I'm curious if anyone has experience with anti-reversionary headers on an M10? How about on any other car? There is one for sale on ebay... Ken, what are your thoughts?
Anti Reversion Header (http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33631&item=7973935999&rd=1)

I did not not like the flanges on the the header. The tubes are so large that when you go to install the small copper nuts, they hit the tubes and you cant tighten them down.

The set up I have is the second picture that is posted. Which explains why mine does not bolt up to the stock exhaust. The two pictures posted are two different headers. So be sure you know what your biding on.

It's not a great design, the primaries are not even close to equal length (obvious). Un-equal primary lengths can cause tuning problems with carbed engines due to each cylinder trying to make power at different RPMs=jetting nightmare. CIS or EFI will lessen those problems but not eliminate them. The "anti-reversion" cones have been used in Harley Davidsons for years to compensate for running pipes with too large of ID (for looks) for the power generated. It's a crutch used to make a poor header work better. Modern thought is port matched headers so the pulse wave reaches the exhaust valve and take advantage of the pressure wave to create a low pressure area in the port as the valve opens. This happens in a fairly narrow rpm band so the tube lengths must be taylored to how YOU drive YOUR car for max benefit.

A really good header will require a custom exhaust to maximize the gains so from my perspective fitment to the factory exhaust is irrelevent.

ken

Thanks Ken, good to know. I figured it was a half assed fix for a poor header design. I plan on welding up my own exhaust some time this summer. IMO, the stock exhaust and performance mufflers designed for it are worthless. I am planning on running 2.5" all the way back and splitting to dual 2" (the duals are for style points...) 2.5" may be a little large for my motor, but I'm planning ahead for a turbo. In the meantime, if I can find an equal length header with a 2.5" collector I'll snatch it up... Out of curiousity, how much do you charge to make a header?