5.0 to 5.7 swap Q's

[G_Hipster]

Did some searching on the site, and have a couple questions I didn't see the answers to. One is the intake. Is the 305 2bbl intake suitable for the true vortec heads port size? I'm seeing that 305's and 350's have different drive ratios and possibly compensated by props? Aftermarket lists the same # flywheel for either engine, but I can't find any Merc cross-reference. I'll more then likely have it balanced, but if there's a difference in balance I'd like to start with the right stuff. Cam suggestions for something stockish or close to? Any other pitfalls or suggestions? Thanks for any input guys.

 

[Scott Danforth]

regarding the intake - same. vortec intake is vortec intake as far as the ports are concerned.

however why on earth would you stick with the heavy cast iron 2-barrel setup. if your going to 5.7, go with a marine aluminum intake (with the bronze water passages) and go with a 4 barrel

regarding the drive ratios, not enough prop to compensate, however may not that big of a deal depending on your boat weight.
regarding the flywheel, unless you pull the motor apart, balance the complete rotating assembly, there is no point (as there is no difference between the 305 and 350 unless you jump generations), and the machine shop will laugh at you.

for the cam, depends on what you are running for a motor.

268 degree max duration for wet exhaust on a flat tappet 270 degree max duration for wet exhaust on the roller motors.

now specifically

what year 5.0, what year 5.7. assuming vortec on native vortec spec'd block puts you 1996 or newer. your 1-piece rear main seal, so the flywheel an external balanced flywheel available in any 5.0 or 5.7 liter equipped GM truck, or marine motor

if you run a cam on the vortec heads, you need the valve guides cut down. your machine shop will help

for the cam, the XM270HR would be my choice for stock exhaust https://www.summitracing.com/parts/cca-sk08-417-8/overview/

 

[G_Hipster]

Thanks, yeah the 5.0 is vortec based. The reciprocating assembly would be balanced, and my guy always asks for the flywheel. Plan is to grab an engine from LKQ and go through it. Stock vortecs I think are around .460 ish is max without cutting. 6k lb boat, Not really concerned with top speed etc. I know 4bbl would be better , but I'm not trying get carried away. Vortecs really turn on with a 3 angle, bowl cut/blend , and some nice valves lol

 

[Scott Danforth]

With a 6k boat, I would be building a 383 stroker With a balanced roatating assembly.

Vortex heads work best with LCQ pistons (low compression quench). Basically a kidney shapped dish that mirrors the kidney shaped combustion chamber

 

[jimmbo]

Volvo makes/installs a real nice 4 bbl manifold on it early 2000s carbed motors. As for the carb, I'm partial to the Holley model 4175 650 cfm spreadbore carb. Have used this carb on my 5.7 VP.
One of the reasons for different gear ratios on different HP engines is to be able to utilize a smaller range of prop pitches for a large selection of engines

 

[Scott Danforth]

Volvo makes/installs a real nice 4 bbl manifold on it early 2000s carbed motors. As for the carb, I'm partial to the Holley model 4175 650 cfm spreadbore carb. Have used this carb on my 5.7 VP.
One of the reasons for different gear ratios on different HP engines is to be able to utilize a smaller range of prop pitches for a large selection of engines

I agree. The manifold was cast at Buddy-Barr foundry. I used one on my SBC that I got off of eBay (new)

 

[G_Hipster]

With a 6k boat, I would be building a 383 stroker With a balanced roatating assembly.

Vortex heads work best with LCQ pistons (low compression quench). Basically a kidney shapped dish that mirrors the kidney shaped combustion chamber

383 would be nice, but it's not in the budget for this boat. I have built some quench engines. Assuming you mean 9.5 ish compression. I'll have to check around on marine intakes.

 

[Scott06]

No sense discussing head work and cams if you're going to stick with 2bbl intake. The above mentioned intake, edelbrock performer, with a edelbrock 1409 would work nicely. If you use an edelbrock carb you can use a Mercruiser throttle bracket off a webber 4 bbl to accept the throttle linkage.

What outdrive ratio do you currently have and what prop is currently on it? In smaller boats typically a 5.0 has a 1.62:1, yours may be steeper in such a heavy boat.

I know it goes against the conventional wisdom but when repowering a 21 ft bow rider from a 4.3 to a 5.0 I was able to us the existing 1.81 drive ratio by going from a 19" to 21" prop. Just bought a 22" enertia to try as my WOT was about 4900. I tried it out and was thinking of swapping the drive later, but it works ok for me.

 

[Rick Stephens]

I don't think you could efficiently go to a 383 stroker and use the existing 1.64 drive ratio. Besides, a 5.7L is so easy to set up and would be easy to prop up a skosh on a big boat like that.

 

[G_Hipster]

No sense discussing head work and cams if you're going to stick with 2bbl intake. The above mentioned intake, edelbrock performer, with a edelbrock 1409 would work nicely. If you use an edelbrock carb you can use a Mercruiser throttle bracket off a webber 4 bbl to accept the throttle linkage.

What outdrive ratio do you currently have and what prop is currently on it? In smaller boats typically a 5.0 has a 1.62:1, yours may be steeper in such a heavy boat.

I know it goes against the conventional wisdom but when repowering a 21 ft bow rider from a 4.3 to a 5.0 I was able to us the existing 1.81 drive ratio by going from a 19" to 21" prop. Just bought a 22" enertia to try as my WOT was about 4900. I tried it out and was thinking of swapping the drive later, but it works ok for me.

That's my tendency to get carried away. The shop I use usually does a 3 angle with a throat cut. I'm not 100% sure on the drive ratio. I just bought the boat in Aug. and upon changing the oil for winter, noticed metal in the oil. I wasn't totally unhappy with the 5.0, but I figured a 5.7 would be easier to source, build it mild, and work with what I have for now.

 

[G_Hipster]

I don't think you could efficiently go to a 383 stroker and use the existing 1.64 drive ratio. Besides, a 5.7L is so easy to set up and would be easy to prop up a skosh on a big boat like that.

The boat has a 19 pitch prop on it now, and when we did the sea-trial it topped out at 41/200 rpm(could be the engine IDK). I haven't run it that hard since, but was thinking it's over-propped and a few more ponies and ft lbs from a 5.7 they might play nice.

 

[G_Hipster]

Thanks for the input guys.

 

[Bondo]

The boat has a 19 pitch prop on it now, and when we did the sea-trial it topped out at 41/200 rpm(could be the engine IDK). I haven't run it that hard since, but was thinking it's over-propped and a few more ponies and ft lbs from a 5.7 they might play nice.

Ayuh,.... Yer rpms are low, 'n ya got room to prop up,....

I'm guessin' a 350 4bbl. carb would wake up yer boat, or Efi, or Mpi,...
Not ditchin' the 2bbl. carb, I think, is probably a sin against the boatin' Gods,....

 

[G_Hipster]

Ayuh,....
Not ditchin' the 2bbl. carb, I think, is probably a sin against the boatin' Gods,....

Deep down I know this to be truth, as I hang my head in shame before them:facepalm:

 

[Scott06]

If you're only at 4100-4200 rpms with a 5.0 now, put a 5.7 in regardless of carb choice you most likely will be fine with your existing drive and prop. I wouldn't expect a 5.7 would get you past 4800 with your current set up