?How to change Merc 5.0/GM305 to 5.7/GM350
 

What is needed to upgrad or convert Merc MCM 230 engine with GM 305 bock to GM 350 block., Merc 5.7 type setup?
The 305 is an 1988, 2 bolt main, 1 piece rear seal, roller cam (block # 14093627)


The 350 is a new style 19991, after market engine with 1 piece rear seal, and center bolt valve covers. It has flywheel from stick shift, not auto transmission.

Can I use the same coupler, manifolds, oil pan, etc.

Doug

what year is the 305 engine?

Is the 305 motor a 1 piece rear seal with center bolt valve covers? If it is, then everything from your 350 motor will fit. If not, then only the exhaust, and accesories ( alternator, water pump, power steering, etc. ) will fit. Flywheel, coupler, balancer, oil pan, intake are different.

I just did the exact same swap. It was a 1981 305 that I swapped out for a 350 vortech warmed over. I thought I could use all my existing set up. WRONG! I had to change everthing! The gimbal housing and the outdrive. The problem was with the old exhuast. The 305 had log style manifolds and the 350 had center risers. The Y pipe wouldn't fit. I got a heck of a good deal on the engine $1700 with 30 hours of fresh water use, and the mech said about $300 for the swap if everything was matching. It wasn't his fault, because I was talking to him about generalities, not the specific swap I was doing. So, I figured $2000 for the whole deal. Here was the final figures.
Engine $1700
Shipping $300
Outdrive and transom assembly $2000
Shipping $200
Used parts $500 (luckily he had a boat to get many parts from, otherwise it would have been thousands more)
New parts $1700
Labor $1100
Total cost $7500

Not bad, only 375% over budget :o :eek:
I should estimate for the US government with that track record!

As soon as I got it back from the mechanic, I decided to install closed cooling, so add another $570.
The most expensive new part I had to buy was the thermostat housing ($199). When I went to install the closed cooling, step one was remove thermostat housing and discard! :mad: :mad: :mad:
Quite an investment for a boat I only paid $3700 for! :o

Cooling schematic
 

Cuda,

I have the center risers and plan to add fresh water cooling for the block only. The Merc manuals schematics are for either seawater or full engine/maniford cooling. Anyone know where can I get a schematic or drawing for block only cooling.? The Merc thermostat housing with 6 hoses going to it does not make it obvious how the system is split for block only cooling.

Doug

Doog, I did see a diagram on how the half system was run, but I can't remember where. I will do some looking and see if I can find it. I am sure it will have a different thermostat housing in the kit. Is there a reason you aren't going with a full system?

Why not full FWC?
 

Cuda,

My Merc I/O is an Alpha 1 that has low capacity internal water pump which is adaquate for some block only FWC's. That would avoid the need for a separate engine driven pump which must be used on full systems.

In normal opeation my max rpm is at cruising at 3000. I only rarely run at WOT to briefly test props. So a half systems should be fine for my needs.

Doug