Please note this thread has been inactive for 90 days. For the best results, please start a new thread.
Results 1 to 22 of 22
  1. #1
    Petty Officer 2nd Class
    Join Date
    Oct 2009
    Location
    ATHENS GREECE
    Posts
    139

    Default MERC 5.7 EFI conversion to MPI

    Here is a question for a MERCRUISER guru.

    I have a 2000 5.7 EFI 260hp Mercruiser in my Doral 250SE.
    I also have a complete injection system (intake, injectors, distributor, wiring, ECU, fuses etc) from a 5.7 MPI 300hp.

    The question is if I change all that on my engine,
    1. will it work?
    2. will that make my engine 300hp too?

    As far as I know and from info around the internet, everything else between those two engines is excactly the same (comp. ratio, engine block, internals, cam etc.)

    Any ideas?

  2. #2
    Chief Petty Officer
    Join Date
    Aug 2010
    Posts
    484

    Default Re: MERC 5.7 EFI conversion to MPI

    Probably no difference. Without seeing the published specs, it seems like the increase in horsepower is because the rating is at a higher rpm.

    horsepower=torqueXrpm/5252.

  3. #3
    Cadet COREY_1's Avatar
    Join Date
    Aug 2010
    Location
    Idaho Falls, ID
    Posts
    10

    Default Re: MERC 5.7 EFI conversion to MPI

    the horse power increase would come from differant cam and pistons.. the efi would have better throttle response.. but it would not add hp
    1998 Campion Chase 580 sport boat

  4. #4
    Petty Officer 2nd Class
    Join Date
    Oct 2009
    Location
    ATHENS GREECE
    Posts
    139

    Default Re: MERC 5.7 EFI conversion to MPI

    1. EFI vs MPI rpm difference is almost 500rpm more for MPI (4880 vs 5200). If we where talking for an engine with a comp. ratio of 12:1, that might have a base. So I do not thing that this is enough for 40hp more.

    2. As for throttle response, from personal experience (seen a 5.7 MPI in action) in no way the EFI is better than the MPI.

    Looks like that the extra 40hp is coming from better breath of the engine due to larger bore throttles and more air available to the engine in combination with more precise injection timing and better air/fuel mix.
    Also both engines have Vortech heads (1998-> today).

    A fuel injector positioned right above each inlet valve is way more accurate both in volume and velocity than one positioned so far away (before and above the throttles). This is because air and liquid velocities are not the same due to weight (air is moving faster) and that fuel is sticking at the walls of the ports each time there is a bend (turn) or turbulance at it's route.

    According to all that, the horsepower=torqueXrpm/5252 is true IF the engine makes more torque with that set up at the same RPM......

    So that brings us to the original question....

    From a practical (mechanical) point of view, is this conversion going to work and have the desired result?

    ....................

  5. #5
    Vice Admiral Tail_Gunner's Avatar
    Join Date
    Jan 2006
    Location
    Portland, Or.
    Posts
    5,363

    Default Re: MERC 5.7 EFI conversion to MPI

    Quote Originally Posted by bannister View Post
    Here is a question for a MERCRUISER guru.

    I have a 2000 5.7 EFI 260hp Mercruiser in my Doral 250SE.
    I also have a complete injection system (intake, injectors, distributor, wiring, ECU, fuses etc) from a 5.7 MPI 300hp.

    The question is if I change all that on my engine,
    1. will it work?
    2. will that make my engine 300hp too?

    As far as I know and from info around the internet, everything else between those two engines is excactly the same (comp. ratio, engine block, internals, cam etc.)

    Any ideas?

    Are you asking.....Will MPI outperform TBI...In a boat probably not..now if oxygen sensors were used in a boat yes you would see a gain..but not much.

    In the end you can get a mpi engine to run a larger cam which will make more HP that is true...However cams that large create something called reversion along with shifting the power band aka you power starts @ 2000 and shines @5000 to 6000...Boats generally run from 1000 to 3500 most of the time..

    ------------------------------------------------------------------------------------


    A fuel injector positioned right above each inlet valve is way more accurate both in volume and velocity than one positioned so far away (before and above the throttles). This is because air and liquid velocities are not the same due to weight (air is moving faster) and that fuel is sticking at the walls of the ports each time there is a bend (turn) or turbulance at it's route.

    Yes that is correct....But without os sensors it doesnt matter....A boat is running on a fairly primitive program...that is it cant adapt to optimal fuel to air ratios...actullay all that wonderful tech gets dumbed down a bit or a lot...The programs run very rich fuel to air ratios and the timing curves arnt that agressive...But they can run all day @ 4000 rpm and not break...There tuned for long term reliabilty..very conservative...
    Stickly a opinion your milage may vary.

