Doing the basic math would point to the exhaust change. If the boat ran 4900 before and now only 4300 with only the exhaust change, you're most likely encountering a water pressure issue (possibly high or low). I'm assuming that the water temp numbers from the exhaust that were provided are numbers while the boat is running hard. If not, double check those numbers to insure you don't have excessive heat in the exhaust.

Good point DMP, sounds like you've been down this road...LOL. Hook up that Diacom and record a run, then go back and study it hard. I bet you'll discover the problem.

Could I have done anything that would cause a water preasure change, in this case lower, that I should check for?

I also have had a terrible season due to CMI ,s if your seapump is scared it puts air in the system makes steam pockets

How did you arrive at that conclusion?

Found my issue this weekend. Sea water pump pressure was at 43psi without engine running! Picking up the sensor today. Have heard there is a high percentage of these failing.

You should have someone scan the engine while running at the wot rpm. Watch your exhaust temps.. The port side is usually a bit warmer, but it should not be excessivley hotter. If it gets up close to 200* or more you are not getting enough water on that side. You will need to balance your waterflow.. Some exhaust systems allow for too much of a difference in waterflow from side to side.. We have seen this many times now with some aftermarket exhausts.. Also check your heat exchanger for cleanliness..

BTW a low seapump reading of 2.5-6psi at idle is sort of normal, for a true high or low pressure reading it should be checked at higher speed (preferably wot for an over pressure fault)..

:) Jamie / Lakeside

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all I did this year was the header my engines are Whippled making 806 hp I have no steam cruising around its at idle plumbed innercoolers back in to starboard side of exhaust new seapumps etc.removed all the blow off valves I just dont know what to do 412 781 0881 Bob looking for advise

You really should scan it & see what theheck you have going on.. Otherwise Its's kind of like having Ray Charles work on it.. What you should look for is inconsitancies in temperature from side to side on the exhaust and your sea water pump at all speeds.. Stuff that may be fine @ idle may not be ok in the upper rpm range.. Again being that you have a non stock exhaust & are running an sc, I would definitley pay attention to exhaust temps.. If need be you can engineer a valve to force more water to a side to even out the cooling temps.. Again assuming that, that is the issue.. Otherwise I recomend having a pro shop look into your problem.. We are on the other side of the state from you (about a days drive), but feel free to give me a shout if you need to bring it in.. :) Jamie / Lakeside

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Well I took it today,kindof difficult to hold wide open throttle for to long I would run out of lake (pond) .
Any way these are the readings:
RPM 4292 Aviable Power 100%
Coolant Temp 161.60 Sea Pump Preasure 22.5
Port exhst Temp 116.60 Starb Exhst Temp 102.20
Oil Preasure 47.92 IAC Duty Cycle 99.15
Throttle Position 96.83% Throttle sensor volt 4.49
Spark Advance 22 DEG Batt Volt 13.92
Manifold Absolute Pres 13.44 PSI Baro Preassure 13.81 PSi
Manifold Air Temp 110.2.
Can anybody see somthing wrong.
Is the IAC supposed to be all over the board. It changed from 0-99 depending on RPM.