Reinstalling MPI back onto a carbed 496 in a 1997 Baja Islander
 

So I picked up this boat that the previous owner bought with a cracked block 454 MPI HO, and he had replaced it with a 496 but opted to just put a carb and distributor on it rather than mess with the fuel injection. I hate carbs and love fuel injection (at the moment anyways) and am in the process of reinstalling the fuel injection. I have only played with carbed small boats before so there is a lot of mystery here.

If anyone has any pictures of what the engine bay should look like that would be greatly appreciated.

How do I set the timing on the electronic distributor? I took the cap off of the electric distributor and oriented the rotor to exactly where I pulled the old one out, but it looks like the timing still needs to be set, yes?

Where is the best source for a shop manual? I've done a search but haven't found anything that looks legit.

Thanks in advance.

There is no way anyone is going to be able to accurately tune/recalibrate the ECM except in the boat or on a dyno. You better figure out who is going to do that first.
You can order Merc manuals at www.mercruiserparts.com

Just curious is this a 496 stroker motor or the 8.1 496 ?

Stroker 496 on a gen xi 454 block.

Gen VI? Or is yours one louder and goes to "11"!! Lol! JK.

What's the HP of the 496 ?

Supposedly 500+. It came off of ebay as more of a truck motor with a lot of Pro-Comp parts which I guess Aren't that great.

This is the motor. http://www.ebay.com/itm/230924067902

It may not be the greatest, but hopefully it will get through a season or two. I tried so suss out whether or not it's a good idea to put the injection back on here, but I couldn't get any conclusive straight answers, so I talked with the engine builder and naturally he said there'd be no problem with it.

I've built some small block chevy's before and a lot of high performance motorcycle engines, but this powerboat thing is all new and very foreign to me so I expect quite a learning curve ahead of me.

It depends how much you like to tinker, nothing written in stone here but marine motors including FI are generally setup with very rich afr's there's very little precise fuel metering going on that is unless one welds OS sensors into the exhaust system..and even with that they generally lean out in the midrange cruising speed say 3000 to 4000 and enrich it back up from there. One can play a bit more with timing curve's and if you have a hot cam in the engine one can tame it down a bit by advancing the timing @ idle to soften it up a bit.....or run the timing on the ragged edge for the last 10 hp...for a experienced programer thats half the fun.

Boater's become very opinionated when it turn's to modification's and a lot of money can flow, but a well built engine with a properly tuned carb will cost far less and preform very well...i doubt there would be any big gain's aside from low speed cruising economy.

Not picking on your motor, the heads look a little rough around the valve seats, the 108 ls cam probably isn't all that good for marine or EFI. I would think the fuel injection would be fine if you know someone that can remap it for your application. First check the vacuum at idle, if it's to low the ecm might think it's under load and run rich. Second check the fuel injectors and find out if they are big enough to handle your new HP.

ok, hate to be the one to piss on your wheaties, but most all that pro comp stuff sold on ebay is absolute garbage, second trying to get the merc EFI to work with that is going to require good tuning ability...you might want to talk to eddie young @ youngs marine, on here, but I can tell you as soon as that thing is started...the pin has been removed...

Thanks for the feedback as it's been super helpful. I've decided to ditch the FI and order a new carb and just enjoy the boat until the thing grenades and then build up a good motor. It came with a 650cfm but needs an 850cfm, so I'll put one on and call it a day. Thanks for the input!

I know you've all ready decided to go the carb route but let me give you another data point for the future. You would be able to install all the EFI stuff from the old motor and get it running, even on the stock tune. Regarding distributor installation you would need to set base timing, which is usually around 8 deg BTDC for Merc motors. Setting base timing is easy.

The stock tune should be sufficient to get the motor running in a stable manner on a test stand, but it most likely will not be ideal. To get things working properly you would need to have the fuel table and ignition table tweaked. You either pay someone to do it or get the software and do it yourself. You would also need wide band O2 sensor installed to get AFR data.

Lastly you need to know what your current injector size is and calculate the max HP those injectors can carry at 80% duty cycle. If you are deficient in that area you should step up in injector size.

In summary your big cost going EFI are:

1) tuning (software) doing it yourself ($600 ish plus your time and learning curve) or paying someone else to do it ($??????)
2)Wide band gear ($200-400)
3)Injectors ($400-800)

I'm not trying to sway you one way or the other, but it can be done, even by a layman IF you take your time and think things through. The learning curve is steep but I found it rewarding.

Now THAT'S the information I was looking for from the beginning. Thanks for laying that out - much appreciated.

I wish you the best of luck regardless of the route you choose.

Did you change the cam?
It says 246 DURATION @.050 ON BOTH THE INTAKE AND EXHAUST
Unless your exhaust is dry to the tips you are going to have problems :(

They are through the transom with those flappy things on them. What problems should I expect and what time frame? Immediate? Over time?

I appreciate the heads up on the matter.

That cam is going to suck water back up your exhaust at idle and seize/hydrolock your engine.

Ah. Well that's a bummer.

So the top end of this motor looks all wrong and cheap for a boat motor, but any opinions on the bottom end? Worthwhile platform to build off of?

Cast crank, depends on what you want to do with it.

I would at a minimum change the cam. As other's have said, kind of depends on what you want to do with it.

So I picked up an 850 double pumper off of ebay, but when I checked the numbers on it it's only an 800. I had an Edelbrock 750 on there and it topped out at about 4k-4200 rpm. Is the 800 going to make any difference or should I find an 850?

An 800cfm is more than enough. Is it a USCG approved marine carb????

Don't forget the correct oil bypass valve!!
 

Rooster, pretty sure you said this block is a Gen VI, with the one-piece main seal. If that is the case, you absolutely have to make sure that the 30 lb oil filter bypass has been installed in the filter pad area on the block, or that it has been blocked off. If the stock 11 lb unit was left in there, then oil will bypass the remote filter and oil cooler in the boat because of the increased back pressure. Then you will have hot, dirty oil going through your engine, and your bearings will not be long for this world. If this engine was directed at the automotive hot rod crowd, chances are it has the 11 lb valve in it. No real way to tell which valve is in it just by looking at it - I don't think there is a part number that is visible once it is installed.

More info on this thread => http://www.offshoreonly.com/forums/g...ef-valves.html

Once again, you will probably be much happier with a stock 454 mag or 502 in this particular boat. It's no fun getting towed in on the water, or having your boat home on the trailer all summer while everyone else is out enjoying theirs. Good luck whichever direction you decide to go.

Yes.