    Speed is how fast you hit the wall
    Torque is how far you move the wall"

  6. #6
    Petty Officer 2nd Class
    Join Date
    Oct 2009
    Location
    ATHENS GREECE
    Posts
    139

    Default Re: MERC 5.7 EFI conversion to MPI

    good points there, but......

    If the intake manifold and the injection system are not what makes the 40hp difference between those two engines (same block, same internals, same heads, same comp. ratio), then what is?



    maybe the MPI and different intake manifold results to: horsepower=torqueXrpm/5252 is true IF the engine makes more torque with that set up at the same RPM......

  7. #7
    Petty Officer 2nd Class
    Join Date
    Oct 2009
    Location
    ATHENS GREECE
    Posts
    139

    Default Re: MERC 5.7 EFI conversion to MPI

    What I am really asking is if this conversion/parts exhange is possible given the rest of the engine is the same.
    Will it work even with no difference?

  8. #8

    Default Re: MERC 5.7 EFI conversion to MPI

    Should work since you have everything just might not see the HP gains.

  9. #9
    Vice Admiral Tail_Gunner's Avatar
    Join Date
    Jan 2006
    Location
    Portland, Or.
    Posts
    5,363

    Default Re: MERC 5.7 EFI conversion to MPI

    That i cannot answer i have no ideal...But a fairly good guess would be cam profile and a more agressive tune

    http://www.obd2allinone.com/sc/detai...?item=mefitune

    Call those guys they can tune you ecm..

    Theres a great little cam.... with tbi a good tune and that cam should net you 350 hp

    http://www.summitracing.com/parts/CCA-12-238-2/


    Two things are important here your ecm type...mefi 1 2 3 4 and the size of your tbi unit...aka does it have 2" bores
    Stickly a opinion your milage may vary.

    Speed is how fast you hit the wall
    Torque is how far you move the wall"

  10. #10
    Vice Admiral Tail_Gunner's Avatar
    Join Date
    Jan 2006
    Location
    Portland, Or.
    Posts
    5,363

    Default Re: MERC 5.7 EFI conversion to MPI

    Quote Originally Posted by bannister View Post
    What I am really asking is if this conversion/parts exhange is possible given the rest of the engine is the same.
    Will it work even with no difference?
    Opps forgot a major issue...ECM type if your orignal boat is mefi 3 and the new controller is mefi 4 No it will not work...The controllers have to the same to the harness to work
    Stickly a opinion your milage may vary.

    Speed is how fast you hit the wall
    Torque is how far you move the wall"

  11. #11
    Chief Petty Officer
    Join Date
    Aug 2010
    Posts
    484

    Default Re: MERC 5.7 EFI conversion to MPI

    Here's the question. Can you benefit from the 400 rpm increase to get "40 horsepower" at full throttle only? Will your exhaust manage the increased air volume? Will the intake/flame arrestor breathe well enough?

    BTw, looks like the 400 rpm increase in rated power is good for 25 of those horses by itself. The bottom line, at 4000 rpms both will be virtually identical..only wide open will a difference be noticed.

  12. #12
    Vice Admiral Tail_Gunner's Avatar
    Join Date
    Jan 2006
    Location
    Portland, Or.
    Posts
    5,363

    Default Re: MERC 5.7 EFI conversion to MPI

    Quote Originally Posted by Aloysius View Post
    Here's the question. Can you benefit from the 400 rpm increase to get "40 horsepower" at full throttle only? Will your exhaust manage the increased air volume? Will the intake/flame arrestor breathe well enough?

    BTw, looks like the 400 rpm increase in rated power is good for 25 of those horses by itself. The bottom line, at 4000 rpms both will be virtually identical..only wide open will a difference be noticed.
    your right....Its really doesnt matter though...his controller is rev limitied to 4950...Sooo who cares..
    Stickly a opinion your milage may vary.

    Speed is how fast you hit the wall
    Torque is how far you move the wall"

  13. #13
    Petty Officer 2nd Class
    Join Date
    Oct 2009
    Location
    ATHENS GREECE
    Posts
    139

    Default Re: MERC 5.7 EFI conversion to MPI

    ok, here is the project one more time.

    Engine is a 2000 5.7 EFI.

    Remove ECM, wiring, throttle body, intake manifold and fuses.

    New parts out of a 350 MAG MPI.

