I'm not sure how sensitive the 741 cam is to comp and realize it's used in engines less than recommended comp (10-12:1) however wondering if you degreed the cams or just installed straight up? Try some 25 p props to get the rpm's up closer fo 5,500 and I would imagine the engines will be happier and you'll gain speed. Personnly I think you would be better with the airgap but just get the blower on and be done with it.

Btw I wouldn't take the timing past 35-36 deg and doubt your valve lash is an issue. 1/4-3/4 turn past 0 lash should be fine. I total see what your getting at but yet think your a little optimistic with your expected gains of 120 to 150 hp. Heads out of the box or ported and flowed? Also did you install new rings or stay out of the bottom end? Both engines the same?

Lower compression with higher flow seems like it would be a bit of a dog without a huffer to help push it through as you have even less cylinder vacuum to gulp in a bigger bucket of fuel, but I'd say that your carb is your limiter.

Cam installed straight up. Heads box stock with corect crane sorings etc. ferrea valves. Redid entire bottom end. New rings. Low tension oil 12lb. Comp ring gap .021.

Also if you get a chance try a larger carb. anything larger that you could potentially borrow and try would cut to the chase. I nearly did the same as you with low compression 555 builds for near future 871's but decided to wait and do it all at once cause I figured I'd be chasing power that I simply wouldn't likely achieve.

Although you can read up on smittys low compression build and pick up on something there. It's a good thread but different CI build.

How much time do you have on it? Rings seated yet? What kind did you use?

2.5 hours 90% over 4k rpm. Total seal rings. I would say rings are seated. It was wide open at one point for 8-10 minutes

Just for the heck of it take a comp test on a couple cylinders and see where you at. I know you probably don't want to but see if you can borrow some smaller wheels. If had had to bet you'll gain worthy speed.

I have mirage 25 std and 27 plus'. 25 mirages bite out of hole good. 27 not a chance in hell. Takes 500 yards and alot of crafty throttle. Problem with both is when i get in rough water at under 35mph the bow shoots for the moon an cavitate then regrabs then cavitates then regrabs. So basically have to stop and restart. Thats why i went 4 blade even with deep drives

Sounds like you have not dyno tuned so I would at least add some O2 sensors and tune on the water, but don't forget to also properly read the plugs.

Thought op said 12.5 afr. Plug reading always a must regardless though.