What can I do to get a 305 (898) to preform as good as the old 351 OMC

[vi]

Hi I am beginning to worry that that the 305 I mistakenly thought was a 350 won"t cut it pushing my 20' Marlin. I am getting ready to do the OMC to Merc swap with an outdrive that came out of a similar size and year boat. Am I having a 305 phobia? When I took the 305 out of my 68 Belair and replaced it with a 350 it was a different car . Any opinions? Should I try to add the vortex heads and a 4bbl, I don;t usually need to kick in the secondary's on the 351. I could be worrying to much but I did the stringers and floor and plan on keeping the boat. I appreciate any input!

 

[Silvertip]

Re: What can I do to get a 305 (898) to preform as good as the old 351 OMC

The switch from the 305 to the 350 in your car increased power because -- well -- you had 45 more cubic inches and depending on "what" 350 you used, probably had 75 or more HP. Therefore, the same logic applies to the 305 vs the 351. If you want a performance increase, sell the 305 and buy a 350. 350's are readily available and even a new crate engine is not a budget buster in the grand scheme of things.

 

[Bondo]

Re: What can I do to get a 305 (898) to preform as good as the old 351 OMC

Should I try to add the vortex heads and a 4bbl,

Ayuh,... That's a nice improvement, but it's still short 45cid...

As the ole sayin' goes,... There's No replacement for Displacement....

 

[haulnazz15]

Re: What can I do to get a 305 (898) to preform as good as the old 351 OMC

Agreed with the above. The 351W had more cu. in. and more torque, which is what gets you out of the hole. I'd go with a 350 if it were my boat, as I've never been a fan of the GM 5.0 (305), especially the early versions. The 327 and 350 were much better motors.

 

[picklenjim]

Re: What can I do to get a 305 (898) to preform as good as the old 351 OMC

I'd be more concerned about the OMC to Merc swap. Have you checked out what it is going to cost? You going to glass in and recut the transom or get a conversion plate? I know last I seen the plates were around $900. Is the boat worth it?

 

[vi]

Re: What can I do to get a 305 (898) to preform as good as the old 351 OMC

nope I'm gonna take a shot at it my self. I had help but did 90% of the work when I redid the rotted transom and stringers 4 years ago.
I agree no replacement for the missing ci, but I guess this is what I have and it is complete. I was looking for a ford powered replacement but... The setup came out of a Wellcraft same size.

 

[thumpar]

Re: What can I do to get a 305 (898) to preform as good as the old 351 OMC

I agree with others. We (my friends) have always called the 305 a turd motor. I would rather have a 4.3 than a 305 because the power is close and you gain fuel efficiency. The 350 is a good motor and interchangeable with a 350 externally.

 

[etracer68]

Re: What can I do to get a 305 (898) to preform as good as the old 351 OMC

The BIG BLUE bottle comes to mind, and hope the lower end of the 305 holds. BLUE BOTTLE (NOS) finds the weak link fast.

 

[scoflaw]

Re: What can I do to get a 305 (898) to preform as good as the old 351 OMC

I agree with others. We (my friends) have always called the 305 a turd motor. I would rather have a 4.3 than a 305 because the power is close and you gain fuel efficiency. The 350 is a good motor and interchangeable with a 350 externally.

Agreed, your fathers 305 was a turd, todays MPI vortecs have some giddyup, and good on gas. No fan of 6's

 

[riskibusiness]

Re: What can I do to get a 305 (898) to preform as good as the old 351 OMC

Assuming the 351 is based on the ford version. It will automaticly be an improvement on the Chevy. LOL. Sorry guys I'm an old MOPAR guy and Chevy stuff makes my skin crawl. Couldnt resist a chance to take a stab at a bow tie.

 

[John_S]

Re: What can I do to get a 305 (898) to preform as good as the old 351 OMC

Go for a 350 vortec 4brl and be done with it.

305 vortec heads can be hard to find, and depending on year of the 305, pistons may need to be changed to keep compression in line. In the end, a 305 vortec 4brl would have close to a non-vortec 350 4brl HP, but still lacking some in the torque dept.

 

[Howard Sterndrive]

Re: What can I do to get a 305 (898) to preform as good as the old 351 OMC

When I took the 305 out of my 68 Belair and replaced it with a 350 it was a different car

are you sure a 305 came out?
the 305 wasn't produced until almost a decade after your Belair rolled off the line.

maybe it was a 283.

305 had a bad rap in cars because it was first introduced in the late 70's and thus was laden with pollution controls and wimpy camshafts
blame the government, and the era, not the engine
305 is a really good boat engine... a good engine in a car too with the right cam

Some of those late 80's 2155 Bayliner Ciera aft cabins went 50mph with the 305 4V.

