M42 exhaust manifold

[Boyracer]

Took few measurements while under the car yesterday:

4-2 part

pipe diameter: 38 mm
pipe lenght: 35 cm

2-1 part

pipe diameter: 45 mm
pipe lenght: 35 cm

To catalysator (and rest of the exhaust I presume)

pipe diameter: 52 mm (there is a dent between resonator and muffler giving even smaller effective diameter)

Incidentally those 4-2-1 manifold pipe diameters are exactly spot on as given in Graham Bell's engine tuning book. BMW clearly did not arrive to those dimensions by pure luck :cool:

I think there are few things that could be improved on stock/almost stock engine:

- 2-1 pipe Y merge/collector does not seem too good, merge angle could be smaller
- exhaust diameter of 2 1/4 could be slightly more suitable

[Letsplayskatch]

Based on that, what do you think of this?
http://www.cdfracing.co.uk/product_info.php?products_id=185&osCsid=84329773c3e052f4d55622d5abecaf46

For both M42 and M44

Scott

[EN318isPDX]

Thats a pretty pipe! I do think that there is not much room for upgrade on our exhaust manifold. I think that money is much better spent elsewhere. Most people get a nice header and than later decide to go turbo so they end up junking there $300 dollar header. I've seen a couple of my M20 friend have to sell there ceramic header because they went turbo. If only i could have used it for the $100 he sold it for!

[Letsplayskatch]

N/A all the way for me nothing beats the induction roar on a quad-bodied 4 pot

But i think thats a really good price for a S/S 4-2-1 manifold. It doesnt look too different from stock, which is good because the stock pipes flow very well, except in a few places. And I think the above header irons out those flaws. Will certainly be going on my M44 wish list!

[Boyracer]

I do think that there is not much room for upgrade on our exhaust manifold. I think that money is much better spent elsewhere.

I tend to agree, stock exhaust manifold is quite good from factory and will be ok with decent power gains!

however, my power goal went from initial 180 hp to about 220 hp and at that point stock exhaust system could use improvement, thats why I have been looking at it.

Most likely I could still use stock primary headers (the 4-2 part) and then I manufacture new parts for everything from that point on. Selection of 2 1/4" mufflers and resonators is quite small so I think I will go to 2 1/2".