Mr Maine

Nice, my biggest worry is moisture killing the sensor. Motors are in the boat, I painted the engine bay white which really brightened it up. Outdrives going on this week so it won't be long. Sorry to derail your thread.

I'm curious to see how you make out once the throttle is fixed and if you will need prop work. I would like to have mine labbed. I have mirage + 23s and 25s. Last year was 5300 and 4900 respectively

bobl

Just an FYI, when those tests were done we actually had real gasoline, not E10. You need to run 3-4 points richer with E10, and that would be the leanest you'd want to go. Richer didn't make more power but does provide more safety margin.

Bob

uncool

Not to sidetrack, but since we are talking about the 496, can some one point me to a better valve spring for the stock heads that is a drop in? Specs on the factory spring that I have come up with seem to only be in the 65 to 75 lb range on the seat.

I have found a comp spring that should fit the bill, but I would like to get your opinions.

I am not ready to rebuild my motor nor should I be for a long while.

Thanks

thirdchildhood

Why do you want to increase wear and stress on the valve train when the stock springs work? Same argument I have made for those who want to second guess Mercury Racing on the choice of 525 springs. Probably should start a new thread since this is Donzi Matt's build thread ...

RGPIII

Wow i just read this thread because im thinking i will want more power from my 496 Mag non HO after this season and im starting to smell a little oil after a hard run. this has been a great read i cant wait until you post your final results.

Matt you also said if you had a single you would have gone a different route? why? if you were to make a recommendation to some one with a single looking into a repower or a 496 build what would you suggest after going through all of this?

donzi matt

If I only had one motor I would have bought a 525EFI, because resale would have been better. I couldn't swing the coin to do that with two motors though so I went this route. Plus, for some reason I like to be different and I am pretty fond of how these 8.1's perform. My biggest hurdle is with tuning the computer. If I had endless time and patience I would like to build a patch harness that would allow me to run something like an AEM FIC-8 so I can manipulate fuel and timing but still retain smartcraft and guardian features.

donzi matt

Just got in from some more testing. First thing I did was fix my throttle issue. The solution to that was changing the oil fill tube to the GM truck fill tube. That allowed the throttle cable clevis to clear. I will post part numbers tomorrow for reference. Had the throttles opening all the way to the stop. Took off for a spin with my wife and after a few minutes of cruising I opened it up. All of a sudden I have beeps and fault flashes on the smartcraft tachs for both motors and a noticeable lack of power. Scanned all gauges, good oil pressure, good water pressure, good temperature. Backed out of the throttle and grabbed my scan tool out of the glove compartment/toolbox. Hooked up and found 3 significant codes and 3 insignificant codes in both motors. The 3 significant codes were 9 - Engine Guardian Limiting Power, 19 Maximum RPM Exceeded, and 122 TPS 1 Range High. Cleared the codes and cruised for about 10 minutes up to about 4200 RPM with no issues. Scanned codes and no codes. Headed home and buried the throttle again. More guardian mode and beeping. WTF. Went home and found the same 3 codes in both motors. Did some thinking and decided to bury the throttles with the key on engine off and sure enough the TPS code went active. Found TPS voltage at 4.85 volts and throttle reading 100%. Decided to adjust the throttle cables down a bit so TPS came down to 4.70 volts and the code stopped going active. Apparently I was over traveling the throttle. Set both motors to WOT at 4.6 volts and headed out again. This took care of guardian mode!

Now at WOT I am hitting 71mph solid and touching 72 spinning 28 pitch Bravos to 4900. These props have been repaired and I am far from in love with them, but they are what I have. This is with full fuel, mufflers in, and very light chop. Before this would have netted me 67 mph on 26 pitch bravos at 5000RPM. 5 mph in this big heavy sled is alright with me, and where I thought I would end up, actually a mph faster than I expected. I plan to pull the GGB muffler inserts this weekend, I have a feeling they are now more of a restriction than before. I need to get the wideband hooked back up and see where I am with and without mufflers. Theoretically it should go leaner if they are a restriction.

I still have a nagging issue that I had before. The port side motor lags the starboard side. The higher the RPM, the worse it gets. At WOT it is down 150-200 RPM's. With the new exhaust I can actually hear it popping as it is misfiring. I have already replaced the crank sensor and plugs with no luck. Plug wires visually look ok but I am going to see if I can find a set and try those. If that doesn't work I am going to start with the swaptronics diagnostics till I figure this thing out. Maybe a cam sensor, maybe a coil, who knows. But I am going to get to the bottom of it somehow or another, it's pissing me off.

To anybody thinking of doing any work on a 496, it is 100% imperative you have a scan tool. If you know fuel injection systems, you can figure out about anything with a good scan tool. I would have been thoroughly screwed with this guardian issue without it.


EDIT IN: adding part numbers for Oil fill tube and cap. You will need these if going to a 90mm throttle body on a stock intake, the factory tube will interfere with the throttle cable clevis.

Oil tube: GM# 12581140
Oil cap: GM# 12573337

MILD THUNDER

Good stuff matt. Great job.

I would definitely start with some fresh plug wires as far as the misfire is concerned. 200rpm loss, its quite possible to be down a cylinder. On the old distributor equipped cars i would work on, i would fill a windex bottle with water , and spray the plug wires down in the dark and watch for sparks .

Ryan00TJ

Great info Matt. Sounds like there is more to be had with some prop fine tuning and getting your miss fire figured out. You've got a few hundred rpm left before hitting the stock rev limit. Hopefully you can get Dustin on board with a custom tune for your setup. I've also experienced the lack of customer service dealing with Whipple. Great products though. Pretty freaking scary you had to go 8psi fuel pressure higher than Raylar spec'd just to get into a semi safe afr range. That would have gotten ugly really quick going that lean.

Naughty Kitty

Matt, I added this wire set from Aftermarket Marine when I did the fresh long blocks last season. The fit is spot on for the 496 Marine application, I've had zero issues throughout the power band and the blue color accents a lot of the powder work done.



http://www.amarket.com/imwo808.htm