 

[joewithaboat]

Re: What can I do to get a 305 (898) to preform as good as the old 351 OMC

I would never start with a 305 on purpose, but don't throw stones at it. They have a bad rap mostly because they were used in the smog era as mentioned. All of the hot rod type magazines and cam companies have done 305 build ups over the years. They easily obtain 325 to even 400 hp with all of the typical bolt ons... roller cam, roller rockers,better intakes,bigger carb, good heads etc.
Marine exhaust and a friendly cam will limit you..... but 300 hp should not be hard at all. Knowing exactly which heads and cam you currently have will be of the most important things to check first. Google "305 vortec build ups".

On the flip side if you are talking 1hp per c.i. which is your "typical" hopped up "small block", 50 more cubes is 50 more H.P.

Good luck! Happy wrenching!

 

[pevaguy]

Re: What can I do to get a 305 (898) to preform as good as the old 351 OMC

Hi I am beginning to worry that that the 305 I mistakenly thought was a 350 won"t cut it pushing my 20' Marlin. I am getting ready to do the OMC to Merc swap with an outdrive that came out of a similar size and year boat. Am I having a 305 phobia? When I took the 305 out of my 68 Belair and replaced it with a 350 it was a different car . Any opinions? Should I try to add the vortex heads and a 4bbl, I don;t usually need to kick in the secondary's on the 351. I could be worrying to much but I did the stringers and floor and plan on keeping the boat. I appreciate any input!

Most likely your '68 Belair had a 307 which was basically a 283 bore with a 327 stroke. It wasn't an impressive engine. But the 302ci. was a 327 bore with a 283 stroke and a real screamer in the Z28 Camero.

 

[nwcove]

Re: What can I do to get a 305 (898) to preform as good as the old 351 OMC

a mild cam, plane the heads, upgrade the intake and ignition.....it will wake yer 305 up, without to much risk of breaking the bottom of the motor. ( short of finding a good 350, its the cheapest way to make more hp.....other than spray, (nos)

 

[vi]

Re: What can I do to get a 305 (898) to preform as good as the old 351 OMC

Thanks all! Will there be problems with a 350 (if I find one) working with the Gen 1 drive ?

 

[greg82255]

Re: What can I do to get a 305 (898) to preform as good as the old 351 OMC

Thanks all! Will there be problems with a 350 (if I find one) working with the Gen 1 drive ?

Nope - that drive is rated for 300 hp. You could always build a 383 if you really want a rocket ship!

 

[Bamaman1]

Re: What can I do to get a 305 (898) to preform as good as the old 351 OMC

It sounds as if you bought a Mercruiser 198 (and outdrive), which is based on a 305 engine. You're last 305 experience was when you replaced a car's 305 engine with a 350 c.i., which was much more powerful.

You're asking if the 198 Mercruiser in a 20' boat will perform adequately?

The answer is that yes, the Mercruiser 198 will push the boat, however not as well as the original Ford engine.

How do you run the boat? If you run the boat aggressively, used heads and a 4 barrel/and intake would be an improvement--if the price is reasonable. I wouldn't suggest going into the engine lower end on such an old engine/boat.

It's going to be tough enough just changing the outdrives over to Mercruiser parts--including rebuilding the transom. With I/O's it's just too easy to put good money after bad money--and spend too much on them.

I/O's are great the first 8 or 10 years, but it's then time to dump'em. Bellows and running gear maintenance is just too frustrating.

 

[joewithaboat]

Re: What can I do to get a 305 (898) to preform as good as the old 351 OMC

I/O's are great the first 8 or 10 years, but it's then time to dump'em. Bellows and running gear maintenance is just too frustrating.

I have a 16 year old, 19 foot, 4.3v6, Mercruiser alpha 1 I/O that runs as well as any new boat and is pretty darn dependable. So YMMV. You must be a clamp on Guy ?

 

[haulnazz15]

Re: What can I do to get a 305 (898) to preform as good as the old 351 OMC

I have a 16 year old, 19 foot, 4.3v6, Mercruiser alpha 1 I/O that runs as well as any new boat and is pretty darn dependable. So YMMV. You must be a clamp on Guy ?

Agreed. He must've had some bad experiences. Most I/O's don't have a whole lot of "bellows and running gear maintenance", otherwise they wouldn't be as popular an option as they are. By bellows has only been replaced about 4 times since we've owned the boat (close to 20 years) and is only replaced due to my limit on rubber fatique, never a leak or a tear. The "running gear" for us has never been more than oil changes and general engine maintenance as well.