John - a freind of mine just went through that exact scenario whith a set of B&B headers. He posted the delima on Rennlist.
The car ran perfectly with a Euro exhaust. Nothing was changed but headers added.
At idle the headers would glow red. After much agony I suggested that the header material may be the culprit (thin tubing or metalergy problem) and the way to find out is by reading surface temperature. He bought a pyrometer and found the surface temperatures were slightly elevated, but not enough that it should cause the headers to glow.
Very long story short, the CO was in spec but the A/F ratio was not perfect. By not perfect I mean 0.5% off at idle. He retarded the cams, cleaned the fuelhead, and adjusted the WUR. Bingo - problem solved.
The point of all that is that in this particular case the header design exposed a "problem" with the engine tuning that manifested itself in a very odd way. The timing events combined with a slightly rich A/F ratio and new plumbing lit 'er up cherry red under moderately high surface temperature readings.
RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Last edited by RarlyL8; 02-06-2007 at 08:57 PM..