Header Design

[GR124]

Hey guys, for those that don't know I'm building a Locost Clubman track car viewtopic.php?f=87&t=74090&start=15
I'm about to purchase some bends to make the headers. Here's a photo, for clarity of what i'm doing, this is not mine, I have the BP4W donk.



I measure the OD of the OE NB8A headers at
Primary's 43 - 42.5mm
Secondaries 38
exit pipe 50.5

My engine is stock at this time, it will get tickled up over time. I know what I put on there wont be perfect but keep in mind the engine will live at 5000-7000 RPM

Primary size is my biggest concern ATM. I have a choice of either 44.45 or 41.28mm. Everything I read tends to recommend smaller, so thinking 41.28mm ???

I know the final exit will be 2.25 inch (57.15mm)

[GR124]

In my build thread it was briefly talked about. So I'll acknowledge the comments some of the guys added on the subject. In no particular order.

Magna_blue wrote
Long 4-2-1 headers as well, rascal, rather than 4-1? I'm thinking better spread through better scavenging throughout the range.

93 Clubman wrote
Yeah, 4-1 suits top end - go with the NB8A OEM headers if they'll fit the build. The ADM ones were fairly good, however the USDM ones were rubbish. There are/were some comparison pics on here somewhere.