Merc 4.3 MPI vs carb

[QBhoy]

Hi TP

I'm not sure about the 7.4 mpi. Only that it was a very early version. As far as I know they made 330hp which was the same as most carbs. It's a strange exception to the mpi rule.
I agree that the mpi is set up or configured to have more HP...ofcourse I do....it's been one of my points all along. Engine evolution.
Thanks TP

 

[QBhoy]

Also TP....with regards to the 7.4 mpi making the same hp as the carb...it may have been an early attempt at mpi engines where the goal was to make the same hp (no idea why it would be 310hp, although it rings a bell), but have a greater efficiency doing it.
You'll also be aware that the more recent generation 7.4 mpi makes 380hp ? These are the generation of engines I was more referring to.

 

[tpenfield]

With any type of engine, the manufacturer can set up the engine to achieve a fairly wide range of HP. I think they have better control of that with the EFI/MPI engines due to the computer control.

I think that the 7.4's of that early MPI era were tuned more for the low-end torque vs. high end performance, so they were rated at less HP than their carb equivalents. The ECM could be re-programmed to achieve a different result. AllDodge did some re-tuning of his ECM when he re-built his engine a couple of years ago.

Having just checked back on the OP's initial question about carb vs. MPI . . . which is better? or which should he pursue? I think MPI is a preferable choice, but a carb'd engine is not a show stopper for an otherwise good boat IMO. It sort of depends on what the 'wants & needs' of the OP are. If they guy does not have an appetite for expensive diagnostics/repair when the engine acts up, then a carb would be a better choice, even though he may be giving up a bit in overall performance.

 

[QBhoy]

Well said TP....I agree.

 

[bruceb58]

Bruce have you been taking crazy pills ?
I sent them over

You said you had specs from Mercruiser. Still Waiting.....

HP is rated based on a function of torque x RPM. If an engine is run at higher RPM, it can attain a higher peak HP. Simple enough for you?

BTW, the outboard in my signature has the same block in the 75, 90 and 115 HP versions. If you look at the specs, they rate them at different peak RPM. Everything except the engine ECU parameters are identical.

You were making the point that an identical displacement engine has way better fuel economy with MPI than carb....I totally dispute that claim. An engine is an air pump. For a certain RPM it pumps a certain amount of air. If you put fuel in with the proper stoichiometric ratio, it doesn't matter what fuel delivery system you have if you meet that ratio.

 

[QBhoy]

MOD EDIT - If you can't be civil, don't reply.

 

[QBhoy]

Are you kidding GA....every second post Bruce had ever made is un civil and condescending .I've tried to be patient and fair about it all...just trying to get my point across...falling on deaf ears though.
I give in...

 

[GA_Boater]

My comment stands for any member.

The OP has decided by now. Closed.