The 34' Phantom with 32" Bravos was turning 4900/4950 rpms before changing from cast-iron exhaust to Gils. ECU were reprogrammed to increase the rev-limiters, and what ever else Tyley Crockett knew that would help (boat still idles at 650 rpms), the larger flame arrestor is more aestically appealing and may gain only some minimal power.

Ther bottomline line is that the same 32" Bravos are now spinning 5100/5150 rpm. The boat was a consistent 84/85 mph boat, now it will run 87/88 mph consistently.

That is the gain in speed gain my father experienced from these changes, as far as how much more hp was gained is ????? Don't know hp gain.

I don't know exactly how much the Phantom weighs, ask Will Smith at Phantom Boats.

Hope that clears up any confusion.

If you want to get some better info modifications, ask Smitty, "Artic Friends," he is very knowledgeable with 502 MPI's and engine mods, he knows his chit!

I have spoken to both Tyler Crockett and Mark at Precision EFI about the ECU for a stock 502MagMPI.
They have programs that will give the engine a little more kick if you are willing to run 91 octane. I'm assuming the timing is changed along with upping the rev limiter.

Rev limiter was increased to 5400 rpm. Boat runs on 89 octane.

I agree. Even though you were to add an upgraded aftermarktet exhaust to a stock engine you may not see a big increase in top end speed as you would like, but where you just might feel it in more places than any other is in the midrange cruising speeds. I have often heard of guys I know who have bought something like a GIL exhaust system and bolt them on without any other mods/changes and say something like, "I didn't gain much in speed on top, but I saw a very noticable difference in the midrange cruising speeds and throttle response/torque."

For the guy who's just learning about this stuff. These stock cast iron heavy exhaust manifolds that you normaly see on these lower grade engines are obviously adequate enough to fulfill the manufacturer's power output goals i.e. just enough to get the job done.

I have had to learn since the early 1980's that having or adding a better breathing exhaust system is the first REAL step in gaining any kind of power or potential for power----even if you only gain very little on top.

I used to hear the 1960-70's term "Free Horsepower" by adding a better breathing exhaust system. The idea being that by adding a better breathing exhaust you will make more horsepower or at least creat a platform for creating more horsepower as you upgrade/modify the engine. Of course we all know that a marine aftermarket exhaust system isn't exactly free. Generaly speaking, once a better breathing exhaust system is installed, then the better the engine will respond to any mods/upgrades thereafter.

Sorry for being so long winded. Have fun :)

Did the exhaust sound make much of a difference? Which model did you replace with ?