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JohnCanoe

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Hi
I found this forum after stumbling onto a thread of Grumpy’s on Chevytalk concerning building a 383. I’m stoked to find a group of knowledgeable guys as I’m planning to build a SBC to repower a ‘76 23 SeaCraft IB. I live in Stuart, FL but I work on oceangoing tugs in the NE, along the East Coast and the GOM. Below is a picture of the project that brought me here. Hoping to have her offshore by 2021.
7F3398CA-4EA3-44E6-B810-D3C24FC9C6FA.jpeg
 
Welcome to the forum from Oklahoma!

When you get ready to begin your SBC build start a new thread and I can run some dyno
simulations with Dynomation 6 if you like.
 
A good question to think about is how much Hp is lost through the Water Cooled Exhaust manifolds on most boats.

Some have Race Headers BBC and Olds 455 Jet Drive boats.

Might be 50-100 Hp less with water cooled ex manifolds.
But needed on most inboard pleasure craft boats.

10 degrees more Exhaust Duration on cam lobe may help.
Old Pontiac Tech.
 
They have flame arrested air cleaners also. Pancake open style and most have a fine mesh flame arrested screen..limit true cfm into engine in theory.
 
Maniacmechanic1 said:
A good question to think about is how much Hp is lost through the Water Cooled Exhaust manifolds on most boats.

Some have Race Headers BBC and Olds 455 Jet Drive boats.

Might be 50-100 Hp less with water cooled ex manifolds.
But needed on most inboard pleasure craft boats.

10 degrees more Exhaust Duration on cam lobe may help.
Old Pontiac Tech.
Click to expand...

She’s an inboard with a v-drive so her thru hull exhaust is less restrictive than a typical I/O’s exhaust but still obviously not as free flowing as a dry exhaust. She’ll be used as an offshore fishing/family fun boat so a dry exhaust system is definitely out of the question. Haha. My first priority in the build is naturally going to be long term reliability but, correct me if I’m wrong, I figured if I build it myself I could get higher quality components and increased performance for close to the same money I’d be paying for a factory marine engine. Besides it just being fun to learn how to and hopefully accomplish building a SBC.
 
JohnCanoe said:
She’s an inboard with a v-drive so her thru hull exhaust is less restrictive than a typical I/O’s exhaust but still obviously not as free flowing as a dry exhaust. She’ll be used as an offshore fishing/family fun boat so a dry exhaust system is definitely out of the question. Haha. My first priority in the build is naturally going to be long term reliability but, correct me if I’m wrong, I figured if I build it myself I could get higher quality components and increased performance for close to the same money I’d be paying for a factory marine engine. Besides it just being fun to learn how to and hopefully accomplish building a SBC.
Click to expand...
There used to be a guy around here that dropped a Pro Built 400 SBC into a Boat like yours. A mild marine spec duty cam with Dart iron Eagle 190 CC intake runner heads. Never seen that boat but I heard it was fast and would run 80+ mph here on the Local Illinois River once on plane.
He then sold the boat and took that 400 ci Sbc engine and dropped it into a 1987 Cutless Supreme. This is about 1994-1995 years. He was 20 miles away in a Famous town of 30,000 people that we street raced at late after midnight.
He had a Sneaky Pete Nitous system plumbed on the underside of the intake.
We spotted the small #4 AN Fuel and Nitous lines and fittings on the rear block China walls coming out.
It was a Fast car and hard to beat !
Turbo 400 Trans with 4.56 gears Posi out back !
ONLY give away it was a 400 SBC was the 8 inch harmonic balancer!

Everyone like 383 SBC but I think 400 SBC is better.
 
Maniacmechanic1 said:
There used to be a guy around here that dropped a Pro Built 400 SBC into a Boat like yours. A mild marine spec duty cam with Dart iron Eagle 190 CC intake runner heads. Never seen that boat but I heard it was fast and would run 80+ mph here on the Local Illinois River once on plane.
He then sold the boat and took that 400 ci Sbc engine and dropped it into a 1987 Cutless Supreme. This is about 1994-1995 years. He was 20 miles away in a Famous town of 30,000 people that we street raced at late after midnight.
He had a Sneaky Pete Nitous system plumbed on the underside of the intake.
We spotted the small #4 AN Fuel and Nitous lines and fittings on the rear block China walls coming out.
It was a Fast car and hard to beat !
Turbo 400 Trans with 4.56 gears Posi out back !
ONLY give away it was a 400 SBC was the 8 inch harmonic balancer!

Everyone like 383 SBC but I think 400 SBC is better.
Click to expand...

I was wanting to start with the Dart SHP SBC and build a 406 and I might still but I’m limited to 400hp by my transmission (even after professional modification) and I thought it kind of felt like a waste of the block’s potential. Replacing the transmission would send me down a modification wormhole I’m not sure I want to enter. Haha.
 
JohnCanoe said:
I was wanting to start with the Dart SHP SBC and build a 406 and I might still but I’m limited to 400hp by my transmission (even after professional modification) and I thought it kind of felt like a waste of the block’s potential. Replacing the transmission would send me down a modification wormhole I’m not sure I want to enter. Haha.
Click to expand...
Is it like an IN & OUT Gearbox?

Read some Inboards are equipped with a Turbo 400 Transmission. They are bulletproof later models with a few Simple mods. Early 1969-1971 best bullet proof stock.

Factory 400 SBC iron block could be used.
1970-71-73 been told best but any year up to 1980 will work.
 
380 Flywheel Hp a good target with all factory equipment intact.
After brute torque.
It possible to get 600 ft/lbs with a Sbc 400 with right cam and have it all in by 5200 rpms.
 
380hp at the flywheel would be great. My goal would be big low end torque as it would rarely be ran over 4000 rpm and what I’d want most is a respectable cruise speed at an economical 3000 rpm. The marine transmission is a Borg Warner model 71C 1.5:1 with a Borg Warner V-drive.
 
JohnCanoe said:
380hp at the flywheel would be great. My goal would be big low end torque as it would rarely be ran over 4000 rpm and what I’d want most is a respectable cruise speed at an economical 3000 rpm. The marine transmission is a Borg Warner model 71C 1.5:1 with a Borg Warner V-drive.
Click to expand...
What octane fuel do you want to use ?
87 octane standard pump gas or 91-93 premium?
 
Couple of different ways to narrow a cam...
Use a short duration like an Isky 256 Mega Hydraulic

Or A 270 advertised with a custom ultra tight LCA & ICA.

Tricky with 87 octane.
Boats drink gasoline fast and 87 octane preferred as its lowest cost to Buy at the Marina and local gas stations.
 
It's gotta idle Ultra smooth also with no heavy lope so spark plugs do not load up at slow cruising speeds in No Wake Zones.
 
Maniacmechanic1 said:
It's gotta idle Ultra smooth also with no heavy lope so spark plugs do not load up at slow cruising speeds in No Wake Zones.
Click to expand...

Yeah, I need it to have low rpm manners. I was originally planning on using premium as I reasoned it’s no more expensive than the REC 90 many people use for their boats but I figure I can save a bit using 87. I really don’t need the extra performance the higher compression would afford me and I was hoping 87 friendly compression would help with reliability and longevity. I know cheap(er) gas will be great when it comes to long offshore runs. Haha.
 
Im sure we can add useful info once we get a bit of detailed info on your budget,
\ what you are working with, an used parts,your skills and if you can do some or all the work,
except for the machine work, most guys must have a local shop do, ETC.
be sure the cam selected is designed for a marine exhaust, as some automotive cams,
will suck water into the engine through a below water surface exhaust design.
 
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