Im exploring my options for a repower on my Commander, the motors are tired and slightly under powered in my opinion. My current set up is the 327F sbc along with the Paragon P-34B. My question; can I repower with a Big Block chevy and still mate up to the Paragon ? or should I stay with the sbc, dart block and go 427?

im not overly concerned with fuel consumption as I own a boat,  of course id only  like to do this repower once so any advice or similar experiences would be greatly appreciated.

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the result i given to you its dyno tested ,was more hp and torque..but i give you the number you will get around 4200-4400 rpm ..because on hevy boat like yours ,you can't go higher rpm,,was a setup of circle track racing ,all  the car was like that,,you can advance the cam 4 degree for more low end torque but the idle was very rough ,,for a boat not so good,,this cam at 0 degree still 110 of intake centerline ,enough for marine use.under 110 you will risk to suck water inside the riser,,you dont want that..the dyno sheet was 382 hp at 5200rpm and 438lbs torque at 4200rpm..with a rochester carb..i actually use this set up for my boat ..the engine show 350lbs at 2000rpm right a way ..if my 327 was good enough to for a rebuilt ,i will just do the same set up and the number will be not far of a 350,,actually i love 327 ,good rod ratio ,tough engine too..my crank was done and cylinder was bad,,was cheaper to buy new part .maybe your engine are good for rebuilt ,who knows maybe put new rings and bearing,,lets your mechanic measure the whole thing.and put vortec head and edelbrock intake ,but you will need all new heat exchanger system,,me i put crusader heat exchanger,the best on market or very cheap durable and simple to install .parts everywhere..and new trans because the 327Q USE the snout of the crank to turn the trans,,this is ridiculous . find ZF HURTH TRANS 63A (ebay or craigslist used )2.5 ratio and no need of 2 different engine rotation,,just automotive rotation,,no need to have 2 kinds of spare starter,raw water pump,and ignition distributor,ect...and buy a raw water pump who is on the crank pulley and use 160 degree MRS GASKET thermostat..i use HEI automotive distributor and i luck the vacuum advance,(amazon have it,), marine power make aluminum manifold for 230$ usd each..cheap !! but more noisy then cast iron,,me i dont mind..lol..

Thanks very much Paco!

I can't quite remember all the details, but my 1968 35 Commander (express) was repowered... it originally came with 427's but previous owners were not able to get them running correctly, or had issues.  Long story short, they were replaced with 454 330hp mercruisers a few years before I purchased her.  We also had another 35 owner in our harbor that had the set up you have... the difference was immense.  I loved the power and speed that the 454's provided...a really nice cruise at 2900 rpm, but anything over 4k and the boat would want to fall to one side...  I'd suggest the same, or perhaps something newer, but as others have mentioned, you'll need transmissions, shafts, and props to match.. ... well, if you're going that far... might as well do it all... it's a big expense, but your basically getting a new boat at that point.  

That's interesting, Chris - on the rare occasion (1-2 times/season), I'll open mine up all the way, and she lists over to one side too.  Wonder what would cause that...

Thanks for the reply Chris, good info. Great to hear others experience with the same hull etc... I’m in the process of getting quotes from a couple engine builders now. I’ve decide to go with the dart block most likely 407sbc There just bullit proof with forged internals and still mount to same place as the 327s did ...I should be in the neighborhood of 450 - 500 hp & torque all below 4500rpm. Going with the stainless exhaust as well, yes it is expensive but it’s my boat lol.
Should last till my kids take her.

Hey Matt the couple times I had mine on plane it did list to port a bit, I think it’s just a weight thing when 1/3 of your boat may be outta the water. K planes took care of that though just my thoughts
My thought, I think with our realatively flat hulls once the come out of the water enough they lay on one flat side or the other depending on the weight. I’ve never gone fast enough to expirence this though as my 31 tops out at 30mph currently.


Matt Cowles said:

That's interesting, Chris - on the rare occasion (1-2 times/season), I'll open mine up all the way, and she lists over to one side too.  Wonder what would cause that...


That actually makes a lot of sense!
Mike H said:
My thought, I think with our realatively flat hulls once the come out of the water enough they lay on one flat side or the other depending on the weight. I’ve never gone fast enough to expirence this though as my 31 tops out at 30mph currently.


Matt Cowles said:

That's interesting, Chris - on the rare occasion (1-2 times/season), I'll open mine up all the way, and she lists over to one side too.  Wonder what would cause that...

morning, Paco you mentioned that you use the stainless marine exhaust manifolds with a short riser...

where did you get them from?  do you remember what price range they were?  thanks!

Scott, I'm curious why you would speculate on such a project when there is a proven solution? Many of us on this forum have done complete repowers with new Mercury 8.1s. They are engineered specifically for this type of application, are powerful, and trustworthy. When matched to ZF 63a gears, the install is about as easy as it gets. You will in fact need to change to 1.5" shafts, which then requires new props, struts, and stuffing boxes. When rigged with Vessel View, you are able to see any engine stats "on the fly".

This project is not cheap, the parts alone will be ~$40k, but knowing you have a trustworthy, professionally engineered system is priceless. 

Morning John, first off id like to say I would like the best of both worlds or get them as close as I can. Im saying the 35' Commander is probably as close to my dream boat as im gonna ever be able to afford. perfect size for my family inside and out. and the lines and styling is classic.   but I also like a little speed..she has a hard time cruising upriver in a head wind.  she will max out at 3400 rpm at about 18 knots. for a 13500 pound boat with a planning hull  < not so good.

its a cruiser boat yes I know but its not a tanker either, I get passed by them...

On ebay they are asking any where from $15000 to $19000 USD for new Mercury 8,1s and that's just one!!

an extra 150 pounds per side going to big blocks from sbc.

I have used actual engine builders in marine applications  in the past with great success.

how about a 434ci Dart Block sbc,  the dart blocks are much strong than original block that's why NASCAR and other racing sport use them, however they remain close to original weight of the sbc all parts interchange with my 327sbc ,with the advantages of bigger bore and strokes. with forged internals ie, crank,pistons rods,bolts...all high quality stuff  with marine cams, head gaskets etc..( close to bullet proof with our wot maxing at 4500 rpm) with aluminum intakes and heads  to match your engines requirement. add a stainless exhaust with marine fibreglass exhaust tubing , probably 2-3 hundreds pounds of cast exhaust piping on both sides.

Mercury 8.1s are approx. 370 - 420 Hp   weight +150 pounds per sideBBC  approx.  from where ive looked, im guessing the internals are not forged either. for about  $16000 -18000 per motor

Professionally built 427 / 434 build are approx. 530hp, 550 ft pounds torque 350 torque from 2500rpm and up, all forged internals,  and yes on regular pump gas in the 9.1 to 1 compression range...dynode and tested for approx.  $7000 -$8000 < I would still have to buy a carb for this so add another $800 ?

this is just what I have come up with over the past few months doing my research as I pray (lol) I only intend on doing this once.

I find you tell someone that its a marine application and they double er up on you   including engines,

again just my thoughts, im certainly no expert in anything but wanted to respond to you question...

thanks

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