It definately has more power, but I am still sorting the Weber carbs. It is running very rich, plugs are sooted, tailpipe is black and sooty.
We broke the engine in, on track, with no real run in period. We ran it for 30 hours, under race conditions with no problems other than a set of soot fouled plugs and an exploded alternator( could not take the revs).I will change from BP6ES back to BP5ES plugs and rejet the carbs. More jets arrive this week.
It saw 8K on every lap, burned 105 gals of race fuel, and did not use any oil at all.
looking for jetting suggestions.
A15, 280 cam,GX head with 37mm valves, weber 40 DCOE carbs(33 mm venturies)

I wonder why it stresses the clutch when it is a high-revving motor. Should have less torque than a stock A15.

Fit a new set of plugs. Run it round the track, shut off during acceleration (coast to a stop) then use a magnifying glass to look at the base of the insulator, to see if it is sooty. It may be that it is only sooting up during low rpm which is common with high-duration cams. In which case you can lean out the idle mixture screw and live with a rough idle loping.