John, you wrote this in an earlier post:
"The ITB cars with essentially the stock exhaust port are getting 150 HP or more at the crank with 4 -1 headers, though not necessarily in a power band appropriate for the street, so it looks to me like improvements in power are possible up to that level with the right exhaust system."

Would you or anybody else know what dimensions the ITB guys are using for 4-1 headers?

Cheers,
Paul.

Paul,

Here is a link to a photo of the BHP header.

http://volvo142racer.blogspot.com/

IIRC, this blog is maintained by a Brickboard member.

Measurements (diameters are absolute, lengths are approximate):

Primaries are 33" to beginning of collector, followed by 6" collector length to a 2" ID pipe. The primaries are 1.375" ID for the first 15", then go to 1.50" for the last 18".

WRT 150 horsepower from an ITB legal B20... hmmmm... Even assuming that's at the flywheel, it sounds pretty optimistic to me. My seat of the pants says my engine is (okay, was!) nowhere near that number, and it is probably as strong as most ITB engines out there. Maybe I'll try to get it on a dyno when I get it running again.

Thanks heaps for that, I am always interested in facts & figures. They are tuned to 6000rpm according to the formula I use.