Prop question/suggestion/problem

Mercruiser made a 260hp efi 350 during the year range his boat was made (like Eddie said, it pre-dates Vortec), and there are no obvious signs (performance or otherwise) that would indicate he has anything other than what he says he has. I don't understand the skepticism.

Maybe it's a hammerhead 383 or a black scorpion or a supercharged LSA... But I doubt it. Probably just a 260hp 350 efi like he says it is.

Luchog wrote: lcgordon wrote: 350 mag Only have a video of it Where did you get that 260hp spec? I'd bet that engine is 280-315hp and already has Vortec heads...so this whole upgrade debate would end up just plain weird. You could use you engine serial n° to find out what engine and specs you have in there.

Nope. The boat is a '92 and the Votec didn't come out til '96.

lcgordon wrote: 350 mag Only have a video of it

Where did you get that 260hp spec? I'd bet that engine is 280-315hp and already has Vortec heads...so this whole upgrade debate would end up just plain weird.

You could use you engine serial n° to find out what engine and specs you have in there.

A couple questions above.
You could switch to Dart cast Iron heads with 64cc chambers and bump compression while also improving flow. Would not affect your limited EFI system at all but would bump power. The OEM heads have 76cc chambers in the 80's up to the Vortec design.

The Vortec heads are hands down the best bang for the buck. Up to about 5,000 RPM they perform as well as some of the very best available at 25% the cost. This RPM range is perfect for a boat engine. I only ruled them out due to his limited EFI System that does not allow changes in timing. and the fact that you would need an aftermarket intake manifold to work with a Vortec Head.
For this combo cost you can buy a set of cast iron Dart heads and equal the performance of the vortec up to 5,000 and outperform it above 5,000 RPM. The Dart would use the factory boat intake and run with the EFI this man has on this boat.
I think they call them Iron Eagle heads for around 800.
The 383 upgrade is a good one also but again, more money and far more involved installation. They do pull much harder for sure over a 350 but once again we bump into the limitation of his EFI system not being adjustable. If you increase displacement you will need more fuel to match this change and this EFI is locked so that can't happen without someone with serious know how.

Dart heads or similar heads will work with OEM timing and just changing compression does not change the fuel mix so your EFI would be fine with the change.
Those are the reasons for my advice but the boat is for sale and this is a dead discussion unless someone else wants to upgrade a high altitude boat.

350 mag

Only have a video of it

This sounds too hard. Ill end up blowing something up or its just gonna run like crap. Ill leave it. Thanks for the info tho. Always great to learn.

On a side note the new prop should be in tomorrow. Hopefully ill get to throw it on and run it.

Thought those did not work?

How would you change comp without switching heads? Mill the ones I got? Smaller head gasket? Or change heads but not vortec ones?

Oh and its not for sale yet. Well actually it is because eveything is always forsale. But im hoping of getting rid of it in a year or two.

I want adam to get an outboard so I dont have too.

Im not going to anyways. And im pretty sure its a 350. I just was wondering. Need to sell this boat have some moeny saved up and get a small loan and buy one I will keep for a while. Then start making that one faster.

If you change camshafts the ECU can freak out and cause issues.
Changing the Heads won't affect the ECU.
It should detect the exhaust fuel mix and adjust properly.
Should be a headache free upgrade.

My 1986 Malibu had the 350 Chevy with a 4bbl Carb on it done by Mercury Marine. Ran really good at sea level and was rated 260 HP. Ran 48 MPH with a stock 13 x13 prop. Never damaged that prop in 23 years of use.
Most of the fuel injected engines had higher horsepower ratings than the carb versions.

Are you sure your engine is not a 305 instead of the 350?

Re Mapping the ECU is re programming the thing.   You can adjust timing and air fuel mixture. If you modify you will have to do this either way.   

In your car the system is set up for EPA, runs very lean.   You can adjust timing and fuel, run richer and more power by re program.   

On my Harley i had a stage 2 done and also increased CID and with the tune I can pull a heritage softail off the ground, for non bikers this is a heavy pig.   

It might work well enough if you modify it without reprogramming the computer, or it might end up a bit too lean and burn things up... without having the ability to modify the programming its a bit too much of a risk for most to take.

It wouldn't take more than 1500 to put into the motor... if yours wasn't fuel injected it would take about the same to put some vortec heads on it and you would be sitting pretty on one foot

I dont really even know what that means