Mercruiser Repower 5.7 or 7.4

JDeemer

Recruit
Joined
May 29, 2012
Messages
2
Ok so I'm new to the forums but wanted to ask some opinions of other Iboaters. I recently bought a 23.5 foot Century 4500 XL. It had a 350 in it that was cracked. My Engine options with the budget I have and the spare parts already laying around are 350 w/vortec heads, aftermarket cam,intake carb etc. with a alpha1 or bravo1 or a 454 4 bolt main w/ peanut heads, after market cam,intake, carb etc and an alpha or a bravo. Just curious what people think. I know the first jump is to the 454 but I'm worried the peanut heads won't make the power I am wanting vs a small block with vortecs. The SBC compression ratio will end up at 9.5:1 where the BBC will be in the low 8's. I always could swap the heads but this is the stuff I have available now and with the budget of other projects on the boat these are my options at this current time. Does anyone have experience with the "Peanut" heads vs a healthy SBC? Dry specs on the boat are just shy of 4000lbs. I will attatch a pic to give an idea of the hull design. If you are curious it was originally equiped with a 260hp 350 and an alpha, but most of these boats had a 330hp 454 and a bravo. I am setting my goals at decent bottom end power with a top speed reaching 60. BTW not my boat but exactly the same boat, It's at my shop right now getting taken apart and forgot to bring the digital camera home.
 

Attachments

  • IMG_2830.jpg
    IMG_2830.jpg
    145.7 KB · Views: 0

cr2k

Captain
Joined
Mar 19, 2009
Messages
3,730
Re: Mercruiser Repower 5.7 or 7.4

What drive are you running? If Alpha I would stick with the SBC.
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
Re: Mercruiser Repower 5.7 or 7.4

I am setting my goals at decent bottom end power with a top speed reaching 60.

That's going to be hard with an SBC in a boat that size unless you do something like a 383 and spend a fair amount of money on it. (you'll need premium gas too with the higher compression)

My 87 Four Winns 211 Liberator (21' and about 4500lbs) came with an OMC (Ford) 460 and King Cobra.
It would do about 60 mph @5000 RPM (but was rather slow out of the hole)

I re-powered it with a stock 1997 carbureted Mercruiser 454 + Bravo III and lost about 3 mph but now it just ROCKETS out of the hole.
The 260hp/Alpha powered 21' Liberators will do about 50 mph and are even "doggier" out of the hole!

There's no substitution for cu-in.


Regards,


Rick
 

NHGuy

Captain
Joined
May 21, 2009
Messages
3,631
Re: Mercruiser Repower 5.7 or 7.4

Do the 454 and a bravo. Later you can do some heads, but that way you will have a base you can grow from.
Otherwise do a bravo with a built, and I mean pretty strong, small block. The bravo can handle your weight and torque, the alpha would be a failure risk. Given the choice, why chance a problem.

Nice thing about the 454 is pump gas, but a built up small block will definitely make good noises, and weigh less.
Of course if you can work on the 454 in the future, that's even better than the built small block. Just not right now.
 

JDeemer

Recruit
Joined
May 29, 2012
Messages
2
Re: Mercruiser Repower 5.7 or 7.4

Thanks guys that was exactly what I was leaning towards doing. I will look around in the mean time and see if I can find some Big block heads for a decent price.
 
Top