5.0gi to 5.7 swap

[Galvez83]

Folks long story short i am going from 5.0GI to a 5.7. I have spoken several times to a machine shop builder and was told to swap the cam from the 5.0 to the new 5.7 if in good conditions. As stated by the shop doing so will not create a need to reflash the ECM MEFI 3. How acurate is that statement? Also are the injectors in the 5.0 the same as the 5.7? If not, is there a need to change them if swapping engines? I have tried to find the 5.7 tbi part number for the injectors but returned with no results.

 

[jimmbo]

If the ECM was Calibrated for a 5 Liter, it sure is not going to Calibrated for a 5.7, regarding Fuel Flow. As for the Cam, does the 5 liter Cam have the same Duration, Lift, Overlap, etc as the 5.7? What you need to do is get Part List for both Engines and compare, line by line, looking for different Part #s. Tedious perhaps, but many have learned the hard way that 'Close' is only good for Horseshoes, Grenades, and Nuclear Weapons

 

[Lou C]

You have 7/10s more displacement to feed so the ECM has to be calibrated differently. On the old days you changed carb jets & metering rods for the same reason

 

[Bondo]

Ayuh,..... There's no reason to swap the cam, if the new motor is a standard production motor,....

 

[alldodge]

Folks long story short i am going from 5.0GI to a 5.7. I have spoken several times to a machine shop builder and was told to swap the cam from the 5.0 to the new 5.7 if in good conditions. As stated by the shop doing so will not create a need to reflash the ECM MEFI 3. How acurate is that statement? Also are the injectors in the 5.0 the same as the 5.7? If not, is there a need to change them if swapping engines? I have tried to find the 5.7 tbi part number for the injectors but returned with no results.

Don't listen to the shop, and as Bondo mentioned don't change the cam.
You will need the ECM reflashed which isn't hard, just need the right software like MEFI Burn. With this software and the right Bin file its a easy swap

Could contact Bob at OBD Diagnostics or a member on Offshore only named Articfriends to see if they can help

 

[Galvez83]

I see this rebuild is going to be fun

 

[Lou C]

Taking a wild guess, I'm thinking that the properly flashed ECM will have the injectors stay open longer, to allow for the .7 greater engine displacement of the 5.7 vs the 5.0. If I was going to put my old Quadrajet on a 5.7 vs the 4.3 I now have, for sure I'd have to re-jet it. Keep in mind the duty cycle of a marine inboard is much tougher than an automotive application. You do not want a lean fuel mix in a marine engine. This is one of a few reasons why I prefer carbs vs EFI for old school GM marine engines. Just easier to deal with, if you understand carbs.

 

[Scott Danforth]

If you are building a 5.7, a 6.2 is not much more money.

Rotating assemblies are within $200 of each other

You already need to reflash your ECM

 

[alldodge]

Could always put a carb on it, but who want's to do that

Merc always sets things up fat on fuel. Being fat means less of a chance of being lean. Meaning, depending on the load (how much the boat and gear weight) it still may be ok with current program. Only way to know for sure is with run, stop, check, repeat

 

[jimmbo]

Taking a wild guess, I'm thinking that the properly flashed ECM will have the injectors stay open longer, to allow for the .7 greater engine displacement of the 5.7 vs the 5.0. If I was going to put my old Quadrajet on a 5.7 vs the 4.3 I now have, for sure I'd have to re-jet it. Keep in mind the duty cycle of a marine inboard is much tougher than an automotive application. You do not want a lean fuel mix in a marine engine. This is one of a few reasons why I prefer carbs vs EFI for old school GM marine engines. Just easier to deal with, if you understand carbs.

Changing the Jets and/or Metering Rods, is rarely needed, but is routinely done to cover/hide other problems, same goes for all the different Accelerator Pump Delivery Curves that a Holley can be customized with. Where changes need to be made, are a little more complicated. Going to a different Displacement, or even a Cam change will alter the Volume of Air at any given Rpm. There is an optimum position for the Throttle Plate with regards to the Transfer Slot in the Throttle Body at idle speed. Changes to that angle to set idle speed, can and will cause fuel delivery issues. Also changing is the point where the Power Enrichment Circuit turns on and off, not easy to do on many carbs, Q-jet being one


Some aftermarket Carb have Idle Circuits(Adjustable and non-adjustable) on the secondary side and also provide an adjustment to alter the idle position of that Throttle Plate, so the Primary Plate to be properly postioned

 

[jimmbo]

Could always put a carb on it, but who want's to do that

Merc always sets things up fat on fuel. Being fat means less of a chance of being lean. Meaning, depending on the load (how much the boat and gear weight) it still may be ok with current program. Only way to know for sure is with run, stop, check, repeat

For me, calibrating a Carb, is far easier than trying to change an ECM program. Too many things to go haywire with the latter

 

[Searay205]

I am curious if an engine is running lean do you always hear "pinging"? Is it possible you hear or feel nothing an still run lean?

 

[Scott Danforth]

I am curious if an engine is running lean do you always hear "pinging"? Is it possible you hear or feel nothing an still run lean?

Yes, it is possible to not hear the lean death rattle

 

[Galvez83]

Update guys, the ECM is on its way to get calibrated.