBHI9NN/...dclip.mp3.html

Viprklr

That is sweet! Ingenious idea! Sounds great!


Matt

McMung

A little update:

Went for a 100 mile drive today, some cruising, some lead footed.

Operation was perfect, a proper mile 2 wild so to speak. Definitely as loud and intoxicating as mid pipe dumps but with a volume switch for when you get on to the freeway/highway. I would have to humbly say that this is the perfect exhaust setup for these cars.

No problems whatsoever, got under the car immediately after and checked everything out, no binding, rubber vacuum line routing was fine, not melty or too soft from heat. I will say that I will definitely be re-making in stainless or mild steel and plating it to avoid corrosion, and would do the aforementioned change w/ raising the pivot shaft and using springs to hold still when open.

VetteFish

bump. is this still holding up?

McMung

Yep, have about 1500 miles on it, works perfectly.

One of these days I'll take it off and paint it (just because it's mild steel) and spring load the pivot to keep it steady when open.

VetteFish

do you think this wuold be easy for a muffler shop to do? how much would you charge to do it again for someone

McMung

It would be easy for a fabricator, but I wouldn't ask Midas to do it if you know what I mean... There's plenty of cutting/shaping/fitting involved so you want someone who pays attention to detail, not someone trying to get it done and out the door in an hour.

I haven't thought about what I would charge to do it again, probably a few $hundred. I would need your midpipe for proper fitment and one of your vacuum actuators, making it basically impractical to "mail order" unless you are willing to ship a midpipe around!

AtlBlkZ06

Thanks bud, it sounds like a great weekend project. Can you post up the tools you needed for this?
This is a great way to use the leftover valve! It sounds absolutely sick when you let go of the gas and its popping!

Only concern: At high speeds, wouldn't it act like a scoop adding backpressure to the exhaust and also picking up debris?