Well what happened already!!!!

Well, I can tell you what happened with mine. My 540 with the ported manifold and bigger throttle body made a very disappointing 567hp. Hade to take a lot of fuel away from on the top end because it simply wouldn't flow enough air. I believe any money spent to modify a MPI intake would be better spent on a different induction system.

Sounds about right the MPI is GREAT for what it is, high torque in the low and mid range, efficience. . But is not for modding big numbers. I do think it is a very good set up for a stock unit.

Are you running supercharger/procharger? Or is This 540 N/A? Im very curious!!

Mine was N/A

My 502 MPI converted to 540 MPI made 630hp at 5300 rpm's. HP fell quickly after that rpm. This build is using TPiS throttle body, modified MPI intake and Dart Pro1 heads. Very happy with the results, Ateco marine did the work.

As to whether it would benefit going to bigger butterflies on the std 502 setup, if i take a vacuum reading at WOT and it still has say 1-2 " of vac still there, would that be a sign that larger TB would help??

Seems as though going from around 1.5" or so to near zero on intake vac it would have to be flowing a reasonable amount more of air. If vac is less than 1, then leave it alone. I don't recall but seems like on a past run it read about 1.5". Will have to check again.

Mine's not exactly stock - I have Eddie Marine manifolds and ells, extended the alum elbows to make it dry to the very back which seemed to help a little also. And K&N air filters, And bumped the timing to 35 vs 30 stock. 32ft boat runs 79 mph stock except for whats listed. Not too bad.

Welcome your comments or knowledge, all these little things that are cheap to do are beginning to add up.