swapping v-6 for v-8

[third times the charm]

Helping my father-in-law put a new motor in my old boat i sold him. Its a 210 canadia four winns, 87 model. It had a 4.3 v-6 that i didnt winterize correctly and blew the block out. He bought a mercursier 305 that has been bored 60 over. Well a couple of questions have come up:

1. He is sure that the exhaust y from the v-6 is the same as the v-8 y. We have both on hand, im not sure if they can interchange.

2. not changing the outdrive, but do i need to change the engine coupling.(v-6 coupling onto the v-8 flywheel)

3. the motor has been competely rebuilt and not ran. I am curious has to what kind of break-in period is needed. (rpm, hours, running at idle or mid range throttle, etc. etc.)
I know we got to modify the motor mounts in the boat ( just glassing in more wood) to make room for the length of a v-8.
other then that i think everything else we got handled. Just need these questions for now. I will start a thread about this in the restor form

 

[achris]

Re: swapping v-6 for v-8

1. Exhaust pipes are the same, just need new tube bewteen the end of the elbows and the top of the y-pipe.
2. Couplers should be the same... But, the ratios in the drive are different between 8 and 6. The V6 will have 1.84:1 and the V8 wants 1.5:1. You might find a prop big enough to make up the difference, but I seriously doubt it, unless it's a big (heavy) boat....
3. Standard run-in is....

 

[third times the charm]

Re: swapping v-6 for v-8

well she is a 22' deckboat, weights about 2200 to 2500 with out the engine, has a 8 to 9' beam

 

[achris]

Re: swapping v-6 for v-8

Some of the early 305s (called '898') did use a 1.65:1 drive, so you might get lucky... What size prop did it run with the V6, and what were max full throttle revs ?

 

[third times the charm]

Re: swapping v-6 for v-8

14.25x23 prop 3 blade stainless. would turn about 4200 wot

 

[achris]

Re: swapping v-6 for v-8

4200 is too low for the V6, so you stand a chance of getting to the right revs with the V8. What carb on the V8?

 

[third times the charm]

Re: swapping v-6 for v-8

a quadajet

 

[achris]

Re: swapping v-6 for v-8

a quadajet

4bbl... the engine should produce about 230hp; I suspect the current prop will possibly be ok... You should be looking at WOT of 4200-4600. Personally, I'd be looking at the very top end of that range, or even a bit over. My engine bangs on the rev limiter (4950) but the driveability at lower revs is superb... and it gioves me that margin for a BIG load of fish (I wish!)...

 

[third times the charm]

Re: swapping v-6 for v-8

cool, i suspect that i will get more horsepower then that, she is bored 60 over. but that at least makes us feel more comfortable with leaving the current outdrive in.

 

[Scott Danforth]

Re: swapping v-6 for v-8

my 2000 searay 5.0 had a 1.62 drive and I was spinning a Solas 15 x 19p prop

 

[achris]

Re: swapping v-6 for v-8

my 2000 searay 5.0 had a 1.62 drive and I was spinning a Solas 15 x 19p prop

Completely different boat, so the prop size you're using will have no relevance to what the OP will be using... He needs to install the engine and take it out on the water to see what he's getting at WOT....