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Discussion Starter · #1 ·
I have a performance exhaust that I’ve built, all the way back to the header. It took a couple revisions but I’ve got it sounding like I want. The drawback back is its little on the loud side then the car is started in the morning and driving slow in parking lots or the drive thru. Basically times when you’re cruising easy.

I know more expensive cars try to handle this with some kind of active exhaust. Did a little reading on online and bought some used parts on ebay and came up with this:



The actuator works on intake manifold vacuum and an internal spring. The valve opens by the spring when there is no vacuum. Start the engine at idle, vacuum is high so the valve will close part way to a preset stop. Mash on the gas vacuum gets low, valve opens all the way again. Well at least that’s the idea. Haven’t run it on the car yet plan on cutting it in the exhaust next week. Some of the parts actually came off an old corvette.
 

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ive seen these before. good idea. and i always see this in BMW stock exhausts with dual tips. basically 1 tip is closed for easy driving but when you full throttle the 2nd tip is opened. good idea and cant wait to see this installed.
 

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Hmm I'm in need of revising my exhaust as well and this sounds like an awesome idea. Funny that I was looking at this thread at my friends shop and he said he just cut one of these off a bmw. So I will be using that on mines. :lol:

So when making your exhaust you'd want the outlet pipe to be smaller than you need to quiet some of the muffled noise coming out?

Sgtspyder, what muffler are you using on your exhaust? I'm currently searching for one thats not too heavy, single in/out universal and not too loud where I could quiet it down with this contraption.
 

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Discussion Starter · #5 ·
Hmm I'm in need of revising my exhaust as well and this sounds like an awesome idea. Funny that I was looking at this thread at my friends shop and he said he just cut one of these off a bmw. So I will be using that on mines. :lol:

So when making your exhaust you'd want the outlet pipe to be smaller than you need to quiet some of the muffled noise coming out?

Sgtspyder, what muffler are you using on your exhaust? I'm currently searching for one thats not too heavy, single in/out universal and not too loud where I could quiet it down with this contraption.
I have two mufflers in series, both Magnaflows and 2.5”. Magnaflows have good quality but are not light.

The trick to get this thing working right might be at what vacuum pressure does the valve start to open. The actuator in the picture opens around -3 inHG. Got another that opens around -6 inHG. I’m using this on a car thats superchargered. Definitely would want a different actuator for an NA car.
 

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and that's equal to less hp more restrictions not worth it
You can get larger and or better mufflers that will make it quieter without a huge amount more restriction. Fujitsubo for example makes exhausts that are OEM noise level and sometimes even quieter but still have performance gain over stock.

To make it quieter you could add 2 mufflers in series, or copy the GP Sports idea and add a "power chamber" which makes it quieter without adding any extra restriction.

You can design an exhaust to be a much more tolerable level without sacrificing alot of performance ... eg. japanese JASMA approved exhausts like the brands i mentioned.

The only downside performance wise to these solutions is the extra weight that they bring with them.

If you still like the idea of being able to have it closed up with a butterfly valve when running normally and open it when you want some sound then theres a company called xforce which makes what they call a "varex" exhaust which is similar to what you are making but is controlled electronically with a remote so you can esentially turn up or down your exhaust volume when you choose.
 

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There's a few companies that make them. Here's one
http://www.jegs.com/p/JEGS-Performance-Products/JEGS-Electric-Exhaust-Cutouts/1231909/10002/-1

You can activate them manually; I've also read of people having them activate at a certain RPM. I remember in another related thread, I believe Oldman (scold me if I'm wrong OM) said something about them sticking after residual buildup. Normally I'd track down the thread, but I'm using the wretched iPad.
Well it seems like a possible problem that may occur considering the amount of black stuff that builds up in an exhaust, especially if you don't operate it often in which case it may be best to set them up flanged or clamped on either side so that they can be removed for maintenance.
 

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Discussion Starter · #10 · (Edited)
Valve is in! First impressions are good. Does seem to quiet down that higher idle start up. At easy cruising, the valve is closed about 45°. Doesn’t seem to affect the driving on city streets. Still need to test on the interstate. Vacuum is still high enough at highway speeds to keep the valve closed to the 45° mark. The higher RPM/ load of highways speed may require that minimum to be opened a little more.
Wish I could get the valve to work a little more proportional with the engine vacuum. Not so open close at one pressure point.

Mash the gas, the valve seems to open instantly and then here comes the exhaust roar and supercharger whine.:cool:




 

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thaths looks very nice I would definetly like to do somenthing like that in my car..
 

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That's not true at all. At all.

http://www.mustang50magazine.com/te..._mustang_muffler_comparison_test/viewall.html

If you look through the results, some of the quieter exhausts are 1/10 as loud as the other mufflers at the same power level. The borlas, for example, are some of the best performing mufflers on the test, while also being the quietest, and they even out performed a straight pipe.
you know in a FI car you want has less restrictions has possible
 

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Discussion Starter · #17 ·
Well first off V8 mustang compared to MR2 with Toyota squirrel cage. Big difference there. What’s good for one doesn’t necessarily work for the other.

I’ve built 4 different versions of exhaust for my car. One verison had a Spintech muffle and it makes a great sound. It was just too loud.

I do like Borla, if they didn’t cost so much I probably would be using them. They make a transverse muffle that I think would work well for a dual exhaust setup. May try a similar setup at some point, but will probably use a transverse muffle from someone else and turn the dual out pipes down to 2” pipe.

Building different exhaust setups for my car has become a little bit of a hobby.
I’ll see about making a video. Still need to play with some adjustments.
 

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I've used Borlas transverse dual exit mufflers last year. Super quiet at idle, droned pretty badly on highway (not as bad as TM duals), wot wasn't anything sporty that I remembered well. Good quality though.
 

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I've wanted to do something similar to this were I to do an exhaust. I've seen the vacuum operated ones but have always envisioned one actuated by a cable tied to the throttle. At say, less than 50% throttle the unit would stay at "closed" position (maybe 45*), and as throttle goes past 50% the unit would open up accordingly so that it is wide open at wide open throttle. This would allow the driver to dial in how much noise/power with the same input that already dials in noise/power (the gas pedal). I'm far from wanting to undergo such an endeavor, as I still need to design up the exhaust and build the thing.

Great post and info for those of us that have teased the thought of doing something like this. Cheers!
 
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