383 build requirements

ejnichol

Petty Officer 2nd Class
Joined
May 28, 2002
Messages
131
Giving some serious thought to replacing my 5.0 GXi in 22 ft boat with a 383 motor. Looking for pump gas as fuel, reliability and the inherent greater torque the 383 comes with.
Trying to simplify my engine system by going back to carb so no more high pressure pump issues and leaving behind Volvo Penta ECM suuport issues

The shop who does work for me does about 50 i/o engine change outs a year and 'seems' pretty well versed on basic requirements for a 383. At first was going with 5.7L but i heard some opinions on here to just go on to a 383 'stroker'.

The builder says either go with a 600 cfm Holley or a Quadrajet but its up to me.

My first question is relating to oil capacity and do I need an oil cooler? What little I see on it is I need minimum 5.5 - 6 qt oil capacity.

Your thoughts greatly appreciated. Thanks Eric
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,958
You will need closer to 700 cfm.

LCQ style pistons. 0.041 quench
 

ejnichol

Petty Officer 2nd Class
Joined
May 28, 2002
Messages
131
So a qjet would work. Think they are there on cfm. The holley he could just order one in that cfm.

I'll ask him on what style pistons he's using.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,958
There hasn't been a new Q-jet for over 35 years.

I personally like Holley carbs. The Edelbrock has been mediocre at best based on my own personal experience.

My 350 came from VP with a 715cfm Holley when it was new back in 1988. VP used the Q-jet on lower output motors. However the carb choice is yours

Back to the motor. You need to have a complete plan before you start.

What do you use the boat for. Are you looking for a lot more top-end to go really fast or a whole bunch of torque down low for watersports? Each build will be different to support one need or the other

Are you assembling the motor yourself, or paying to have it assembled?

Are you sticking with stock manifolds, or aftermarket?

Exhaust thru the drive or thru-hulls?

Do you boat in fresh water or salt water?
 

ejnichol

Petty Officer 2nd Class
Joined
May 28, 2002
Messages
131
What I want is a motor with more power overall and durability/reliability. The 5.0 is a little anemic but is a decent(reliable) and with big 4 blade it moves my 22 ft with some authority. Prior boat was 21 ft SeaRay with '96 5.7 Brv1. Significant difference with felt and actual power, though it was only rated at 260 hp I believe. It always had a very subtle light knock after a near rated wot run so I know these stock motors will blow even if kept below redline.

60-75 % percent of my running would be towing watersport and and remainder lumpy activities ie cruising with the wife and in laws with 10% being 3500 - 4500(or near rated wot whatever new motor is) rpm runs

If I'm on inland waterway going from Swansboro to south of cherry point and want to go 40 - 50 mph for 15 mins as its boring stretch. Don't want a build that can't stand this and leave me dead in water. I boat in fresh water 95 % of time.

So to summarize I want a all around performer that's build to stay together.

Through drive exhaust as my hearing is damaged from too much noise.

At this point someone else will build. I have successfully rebuilt a volvo car engine years ago and have some class time at local CC in engine building. If I had a lift to r/r engine I would build for the challenge and stimulation.

The shop is obviously proposing a budget build now but he installs marinized builds from a local race engine builder. I got interested in this as they had changeouts going on regular basis, budget build with changeout I could handle the $$ and the owner I work with is pretty sharp. I can afford more and it will cost more after reading so much about this online. I will go with stock to save on $ where it doesn't diminish durability. Having the highest output is secondary to durability.

