5.0 mpi-5.7 mpi
 

would like to change an 5.0 mpi Mercruiser with 555 ecm to a 5.7 .What would need to be done to insure it's not running lean ...Other than buy a 5.7 ecm (hoping to not have to do that).Motor froze so it needs to be longblocked anyway...

your outdrive gear ratio will be different between the 5.7 engine and the 5.0 engine. Changing props could get you in the recommended rpm range but that will move your torque curve. To correctly follow what your asking, you want to replace the 5.0 engine with a 5.7 engine and use the 5.0 ecm 555 on the 5.7 engine.

You will be running lean on that change over. The air fuel ratio's are different between the ecm calibrations. You need to have the ecm remapped or buy the correct 5.7 ECM controller or stick with another 5.0.longblock & heads.

Who can remap the ecm

Dustin Whipple. He's authorized by mercruiser, since he's selling his product for Merc engines with ECM 555

Motor, just a thought...might not be much more to upgrade to a 377 or 383 (6.2) over the 350.
With the right cam and maybe heads it should not be hard to reach 330-350 prop H.P.

Go big or go home :). There is 575 SCI for sale in Vegas on CL. good price on it also.

That is not necessarily true that the new motor would be lean. The only way to tell is run it with a wide band and see where you are at. The 5.7 should start and run with the 5.0 ECM and tune. It will likely not be optimized, but it would run. Problem is the 555 tuning is limited to a few individuals. Weigh the cost of getting that ECM calibrated with a whole sale change over to a MEFI-4 and see what works best. The EFI stuff can be daunting but it is very do-able.

If you are going from a 5.0 to 5.7, as others have said you might as well go all the way to a 377/383.

This is actually a friends boat ..A 2004 240 sundancer that he bought with a 5.0 Bravo,not knowing any better .He let the motor freeze and i am going to put in long block for him ..We did talk about a 6.2 instead of a 5.7.I own a 6.2 i would like to sell him(just a longblock)I just don't want to get him in to more cost than reasonable ,considering it's never going to be much on performance ...Are the injectors the same on the 5.0-5.7 and 6.2...Any idea what it cost to remap an ecm...Thanks

I can order you a 383 stroker thru Mercruiser reman it is a complete drop in and dropped shipped to your door.

next anytime CID = cubic inch displacement gets bigger the need for more air to enter & exit the engine. More air always = more fuel. Of course it will start and run with any computer installed on it but you want it to run properly and looking for an upgrade in performance. Correct ?

Next the 5.0 and the 5.7 do not share the same cylinder heads nor the same intake valve. 5.7 has an intake valve that is slightly larger - larger intake valve means more air & fuel.

Also the bore of the 5.7 is 4.00 inches compared to 5.0 bore is 3.74 inches. Motor 101 tells me the stock 5.7 compared (apples to apples) to the 5.0 is the 5.7 needs more fuel as it is a heavier breather than the 5.0. Again more air always means more fuel to achieve proper air / fuel ratio's.

Next you are going backwards by using a MEFI system on your app as the ECM 555 is calibrated for a shift switch starting around the 2003 / 2004 year model. Most MEFI systems on the 5.0 and 5.7 were set up for TBI injection on the marine end plus the engine harness is completely different from MEFI to ECM 555..

ECM and PCM 555 started for Mercruiser late 2000 model year 2001 with MPI. fuel injection. Also if you have smartcraft you need ECM 555 controller because MEFI will not work for any smart craft nor DTS.

DTS = digital throttle & shift only works for ECM or PCM 555 or the current 09 mercruiser computer controllers. Also the distributer & ignition set up is totally different from MEFI to ECM 555 for the jist of things not to make a story book.out of this.

Also the injectors are all the same for the 4.3 L MPI thru the 6.2 L MPI. Its the computer that controls the air fuel ratios along with the sensor inputs. ie: CTS, MAP, TPS and so on. Also timing is controlled by the ECM as all timing on a ECM 555 & PCM 555 is non adjustable.

I would opt for the 383 complete drop in and again your gear ratio is the difference along with prop change..

Thank you .What I get from what you wrote is that I need a 6.2 555 ecm which I would have to buy used ,to make sense .But thanks for offering to Sell me an engine on this do it yourself forum

look up the mercruiser reman on the 383 it is a complete drop in with the computer completely reman by Mercruiser with a warranty and more hp and torque than the 6.2 / 377 CID.

5.0 usually takes same ratio as 5.7. unless it is a 1.62 some builders put in bigger boats with smaller motors. with either ratio you are probably going up 2 inches of pitch. and be ok with that drive. a dancer is no speed boat. you would need previously mentioned 575 sc to go up 4 inches. all the power in the world will not noticeably change that hulls performance characteristics. it will make it not feel underpowered though.