    Install new ECM, wiring, intake manifold, injectors, throttle body and fuses.

    No need for matching ECM's or reflushing, rewiring or cam change.
    Everything OEM.

    Exhaust and all other parts of the engine are the same between those two.
    We are not talking for a car engine with headers and muflers restricting the flow. The diameter of that exhaust can support twice that horse power.

    The goal is not the extra 400rpm (and more consuption) BUT MORE TORQUE at the SAME RPM resulting to more BHP. (due to better volumetric efficiency from the intake manifold and multi point injection.)

  14. #14
    Chief Petty Officer
    Join Date
    Aug 2010
    Posts
    484

    Default Re: MERC 5.7 EFI conversion to MPI

    You're not gonna get a noticeable difference just by swapping the fuel injection. If it gets the proper amount of fuel, it's gonna make the same power.

    The BIG difference in sequential multiport injection is the fuel control at LOW rpms. After a certain rpm, the event duration is so short the injectors are spraying 100% of the time.

  15. #15
    Fleet Admiral HT32BSX115's Avatar
    Join Date
    Dec 2005
    Location
    WA
    Posts
    7,799

    Default Re: MERC 5.7 EFI conversion to MPI

    Mercruiser rated the MAG 350 MPI engine/drive at 300 HP.

    That's PROPSHAFT HP.

    If you transfer all the MAG 350 "stuff" over to the other engine and it's built the same as the MAG 350 MPI engine (cam, pistons, compression ratio, etc)......It WILL make 300 propshaft HP.


    The question is if I change all that on my engine,
    1. will it work?
    2. will that make my engine 300hp too?

    1. YES.

    2. YES


    3. will it make a difference? probably not a lot......Do it and compare the performance!


    take pictures and videos and share!!


    Cheers,


    Rick
    73 de Rick
    ----------------------------------------------------------------------------------
    I use xxx oil and have never had a problem........
    1987 FourWinns 211 Liberator, 7.4L- Bravo III installed by ME,
    Formerly OMG 460 King Kobra powered
    1947 Stinson 108-2 Station Wagon
    , Franklin 6A-335B. Hartzell CS 2-blade prop
    -
    All PM's cheerfully answered! Please ask tech questions in the appropriate forum so everyone's included

  16. #16
    Petty Officer 2nd Class
    Join Date
    Oct 2009
    Location
    ATHENS GREECE
    Posts
    139

    Default Re: MERC 5.7 EFI conversion to MPI

    Thanks for the replies guys.

    Low end torque is what I need (2000-3000 rpm).
    Drive is a Bravo 3 with SS 22 props.
    What I am aiming for actually is not a 50mph boat but faster planning time and crusing at 30mph at 3500-3800 at salt water (more drug). WOT is a very rare thing with a 25 foot boat in the rough Aegean seas here in Greece.

    My Doral 250SE has a hard time getting on plane without trim tabs with dirty props or 4 people on board.(two people and clean props = no problem).
    I also usually carrie a full 314 lt tank of fuel and 145 lt of fresh water.

    That is way I am looking for more HP without the extra fuel consuption and cost of a 6.2 MPI. (my next choise)

  17. #17
    Chief Petty Officer
    Join Date
    Aug 2010
    Posts
    484

    Default Re: MERC 5.7 EFI conversion to MPI

    You CAN move the power band down by ADVANCING the cam 4-6 degrees.

    There's no substitute for cubes..a 377/383 with long rods is a torquey little devil!

  18. #18
    Vice Admiral Tail_Gunner's Avatar
    Join Date
    Jan 2006
    Location
    Portland, Or.
    Posts
    5,363

    Default Re: MERC 5.7 EFI conversion to MPI

    Yes you are right bolting on mpi stuff can be done....But is your boat wired or pinned correctly to the new ECU....Your gauges and switches might not work
    Do not assume both the new ecu will function correctly with existing Boat wiring.. If the old ecu is a mefi3 and the new is a 4 or a 555 Will the the new ecu be compatiable with that harness...If there both the same then it should be a yes....and no just because its a merc on the outside does not make them compatiable

    This part
    Stickly a opinion your milage may vary.

