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Discussion Starter · #1 ·
Hey guys, just got a 1981 233 LS, the previous owner put a new GM 350 carberated and a new drive on it 2 years ago.

Had it on the water and it ran 45 mph on the gauge at 4 rmps, with 4 people in it. How does that sound for full throttle? I would like to get some more mph out of her, where would you start? It has thru hull exhaust.

How do i tell what drive it is, all it has on it is mercruiser?

Any help and ideas are welcome, Besides droppin a Big block in her!!!!!

Thanks guys, and what a awsome forum.
 

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Probably an Alpha drive and a big block is an option but a built small block will make it run almost as fast without the BBC problems.

Where in OK? There are a few of us Formula owners in OK
 

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Stick with your small block! I have a lot of guys pretty envious with mine that have been "touched"! :winker:
 

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zdek said:
Stick with your small block! I have a lot of guys pretty envious with mine that have been "touched"! :winker:
TOUCHED? that is like saying a HO has been kissed :laugher:
 

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Discussion Starter · #5 ·
Opie I'm in northern Ok, ponca city, where are you at? What do you think about the rpms and speed? been thinkin i should try a different prop. I would think the engine at full throttle should be up in the range of at least 4500. No matter what I do with the trim it stays at 4000.

Not sure the pitch on the prop now, maybe a 21?
 

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Doc14 said:
No matter what I do with the trim it stays at 4000.

Not sure the pitch on the prop now, maybe a 21?


That is definately to low. The engine is bogged to hard.
Alpha drive would be normal production for that boat with a small block.


Have you checked some prop calculators online? Using your real numbers as it runs, your shippage % would show to be low. You want no less than 12% slippage, so if yours shows too low then tweak the prop pitch untill the slippage shows better and try that prop.
I think your rpm should be at least 4600.
 

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what pitch is ur prop right now? i have 2 of those engines in my boat. they seem to run real happy at 4500 rpm wot. im swinging 19 pitch 3 blade aluminums (crap). that gives me a solid 61 mph on GPS.
 

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Discussion Starter · #9 ·
I have tried the 21 and a 19 on there now, both 3 blade, not sure brand.

Both these props have the boat at 45mph non gps, the 19 gives 4500rmps where the 21 gives 4000rpms

I like the 19' really gets the big heavy boat up and out quick. I still would really like to get to atleast 50mph!!! Over winter I am thinking New heads, New Intake, New cam, and see where that puts me, what do you guys think can I hit 50+??? :D
 

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im not to sure id go putting a top end kit on an older motor. id look into getting a rebuilt engine. at least that way u know everything is new or fresh, it'll also have a warrenty so u can run the supreme piss out of it. then u'll get ur 50+ mph. :D
 

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Discussion Starter · #11 ·
Dozer, it's not the orininal engine, the past owner put a newer SBC in it 2 years ago. But I agree I would still like to pull it and just go through it to make it solid.
 

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what stule engine is it? are they center bolt hrads or flange bolt heads? i built a 355cid for my truck thats around 400hp, and it only cost me about $1800.
www.naparts.com This is the place i got all my parts and they covered everything and answered any questions i had.
 

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Doc14 said:
I have tried the 21 and a 19 on there now, both 3 blade, not sure brand.

Both these props have the boat at 45mph non gps, the 19 gives 4500rmps where the 21 gives 4000rpms

I like the 19' really gets the big heavy boat up and out quick. I still would really like to get to atleast 50mph!!! Over winter I am thinking New heads, New Intake, New cam, and see where that puts me, what do you guys think can I hit 50+??? :D


That 19 prop gets your rpm closer to where it is supposed to be so that is very close to where you need to be.
A three blade prop will be best for top end speed and a four blade prop is best for out of the hole and mid-range, where the boat is operated most of the time anyway.



You could re-top that engine and make it breathe better if as you say, later model in good shape. Using smaller chambers you can raise the compression as long as it is not high now. Plus all the other parts you could see a strong 50mph with the boat loaded, fuel and people.

Sounds like a winter project that would have a nice spring payoff. I would have to mess with it if it were mine :bigsmile: :bigsmile: :bigsmile: :rambo:
 

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Have you verified that your tach is accurate with a known good tachometer?

That should have been your first test.
 

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Discussion Starter · #15 ·
Winter project indeed, AquaForce, we shall see next summer if I do get to 50+ MPH!!!

ghart, no I have not tried another tach, nor a gps, I have a lot of options and this too is a good place to look into, thanks for the advice.
 

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You don't have to replace the tach just hook up a known good hand held tach to see if the readings agree.
 

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Bring someone's GPS next time too. Sure would suck to throw a ton of money at something because the stock speedo gauge was lying to you.

While my stock speedo is remarkably accurate to about 60mph, it's real true value is only to know when something is caught on the outdrive.

It seems to me a tad unusual that both props, with a 500rpm difference, are showing the exact same speed. Check all the simple easy stuff before deciding to throw a ton of money at it.
 
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