CDaniel525

Ok, well its not for a corvette, or for a car for that matter, but its still a SBC. Moderators, if you want to move this, its ok with me, but i dont where else to post....
My father has a 76 cigarette 28SS, with dual 350 magnum motors(270HP). He is looking to gain some serious HP out of these motors, but i dont see it possible without blowers, which he agrees. In the meantime he would like to build them up to about 375-400HP, by adding cams, heads, high performance manifolds(they dont make marine headers for SB :bs) , carbs. First off, do you think this is possible with 8.5:1 compression? If not, about how much HP do you think ill be able to add??
In any case, can anyone make any suggestions to a cam. It needs to maintan torque throughout the RPMS as well since in boats torque is needed.
How about heads?? Anything good out there with the Icanel(sp?) valves or a suggestion of a set of heads that can get him around his HP range, which we could add the valves later on??
Please keep in mind he will be adding a blower later on, if it makes a difference. I appreciate any help in advance.
Chris

Shark Racer

They don't make headers for SB chevies? The LT4 in my friend's Mastercraft would suggest otherwise... I don't know they made 3" thick exhaust manifolds...
If building up a boat motor is anything like building up a car motor, go w/ a roller cam, and a good pair of ported heads. AFR will keep the compression low if you decide to put a blower on later on.
-Steve

mountainmotor

Finally a boat motor question! :)
The HP you want will be easy to get with the small inch Weiand blowers.The Inconel exhaust valve's will be a nessesity when cammed correctly due to the heat from the resulting 118 exhaust lobe centerline when installed.So will hardened ex seats.The cam and carbs came to mind immediatley but the prop size was not mentioned . What brand out drives are on the boat?What are the head casting numbers and do they have srew in studs? What RPM are the motors running at now? Forged pistons will be absolutley mandatory for this as well.

Lighting Manufaturing makes a nice Exhaust for the boat motors that you can check into if you want.They are not headers but perform close in the RPM range you will be running in.They might not be needed if willing to change the props.That wiil save big bucks!

Ganey

mountainmotor

Thought you might like that !

:cool:

mountainmotor

Ganey,
For a guy like me who lives and breathes boats there is just not much going on in the way of boat motor discussion boards on the net.Been thinking of taking up needle work as a hobby anyway because it is cheaper!

" On this trailer lies a disease for which there is no cure"

CDaniel525

Pacin'California, i jsut havent seen them available out there at all....do you happen to know the brand on your buddiies boat??
I was trying to convince him into the AFR's, but i was wondering if they can assemble them with inconel valves and hardened exhaust seats??
as far as the boat, they have TRS drives, and props will definitely be changed in the long run. Even though hes gonna change the props, he wants to change the heads to 2.02's.

Any clue on a certain cam that would be decent??
Thanks again
Chris
Thanks again
Chris

mountainmotor

An effort to make max power at around 5k and a cam picked accordingly will be needed to maintain a a smooth enough idle so not to gut the drives when putting into gear.With the small blowers I would say a single pattern cam hydraulic with duration of 220@0.50 ground on 112 Lobe Center would be a good baseline.Put the intake in at 107 centerline.114 would be OK also but the compression will be critical.Would keep it at 9.1 if at all possible.If the boat tends to get air often you might want to think about a flat tappet solid lifter cam for added insurance against stacking up valve train parts during severe over rev.

Cast Iron heads would be the Premium choice here because of the cooler water flow in a boat head that makes more heat in the combustion chamber desirable.Dart Iron Eagle 180's would be a good choice both economicaly and power wise for this type of motor.

The thing about using a hardened seat in a boat head is that a the fuel demand for a marine motor"especially blown" is much greater than a car.Race fuel pumps must be used to avoid high speed lean out.If you lean a normal head out the valve will tulip and or sink the seat a little when lean out occurs but if that happens to a hardened seat the head is shot,unrepairable and not heavy enough to anchor a boat. 3/8 fuel line will be large enough here.

If you have the clearance under to motor cover to prevent a fire there are true through hull water injected headers available from Basset,Lightning and others.I will look around and mail you some styles and sources.

If you get a chance tell me the prop size and I can tell you how close you are.