I did not know that Mark ran a modified version - which mods have been made there? Was the carb modified to hold the needles in place?
I tested the stock Arrow GTR on two pretty much full throttle tracks (one had a good rain the night before and was high traction, the other one was very dusty but one could push very hard due to the layout) and never came over 9 minutes runtime. The initial test-driver who broke the engine in also ran around 8:45 with it and the last test-driver who installed the 6 mm venturi reported runtimes between 9:10 and 10 minutes. So maybe it is the air you guys have or you are really light on the throttle, but I cannot see, under no circumstances, how this engine could be good for 10 minutes stints in a race. I ran it with 2060 and 2041 with short and long manifold, no major changes in runtime, but I found that it is way stronger (not that high rev top end though) with the 2041.

I am sure as hell no one who needs a big price tag on any part of my car but I also stopped praising budget parts over the moon as well. I really think it is a great engine for the money, but still not a Speed. I switched on the second testing day back to my 30 liters old Speed and it is that much more powerful in all situations and still needs less fuel.
That is what I meant with keeping it real: I dont crucify the Arrow, I really dont, but I just read Marks post and thought "Wait, isnt that the engine you tested two weeks ago?" Okay, obviously not - so please take my post as a commentary on a stock Arrow GTR.