Pavlo

If you have purchased the Gruppe-S headers, the following maybe of some interest (probably applies to many others too).

I checked the flanges on my new Gruppe-S headers last night, and found the ports are not properly aligned with the holes in the flanges.

This appears to be caused by inaccurate holes on the flanges, which differ from side to side, they are drilled and not cut in with the rest of the profile.

My intention is to slot the holes a little (1mm or so) to allow alignment and drill through flange, gasket and into head so I can fit a very small dowel pin, about 3mm in diameter ought to be fine.

With just a single dowel, and remaining clearance on the holes, I don't think it will be over constrained. The centre is slip jointed to.

Paul

JamesS

Same as HKS then.......just copied the std header castings - crap port matching `in-all.......

Pavlo

no not the same as HKS, the flanges are counterbored to locate the pipes accurately and give a perfectly round hole. The HKS just come through the flange and can vary in their actual postion and roundness.

The 3 holes for the studs appear to be drilled, perhaps from pilot holes, but they are not where they should be. The actual exhaust holes in the flange are fine.

The ports in the heads vary anyway, as they are subject to placement of sand cores in the mould. You can easily get 1mm misalignment compared to the gasket.

Paul

Andy.F

What do you think of the mod Pats headers have ? Where there is a designed step up in bore right at the head flange which then tapers back to primary tube size ?
Seems to work when you port out the cast headers

Pavlo

I think that a good match, or at least head port slightly smaller than manifold is the way to go.

It would be nice to have a few mm to play with and match the head to the tube.

I think the H&S headers have the primaries flared a little rather than a 2 piece fitting, forgotten already.

The very small welds (would benefit from slightly larger fillets anyway) on the Gruppe-S don't really allow to open out the flange much. Still, you can probably put a 15º taper chamfer on the inlet to open it up a mm or more.

I think the very poor shape of the cast headers isn't a good comparison. Especially as the very short primary length allows exhaust gas from one cylinder to polute the other (much less a problem with the longer primaries of the 4:1).

I will at least get them as concentric as possible.

paul