e12 with e28 exhaust/mufflers, confusing

[Mark]

Befor I start, ive looked at previous posts, talked to BMW specialists, and hunted on the internet. My e12 has a 3.5 conversion, my manifold (header ?, im from the Uk originally so I call it the exhaust manifold, hope thats right) just has a single down pipe, into a small cat under the car, out of the back of the cat it then splits into two smaller pipes, then a flange, then into a long muffler (silencer ?)box, then still two pipes under the drive shaft, into another muffler/silencer whick doesnt look right for the car as its been bashed in on one side to make it fit in the space, this has two pipes exiting the back of the car. So, im sure that the manifold/header is from the original 2.8 engine, along with the rest of the exhaust system up to the odd looking back muffler/silencer. If this is right then im guessing it will be pretty restrictive. My plan is to get hold of a 3.5 e28 header, which I believe has 2 down pipes, after that im not sure what to do. Ive read the posts about the 635 euro down pipes but that could be expensive or difficult to obtain. Im thinking of going into an aftermarket hi flow cat, then just 2 pieces of straight pipe into the current rear silencer. My friend has an e28 3.5, twin down pipes, but the cat under the car is huge, a great big long thing, not sure if it will fit on an e12, any thoughts, needs to be cheap, free flowing, and easy to get,

[Mike W.]

The original isn't bad at all as long as the cat is still good. An E28 535 will flow better, and kind of fits, I've got one on mine, but with some interference with the idler arm. The dented muffler is stock too, that's the way they came. As an aside showing just how important it isn't, E28 533s which were rated at 1HP less than 535s, used a "Y" downpipe to go single pipe into the cat, then two out. Now I have run into aftermarket systems that resulted in a noticable loss of power due to restriction, but stock E12 is pretty good. Not that it can't be improved on, but I doubt you would notice the difference.

[Mark]

Thanks for the reply, in light of that I might just keep the standard e12 2.8 system on my 3.5 conversion, but what do you think it would sound like if I remove the long silencer under the car, the one between the CAT and the rear silencer, then just fill the gap with 2 pieces of straight pipe, in theory I would loose about 15 lbs of weight, improve flow possibly, but would it sound awful, louder is ok, but the right kind of loud.

Thanks.

[Mike W.]

I don't know what it would sound like, but I'm fairly sure the resonator is just straight thru, holes internally for sound deadening, but no diversion of flow or anything like that. I have heard some say E28 exhausts do not sound good with the resonator alone removed, but I've never heard one so I have no first hand experience.

[Mark]

Thanks for the advice Mike, if its not going to sound right then maybe this might work, ive found some short 12" long walker resonators, they look like a cheap version of a cherry bomb, walker 20627, walker pf41 and cherry bomb 87521. Maybe the answer will be to take out the large resonator from under the car, and plug the gap with 2 of the above as there are 2 pipes, and the rest in straight pipe, hopefully it should sound a bit raspy. Ive posted my car for car of the month, I think im May, hopefully by then my door panels will be made from thin Kydex (plastic) and with all the other stuff ive taken out I should have lost 180 lbs from the car. My new porsche 914 lightweight front seats are superb, I can feel the difference already as ive lightened the car by 153 lbs so far, 30 to go.

Thanks again,

Mark

[wkohler]

Some folks have said the best sound from an M30 is a stock Boysen Euro E28 rear muffler and no resonator.

Just sayin'.