A quick note on exhaust gaskets ...

[LateApex]

Let me suggest a bit of care be taken when selecting exhaust gaskets for your build. The gaskets I received with my kit in '21 were a "bottom of the line" Mr. Gasket p/n 4825G for my SBF. This is a 3-layer stainless steel gasket, and while it may do for certain exhaust / engine combinations, it is likely not suitable for mating AL heads and FFR headers as in my build.

I have been chasing raw gas smell on deceleration for a bit, tweaking EFI parameters, ..., etc. I finally pulled the headers today after studying EFI data logs, and deciding to look for exhaust air leaks which might generate a false lean reading by the WBO2 sensor. Thar she blows! Blow by traces near cylinder 1, which happens to be on the side where I have installed the O2 sensor. And yes - I had re-torqued manifold bolts per the script.

Gasket material / quality is one thing. Another is that the right side header flange is not flat. It is not twisted, just bowed. You will not pull it flat with 18 ft/lbs of torque. Bowed enough to compromise the seal at the forward end (#1).

I am embarrassed that it took me this long to chase this down - I wasted a lot of time examining base fuel maps, learning parameters and other EFI tid-bits. If your build is carburated, you may never notice this. If you run EFI, an air leak in the exhaust will screw up closed-loop on fuel control, which is why we opt for EFI in the first place, right? And potentially cause more serious issues down the road.

As a side note, I am done with the FFR Coupe exhaust. It has been a complete waste of my money and time. I have lost count of how many times I have needed to tighten the ball flange, and the stock side pipes are stupidly loud.

FWIW

[David Williamson]

I use Ultra Copper instead of gaskets, it works and is more forgiving with surfaces that are not machined flat.
David W