Thoughts on repowering....383?

SeaHare

I currently have about 1100 hrs on the ol' 350's..  They still run great and are virtually trouble free. However, im starting to prepare myself for the time they decide to give up the ghost.  Whether its this year, next year, a few years....who knows.
Anyway, when the time comes im thinking about building these 350's into 383's. I have read till my eyes bled on what it would take so im pretty familiar with engine talk..  So for one, would it be worth it to spend the extra money and build 383's or am I opening a can of worms i dont want?

Current engines - 2001 5.7's
880 roller block
906 vortec heads

reneechris14

If you talking about redoing the original motors the cost is not much more then a complete rebuild. Different crank and some machine work to the block. You will need to change computer or injectors, you said 01 not sure if that's a throttle body. I just you have to weigh out the extra 50hp is worth it.

PickleRick

Out of curiosity, what's the cost for a new or reman  383 long block from Michigan motorz or other reputable builder vs what you'd pay locally? I don't know how good your local shops are.   Michigan motorz has a great reputation for being a quality marine engine supplier.  

Put all your accessories and bolt on parts from your motors onto the new blocks.  They can use your serial number to tell you exactly what motor would be a direct fitment.

Add fresh water cooled if not already equipped. 

Then sell your good running blocks for a pretty penny while they are good runners.  Stick some boat bucks back into your bank account.

You'll likely need to use that cash to pay for new props to account for added power.  


I wouldn't say its opening a can of worms if you are keeping the boat for the foreseeable future.  Its not worth the extra cash if you're just going to flip the boat.


Isn't every 10 hp added 1 mph faster roughly on a gas motor?

I'm not sure if the ecu needs a reflash for the 383 upgrade, @J3ff can chime in. He has one in a 270.

We just repowered  a 6.0 in a Chevy truck with a newer motor/50 some odd rated more hp 6.0 gm crate motor and didn't require a new tune but thay may be different with your application. 

Handymans342

Who would you get to reflash a computer??

Michael T

@PickleRick yes, 10-12HP will yield 1 MPH depending hull etc. @SeaHare....won't cost much more to go 383 and you will get a lot more bottom end depending on the cam you choose. Would highly recommend. You might save on fuel too as they will not be working as hard.

SeaHare

I guess i should add my engines are carbed, thunderbolt V ignition. 

Currently have 2bbl intake and carb so i assume i would also need to go to 4bbl carb and intake for 383

This is on an FV310

I could care less about speed...my current 30mph cruise is fine.... im just looking for that extra oomph when i have a boat load of people and full gas to get up on plane

A 383 long block from Michigan Motors is about $6k... i was hoping to be around $3-4k to build my own...

PickleRick

Handymans342 said:

Who would you get to reflash a computer??

No idea,  I'm still trying to find someone to write me a tune for a LBZ duramax with the turbos ditched for a whipple super charger.

PickleRick

SeaHare said:

I guess i should add my engines are carbed, thunderbolt V ignition. 

Currently have 2bbl intake and carb so i assume i would also need to go to 4bbl carb and intake for 383

This is on an FV310

I could care less about speed...my current 30mph cruise is fine.... im just looking for that extra oomph when i have a boat load of people and full gas to get up on plane

A 383 long block from Michigan Motors is about $6k... i was hoping to be around $3-4k to build my own...

The 2bbl vs 4bbl carb is a debate that goes back further than hardtop diesels vs other crap people call a boat😂.  Got any real old school carb guys in town that can set you up with some marine carbs? 

Even if it didn't give much more power on top I'd think running on the small venturi at lower rpms would lower fuel consumption vs the 2bbl

PickleRick

Alswagg said:

A Marine Vortec 383 with the correct carburetor, Holley 4160 750 cfm will net at minimum 330 HP.   This is a very reliable set up.  I would highly recommend.   

Sounds like a carb GM would recommend!!!  

Since he's rebuilding what cam would you recommend? 


