Im doing a repower at the end of the season. Trying to decide whether to build 509's or spend the addition $$ and build 540's, so my question is with all things being the same on the two different cu in motors, injection,heads,cam ect. how much more power will the 540 make over the 509.

Currently running stock 502's / 415 hp a side

Not that much even if your making 2hp per cube which is pretty darn rare, so with the same top end and just the extra 31 cubes you will probably be 30hp higher from a 509 to a 540.

Keep your costs down by going with a 509. Spend the money that you would have spent on 540 rods and crank and use it to buy good heads and a matched camshaft. Then send your motors to Mark at Precision for the fuel tuning. If done right you could see 550 hp or more. Also cut down the runners to be flush with the upper plenum to increase top end flow. Then you have to radius the runners. See pics. Doing this is good for 10-20 hp.

Smitty

When it comes to measuring an engine's performance in a boat; the obsession with horsepower must be dispensed with, and a greater focus given to the engine's torque.

This is an excellent article on the subject.

Bingo! Go with the 540's. If you want that power to put you back in to that seat you need torque not HP. Do it now while everything is coming apart you won't regret it.

good article, I didn't mean to exclude torque in this equation and I know the 540 will make more vs the 509. My thoughts were also to build the 509's, and put the extra couple grand per side for the rotating assenbly's in cam and heads.

Totally agree on the torque issue. I have tons of torque with my setup. That is why I stated to spec a specific cam based on your exact setup. An off the shelf cam will leave HP and torque on the table. Call Bob Madera and have him grind you a specific cam. Money well spent. Bob is at 585-654-8583.
He will have a lot of specifc questions so make sure to have all your specs ready from your motors and heads. He can also help you pick the right componenets based on your goals.

Tell him Smitty sent you !!!

I'm putting 500 EFI units on the new motor's does this machineing apply to them also. I cant tell what the pix are.

ya, I just pulled mine apart, there is an O-ring seal between the manifold and the plenum.

540s may be more harsh on the bravos.

I dont want to start the domino effect and tripple the budget or the wife will have my privates on the wall, or has it already started.