JohnnyM

I am repowering a 35' Cig with 502s and I have the original 1995 MPI units (not cool fuel) and and also intakes and carbs. Would like to know if anybody has run both in the same boat and could help with some consumpsion numbers? Or any other pros and cons of both induction systems. I plan to make 100 to 300 mile trips with it and I am more worried about mpg then mph. Believe me I never thought I would say that !!!

paradigm shift

I have no pratical applications like you are asking. Everytime I went from EFI to carb I went up in HP so not comparring apples to apples. I do think your MPI or EFI is great if you stay stock. If you are going to modify you better have a good engine builder with dyno a facillity that can tune you ECM to match your combination. There are some proven packages out there that are an option also. I know that most usually say EFI is more economical but in a boat they are set up a little rich so if a carb is set up correctly I am not sure how much that applies. Fuel injection will adjust better for alttitude changes where a carb won't. If you look at the market EFI is the direction it is headed.

I am kinda of old school I like carbs because I understand them better and can adjust them. I do not have the tools and you can't even get them to adjust factory ECM. Didn't really answer your question but just my opinion. Nice project! Oh yea Carry Spare parts.

JohnnyM

Thanks for the imput Paradigm Shift.
The carbs are the simple way out for me, thats for sure. I have one of the 509 motors in my 25 cat now and it seems to be using a ton of fuel. How much hp did you pick up when you switched to carbs? Also any imput on hours between rebuilds on carb verse mpi or efi?

bajadude

Here's a link to a good thread about this subject from a few weeks ago

I'm old school like paradigm shift on carbs. I understand 'em and can work on 'em. Other than really basic stuff (if there is such a thing) I wouldn't know where to start with EFI / MPI.

paradigm shift

I stepped up big time. Complete blower motor. Kept old 502mag MPI as a spare, you never know. As for time between rebuilds I think it is a wash either way. Boat EFI are set rich usually and have no O2 sensor so they do not run on the ragged lean edge like your car would. Hence the frequent oil changes still required. Service and how hard you drive will determine rebuild times. 500 to 800 hrs is not unheard off but - There are to many variables to really say accuratly. Some can go alot more or a lot less. You might try some searches there have been several threads on 502 rebuilds like you are looking for. Try this link.

http://offshoreonly.com/forum/showth...threadid=31011

I should mention especially if you are looking at doing the assembly your self check out Dennis Moores book. Big-Block Chevy Marine Performance.

JohnnyM

Thanks Bajadude.....Great thread