Have any of you guys done this to a 454mag or 502mag without any other modifications and had good results?

You mean add a custom chip or program? It is really not worth any horsepower gains unless you are doing it to accommodate other mods such as cam, larger TB, bigger injectors and so on. Doing so stands a better chance of hurting you than helping you.

Roby

Like sending your ecu to Arizona Speed and Marine or someone that does recalibrations.

Well they can recalibrate it but the question is does it really add HP to a stock engine? If it does and the increase is substantial then it means that Merc wasn't doing a good job of programing the ECU to start with.

Roby

I had my 502 mag ecu modified in an Eliminator 22 eagle xp and saw absolutely nothing. I was told it should add 300-400 rpm. ($375) waste of money. On the other hand, I plugged in a hypertech re-programmer on my gm 6.6 turbo diesel and it ripped my head off. 95 hp and 170 ft lbs torque for $375, wow! Wish it was that easy with a boat. I guess keep dreaming.

call mark at my signature below , he will give you a honest heads up.

You can reprogram to alter the rev limiter. You can reprogram to clean up the transom at idle a touch. You can reprogram a factory blower motor a little leaner (cause they come very rich with factory settings). But programming a box doesn't get any additional airflow thru the motor. So you shouldn't expect to see any power increases on an otherwise stock motor.

If you live at a high altitude, you can probably improve on the factory map, though.

Cars, in the early EFI days, were a LITTLE different. You could drop a chip in them and feel real increases thru the midrange, cause you were changing from SMOG settings to performance settings. On a boat, they simply try to program a curve that provides close to an optimal fuel mix at most throttle settings, at most altitudes. No doubt, though, that the factory map is best at sea level or close to it.

I didn't think it would help,I just wanted to bounce it off a couple more coconuts and see what the opinions were.

I typically boat at ~6200', what kind of difference would a reprogram for high altitude make? Would it just clean up the transom or would I see anything different in performance/response, etc.

I've not run a 500EFI at 6200 feet so I don't know how "out of whack" the stock map is at mile high. I'd be surprised if there wasn't room for improvement, though.