I've heard some stock gm vortec truck cams are even and improvement over the marine cams.

Michael T

Have to be careful with some truck cams as there can be valve overlap causing water ingestion in a marine application. 

SeaHare

From all the online reading, it looks like D-dish pistons that mirror the vortec heads are recommended. Around a 9.1 static compression ratio.  Also there alot of talk about building a "quench' engine. with .043 quench.  I beleive quench is determined by decking, pistons and head gaskets. 

PickleRick

Alswagg said:

Never use an automotive cam in a marine application. Never never never just stop thinking about it 

I always thought the vortec/roller cam set up allowed for a little more aggressive cam vs the old flat tapper.  When I was looking at rebuilding my 350 with vortec heads I looked hard at a summit  14097395 cam which is automotive cam but very popular for 383 marine builds. I've seen them come across ebay for sub 120 bucks. 

Its been a while since I looked at the specs but the stock  vortec 5.7 cam didn't look far off from the marine 5.7 cam.  The price was far off between the two.

PickleRick

Correct. Over lap will cause water intrusion.  Look at the specs of the cam i posted and tell me what you think.   Seems a huge step in performance over a stock mercruser cam and well within safe limits of over lap especially with a 383 build in mind. 

PickleRick

Alswagg said:

It’s all about valve overlap with a marine cam. This is nothing new.  An automotive cam will create a negative pressure in the exhaust and will actually suck in water and create a hydro lock situation 

I stand corrected.  After searching  the part number I found that the 14097395 cam is a stock GM ramjet  350 crate motor cam and 383 cam found in stock gm crate motors.   

It is also a stock replacement for mercruiser  without  the marine mark up price tag.  

Crane actually makes some slightly more aggressive cams for maine applications. This one stuck out to me because of both price (affordable) and great torque numbers from 2500 rpms up. 

Also no valve trian mods needed to run this cam on stock vortec heads/roller block.   Budget build for those of us who don't want to have to drink natural light all summer long. 

PickleRick

SeaHare said:

From all the online reading, it looks like D-dish pistons that mirror the vortec heads are recommended. Around a 9.1 static compression ratio.  Also there alot of talk about building a "quench' engine. with .043 quench.  I beleive quench is determined by decking, pistons and head gaskets. 

Talk to your engine builder first before buying parts.  Make sure what you buy they are comfortable and familiar with using. 

https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.baylinerownersclub.org/forum/current-topics-gc6/technical-discussion-gc12/47265-383-quench-piston-compression-gctid411407&ved=2ahUKEwi26Y_l29zyAhXVQzABHQkSAdoQrAIoAXoECBAQAg&usg=AOvVaw2YVZB0g94SHtY7_TeRlj3s

This thread goes in about compression,  piston style and how some builders may vary on opinion.

SeaHare

Thanks for that link PickleRick...i have previously read that and found it very interesting..

I certainly would use a marine cam, im aware of inversion with auto cams.i just havent really looked at any yet and dont really know what to get

So would the flywheel from the 350 be able to be reused? What about initial timing the 383.. i know my 350's are 8 or 10*BTDC... Would it be the same for the 383?

I was thinking for a carb using edelbrock marine 600 or 750 cfm and edelbrock performer intake 4bbl

Pretty sure my 2bbl mercarb wouldnt cut it

PickleRick

I had the same holly on a 5.7 that Alswagg recommended.  Once rebuilt she was flawless.  One thing I'd do if I was installing in a fresh water cooled motor is ditch the cast iron  intake for aluminum.   Im also a fan of the stock marine quadrajet. They are 650cfm.

I don't see why you'd want replace your flexplate, the shop will ask for  it when they check the balance of the crank.   So long as it's not damaged. 

I don't remember timing off the top of my head,  nearly everything I run now is diesel. 

8 degrees initial timing is what I remember but my 5.7 was old thunderbolt bolt ignition and thats been 3 years ago .