305 vs 350 - educate me!

[the man]

i have done some searches- but the search engine does not recognize 3 letter inputs so not much that i have found. probably a subject that is beat to death, so maybe a reference to another thread... ??

i am going to repower a boat i have, with twin something. it had (2) 351s in it in 1973. but here is my question for general purposes beyond this repower: why go with a 305 over a 350? it seems like the 350s are more abundant, and even less expensive, especially if replacing one. gas consumption seems to be related to hp, not displacement... so if a 305 would be enough HP, but a 350 wouldn't be too much, why would i, or anyone, go with the 305 ? are they more durable, or maybe use less fuel at the same hp output? is it just a price issue? why are there so many out there in boats?

thanks in advance

 

[the man]

Re: 305 vs 350 - educate me!

i was going to go with a mercruiser package with bravo 3s- so i thought this was a mercruiser issue- but someone moved it to this forum. oh well! still same questions....

 

[geneseo1911]

Re: 305 vs 350 - educate me!

I can't figure it out either. A 350 is superior to a 305 in every way. It's even lighter. And yet almost every boat you see is a 305. Don't think too hard. If you want a small block Chevy, get the 350 (or 383!) and don't look back.

There's no replacement for displacement. Except supercharging. But that's kinda the same thing.

 

[achris]

Re: 305 vs 350 - educate me!

i have done some searches- but the search engine does not recognize 3 letter inputs so not much that i have found. probably a subject that is beat to death, so maybe a reference to another thread... ??

i am going to repower a boat i have, with twin something. it had (2) 351s in it in 1973. but here is my question for general purposes beyond this repower: why go with a 305 over a 350? it seems like the 350s are more abundant, and even less expensive, especially if replacing one. gas consumption seems to be related to hp, not displacement... so if a 305 would be enough HP, but a 350 wouldn't be too much, why would i, or anyone, go with the 305 ? are they more durable, or maybe use less fuel at the same hp output? is it just a price issue? why are there so many out there in boats?

thanks in advance

Got it right there....

Boat builders want to offer their products at the most competitive price (cheap bastards)... The actual cost of producing a 305 vs 350 would equate to a few cents, maybe... As you've already said, apart from the bore (and hence the pistons), EVERYTHING else is the same.... Even down to the camshaft. And the only difference in the carb is the jet sizes... Same wiring harness, and in most cases, same ignition module...And definitely the manifolds are the same... You might hear that it costs more because of the research costs... I say 'rubbish'...

It's priced on output... more horsepower, more you pay, more money the manufacturer creams off the top...

Same with outboard engines. The Merc 135 and 150 are EXACTLY the same with the exception of the carb size.... But the engine is about $2000 difference....

HTH,

Chris......

 

[thumpar]

Re: 305 vs 350 - educate me!

I would go with the 350. Personally I prefer the 4.3l over the 305.

 

[achris]

Re: 305 vs 350 - educate me!

I would go with the 350. Personally I prefer the 4.3l over the 305.

Agree, but this is a 305 vs 350 thread....

 

[Bondo]

Re: 305 vs 350 - educate me!

i was going to go with a mercruiser package with bravo 3s- so i thought this was a mercruiser issue- but someone moved it to this forum. oh well! still same questions....

Ayuh,.... I moved it because it's about motor differences, not motor/ drive Repairs,...

I agree, the 350 is the only answer,...

 

[HT32BSX115]

Re: 305 vs 350 - educate me!

Yeah. If you can get the 350, that would be the best "bang for the buck"

gas consumption seems to be related to hp, not displacement.

That's true.........(it's called BRAKE SPECIFIC fuel consumption... BSFC and most stock marine engines exhibit similar BSFC)

Understand that you could put a 4.3L, 5.0L, or 5.7L engine in your boat There would be performance differences. (hole-shot and top speed)

But if you ran the 3 of them them side by side at approx the same speed and did the same things (same acceleration out of the hole, loaded approx the same etc) They would all use approx the same amount of fuel. [in the same boat, loaded approx the "same" the 5.7 will not use significantly MORE fuel unless you have a heavy right foot!! [or heavy right hand])

BUT, since you will always want more power out of the hole and slightly higher speed , go for the bigger engine. Understand, if you USE that additional HP, you'll use MORE fuel.........

i was going to go with a mercruiser package with bravo 3s

Well, you could also go to Volvo Penta DUO-Props.....

You said this would be a twin? I would also definitely go to Bravo III's. (it won't be cheap though)

The difference will be spectacular. I did it in my 21ft Four Winns Liberator, removing a single (340 crank hp) Ford 460+ single prop King Kobra and replaced the entire mess with a 330(crank HP) Mercruiser 454+ Bravo III.