I've already stated I know it will never perform. The point of not feeling underpowered is what he is looking for .Doesn't a 6.2 run a 1.5 to 1 ratio also ?Boat has 5.0 bravo setup .He doesn't want weight of bb

2004 only lists the Bravo apps for the 6.2 no alpha apps for the 6.2. Alpha stopped on the 350 MAG 300 hp engine. I have the OEM Mercruiser 2004 dealer handbook in front of me now and double checking plus dealer ordering on new boats in 2004. I am Mercruiser dealer and had new boats at that timeframe. Also confirmed it 3 times now with 2004 brand knowledge product handbook Mercruiser guide.

The 5.0 MPI 260 hp alpha outdrive the primary gear ratio was 1.62 and the 1.47 was optional so you have check which gear ratio you have.

The 5.7 carb 250 hp alpha outdrive used a 1.62 as the primary gear ratio.
the 5.7 MPI MAG 300 hp used a 1.47 alpha outdrive as the primary gear ratio. There was no Mercruiser engines in between what I just mentioned for 2004.

the 5.7 MPI Horizon 300 hp only used a bravo app also no alpha app on this model either. Bravo was 1.50 for the primary gear ratio.

The MX 6.2 320 hp 377 CID again only Bravo app used a 1.65 gear ratio as the primary.

the MX 6.2 320 hp Horizon only Bravo app used the same 1.65 gear ratio.

Now the bravo drives between the 5.0 MPI 260 hp and the 5.7 MPI MAG primary gear ratio was 1.50 and 5.0 MPI 260 hp primary gear ratio was 1.65 again Bravo 1 drive apps and primary ratios. Of course their is the optional and high altitude gear ratios but that's something you are going to have to check out for yourself.

Prop pitch will have to be changed regardless no matter how or what you put in their unless the same app. I understand that. My point was gear ratio's moves the rpm in which moves your torque curve. You want to keep your highest torque number around 3200 to 3600 rpms.

If anyone wants to disput this PLEASE call Mercruiser as this info is from all their dealer product books and new boat orders hand out materials. I know how everyone up here thinks they have better info. If you need Mercruiser's phone number I will gladly give it to you. Your swap over is not just a easy bolt in / easy plug and play / easy lets go boating.

We do 30 to 60 repowers per year with new or reman motors. Mostly stock Mercruiser and Volvo Penta. Anyone have more experience lets hear it.

i was joking about the big block, and a 330 hp454 wouldn't be a bad choice but 575 sc? no way! no, what i am saying is it will be fine with that drive regardless of ratio. 1.47 to 1.62 is 10%. 2 inches of pitch is roughly 10%. if a 1.5 drive you are not running much more than a 15 or 16 prop. with 1.62 drive 17 mebbe 19 tops. most likely 17. do motor upgrade. go 2 inches bigger on the prop. down the road consider changing drive ratio but won't be much diff in cruise-fuel consumption either way. boat may be a lil better on fuel cuz it isn't working so hard just to do 25. i took 350 out of 79 24 dancer and put 406 small block in. very little change. but i wish i still had the 406 now.

The problem is the Merc motors are set fat to begin with. I've done back to back testing between a stock 350 Mag EFI/MP and then modified it (stroke, cam, heads, bigger valves, displacement, compression) keeping the bone stock tune and injectors and the bigger modified motor was not lean. Was it perfect? No. Would the layman even notice the difference standing next to the motor idling? No. Would I recommend using a stock tune on modified motor as a long term solution? No. Point is you can modify a motor and get it up and running with the stock tune.

MEFI maybe technically going backwards but it has infinitely more access in the tuning department. If you need the smartcraft, DTS etc, then by all means stick with the 555.

The MEFIs were utilized on TBI and MP motors as far back as 1995.

A crate motor drop in is obviously the easiest route, but not always the cheapest.

MEFI 1 for Mercruiser started in 1993. It is long gone. If anyone is looking for the cheapest route just drop in a carb app. You can buy a 5.7 bobtail for around 3500 bucks brand new with a warranty. Again just saying, no tune - no fuel injectors - no remapping.

I have the Bravo1X diesel drives with 1:65 ratio in my boat behind MX 6.2 Mercs. Engine turned 5150 with B1 26P props that I found were less than 25P on the gauge, engine now turns 5000 @ WOT with props tuned to true 26P. . I'd recommend to the OP 6.2 takeout or reman 383.