Repowering from V6 to V8

flightrisk

Cadet
Joined
Mar 31, 2013
Messages
6
Hello all. I have a 2000 Larson SEI 186 bowrider with a 4.3 Vortec V6 that broke the crank shaft. The outdrive is a VP SX with 1.79 gear ratio. While I could possibly rebuild or replace the V6, I am thinking of repowering with a 5.7 vortec V8. I realize the accessories and harness, etc will swap over with a few changes in hoses, etc. I have plenty of room for the engine and the motor mounts have plenty of room to move forward as well. My main question at this point is the outdrive. I know the gearing is different for V6 vs V8, but will the change be an issue if I just reprop it, is there any problem with torque or wear by stepping up the engine size?
 

Howard Sterndrive

Rear Admiral
Joined
Nov 5, 2008
Messages
4,603
an 18 footer with a 350 will need a lower ratio drive unless you're boating way up in the mountains. 1.79 won't work with any common props on that little boat. You're talking about 60 mph in all likelihood. Need the V8 ratio.
 
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flightrisk

Cadet
Joined
Mar 31, 2013
Messages
6
Thanks Kelley and Howard. That was my understanding that the SX was capable of handling the power. So with my V6 I was swinging a 14 5/8 X 23 prop. If I go to a V8, are you saying I will not be able to get a big enough prop unless I change the gear ratio? Can I step up to a 25 pitch to offset it?
 

White90GT

Petty Officer 2nd Class
Joined
Jul 5, 2011
Messages
161
Is there something wrong with the V6 that's in the boat now? I have a 17" Chris Craft with the same Vortec 4.3L motor and 1.66 drive ratio with I'm pretty sure a 19 pitch prop. My boat jumps up out of the water and tops out around 54 mph with one person. I can't imagine an 18 foot being that much heavier than my little boat. Are you just after the sound and want to hot-rod it or what? Inquiring minds want to know.
 

flightrisk

Cadet
Joined
Mar 31, 2013
Messages
6
So yes, I was compelled to go V8 for power and speed, but the 4.3 has been an awesome engine for the boat. I run about 54 as well. I have thought through it and the V6 is getting rebuilt and going back in. Thanks for the feedback from everyone!
 

Walt T

Lieutenant
Joined
Mar 16, 2002
Messages
1,369
Have the crank and cam journals all checked for alignment and possible line boring. Broken cranks can cause a lot of unseen damage to a block. Personally I wouldn't bother with it, I would replace it. But then I have to warranty it. If it were my own personal motor I would at least check pricing on alignment checks with cam and crank journals and decide if I want to pay it or buy a buildable block.
 
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Fleetwin

Lieutenant Junior Grade
Joined
Nov 23, 2011
Messages
1,141
I have a similar boat with a 3.0. Which is adequate. I can't imagine a V-8. I think the 4.3 is perfect. Plus, the boat is already a bit stern heavy.
 
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