350 MAG MPI swap to 383 Stroker Help
 

Hello all! New registered member to the forum. I own a 2003 Rinker 270 Fiesta Vee with a single 350 MAG MPI with Bravo III drive. We had issues with the boat so the past few years the boat has sat. At idle now the boat runs rough. Probably not a huge issue but enough to warrant a look into finally getting rid of the "dovish" 350. We previously had issues planing with 6 people on board and WOT never exceeded 31 MPH. Our goal is to be able to have 8 or 9 people onboard or around 1300 lbs and plane without issue and increase our WOT to around 40 MPH. Can this be done with a short block? Can we have our current motor modified to accomplish this? Is the best option a new Mercruiser 383 stroker? I am on LI, and could really use some advice and guidance because our other option is selling the boat as is and buying a new Cruisers 258 bowlder we've been eying. ;) but would love to have our Rinker if we can get some rocking performance out of it.

Thanks!

Unless you REALLY love that boat, I wouldn't spend the money required to achieve the performance you're expecting.

If you insist on modifying your boat to do what you are looking for consider this:http://www.michiganmotorz.com/stroke...mpi-p-502.html

As you can see you will spend $10K plus labor to swap to this power. You need TORQUE to achieve the results your looking for. You could possibly cdopletely rework what you have but you will only save about 25% at the end of the day.

It comes down to choices and dollars. Sounds like you need a bigger boat with twin engines.

Thank you for your response Sprink. We are prepared to drop $12k or so into a re-power just as long as the performance is a drastic improvement. At the end of the day it's still a Rinker and still a single screw, but we've owned the boat since 2008 and have taken very good care of it and spent good money making the boat right. The question is whether the 383 stroker will do the trick so we will be happy with it for the next 5 or so years before upgrading to a larger twin screw boat.

Big block. Find a take out 496 MAG HO or a 502 MAG MPI.

I was thinking about a big block but would the performance be enough considering the addition engine weight?

Yes...if you find a fresh late model 502 MPI Mag that would be the way to go. Depending on the hours on your Bravo III you might consider re-working it at the same time to handle the additional torque.

Humm, very interesting. Now would the 502 be a drop in using the current motor mounts where my 350 sits or would that need to be customized? I wonder what type of labor costs would be involved in this installation??.....

Yes the bbc sits on the same mount locations as the old school small block. You need about 3 inches in front, 2 inches either side, and 3 inches on top for engine to fit where small block is now. Stock exhausts go to the same thru-prop y-pipe.

Thats good news. I found a shop in upstate NY that specializes in rebuilt marine engines. I just spoke with them. They suggested a rebuilt 454 that is built on the 502 platform. He said they make around 510 ft lbs of torque and 430 HP and would be a drastic improvement over what I currently have. He also said my Bravo III would work just fine with this new motor. He has it in a carb ($6500) or MPI ($8000) option. Of course I would need it installed which from what I am seeing would cost around $1200-$1500 plus the shipping of the engine. Then hopefully I can sell my 350 MAG MPI for a couple grand to help my upfront costs a bit.

Thoughts?

Trying to upload a pic of what he has

http://http://www.ebay.com/itm/502-mpi-8-2-Mercruiser-replacement-motor-efi-computer-454-gen-6-dyno-tested-/262195758040

MPI will be the way to go. Talk to the engine builder about making sure of MPI Computer Programming compatibility. You are after total "Turn Key" operation with the engine swap. Use that term freely when you speak to purveyors of this type thing. The last place you want to find yourself is constantly needing to "Fiddle Around" with your boat instead of enjoying it.

Also...a 502 will be a better choice because of the new technology associated with it. There are still older 2 bolt main, small port head 454's in circulation that may disappoint you in the long run.A Gen VI 454 is a viable option, just make sure it is in fact a GEn VI and get Dyno Sheets to confirm output. Check references.

Damn $6500 sounded really nice. lol We are trying to balance cost vs resale of the boat so this is especially tough. We just don't want to dig ourselves in a whole that we can't get out of when it comes time to sell.

The boat is now running. You take out a live engine and replace it, you are not appreciably increasing resale. This is not a performance boat. Most likeley buyer won't know or care the diff between engines. Either sell it like it is, or upgrade it for yourself. BTW, an early design 2-bolt peanut head 454 will still be WAY ahead of a 383 small block pushing that large resin bucket around...

Yea...that's where my thinking was with my first reply.

