I can't comment on the others as I've only had PD manifold. But referancing back to an even older issue of performance ford magazine (its a hive of info) Primary Designs did a 4 page spread on their workshop and fabrication facilities and a bit on FRS manifold which I was impressd by. They can offer you inconel and titanium stuff aswell as stainless. But what drew me right in was the way they weld the manifold collector (where 4 tubes come to one) they weld it from the inside and the four tubes just blend and flow together nicely . The GGR one all four tubes just gather in what looks like an upside down mushroom. Don't know the diferance in performance figures between them so cant comment on that. I just preferred the PD set up, and I was also able to get GGR one brand new for £700 through a contact, and still chose PD one @ £1300.

I could be mad eh!

Primary Designs have also made products for formula 1 and WRC cars, this can only be a good thing.