Ok So I was talking to my friend about the BMWs he's been looking at. We got to talking about how it has 4 different O2 sensors, and then I found out it has 2 exhaust manifolds, 2 cats, and then all goes back into the muffler. Ok so my question is, does this have an advantage over our Z inline-6's with one manifold?

 

What do you mean by "two exhaust manifolds" ??? Are you talking about the two part flange?

 

At one time I was comparing six into two headers and long tube equal length headers into one pipe. The long tube with a single exhaust were said to put out slightly more power. Most cars run that have twin exhaust run them together in the middle in an X pipe or H pipe.

I'd say the BMW design sounds like a bad design but they usually put some effort into their performance.

 

What I meant was you have the head, and unlike how our exhaust header is one big piece that routes all 6 exhaust ports into one pipe, the BMW design has two separate headers that route the exhaust into 2 separate pipes. So two separate 3-1 headers, that lead into 2 separate pipes, go along, 2 catalytic converters, then eventually both run into a big muffler that has a dual tip. I was just wondering if there was an advantage of that over the 6-1 exhaust header that we have on our Z's.

Here for example Front Manifold:
http://cgi.ebay.com/ebaymotors/BMW-F...spagenameZWD1V

Rear Manifold:
http://cgi.ebay.com/ebaymotors/BMW-R...spagenameZWD1V

 

6 into 1 isn't the only header available for the L series motor. Search for "header" on the MSA website... they sell many 3 into 2's. Just because BMW made a 2 piece header, doesn't mean the 1 piece isn't good quality. Also... remember the BMW heads are DOHC... the L series is SOHC.

 

I didn't think of that, I just meant as far as stock goes, if there's an advantage one way or another. My thoughts are maybe it's meant for better emissions, because maybe the ECU manages the injection in two sets. One for the first 3 cylinder and one for the other 3.

 

for the z, they are called twice pipes. its a different thought on the exhaust system and not commonly used any more. they used to take a 321 header and not join the bottom half, the 2 1 part, and run 2 smaller tubes all the way back. i think it doesnt really hinder exhaust, and produces a very unique sound.