Intake manifolds

[oldsub86]

What is the most common sort of intake manifold on a small block chevy v8 in an i/o? Single plane, dual plane etc. Do the same sort of principles apply as in an auto engine? Normally the dual plane intakes are better at lower rpm in a street car.

My reason for asking is that I am collecting parts to put together an engine to drop into the boat come spring. The original is still in place and my intention is essentially to have a reasonably complete engine to swap in. I have a 350 short block assembly and will pick up some heads shortly. If I pick up an intake and an oilpan etc then i am close to having enough engine to swap without changing over much apart from the carb, distributor starter etc.

Randy

 

[picklenjim]

Re: Intake manifolds

Dual plane by far. Same principles as in a car. If running a single plane you need all the parts to compliment it, cam,heads,carb,exhaust.

 

[TilliamWe]

Re: Intake manifolds

Dual plane all the way.

Since you are a car guy, I caution you not to make the mistakes that most car guys make. Don't put in a high lift/high duration camshaft, thinking you're going to get 5500rpm out of it. You want to build for torque, and keep your horsepower max at 5000rpm or even a tad below. The outdrives like it better that way. Also, no doubt you'll hear that you have to have open exhaust. Well, it won't build any power by itself, but it does help, in conjunction with heads and exhaust manifolds. Just remember, the stock exhaust manifolds are restrictive to say the least. Good luck.

 

[jtybt]

Re: Intake manifolds

Not giving engine year, just make sure you match up engine with flywheel and oil pan. Marine oil pan is larger than auto. Some marine oil pans don't have windage tray built into the oil pan.

Try to get your hands on a book about marine engines. I like 'Small-Block Chevy/ Marine Performance' by Dennis Moore. It'll give you great insight to marine builds.

 

[Alpheus]

Re: Intake manifolds

If you dont have the heads and intake yet,consider using Vortec heads and intake. Its a direct bolt on and all you need is self centering lifters if they dont come with the heads. Its a 20-30 HP increase over stock...

 

[Bondo]

Re: Intake manifolds

Ayuh,... I totally Agree with those above,....
A Mid-rise dual plane manifold on Vortec heads will be a Great package....
If you want to Really build some Horsepower, the stock exhaust manifolds are the 1st thing that gotta Go...
And,...
Charlie's Right, Dennis' book is pretty much the Bible on building Big Horsepower SBCs for boats...

 

[wire2]

Re: Intake manifolds

I replaced the stock intake on my 350 I/O the first year I had it, partly for the increased flow capability, but also for the weight reduction. The stocker was 68 lbs, the Holley I replaced it with was 18 lbs.

The following season I fabricated a set of double wall stainless headers to let the extra air out again. Shaved another 78 lbs.

For anyone wondering, I found it noteworthy that switching from outdrive exhaust to thru hull at speed netted only a very minor increase in power. At 4400 rpm, going from prop to open bumped it to 4500, with almost no discernable acceleration. That attests to the efficiency of the water stream sucking exhaust thru a prop.

 

[oldsub86]

Re: Intake manifolds

OK, good to know. I sort of assumed that the dual plane was the way to go. I am not looking to create monster power - just trying to put together something that will last for a while.

I maybe should have acquired a newer block than I did based upon some recent reading. The newer blocks tend not to wear like the old ones did.

However, I have already acquired a 350 4 bolt main block from the early 70's. It has been rebuilt in the past and run some but the current wear seems minimal so I plan to put some new bearings in and a new cam and timing chain set up and carry on. Will likely just hone the cylinders and put some new rings in too.

The vortec heads sound like a plan.

Randy

 

[Alpheus]

Re: Intake manifolds

Just make sure you have the block proffessionally cleaned and magna fluxed to make sure you are starting out with a good block. Mic everything out to make sure they are in spec mains,rods,bore,etc. Change your freeze plugs and dont use an automotive water pump...