Big Block Boat

SMOKEmUP · Posted: Mon Feb 20, 2012 7:32 pm Post subject: Big Block Boat

I'm going to look at a new to me boat. It's a 1995 Donzi with a 7.4L (454) in it. The motor is probably toast, he didn't winterize it and it's not pumping any water through the motor. The boat motor big blocks are only rated at 310 HP. I'm not sure what heads come on it and the compression ratio is low, around 8.5:1 I think.

I've never had a big block before. If I get the boat for the right price I'm thinking of going through the motor, nothing crazy, forged pistons, bump the compression, and some aluminum heads. Any suggestions as to who makes a good set of big block head? Or is it better port the stock ones?

af2 · Posted: Mon Feb 20, 2012 7:59 pm Post subject:

Those are either the tiny Vortec or peanut port pre Vortec heads.
I wouldn't waste my time on them.

Aluminum heads and a small dome will get you 9.5ish :1 compression and run way better.

The RHS looks like a nice piece and have not heard bad about them in the forums. Any 4032 piston would be good.

journeyman · Posted: Tue Feb 21, 2012 7:24 am Post subject:

I just installed a pair of Feuling center fire heads like these:http://www.454ss.com/cgi-bin/forum/YaBB.pl?num=1297801310
on my 454. Unfortunately, I am still getting the thing rebuilt (another, unrelated issue), so have driven them very little. They are supposed to make the combustion efficiency much higher as they are fast burn heads. They also relocate the spark plugs away from the exhaust manifold and into the center of the combustion chamber.

Right now my project is delayed, so testing will take a while.

Again, they are supposed to be VERY good, but as of yet I cannot attest to that personally.

Oh, and they look pretty cool.

clay · Posted: Tue Feb 21, 2012 11:08 am Post subject:

If you search on Chevelles.com for Vortecpro or mike1231 he has done some impressive stuff with peanut heads - ported and unported. I vote to do what you can with the heads you have, swap the cam, intake and maybe carb. Then spend the money you saved on the Camaro or Camaros Very Happy

. Clay

journeyman · Posted: Tue Feb 21, 2012 2:39 pm Post subject:

Also a lot of positive stuff about L29 heads (99cc chambers)

SMOKEmUP · Posted: Tue Feb 21, 2012 4:41 pm Post subject:

I'm going to look at the boat tonight. I'll keep you posted.

Big Dave · Posted: Tue Feb 21, 2012 10:14 pm Post subject:

If it is an I/O be sure the foot is in good shape. Those I/O units have tiny gears that big a motor will break. I would see if the motor is disconected if you can turn it over by hand (to feel for a broken or chipped tooth). If ok check the shear pin (woodruff key on the prop for damage to the slot). In board only and you are golden.

Big Dave

SMOKEmUP · Posted: Wed Feb 22, 2012 2:53 pm Post subject:

Looked at it last night, made the guy an offer, and he accepted but didn't take it since the trailer lights weren't working (it was at night). Also I'm unsure how this will tow since it's been sitting in the same spot for almost two years. I had the kids and an hour plus drive back I didn't want to chance getting stuck with seized brakes etc. I need to go back and get it during the day next week (if he still has it).

The motor started and ran. No water was coming out the pisser indicating a cooling problem. The good news is it started, good oil pressure, no water in the oil, no leaks. The boat only has 205 hours on it so the motor might be good and only need the cooling pump rebuild but you never know. Problem is big block boat parts are crazy money.

Paul P · Posted: Wed Feb 22, 2012 5:31 pm Post subject:

I guess there are 2 choices.

1. Keep the boat anchor Big Block and work with it .

2. For the $$ throw an aluminum or Iron block/aluminum head LS motor in there. Would likely make more power and be better on gas.

Big Dave · Posted: Wed Feb 22, 2012 7:10 pm Post subject:

Basically the only difference between an OMC Marine block and a Mark IV automotive block is the exhaust manifolds are water cooled and use water from the I/O foot. The motor's cooling is by way of a closed system with Glycol antifreeze that pumps water through a heat exchanger on the bottom of the boat that can get plugged up with aquatic vegetation. So far as I know all "Marine" blocks are standard deck height high nickel content four bolt main two piece blocks right up until they cast the tall deck 8200 Vortec engine. This makes them desirable and therefore expensive.

Marine engines are stationary power plants that are set on cruise and left for hours. As such the cams are designed to be low RPM stump pullers that has a very peaky torque band, and carburetors are small in CFM. You generally change the prop, not monkey with the motor on a boat to affect how you want it to behave.

Big Dave

10sec.et · Posted: Thu Feb 23, 2012 11:48 pm Post subject:

Paul P · Posted: Fri Feb 24, 2012 9:15 pm Post subject:

Big Dave · Posted: Fri Feb 24, 2012 10:16 pm Post subject:

Used to be I had thick skin. Now I'm so old catching a fold of skin on anything harder than Q-tip tears it off. Good news is with my neuropathy I don't feel anything any more so poke away! Wink

SMOKEmUP · Posted: Mon Mar 05, 2012 2:06 am Post subject:

Picked up the boat today.

journeyman · Posted: Mon Mar 05, 2012 4:14 am Post subject:

As much as I don't want to admit, the suggestion for an LS motor does make a lot of sense when you consider what you get for the investment.
Smooth running, wide power range, high efficiency port design (great combustion efficiency), fuel injection, lighter weight, etc.