underpsi68

Best of luck with it. I'm sure you will find it soon and it will moody likely be something small.

donzi matt

For chits and giggles, I swapped plugs again Friday night. I didn't see any cracked insulators or signs of carbon tracking but sure enough my misfire is gone. Port engine still lags the starboard by 100 RPM or less, but this boat has done that since the day I bought it, and at this point I am just going to accept that's the way it is. An interesting note is I pulled NGK TR55's out of the motor and reinstalled the AC Delco OE plugs. I don't know why I chose NGK's last time other than they usually are a solid performing plug for me. The AC plug does have a slightly more projected tip than the NGK's. After a full day of running the boat Saturday I am satisfied it isn't misfiring.

The boat is a totally different animal now. Midrange is tremendously stronger, and the boat feels much more nimble than before. Where the stock 496's seemed to fall flat over 4000, they keep pulling hard now to WOT. After a couple miles at WOT, oil temps stay rock solid at 190. Cruise speed is much better as well. 45 is at 3400 RPM and 4100 gets me 60. I'm very pleased with the improvements.

Now that I have the misfire handled, I am going to try a couple different props. I am currently spinning 28 pitch Bravo props (previously repaired, and not well) to 5000. I have a let of labbed Hydromotive Q4 27 pitch props to try that I think may work well and I also have a set of Spinelli 14X29 labbed props to try.

Gimme Fuel

I had the 8100 vortec (same as 496 mag) in a truck and had same issue. Apparently that ignition doesn't like any plugs but the OE Delco's. I ran autolites and were junk and misfiring at 20,000 miles after they were changed. Put Delcos back in and all was well again.

donzi matt

In my rambling I forgot one other improvement I made this weekend. When switching to the Accufab throttlebodies there is a provision for hooking up the IAC hose, but no provision for an IAC muffler. This makes for two issues. The first is there is no filter to keep debris from making it to the IAC, and the second is an extremely loud hissing noise whenever the IAC is opened. I decided to do some modifying. I started out by ordering two of these: http://www.amazon.com/62-1600RD-Vent...ilpage_o01_s00

I then removed the IAC hose from the throttle body, removed the grommet from the filter, and shoved the end of the hose into the filter. Being that the base is just stamped metal, the edge of the base acts like a barb and keeps the filter held secure. I then zip tied the IAC hose in a loop so I didn't have to cut it and secured it and the hose to the rear harness. I can't hear the hiss at all anymore. It's one of those things that is minor but makes a huge difference with me for under 20 bucks. I think I would have probably done this with the motors stock just to feed cleaner air to the IAC's.

underpsi68

Great info!!!! Thanks for sharing.

I'm glad you found the problem.

donzi matt

So went prop testing tonight. Big time fail overall.

First, were the Hydromotives, I had such high hopes. These were 15.5"X27 labbed 4 blades. They were nearly impossible to get on plane, but I finally managed to get them there. This was with difuser rings already. Once on plane, they gave up cruise speed to the Bravo's, and gave up a mile an hour on top end. Interestingly though, both motors were dead nuts even on RPM all through the powerband, so that answers the mystery of my RPM lag. They topped out spot on at 5000 RPM's.

Next up were the Spinelli's. These were 14X29 4 blades, lab finished. They were even worse trying to get on plane, which surprised me as they were a smaller diameter than the Hydro's and the Bravo's so I thought they would pop right up. Out of frustration, I gave up before I ever got the boat on plane.

So for right now I haven't found anything better than Bravos for this boat. Even those blowout slightly getting up on plane but are pretty effortless overall. Let them slip a bit to about 3200 and the boat hooks and goes. My X dimension I believe is at 18.75" so that only leaves the propshaft about 3.25" below the bottom. It makes for some great manners but it is pretty sensitive to props apparently. Maybe I will search out a better set of Bravo 28's then the ones I have now and have them labbed.

MILD THUNDER

Sounds like it likes the bow lifting characteristics of the bravo over the hydros. Might be worth trying spinning the props in for a little more bow lift and see what she does. Should help planing a little too.

myturn

Any updates?

thirdchildhood

Maybe try five blade props?

donzi matt

Honestly, I've just been using the boat. This thing is just as reliable as it was with the stock motors. I think I have put about 20 hours on it so far this season and aside from the misfire I had at the beginning of the season it just starts and runs as it is supposed to. I should do some more tuning with props and with fuel pressure but it seems like there is no free time for that stuff. I listed the boat for sale on a couple of sites because I would really like to get into a top gun, if it sells I will move up, if it doesn't I'm going to keep adding power to this one. I am all over the new 540 shortblocks Raylar is offering so if I still have it this fall I will buy a pair of those and possibly whipples, then figure out what I am going to do about drives. This really is a sickness.