40hp to 60hp; new ECU and intake restrictor removed

cricketchaser · Post by **cricketchaser** » 13 Jan 2021, 00:56

Has anyone ever heard of this, if you own a 40hp 4 stroke Merc, with the simple purchase of a 60hp ECU, and removal of the intake restrictor, your motor magically turns into an 60hp?

Riverbean · Post by **Riverbean** » 13 Jan 2021, 01:16

Probably gonna hafta say what year and model mercury your talking about...either way idk the answer but id say its a good possibility the 40 and 60hp's have the same powerhead...

eeshaw · Post by **eeshaw** » 13 Jan 2021, 14:10

I've heard the same thing but don't have an answer. You might want to try comparing a parts list of the two motors to one another. If they have the same power head it's entirely possible. If you find anything post it up, I'm curious also.

onthewater102 · Post by **onthewater102** » 13 Jan 2021, 17:13

Assuming they use the same powerhead then for starters I'd make sure the fuel injector/ fuel regulator (if any) are the same, otherwise it's not just an ECU swap.

If they are, or if the fuel rail is the same and the correct injector can be swapped in, then there will need to be something in the air intake side of the engine that restricts the airflow to match the shorter injector pulse (or reduced fuel delivery from a smaller injector) to keep the air/fuel mix stoichiometric. Beyond a restrictor plate, look for any cast part numbers to be the same (for any intake plumbing and cylinder heads) and that the cam and valves are the same on both engines.

There may likely also be a timing difference even if all they use for air control is a restrictor plate - you need to find how the ECU determines the cam position to direct the engine to fire (cam position sensor or some other device) and make sure those components are common between the engines.

This is all just basic fuel injected motor knowledge, not specific to the outboard in question.

Lastly, don't expect the performance to be the same as the different motor classes tend to have different lower unit gear ratios. I'd be warry about running 50% more power through a gear box if it's not designed to handle the increased torque. Even if it holds up, you will end up needing a different propeller to keep your engine at the proper RPMs at WOT with such a change in power.

Post by **DaleH** » 13 Jan 2021, 17:28

onthewater102 wrote: ↑13 Jan 2021, 17:13 ... I'd be wary about running 50% more power through a gear box if it's not designed to handle the increased torque.

Translated ... that means KaBOOM!

eeshaw · Post by **eeshaw** » 14 Jan 2021, 21:58

I know when it comes to vehicles that the ECU will control the air fuel ratio depending on what feed back it gets from sensors so that's something to look at as wellthe sensors that is. I have both engines and the lower unit on my 60 is different than the 40 I have but I believe that's because the 60 is a Bigfoot model. I know the gear ratio is different but I haven't really compared the case and other parts. It would make sense though since the 60 develops more torque and hp.

bcbouy · Post by **bcbouy** » 15 Jan 2021, 13:13

seems like a lot of expense for a couple mph and a higher fuel consumption.but i'm not an outboard mechanic.

turbotodd · Post by **turbotodd** » 18 Jan 2021, 00:43

Ain't many outboards that run a closed loop efi system.

HPDI's did (I think) but to my knowledge, and I think a few Honda's but thats all I can remember

that potentially makes them simpler yet if modifying and not enough knowledge of what you're modifying, potentially dangerous as in damaging.