Need help choosing 454 mpi Cam!?!?!?!
 

Hello, Ive used OFO as a great resource for years now but this is my first time posting as Im starting a build on my 1998 Campion Chase 800 (27ft). I have the Merc 454 (7.4L MPI) 330hp I believe and am looking for input on upgrading the camshaft to gain a little more breathing room in the top end of the rpm range for longer trips. Everything in the motor is stock currently. Its getting pulled due to low pressure from the fuel pump, bad head gasket and a messed up injector. The guy who had the boat before me was very DIY and as a result the engine isnt as clean and put together as Id like it, so im pulling the entire setup to go over it and clean it up cosmetically and figured while it was out thats my best opportunity to add a little extra reliability in terms of quality of internals, as well as power.

Boat currently runs 62mph flat out light on fuel on the right water. Would like to do add more mid range to help with crusing as well as a little top end for those times we need to outrun the weather.

Any input is appreciated.

The best thing to do with that engine is leave it the way it came from Mercruiser. It is not a performance engine, and the costs to get anything out of it will far outweigh any performance gains.

If it runs well, pull it/clean it up and sell, then try to find a 454/502 Mag MPI, or perhaps a 496 Mag or Mag HO. You'll be well ahead of the game going that route.

Thanks Tom, the only reason I’ve considered going this route is because I’ve found it hard to come across a 454 mag or 502mag at a reasonable price here in eastern Canada and when I do they’ve got 600+ hours on them.

I’ve even laid out the plan to tear this motor down to the block, have it bored and put a 496 stroker kit in it, forged setup, switch the heads, and convert it to carb setup with a larger intake. Canadian pricing puts that venture around the 8K mark with all the labour being done by yours truly.

Which is is why I put it out there to see if anyone had had success just swapping out 2-3k worth of parts to kind of “bring this motor to life” and just enjoy a trouble free setup that still makes decent power.

I agree with TomZ.

It takes at least 50hp to notice any significant difference and you may lose some valuable low end. You’ll be money and time ahead finding a complete 502mag and refreshing it.

Going the stroker route that you speak of you’ll also need to upgrade the oil cooling system and fuel system, which for me was just shy of $2k in parts alone.

If you're going to spend the money on building up the short block with a bigger crank and so on, you're going to run into some serious sticker shock doing the top-end. The existing peanut port heads will not do the job. From a cost standpoint, it just doesn't work. Read through the site and you'll find this has been played out over and over again.

Start with a good foundation... sell what you have to recoup some of the cost.

A 454/502 MAG, if taken care of reasonably, will run a good 1000+ hours or more before needing major (as in bottom-end) repairs. You may need to refresh the heads at the 600 mark, but that' not a huge expense especially if staying stock-ish.

Hope this helps.

Don't forget the upgraded exhaust if you go bigger cam. It will (with stock exhaust) want to revert and throw all of your time and money into the scrap pile.

Here you go and $1,000 in extra parts to sell.
https://www.offshoreonly.com/forums/...-454-sale.html

Cam
 

Tom Z said it perfectly
any change in cam will change the vacuum on that engine
that processor is set up to read a certain cam readings
these parameters are set in the characteristic maps internally and once you change the stock spec that motor will never right. Ever. Don’t waste your money on that, build another engine with a nice big blower sticking out of the top. The chicks love blower motors

Thanks everyone for the valuable input. so now that its clear this motor isn't the best choice for my goals......Ive tracked down a 454 MAG about 5.5hrs south of me, its a long block, completely rebuilt from the bottom up and he's suppose to have the recepits to prove it. Full forged internals, little cam upgrade, rectangle port heads and improved valve train. Its originally an EFI motor so my question is, does my 454 MPI intake setup work on a mag? I imagine the bolt pattern to be the same, but I was more concerned that the intake may be different and not flow enough to feed those heads or something? Can I have the computer re-mapped to feed the 454 mag? Do I even need to have that done?

GLENAMY 242SS - thats a nice setup for sure and a decent deal! but my exchange rate + shipping + taxes at the border drive that up to a almost 10K setup for me unfortunately

Thanks again for everyones input and feedback, this is my first boat, and well I know my way around an engine Im just not well versed enough at this point with the marine engine world

Does the engine package in question have an intake? Since it has been upgraded some, you might want to consider a carbureted set-up vs the EFI. The EFI set up will require a lot tuning that should be done on a dyno by someone that can write the tune properly. Having it be wrong leads to broken parts.

It does, but its not programmed for the motor either. Story is he was building the setup for himself and collecting pieces as needed but life got in the way and hes got another child on the way so the wife has shut down boat building plans.

Heres a list of whats been done to the motor-Rebuilt 1997 Mercruiser Magnum 454, .030 over.
4 bolt main, block #
Was pressure tested prior to machining.
Fresh rebuild, as pictured.
Cam info in pictures. Piston part number in pictures.
Engine has forged gm performance crank,
factory forged rods,
sealed power forged pistons,
comp cams cam shaft part # CBVI- XR276-HR-10
Factory roller lifters,
Factory non roller rockers.
New valve springs- some info in one of the pics.
Gm performance 088 heads (rect port), all freshened up, valve job, seals, springs, ARP head bolts.
New gaskets..
NO intake or carb. ( Was an EFI motor)

Oiled and sealed up.

Unless you have someone to tune the efi, THAT KNOWS WHAT THEY ARE DOING, you will phuck sh!t up. Car EFI uses oxygen sensors that read whether it is running rich or lean. Your marine EFI dies not have this. So it will not be able to self figure out the correct a/f ratio, The rev limiter is different too.....
FYI..the 17 year old kid down the street with the honda civic nor the 22 year old kid down the street with the rusted out dodge turbo diesel belching black smoke will be able to tune it either...

A good marine engine/dyno shop should be able to make it run great. A decent manifold and carb could also be easily set up.

I do have a local shop that can tune it if I stick with EFI, he's a reputable builder and has built plenty of motors for guys all over the place, everything from performance marine, dirt car and even worked on "my way" the turbine driven 50' outerlimits cat hull located right here in the 1000 islands.

Back to my original question though....does my 454 MPI intake and injectors work on a 454 MAG if I get it tuned properly? or will it not flow enough air and fuel for the mag motor?

Ask the guy at your local shop that has tuned plenty of motors, he should know.

Wouldn't recommend installing a round port truck intake on rectangular port heads with a bit more cam.sell the mpi pieces and go with a holley 750 or 780 double pumper or source a early mpi mag injection make sure you have your timing Control for the dist.if you go carb

Long time no here, welcome back.