Can I replace my 1994 Mercruiser 5.0 2BBL (305) with a 1998 5.7 2BBL (350) ?

[Marko_f1]

I have a 1994 Bayliner 2452 with a 5L mercruiser/alpha 1 gen 2 outdrive which went on me (likely head gasket) and I am wondering if can swap it out with a 1998 5.7L while keeping the same outdrive.

I had the boat for 2 years and it always felt under powered (a lot of people with the same boat/engine agree) and since my engine is toast, I think it's a good opportunity to upgrade it to the 5.7, especially since I found a good deal on a complete engine with only about 400 hours, mine has over 1,400 for comparison. A guy told me the gearing ratio would have to be changed while my research online tells me otherwise.

If somebody is familiar with this and especially if you've done it, is it as simple as pulling the 5L out and throwing the 5.7L in or are there other things that must be done to make it work?

Thanks for your help in advance!

 

[jimmbo]

It should be an easy swap, as both engine are SB Chevys, Yes the Gear Ratios are different. In theory a few more inches of Pitch to the Prop would work out to be the same. but for reasons I have never figured out, the performance was never as good as what would be achieved with correct ratio.
You will notice a Real Improvement in regards to the Hole Shot, as the 305 was always weak regarding Torque.

 

[stresspoint]

you should be fine , i am with jimmbo on the gear ratio change as a prop change is sufficient to change the RPM up the top and load when under acceleration ,
iv hotted up many outboards and never yet have i changed a gearbox ratio to get the performance figures i have aimed for. just a prop change has always done the trick.
i have recently hotted up a 4.3 from stock to around 250 hp and the 1.8 ratio drive with a prop change to give top speed gets me close to 60mph and a cruise @ 40 mph without over revving the little motor , right where i want it.

think of the 5.7 as a hotted up 5.0 , you are not gaining a big heap of HP but you are going to be gaining a lot torque so with a bit of finessing with prop tuning you will be very happy with a 5.7 , and good thing is its a direct bolt in mod..

ready for the xsputs opinion .

 

[Lou C]

Agreed if I were doing an engine replacement on a boat with a 5.0 Chevrolet I'd for sure go with a 5.7, it is the exact same physical size and weight but has much more power potential, also make sure to go with a 4bbl intake and carb, don't cheap out with a little 2 bbl carb. For carbs, you can use a Quadrajet (hard to find good ones but an excellent carb), Edelbrock (easy to rig if the boat was a Merc boat due to being the same as the Weber 4bbl) or Holley which is everywhere in the aftermarket. If you can get a later model engine with the roller tappet cam and Vortec cyl heads that will give you close to 300 hp and a lot more torque than the little 5.0.

 

[jimmbo]

When picking your carb for the motor, make sure you chose a Carb that is USCG certified, not just any old carb, you find. Same goes for Fuel Pumps, Distributors, Alternators, and Starters.

 

[QBhoy]

you should be fine , i am with jimmbo on the gear ratio change as a prop change is sufficient to change the RPM up the top and load when under acceleration ,
iv hotted up many outboards and never yet have i changed a gearbox ratio to get the performance figures i have aimed for. just a prop change has always done the trick.
i have recently hotted up a 4.3 from stock to around 250 hp and the 1.8 ratio drive with a prop change to give top speed gets me close to 60mph and a cruise @ 40 mph without over revving the little motor , right where i want it.

think of the 5.7 as a hotted up 5.0 , you are not gaining a big heap of HP but you are going to be gaining a lot torque so with a bit of finessing with prop tuning you will be very happy with a 5.7 , and good thing is its a direct bolt in mod..

ready for the xsputs opinion .

Jeez. You must have had some serious pitch on her to have her running like that. 25” upwards anyway I’d guess ? With a low slip

 

[nola mike]

Always been curious as to why the 5.0 even exists. What is the purpose of that motor when there is a 5.7? Real question.

 

[jimmbo]

Cause some people don't want/need a 5.7 liter, and a 4.3 is too small.

Given the choices of a 4.3 and 5.0 making, say 200hp, I would take the 5.0 on a heartbeat.
Same goes for a 5.0 and a 5.7 making 260hp, again the larger one.

My Boat was supposed be made with a 260hp 5.0 FI engine, It instead got a 260hp, 5.7 2bbl carb engine(which wasn't an Engine Option). When I saw it in the dealer showroom, I went in to the Owners Office, and we worked out a deal.
I have went up against identical Boats, that have 5.0 FI engine, mine out accelerated them by a good margin, and had a higher top speed. As far as I know it was the only hull that got a 5.7.

 

[QBhoy]

Always been curious as to why the 5.0 even exists. What is the purpose of that motor when there is a 5.7? Real question.

Wondered this myself. Especially with some of the carb older versions. At one point there was a AQ205 4.3 at the same time as a AQ211 5.0 !

 

[jimmbo]

As I said above, I would take a 5 liter over a 4.3, even if the 4.3 had a few more horses. Torque is more important in a Boat.

