any one have a rough idea with the following mods hp gains? ecu reprog. az speed and marine , msd ignit, k+n air filter , adj fuel reg. rev. marine exhaust , machining to intake manifold (az speed and marine ) and new cam ( az speed and marine ) not sure of cam dimensions.? also i am running 89 octane fuel would i have to go with 92+ with these changes ? , that's the best we can get where i boat. these mods to be done on 1998 502 efi.

the cams the big question ?? it would help be sure to add springs
and a head chage to merlin iron heads really wake it up

ECU reprogramming = 6 - 10hp
MSD = 0
K&N = 4 - 6 hp if you're lucky
adj. fuel reg. = 0 (helps w/ reliability)
intake porting = ??
cam = ??
92 Octane required? Actually, 91 will be your minimum unless you tell Arizona to set the ECU for 87 or 89.

Bobby, have you done this sort of work to Merc 454/502 MPI motors (without getting rid of the MPI)? What seems to work best? What kinds of results have you had?

I just installed all the az. speed and marine stuff on my hp 500efis. Port side. the timeing wont set and is real lazy. My eng. builder has called Az. speed and marine 6 times yes 6 and not one ret. call. On the dyno the only thing that made an hp. gain was the throttle. 9hp. I'm going to write them a letter and tell them how much the helped me ,zero.

I fully agree with Tom above !
We've done alot of those and it works easier and cheaper in the long run with the injection off as anyone can tune it ,ect

we run the motors cold and 9 to one comp. a cam we have ground and nerlin heads ((for the price and performance))
and they make tons of power and are turn key and drive off
--------------------------------------
or you can with the ecm
Pocket port and clean up heads
install cam
up comp. alittle
put new heads on
it will really go


great results you'll think you bought a new boat

Can you also do bore notching on a 454 with an ECM? Does this help as much as people claim?

Don't even think about it! Had a set of perfectly running 502's after sending ECU , Manifolds, Injectors, etc., to Arizona Speed, nothing but a waste of money, and nothing less than Migrain Headaches every damn day. Scrapped engines and had to go for New 500EFI's. NEVER AGAIN

The bore notching helps but not alot the ecu is a tough thing to get right but we've been lucky most of the time

Try this-- I think it will take about around 20 horsepower just to gain 1 mph in top speed. This is what you should be looking at. Why spend all that money if the net result is 2 mph ??

Spend your money to make sure your prop is perfect. This is biggest bang for the buck. Do a search here to find someone close to you to have prop labbed.