I probably wouldn't buy it, but someone may like it.

[georryan]

http://cgi.ebay.com/ebaymotors/ws/eBayI ... 2431550404

[ciper]

Bell mouths suck.

[czo79]

Please Ciper....Do explain? I'm pretty much a novice when it comes to exhaust stuff....but whats so bad about bell mouths? I would think at the least it would be a pretty big improvment over non bell mouth dp's...although not as good as twin dump downpipes or whatever the ones with a seperate pipe for wastegate exhaust is called...
I'm curious...
thanks
Micum

[ciper]

You are right that they are far better than what is installed on the vehicle to begin with. But quality seperated designs can be had now for fairly cheap.

The bell mouth allows the exhaust from the wastegate create turbulance in the exhaust from the turbin. The waste gate exhaust comes out at a funky angle while the turbine air is a pillar of spinning exhaust.

For less than 300 SHIPPED you can get a perrin DP!
http://www.perrinperformance.com/produc ... wnpipe.htm

Its not the best performance pipe, but its the best performance for the $

[Brat4by4]

Hmm... the turbulence creates back pressure, but the outlet diameter is 3.25". I wonder if they would offset each other. 3.25 is a lot of flow and means there is very little restriction in the piping itself.

[ciper]

You know, a bell mouth with a small seperator plate would probably work very well. The turbulence I speak of would only happen near the turbo. A seperator plate of only 2inches long would probably be plenty!

[vrg3]

Yeah, a couple inches of separator plate would actually approximate a short-divorced-wastegate design like the Perrin downpipe.

[Matt Monson]

http://www.cobbtuning.com/tech/exhaustdesign/index.html

[eastbaysubaru]

The bellmouth with the seperator plate is exactly how the MRT one is setup. It looks like a top-notch system too.

-Brian

[ciper]

I take back what I said at first, bell mouths dont automatically suck. Just the majority of the ones for sale and the price they go for.

"bellmouth with the seperator plate is exactly how the MRT one is setup"
Great minds think alike



It isnt exactly a bell mouth, more like two big pipes welded together. Something inbetween the perrin and a bell mouth. It seems that a low cost bell mouth with seperator would be a hot seller and fairly cheap to produce. The MRT unit is listed at around 400 dollars.....


The important part of the Cobb article that was posted is copied here:

Turbulence is one main factor. If the gasses are all stagnating and/or running into protrusions or running into each other it creates more backpressure than a well designed system. The more laminar (smooth and straight) the gas flow, the more the system can flow for a given pipe diameter. Steep angles and abrupt pipe diameter chances should be avoided.

The methods of collecting the outlet gasses and the wastegate gasses add another part of the equation to change. It would be optimal not to join the outlet from the turbo and the wastegate together, but the real world messes with our fun. Just dumping the wastegate to atmosphere is great for a racecar, but not a street car. So a street exhaust should combine them to get all of the gasses through the same cat and muffler system.

Some of the turbo outlet designs include: flanges with a simple pipe, bell mouths, divorced wastegate, and split bell mouths You also have castings and formed piping to choose from. Which one works best is also determined by quite a few different factors and how well they are designed and manufactured.

They then explain the different types! Thanks Matt Monson
The one problem I have is that they let laziness be the deciding factor in which pipe is recomended. They chose the plain bell mouth because it was cheap and simple. They barely mention that divorced or split bell mouth are better but counter it with problems that could happen. One example is the waste gate hitting the splitter. Thats something pretty easy to check for and if built right shouldnt be a problem.