Last summer I swapped from a 454 to a new 502 Gen VI with roller-cam rockers and push-rods... And also installed Stainless Marine risers and manifolds and used with K&N air filter and computer was reporgrammed. There was no noticeable difference between the motors, and by GPS the speed was the same with the new 502 as it was the summer before with the 454. I used the 454 upper and lower intake and fuel system on the 502 and I was wondering if anyone had any suggestions to get the performance I should have. I tried several props all summer long, with no noticeable difference. Any suggestions?

What boat was this done to. Did it have a 454 Mag EFI?

It was a 95 Baja 272, and yes it was a 454 Mag EFI

I thought you might say that. I think that its going to take more than 40-50 Hp to see much difference in that boat. If you did not dyno the new 502, you really dont know what kind of power its making.

would bigger injectors make a differance? It's not running rich at all

You can jack with it forever or put in on a dyno. I wouldnt spend a whole lot of time messing with an EFI engine in the boat if I didnt at least have an O2 sensor in the exhaust, fuel PSI gauge, and a scan tool in my hand. Otherwise, you really dont know whats going on.

Not to be smart but who did the computer for you ? There are a lot of guy's that think they can fix them but only a few that really can do it right. This is the first thing I would look at, easy and cheap compared to 02 sensor,psi gauge and a scan tool which is the next move like Tx said. Just my .02 Jeff

Just a question, but are you getting more RPM's??? Did you try more prop?? you could put 1000hp behind the boat but if the RPM's are the same (rev limiter set) and same prop you will run the exact same speed.

Just a thought

Rpm is the same and tried different props. i was Told my computer got changed when the motor got replaced. will this boat run with the computer programed as a 454 compared to 502?

Without knowing the specs on the 502 you installed, there is no way to tell if you should have gained HP.

A 502mpi is only 30hp more than a 454mag mpi. That equals about 150rpm and 2 mph.