 

[nola mike]

As I said above, I would take a 5 liter over a 4.3, even if the 4.3 had a few more horses. Torque is more important in a Boat.

Right, so skip the 5 and go straight to the 5.7. We weren't talking about the 4.3 at all.

 

[jimmbo]

Someone else was... I was responding to them

 

[stresspoint]

the 5.0 is a good motor , a couple of things i like about them is:
#1, they are robust , in stock form they don't make enough power to hurt themselves
#2 , i have seen a few making big power and almost bullet proof with only bolt on performance bits and a properly dialled camshaft.

a 5.0 can and will suffer the exact same fatal problems as a 5.7 if not maintained , only difference is the 5.0 will hang in there longer because of the low power output.
jimmbo to save from thread jacking , PM me and i will link you to my restoration thread with info on my 4.3.

 

[Scott06]

I have a 1994 Bayliner 2452 with a 5L mercruiser/alpha 1 gen 2 outdrive which went on me (likely head gasket) and I am wondering if can swap it out with a 1998 5.7L while keeping the same outdrive.

I had the boat for 2 years and it always felt under powered (a lot of people with the same boat/engine agree) and since my engine is toast, I think it's a good opportunity to upgrade it to the 5.7, especially since I found a good deal on a complete engine with only about 400 hours, mine has over 1,400 for comparison. A guy told me the gearing ratio would have to be changed while my research online tells me otherwise.

If somebody is familiar with this and especially if you've done it, is it as simple as pulling the 5L out and throwing the 5.7L in or are there other things that must be done to make it work?

Thanks for your help in advance!

Absolutely worth doing the upgrade. Thats too much boat for a 5.0.
it should be drop in as stated you may need to go up in pitch if it was previously propped to the upper end of wot rpm. I did a 4.3 to 5.0 swap kept same drive ratio went up in pitch 2” .
given vintage differences between your two engines as long as you keep the accessories with the new engine should be ok. The new engine willbe a serpentine belt where your original non vortec engine will have V belts … could run into fit issues if mixing up parts.
going from non vortec to vortec should be nice hp increase. Is the new engine a 4 bbl. If not might be a nice upgrade and get you close to 300 hp.

 

[Marko_f1]

Thank you everyone for your very helpful and informative replies!

So the 1998 5.7 that I found is a complete unit, meaning its got all the bolt-on's/accessories (alternator, carb, exhaust & intake manifolds etc.) so it's ready to go as soon as it's in the boat.

 

[Marko_f1]

Absolutely worth doing the upgrade. Thats too much boat for a 5.0.
it should be drop in as stated you may need to go up in pitch if it was previously propped to the upper end of wot rpm. I did a 4.3 to 5.0 swap kept same drive ratio went up in pitch 2” .
given vintage differences between your two engines as long as you keep the accessories with the new engine should be ok. The new engine willbe a serpentine belt where your original non vortec engine will have V belts … could run into fit issues if mixing up parts.
going from non vortec to vortec should be nice hp increase. Is the new engine a 4 bbl. If not might be a nice upgrade and get you close to 300 hp.

I made my mind up and just made a deal with the seller, so 5.7 it is! It's got a 2bbl not a 4bbl unfortunately. Is it a matter of simply replacing the intake manifold/carb or are there other things needed to convert it to a 4bbl?

 

[jimmbo]

Make use to get a Marine Carb, I like the Holley 650 Spreadbore

Holley FR-80552 650 CFM Spreadbore Marine Carburetor - Factory Refurbished

This is an official Holley Performance Factory Refurbished Carburetor.

www.holley.com

also available in factory fresh

I would also recommend an Intake that was cast with marine usage in Mind.

Search results for: 'marine intakes' - Edelbrock, LLC.

Edelbrock is the most respected name in performance! Since 1938, Edelbrock has manufactured its core products like Carburetors, Cylinder Heads, Intake Manifolds in the USA for quality and performance.

www.edelbrock.com

 

[Scott06]

I made my mind up and just made a deal with the seller, so 5.7 it is! It's got a 2bbl not a 4bbl unfortunately. Is it a matter of simply replacing the intake manifold/carb or are there other things needed to convert it to a 4bbl?

Manifold, carb, and throttle bracket are needed.
have you seen the new engine run , easy to run on the ground. Would do a compression check on it before paying

 

[Scott Danforth]

I made my mind up and just made a deal with the seller, so 5.7 it is! It's got a 2bbl not a 4bbl unfortunately. Is it a matter of simply replacing the intake manifold/carb or are there other things needed to convert it to a 4bbl?

Yes

 

[QBhoy]

I made my mind up and just made a deal with the seller, so 5.7 it is! It's got a 2bbl not a 4bbl unfortunately. Is it a matter of simply replacing the intake manifold/carb or are there other things needed to convert it to a 4bbl?

I think just with the 2 barrel, you’ll find a world of power and difference in comparison. Especially down low. Prop change will now be required, as you’ll know too. Exciting times.