Had my boat just in there for drive r/r new gimbal, alignment check, new fuel supply lines and misc others things. Sorry for novel
 
Last edited:

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,958
My only issue with teh GM crate motor is the mediocre cam, -0.020 deck height and 4-valve relief cast pistons. which leaves a bit of power on the table.

for about the same price you can build one with a fatter torque curve and a bit more top end using the correct parts

and that is starting with brand new parts you buy from GMPP, Comp Cams, and Competition Engineering and assemble yourself.

either will run flat-out for 15-20 minutes or longer without any issues.

talk to your local builder if that is your choice. however a roller block, vortec heads cut for higher lift cam and modified for better valve seals, a Scat crank and rods set up for floating pins, D-shapped 12cc dished piston from speedpro or KB, coated clevite bearings, XM264HR or XM270HR K-kit, Felpro MLS head gaskets, Medium rise air-gap intake, 1-1/2" carb spacer and a good performing 700 CFM carb and you have close to 400-420 flywheel hp in a solid marine build that will last right up to the point of non-winterization.
if starting with a used truck block (too much rust in a boat block), make sure to zero deck, and align hone the mains

The stock manifolds, thru-drive exhaust will knock off about 15-20hp.

I would run a heat exchanger if you ever look to boat in salt water just because its the right thing to do.
 

ejnichol

Petty Officer 2nd Class
Joined
May 28, 2002
Messages
131
What about buying a short block assembly from a reputable engine builder and have my shop add vortec heads, push rods, rockers intake, carb, wtr pump, distributor, accessory drive for ps, and alt. etcc. Thinking of a strategy that may simplify build and minimize chance for errors at least in the shortblock construction and component quality.

What is the situation regarding the small block base block regarding 2 bolt vs 4 bolt main bearings. I was reading where it looks like 4 bolt are fairly rare with most now are 2 bolt at least from what able to use for remanufacturing. Is using two bolt main bearing a issue?

The shop I'm talking to takes a used block vats it and magnaflux for cracks and bores it out. I bet it would be 2 bolt main bearing.
 
Last edited:

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
12,077
Ayuh,..... Brand new, from yer local GM dealer,.....
ohh Bondo now there ya go, giving me ideas....
that looks great
is the cam OK for marine use?
what about the head gaskets and core plugs?
Lol It would probably blow up my old Cobra drive, which I'm surprised is still working just fine but a V8 will fit my boat, the engine mount pads are long enough and already there....
....but....it's only money......ha ha.....
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,958
Is using two bolt main bearing a issue?

The shop I'm talking to takes a used block vats it and magnaflux for cracks and bores it out. I bet it would be 2 bolt main bearing.
2-bolt will be fine in a boat.

regarding the used block. if you are going to stroke it, make sure to clearance it before all the other machine work and after the mag test. this is where you can save money if you do it yourself.

remember to zero deck (helps with quench) and align hone the mains (because the block will not be true unless you do this step)

I would also spring to do a full balance job if you want to run at WOT for really long periods of time. aftermarket pistons will be within 2-3 grams. GM has a tolerance of closer to +/- 25 grams
 

ejnichol

Petty Officer 2nd Class
Joined
May 28, 2002
Messages
131
Is that a typo GM has a tolerance of +/- 25 grams between pistons?? or is that 0.25 grams between pistons. That like an ounce

When you say clearance your talking about the grinding done to bottom piston bore for connecting rod to cleared at end of stroke.

Your knowledge on this subject leaves me in kindergarten just based on vocabulary alone. I appreciate you replying to this thread.
 
Last edited:

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,958
Is that a typo GM has a tolerance of +/- 25 grams between pistons?? or is that 0.25 grams between pistons. That like an ounce
+/- 25 grams. as in 0.88 ounces as in a big discrepancy on the slugs in a stock GM bottom end.

My last Wiseco pistons were 1 gram spread between all 8
 

ejnichol

Petty Officer 2nd Class
Joined
May 28, 2002
Messages
131
Scott can truck/car gm short block assemblies be used in fresh water marine build with brass freeze plugs installed?
Are aluminum blocks and heads to be avoided.?
Are flat top pistons with only the two valve relief cut the best design to use for a 383?
 
Last edited:

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,958
For decades, all marine motors are iron truck motors with brass core plugs

If you want to run aluminum, you need a heat exchanger

D-shaped LCQ is the best followed by flat tops. Depends on how you build the motor. For low end torque, or high end rpm
 
Top