There was NO comparison in hole shot between the similarly powered engine/drives. The 454/Bravo III just about beats everything out of the hole.

Tops speed was slightly less with the Mercruiser.

2 identical boats will be slightly SLOWER at WOT with a Bravo III over a Bravo I (3-5mph according to Mercury) I don't think the difference will be all that significant in a cruiser type boat.


Cheers,


Rick

 

[the man]

Re: 305 vs 350 - educate me!

You said this would be a twin? I would also definitely go to Bravo III's. (it won't be cheap though)

yes, it has (had) twin 351s (1973, carburetors) with some older volvo outdrives. i will start a new thread for the outdrive decision when i get there. just trying to take one step at a time. sounds like a consensus- 350s it is. thanks to everyone for all the input.

 

[HT32BSX115]

Re: 305 vs 350 - educate me!

yes, it has (had) twin 351s (1973, carburetors) with some older volvo outdrives. i will start a new thread for the outdrive decision when i get there. just trying to take one step at a time. sounds like a consensus- 350s it is. thanks to everyone for all the input.

1973.


I do hope you understand that repowering most 1973 (Volvo powered) boats will require a transom replacement so you can re-cut the "holes". (or that prohibitively expensive adapter plate that I am not even sure exists any more)

That, coupled with "new" engines and drives could easily make the re-power cost FAR more than the finished product would be worth in any market.

Of course, If you're planning to be "buried" with your boat, it won't matter.

And, you'll want to post any transom, hull, floor, stringer work etc in the appropriate forum....

Cheers,


Rick

 

[the man]

Re: 305 vs 350 - educate me!

1973.


I do hope you understand that repowering most 1973 (Volvo powered) boats will require a transom replacement so you can re-cut the "holes". (or that prohibitively expensive adapter plate that I am not even sure exists any more)

That, coupled with "new" engines and drives could easily make the re-power cost FAR more than the finished product would be worth in any market.

Of course, If you're planning to be "buried" with your boat, it won't matter.

And, you'll want to post any transom, hull, floor, stringer work etc in the appropriate forum....

Cheers,


Rick

yes, aware of this... although a transom "replacement" was not what i was thinking, more like a transom rebuild or repair of sorts. but this is why i am here- to learn what to do. also was thinking of an outboard bracket ... but these are discussions for another thread. i am starting one now and will post link here in a few.

 

[HT32BSX115]

Re: 305 vs 350 - educate me!

yes, aware of this... although a transom "replacement" was not what i was thinking, more like a transom rebuild or repair of sorts. but this is why i am here- to learn what to do. also was thinking of an outboard bracket ... but these are discussions for another thread. i am starting one now and will post link here in a few.

The transom thickness is fairly critical and even with only 1 engine and drive, there's tremendous forces at work on that transom. (double with twins)

You're not just going to be able to "caulk the old holes and drill new ones" PLUS, with a boat as old as you have, you're almost guaranteed to have rot in the transom some place.

Your best bet since you're going from larger holes to smaller ones will probably be a complete transom replacement.

Of course, you'll find out when you "get in there".



Good luck,


Rick

 

[the man]

Re: 305 vs 350 - educate me!

The transom thickness is fairly critical and even with only 1 engine and drive, there's tremendous forces at work on that transom. (double with twins)

You're not just going to be able to "caulk the old holes and drill new ones" PLUS, with a boat as old as you have, you're almost guaranteed to have rot in the transom some place.

Your best bet since you're going from larger holes to smaller ones will probably be a complete transom replacement.

Of course, you'll find out when you "get in there".



Good luck,


Rick

probably a subject for another thread - to be started soon- but this boat is all fiberglass in the transom and is 2" thick. made for strength to begin with. it did start its life with two 351s and did cruise at 45+, so its not like i am introducing something new to the mix. trust me, i will be careful and i always overbuild, so no assumptions here. just gathering info for now. pulling old outdrives out tomorrow- let the party begin! will post in restorations when i get to that.

 

[HT32BSX115]

Re: 305 vs 350 - educate me!

probably a subject for another thread - to be started soon- but this boat is all fiberglass in the transom and is 2" thick. made for strength to begin with. it did start its life with two 351s and did cruise at 45+, so its not like i am introducing something new to the mix. trust me, i will be careful and i always overbuild, so no assumptions here. just gathering info for now. pulling old outdrives out tomorrow- let the party begin! will post in restorations when i get to that.

Well,

if it's a cool boat now, it'll be even cooler when you get it repowered!