Damn the stock exhaust manifold looks like shit. Dump those things for some headers immediately. As far as that design im not surprised at all. My E39 M5 and E36 M3 stock exhaust manifolds look like shit too. Very similar to the E60 and headers on my E39 also give 35hp like the E60 you have. And on my E36 headers give that about 25hp. The best stock M car manifold ive seen was on my E46 and even that wasnt that good but it was the best stock one ive seen on any Mcar before.

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Dinan M3

2006 X5 4.4i Sport Current Vehicle
2006 CLS 55 AMG Current Vehicle
2010 FORD F-450 King Ranch Current Vehicle
2012 GL 550 Current Vehicle

1999 M3 Dinan S3 SOLD
2001 M3 Dinan S2 SOLD
2002 M5 SOLD
2004 X5 4.4i sport SOLD
2007 335 XI Lease ended
2009 E92 M3 SOLD