Re: question for efi engine experts
 

Those NGK are not the best in the world even on the MSD. Cut them back to .035 and restore your initial advance on the dist. Personally I have had best results from the AC spark plugs from SBC and BBC. You wouldn't think it but they are tough, reliable and easy to read plugs.

Also you boasted about your fuel pressure but no matter what anyone tells you a fuel pressure taken at idle only tells you one thing: "That your fuel pump is running". On an EFI you MUST get a true reading at WOT being sure it holds maximum pressure with NO drop off until the throttle is pulled back. Otherwise fuel pressure readings are as useless as a screen door on a submarine.

Roby

Re: question for efi engine experts
 

robyw1 what part no. do you recommend for the ac plugs ? thanks for the info !

Re: question for efi engine experts
 

As Tomcap has stated, your boat will see the best speed with a 3blade, ( deep V with conservative X setting) which is why you lost speed with the 4blade...
With the engine...my best guess is the exhaust you chose doesn't flow enough to take advantage of the ecm reprogram which has resulted in a rich condition and thus loss of power and response. Only a few aftermarket exhausts actually require a reprogram of the ecm because they put the 502EFI into a lean condition...most will not and work best if the ecm is left alone. The only headers that I know of that require ecm reprograms are basically tubular headers, such as CMI, Lightning, Stellings, Eickert.

Re: question for efi engine experts
 

One more thing...its not your plugs..and NGK are the best in the world and what I run in all my cars and boat with no problems.
My engine? HP500 built by Innovation Marine. Plugs they install in this and thier HP525 and HP600? NGK V-power #7's. Gap at .045.

The ecm reprogram will or should have a more aggressive spark advance in it.

Re: question for efi engine experts
 

Use the reccomended AC plug for your engine and depending on how you run you can step up a number colder or hotter. Don't go over plus or minus 1 in the heat range unless you have pretty extensive mods. Oh and stay away from the Rapid Fires. They work beautiful at idle and cruise providing me very narrow x-counts from the O2, but with high compression, high RPM, heavy loads, boost, I have documented with (TTS Powersystem's) datamaster that they tend to be more detonation prone by consistantly sending the knock retard numbers up. I have also experienced less than ideal plug life. (However to be fair I have not tried the rapid fires in a big block)

Roby

Re: question for efi engine experts
 

The AC plug of choice is MR43TS..or if you don't boat in salt water you can use the auto version, R43TS. This is the extended tip version of the R43T plug and gives you a smoother idle and better resistance to fouling and recommended by Dennis Moore in his Marine Bigblock and Smallblock GM performance books.
PS. Same plug used for small block GM's.