WF-S2K

I'm hoping someone can help with some advice!

I'm going to need to change the manifold on my F20C, I'm just gathering together the parts to convert from ITB to a Rotrex based supercharger set up. The problem I have is the exhaust manifold; the engine is in a kit car and is currently using the Kit car makers stock S2000 manifold, which for reasons to go now, is poorly designed and doesn't even use the stock Honda pipe sizes. So I have nothing to measure and use as a reference. The current set up is fairly restrictive, unfortunately, it makes a standard engine approx 17 bhp down, at the crank. It also seems prone to back pressure issues.

Obviously, as it's a kit car, (Caterham/Lotus 7 style), I can't simply buy an off the peg manifold, I have to have something made. Trouble is, I've no idea what even the stock dimensions are.

Due to space limitations in the car, I'm using the TTS/Rotrex bottom mount kit, replacing the unused(!) AC compressor, with a C30-94 'charger. output is typically somewhere around 350 bhp at the crank on similar installs. (The cars are typically below 700kg/1500lbs so you wouldn't want too go too extreme with the power, it'll just spin the wheels up all the time!!)

Can anyone advise with some suitable dimensions - even the stock ones would help give something to work to?

Scigheras

I'd look at the official web pages of some popular aftermarket headers. Most reputable companies list at least the different pipe diameters used. E.g. J's Racing header is 4-2-1 structure [ 4(50Ǿ) – 2(50Ǿ) – 1(55-60 Ǿ taper)].