Engine room is super tight and though I like my Gils they are literally touching in twin engine bay- can someone compare difference in flow between Gils and stock Merc 502 MPI manifolds?

at what HP does it start to matter?

Thanks!

The Gils are probably adding 10-15hp on stock 502 mpi's.

I'm not a twin engine owner but want to know about "stuff"
Touching won't last. Could you put a wedge gasket under the Gils to tilt them a bit? Or a thin exhaust gasket? Or both.
You probably can't tilt the engines on their mounts without throwing off their alignments to the transom plates.
I'd put up a lot of fight for 10 or 15 horsepower.

10-15hp per engine in his boat is prob only a 1/2 mph on top end

not even Grif - but if I put a blower on it ;-)

looking at a pair of stock 502MPIs which come with stick exhaust - I already have Gils in the boat.... so thought I ask.