Hey folks new to the forums. I was forwarded to you guys for guidance. I am replacing my 5.0 Volvo Penta TBI to a 5.7. I have been receiving conflicting info regarding the swap. Engine builder said he needs the 5.0 cam from the old motor to put in the new 5.7. He stated doing so would not requiere a tune to the ECM. I have also heard some people don't really need the tune and their engine works fine. I have also heard that the old injectors also need to be replaced because of the higher flow of fuel. If anyone can shed light on the matter and guide me to "if new engine needs it" ECM tuners.

There is more than just the cam being different between the two engines, is the 5.7 just a long block ? the 350 will make more hp and torque, the 305 is a pretty weak engine, your mefi 3 can have a 5.7 tune put in it

F-2 the 5.7 will be a rebuilt long block. The machine shop is waiting for my 5.0 cam to install. I found it weird but then again engine internals is not my strong suit.

I wouldnt put that cam in the 350 it wont run right, you need the 350 cam to stay in the engine and remap the ecm, it would be like running a 502 cam in a 540 to small for the cu in's

Do you have any idea as to where i can get that reflashed?

Smitty on here does a lot of mefi tuning, don't know if he has a 5.7 tune or not, or you might check with I think his name is George at OBD Diag

https://obd2allinone.com/mefitune.asp

Is the cam a hydraulic roller ?? If it is a regular flat tappet cam there is no way I would swap it to a different engine and expect it to live. If it is a hydraulic roller I would not be a bit surprised if Volvo used the same exact cam in the 305 and the 350.

Yes the cam is roller

my opinion is what Id do you do what you need to do with your builder

We need to break this down into simpler steps. I would NOT install a 5.0 cam into the 5.7 thinking the ECM will not require a tune UNLESS it is the same cam. A super common cam in SBC marine motors is the GM 395 cam. If the 305 has this cam installed it will work fine in the 350 but you would likely need to alter the fuel tables slightly.


With the stock 5.0 tune and injectors the new 5.7 will start and run. How well it will run is to be determined. You will need to run a wideband O2 sensor to see what the AFRs (air to fuel ratio) are doing throughout the rpm band.


Your stock injectors will likely be fine going from a 5.0 to a 5.7. It really depends on their flow rating and duty cycle. I doubt the injectors are tapped out at higher than an 80% duty cycle on the 5.0 so you would likely have the headroom for supporting a 5.7 at stock fuel pressure. (Don't jack up the fuel pressure, some do, but I am not a fan of that method).


Given the stock injectors flow X amount of fuel per hour, and going from 300 cubic inch size motor to a 350 you simply need to increase the injector pulse width (how long the injector is open) to accommodate the increased volume of air flowing through the motor, else it will run lean. Not necessarily "danger" lean, but less than optimal. Hence you need wide band and this is where tuning the ECM comes into play. You are simply modifying the MEFI 3 fuel tables by increasing the base pulse width (BPW) of the injectors at various break points (RPM and MAP).


How do you tune the MEFI 3? First is to find a guy who has the software to do it OR purchase MEFI Burn and do it yourself. I have MEFI Burn and do my own tuning. I am not for hire though...I will and can guide you through the process. It's not a cryptic as one may think. If and when you begin to tune just start with the BPW/RPM/MAP table (aka fuel table) within TunerPro. Stay out of all the other dozens of variables, scalars, constants, flags etc. Those in most case never need to be touched.


So what I would do if I was in your shoes is to get the motor assembled and on some sort of simple test stand. Start and run the motor on the stock tune and injectors observing the wide band AFRs under idle / no load conditions. This is a good time for leak checks and setting base timing. If all goes well then install it in the boat and begin on the water tuning. I don't want to go too in depth into that right now because thats like putting the cart in front of the horse right now.


I hope this clears some things up.