Re: 735 muffler

[Polands <polands@xxxxxxxxxxxx>]

Kevin wrote:
Date: Mon, 16 Oct 2000 22:25:10 EDT
From: Kae2812@domain.elided
Subject: muffler Tips

    Hey Everyone, I was given an 86 735i ...I need a new muffler. 
Should i go for the $385 bmw muffler (uninstalled) or the el cheapo 
($185 muffler, installed)?  the bmw muffler has two tailpipes, while the 
cheap one only has one. Any suggestions welcome,
Kevin, VA.

Kevin,
You should take a measurement of the inside diameter of the stock
exhaust pipes, and caluclate the combined cross section area.  At the
very least compare this to the cross section area of the single muffler
tip, and if it doesn't equal or exceed the existing area, I'd recommend
against it.  Of course that won't tell you anything about the inside of
the muffler, but its a good starting point.  The stock BMW exhaust
system is excellent in terms of efficiency and sound, as it's designed
for performance.  

The big six needs to breath.  I got stuck for a year with a "cheapo"
catalytic converter that had 2 pipes into 1 fore and 1 into 2 aft of the
cat.  The car was definitly down on power, and under hard accelleration,
or any time over 3000 rpm it had a wretched loud compressed air nozzle
noise caused by this constriction.

I later experienced a set up that has two 2-1/8" id pipes all the way,
but with 1" diameter noise control orifice inserts in the tail pipes. 
This net 1.57 sq. in. free area was even worse restriction than the
single pipe cat.  The supplier replaced these with 1.5" id. inserts
(3.53 Sq.In. net area) and it now flows very freely although louder than
stock.  You can see that a little diameter makes a huge difference in
area.

I also had a reasonably priced steel ANSA muffler at one time, it had
two pipes in and out, sounded about like stock, didn't feel restricted,
and was around $300 installed.  It was still intact after 4 years when I
replaced the entire exhaust system with a stainless one.

Enjoy your big six!

Steve Poland
'88 535is - 196,000 miles
Portland, OR

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