    Speed is how fast you hit the wall
    Torque is how far you move the wall"

  19. #19
    Petty Officer 2nd Class
    Join Date
    Oct 2009
    Location
    ATHENS GREECE
    Posts
    139

    Default Re: MERC 5.7 EFI conversion to MPI

    Quote Originally Posted by Tail_Gunner View Post
    Yes you are right bolting on mpi stuff can be done....But is your boat wired or pinned correctly to the new ECU....Your gauges and switches might not work
    Do not assume both the new ecu will function correctly with existing Boat wiring.. If the old ecu is a mefi3 and the new is a 4 or a 555 Will the the new ecu be compatiable with that harness...If there both the same then it should be a yes....and no just because its a merc on the outside does not make them compatiable

    This part
    Quote Originally Posted by bannister View Post
    ok, here is the project one more time.

    Engine is a 2000 5.7 EFI.

    Remove ECM, wiring, throttle body, intake manifold and fuses.

    New parts out of a 350 MAG MPI.

    Install new ECM, wiring, intake manifold, injectors, throttle body and fuses.

    No need for matching ECM's or reflushing, rewiring or cam change.
    Everything OEM.

    Exhaust and all other parts of the engine are the same between those two.
    We are not talking for a car engine with headers and muflers restricting the flow. The diameter of that exhaust can support twice that horse power.

    The goal is not the extra 400rpm (and more consuption) BUT MORE TORQUE at the SAME RPM resulting to more BHP. (due to better volumetric efficiency from the intake manifold and multi point injection.)

    I have all parts needed from the donor engine............

  20. #20
    Petty Officer 2nd Class
    Join Date
    Oct 2009
    Location
    ATHENS GREECE
    Posts
    139

    Default Re: MERC 5.7 EFI conversion to MPI

    Today confirmed my theory with a Mercruiser certified mechanic.

    The conversion is possible with no problems.
    It will make my engine a 300bhp.
    And yes, the 40bhp difference is coming from more torque produced at the same rpm due to the manifold, throttle body and more precise injection.

    So, if you have a 1996 and up mercruiser block with Vortec heads, go to a yard and look for 350 MAG MPI leftover parts......

  21. #21
    Chief Petty Officer
    Join Date
    Aug 2010
    Posts
    484

    Default Re: MERC 5.7 EFI conversion to MPI

    Just remember, you MAY get 40 hp. more at full throttle, but you'll only get maybe 5-10 more horsepower at 2000 rpms. It simply isn't 40 hp across the board.

  22. #22
    Rear Admiral
    Join Date
    Jun 2004
    Location
    NY
    Posts
    4,267

    Default Re: MERC 5.7 EFI conversion to MPI

    Quote Originally Posted by bannister View Post
    Thanks for the replies guys.

    Low end torque is what I need (2000-3000 rpm).
    Drive is a Bravo 3 with SS 22 props.
    What I am aiming for actually is not a 50mph boat but faster planning time and crusing at 30mph at 3500-3800 at salt water (more drug). WOT is a very rare thing with a 25 foot boat in the rough Aegean seas here in Greece.

    My Doral 250SE has a hard time getting on plane without trim tabs with dirty props or 4 people on board.(two people and clean props = no problem).
    I also usually carrie a full 314 lt tank of fuel and 145 lt of fresh water.

    That is way I am looking for more HP without the extra fuel consuption and cost of a 6.2 MPI. (my next choise)
    You will not see much, if any noticable improvement in the 2-3K rpm range. Unless there is something wrong with your current set-up.

    Do a very detailed parts check-out between the EFI and MPI. There could be parts differences. ECM might be drive type and open/closed cooling differences. Need to check via serial number. For example, some 350 MAGs used cam 431-866022T vs 431-811658.

    The 6.2L would make a noticble differance.

Similar Threads

  1. OMC to Merc Conversion
    By Robert4Winns in forum Mercruiser I/O & Inboard Engines & Outdrives
    Replies: 2
    Last Post: May 12th, 2010, 10:01 PM
  2. OMC to Merc conversion ?
    By howlnmad in forum Mercruiser I/O & Inboard Engines & Outdrives
    Replies: 5
    Last Post: October 21st, 2009, 09:52 PM
  3. Pre-mix Conversion Merc 115
    By GLASTRON007 in forum Mercury & Mariner Outboards
    Replies: 8
    Last Post: May 30th, 2009, 02:31 AM
  4. 1963 merc 850 to merc 1000 conversion
    By Doug Redinger in forum Mercury & Mariner Outboards
    Replies: 11
    Last Post: May 29th, 2007, 10:31 AM
  5. MERC 7.5 H.P. TO 9.8 H.P. CONVERSION
    By PICSTEVE in forum Mercury & Mariner Outboards
    Replies: 5
    Last Post: August 29th, 2005, 03:15 PM
  1. iboats Forum Directory - Over 100,000 forum posts organized by topic