As stated, what is the big difference? I have heard that the SCCA frowns upon the RB ones....

 

I think the difference is the angle of the port sleeve. The MFR comes in straght and level like the exhaust (If I remember right), while the RB is angled down perpendicular to the sealing surface.

 

On the intake side, the MFR have a flanged connection to the intake manifold instead of a spigot, and the port goes in "straight" instead of angled in. (Of course the MFR is cast this way, it's not a modified stock part) I forget port timing difference.

MFR housings have relatively mild exhaust port timing, opening slightly *later* than the street parts. The exhaust flange is different from OEM as well.

I have also "heard" that the chrome is directly on aluminum, no sheet metal insert, so lightweight apex seals are mandatory. No iron seals.

 

yep the exhaust ports open later, and close later.

 

so MFR are better for top end performance then?

 

And for a lot of other benefits including the total power output.
You can duplicate the same for a lot less although the RB housings are not the way to do it from my experience.

 

but getting the MFR housings is difficult, correct?

 

Not difficult, just pricey.

Put it this way: Take the TII you just bought, and what you paid for it is what each housing costs...

 

cheaper than a stock posrche 911 piston and sleeve kit....

 

ouch

 

Aren't they like $1400 each?