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Discussion Starter #1
Took boat out for the first time since engine swap and the performance sucked...trying to eliminate possible issues with the boat..before I start screwing with the engine..

the boat had a ford 390 in it before I purchased it, and I just installed a small block chevy.
Wondering if gears and prop set up would be drastically different for big block ford set up... And now being small block chevy... Could this be a potential issue in performance?

The engine is a mild sbc...350 hp. 1968 Stevens

checked gears...see pic...difference in gears is about 17??...am I interpretaing this correctly?

only marking on the prop are a "15". Three blade..


What do u think?
 

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Discussion Starter #4
I have another vdrive boat that rips pretty good. Similar engine set up...300 hp sbc. I just checked the gear ratio in that one...and it looks pretty damn close to 1:1.

With the sluggish boat gear ratio at 1:1.18....am I going to see a drastic improvement in performance by swapping the gears to a less overdriven set?

I've got the prop off... Going to take it to the prop man for him to ID.

I have a fresh sbc ready to go...I hate to throw the new engine in...and find out it was gearing/ prop keeping me down...
 

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Discussion Starter #5
The guy I bought the boat off of put together a pretty stout ford engine...put it in the boat...and wasn't happy with the performance (not fast enough).....he blamed the crappy performance on "the boat"..... With my recent experience....and the previous owners input...it's making me look at the gears/prop a little closer..
 

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I am thinking a gear change to 6's or 9's. How about a pic of the prop? Is it steel or bronze 3 blade? Need to know max rpm and speed.
 

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Max rpm that I was able to get out of the boat was barly 3,000....and that was a struggle.

The prop on the boat is marked with a "15".....I think the prop is a 12x15.

i just checked the prop on my other sbc powered v drive that does go good....it has a 12x13 "cup".

i have a spare 12x13 and a 12x14. Could changing props have such a drastic rpm/performance gain?

pic of prop ran on poor performing run.
 

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Might try the 12-13 and see what happens. That's a lot easier than changing gears and will give you some info, although 18 gears for a small block seems like too much gear for sure.
 

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Might try the 12-13 and see what happens. That's a lot easier than changing gears and will give you some info, although 18 gears for a small block seems like too much gear for sure.
X2.. The 12 x 15 prop is waaay too much. Just did a gear change for a customer with a 500hp small block in a Hondo form 18's to 12's.
 
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