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camshaft selection for 350 chevy economy

R

roysbb

New member
Hello, I am the proud new owner of a 1988 25' Bayliner Trophy / Command Bridge with a 5.7 / Volvo Dual prop for power.
I intend to use it for offshore fishing here in California. I plan to add fuel tank, and try to maximize economy and reliability.

The engine is a 350 chevy with iron heads, it has center bolt valve covers and is carbureted. Is this a first gen small block?

I plan to start stock piling parts to build a new engine for it.

My first thoughts are to start with a core from a 87-88 corvette maybe a L-98 350 TPI with aluminum heads.
My corvette could knock down almost 30 mpg at about 1500 rpm.

How difficult would it be to step up to an LS series engine?

I will be balancing and blueprinting this engine, with new pistons to achieve compression ratio of about 9 to 1

Are there camshafts available designed to maximize economy in the 1400 - 4000 range?
And will they still provide enough power to get this big boat up on plane?

What kind of performance / economy are other people getting with 5.7 and a dual prop?

Thanks in advance, Roy

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Roy:

Welcome to ME.com!

I'm sure Ricardo will chime in and give you his view...he has much more SBC experience than I but here's my two cents...center bolts = newer generation stuff, not early stuff.

The load a boat places on the engine is nothing like that done by a car - the recommendation is to reset your expectations. You don't want a car engine mindset, but more like a worktruck point of view...you will want to maximize your torque curve at your cruise rpm. Based on my limited BBC experiences, for the money, the OEM cams are most cost effective (IOW, a custom ground cam won't gain much). The other item to look out for is internal efficiency - minimize internal friction wherever you can. Finally, mimimize the weight carried in the hull as well as friction created by the hull and you'll get decent economy.

If you want to tweak the engine to max economy, you may want to consider a custom tune and use a MEFI controller but you really need to be careful leaning the mixture down....you don't get too many second chances with a marine engine.
 
Corrosion is the major drawback...if you run closed cooling (w/ a heat exchanger) then its much less of an issue...if you boat in a freshwater environment, vs the ocean, the aluminum is much less of a concern.
 
Hello again,

Are aluminum heads really a problem in a marine build? I have seen iron exposed to salt water start to bleed before my very eyes.
It sure seems there would be less corrosion with aluminum heads. There are aluminum head manufacturers that even sell them with a special marine coating.

My build plan was to use small port (high-velocity) heads with good stainless valves, an aluminum intake, forged pistons for 9 to 1 compression with plenty of quench.
I will balance and blueprint the entire assembly to reduce friction.
I am definitely going with a cam optimized for economy at my cruise RPM, NOT an off the shelf 30 year old marine grind with symmetrical lobes. This is 2014.
I am also considering using Rhodes type hydraulic lifters to bleed off some low end duration.

Since the object is an extremely reliable engine in the marine environment, I have decide carburetion is the way to go, and an ignition that doesn't need a full 12 volt to start.

I just can't get my head around the idea that cast iron would be a better material for the heads and intake.
I know that I will pull this engine and refurbish again within 4 or 5 years.

Anybody out there with aluminum heads and/or aluminum intake manifold on their ocean going boat? Fresh water cooled? How have they lasted?

Thanks again for your input - I am listening - is this really the consensus?
 
From an OEM perspective, the Aluminum is not cost effective....If cost isn't a concern and you understand the risks, then by all means, use them....the weight savings won't hurt....same for the money for the cam...as far as consensus goes, just go around to the local marine shops and ask them how many boats they can take you to, today, that have major aluminum components....

Second on the carb choice...it will also allow you to dial in the air fuel mixture if you want to spend the time.
 
Mark is correct. We want torque, and lots of it.
If you stay with the 3.480" stroke of the 5.7L SBC, the best method to achieve torque is via a good tight quench in the chamber.

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roysbb said:
The engine is a 350 chevy with iron heads, it has center bolt valve covers and is carbureted. Is this a first gen small block?
No... the first gen SBC was introduced in 1955 as a 265 cu in V-8 engine.
And gues what..... it incorporated a flat top piston that offered a Quench Effect! :D

It wasn't until the early 70's that GM screwed this all up with the full dished piston.

Are there camshafts available designed to maximize economy in the 1400 - 4000 range?
First of all, marine engine loads are substantially different from that of automotive. The loads are continuous and heavy.
Operating at 1,400 rpm may be OK, because the boat will be at or near "Hull Speed".
Anything above that rpm until you reach planing attitude rpm, will over-burden the engine, and your fuel economy will suck!

So... basically we have two fuel efficent speeds.
Hull speed.... and planing speed.
Planing speed or planing attitude is best when just above what's require to get the hull on top of the water.


What kind of performance / economy are other people getting with 5.7 and a dual prop?
Your Duo Prop drive is your best asset here.
Click to expand...

roysbb said:
What are the disadvantages of aluminum heads in a marine environment?
In order to use aluminum cylinder heads, you'll want a closed cooling system to keep a PH balance.
The aluminum cylinder heads are excellent at heat obsorbsion, and will allow for a tad bit more on the Static C/R.
Click to expand...

As for forged aluminum pistons.... take a look at today's Hypereutectic pistons. We've along way with alloys and the process.
The Keith Black pistons that you linked us to in your other thread, are a high silicone Hypereutectic.

As for camshaft profile, I'd first make your piston, C/R and Quench Dimension selections...., and then contact a company such as Comp Cams or any good Camshaft Company.
With your data, they will be able to make a suggestion.

.
 
Roy, another thought......
Are you planning to begin with a later cylinder block that would be capable of roller cam followers?
That would be a plus in my opinion!

I believe that you also mentioned General Motors Vortec cylinder heads in your other thread..... Yes/No?

My personal recommendation for some Dos and Don'ts for the SBC marine build:

no no full dished pistons
no long connecting rods and short skirt pistons
no high top ring landings
no large degree overlap cam profiles

LCQ style piston if Vortec heads are used
D dished style piston if non-Vortec cylinder heads are used
.038" to .040" quench target


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