Yeah

I heard I can use my current 350 MAG MPI and have it made into the 383 stroker? That would increase performance (although I'm sure not to the level I would like) and be a lot less expensive.

Let me add a few thoughts....

For your size boat I would advocate a big block.

For resale concerns a Merc drop in engine is going to look more favorable than some modified motor to the average consumer. Get a turnkey 502 and plug it in. Fitting was addressed in other posts.

I would make sure you have an EFI motor.

The increase weight due to a big block is insignificant in the overall performance. It might weigh 180 ish pounds more. That's like one person or half a tank of fuel. That should be the least of your concerns unless you were installing the motor in a 15 foot aluminum Jon boat.

Best of luck

Looks like I'm going to try and hunt down a 502 take out with low hrs this weekend.

I was told my current gauges would not work with a 502?

That may or may not be ...depending on programming. I would suspect that if you get a Merc MPI your gauges would be compatible. Some guys on this forum can chime in but seems to me that a certified Mercruiser guy can tell you what you need to do. You're not the first one to do this and you won't be thew last LOL !!

10 pin or 14 pin standard canon plug would likely determine if the gauges would work. Match the plug and it should work out. The gauges are nothing crazy.

I think I may have found my solution. I found a shop ini CT called Northeast performance. From what I have been told, they are former race boat guys with Shockwave who now own line of race boats called Rage Powerboats. They have a low hour 502 MPI motor with new manifold and risers. I've been speaking with Mario who is speaking with Rich Stroffolino the lead mechanic this morning about my gauges. If all goes well, we will buy the engine and transport our boat up to them and have the engine installed and everything tightened up for what we hope to be an amazing season onboard our older boat with a new attitude. Thanks for the suggestions and advice all. I will post updates if this is the way we go. Any other thoughts/ideas please do share.

Thanks!

The motor we are considering is a 1998-99 502 with around 450 hours. New manifolds and risers but other then that it's the original motor. It is not a rebuild. How can I tell if it's a strong motor that will last?

Do a leak down and compression test. Have a scan pulled off the ECM to see total hours and run time at various RPM ranges. If the motor is in good shape I would estimate you could get another 300-500 hours before it needs more attention assuming you didn't thrash it at WOT for hours on end.

One thing that hasn't been addressed is you will likely want thru hull exhaust to let the big block breath.

Very interesting remark about the thru hull exhaust. The shop quoted me for install but didn't mention anything about making a thru hull for the exhausts. I am scheduled to go look at the engine Monday morning. I will ask them if they will do the mentioned tests for me on the engine. Thanks for the advice Trash!

I think shoving 502 cubic inches of exhaust through a B3 would be too restrictive. Use your manifolds and elbows with 4" hose out the tail with some GGB muffler inserts to tone the bark down.

If you are just looking to get on plane better and cruise at 2500-3500rpm, I don't think thruhull would be needed. If you did go thru hull, I'd want mufflers on a cruiser.

I would say yes our goal is to plane easily and run strong mid range around 25-30mph (which should be around 3000 rpm) with 8 or 9 people onboard. But I'm not going to lie, if I have the power I'm going to use it from time to time and run wot!

Spoke with Rich at East Coast Performance Marine and he said he does;t recommend installing an older engine in a newer boat unless it has been rebuilt and I agree. I would hurt my resale value. Turned out that 502 was also salt water cooled. We spoke about stroking out my current 350 MAG MPI. He said we can get between 400-415HP out of it and be able to keep the wet exhaust through the B3. He is going to let me know tomorrow of a price and HP numbers. He also may have a lead on a 502 from a 2005/6 boat with low hours and fresh water cooled. We shall see but I am itching to get my boat going!

There's no doubt a well built stroker will improve your performance. Had your boat been smaller I would have recommended that route. If you go with the stroker SBC don't forget to factor in proper injector size (if required) and tuning.

Good call on scrapping the salt water cooled motor.

Look for a 496 HO takeout with closed cooling.

I found a 2008 496 closed cooling take out with DTS (unsure if HO or standard 496). Is it a huge job to convert my current mercruiser shifter and Bravo III drive to DTS? He said he is selling the shifter and all cables with the motor.
Thanks

Weeks go by and still all the shops I call, repeatedly, refuse to call me back. I have cash in hand ready to spend but the struggle continues to try and find a good mechanic who is reliable.......

you ever find a motor?