Repowering-Upgrading Twins

Lubak572

Petty Officer 1st Class
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Jan 4, 2018
Messages
235
I am going to be buying 2 new long-blocks this week finally. Still trying to decide to upgrade. I have an 2001 Four Winns 298 Vista with twin Volvo Penta 5.7 GSI PEFS motors and 1.95 DP-SM duoprop drives. The motors are 280 HP TBI with MEFI 3 ECU. Just had injectors sent out to Witchhunter Peformance (cleaned/tested) and rebuilt throttlebody and fuel pumps. I plan on keeping OEM intake and TBI and having MEFI Bob remap ECU for 1 of the following long-blocks.

VP 5.7 GXI 320 HP
https://www.michiganmotorz.com/350ci-volvo-penta-base-engine-320hp-1999-2015-p-10888.html

GM Marine 6.2 Stroker 340 HP
https://www.michiganmotorz.com/377ci-stroker-base-marine-engine-2000-current-replacement-p-545.html

GM HT383 323 HP
https://www.chevrolet.com/performance/crate-engines/small-block-ht-383

I also plan on running Hardin Marines Seaward series exhaust and adding Freshwater cooling. What do you think?
 

Bondo

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Apr 17, 2002
Messages
70,468
Ayuh,..... Option #2 would be My choice,...... ;)

Comes with a forged steel crankshaft; heavy duty rods; and forged aluminum pistons,

Hmmmm,.... It would be interestin' to see the profile of the piston crowns,......

GM's traditional full dish, or bein' forged, maybe a D-dish,..??.......
 

Lubak572

Petty Officer 1st Class
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Jan 4, 2018
Messages
235

alldodge

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Mar 8, 2009
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40,582
Yes, fresh bore, pistons, rings etc

You know, if you were in fresh water, you could rebuild your old block and build a 383
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
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Jul 23, 2011
Messages
47,306
You can build new 350 or 377 yourself for about $4k. About same cost as reconditioning your current block and heads

New gm block is $750
New vortec heads $650
New scat rotating assembly $900
new comp cam k-kit $900
new felpro gaskets $150
Oil pump and dizzy drive $70
brass core plugs $11
New stamped steel oil pan $120
Hardware $200

Modifying the heads for screw in rocker studs and for cam lifts higher than .420, about $200

Check with your local engine builder on rebuilding yours
 

Lubak572

Petty Officer 1st Class
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Jan 4, 2018
Messages
235
Current motors are 18 years old, I am the 4th owner. Boat was originally sold in Florida so had salt. That is why I want new/different motor. I didn't price machining/assembly cost locally, but based on other posts i think it would cost more than buying a long block. Now I am running into time issues so just want to get this done.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
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Jul 23, 2011
Messages
47,306
Current motors are 18 years old, I am the 4th owner. Boat was originally sold in Florida so had salt. That is why I want new/different motor. I didn't price machining/assembly cost locally, but based on other posts i think it would cost more than buying a long block. Now I am running into time issues so just want to get this done.

just talk to your local machinist and get pricing. some times they have really good deals.
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
So jealous that you guys have such options available to you. Amazing.
 

BRICH1260

Lieutenant
Joined
Jul 6, 2011
Messages
1,342
I purchased a new Michigan Motorz engine last fall, VP 320 HP. While the new motor is not yet installed in the boat, I was pleased with the purchase and shipping process. They seem to know what they are doing.
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
11,802
So jealous that you guys have such options available to you. Amazing.

The ubiquitous Chevrolet small block used to power millions of cars here. Still being built for marine and industrial use.
It started in 1955, 265 cu in, then went to over the years:
283
305
307
327
350
400
also destroked to 302 cu in for Trans Am racing sold that way in the original Z//28 Camaro

What you can have when the government doesn't over-regulate and tell you what you have the right to drive. A good thing for all Americans to remember.
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
Agree with that....fuel cost and the road tax such engines would result in....just don't make them viable here. The preference for most is smaller displacement and more advanced wizardry to make up the horsepower. Jeez, my bmw diesel car has about as much HP as my V8 MPI with a cam and exhausts....and it's only a 3.0....prefer the V8 any day though.
 

Lubak572

Petty Officer 1st Class
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Jan 4, 2018
Messages
235
Got my Exhaust....new 6.2's are on the way!
 

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alldodge

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The exhaust have a low rise, you sure they are high enough to keep reversion down?
 

Lubak572

Petty Officer 1st Class
Joined
Jan 4, 2018
Messages
235
Yes I have to raise it a hair about a 1/2 inch. We had them side by side at the shop. I will make it work.
 
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