Concerns, swapping cracked 305 for 350

[eztiger12]

Hi

Wondering if anyone can help......

I just pulled out my Mercruiser 305 2 bbl out of my 1995 Bayliner 2355 because of a cracked block. Prior to pulling out the engine, it was in great working order despite the crack. No water in the oil.

I'm now thinking of replacing my 305 (1994 - 1 piece rear seal ) with a 350 to get a little extra horsepower.

Correct me if I'm wrong, I understand that I can get a 350 long block and take all the tin off of my 305 on put it on the 350.

One of my concerns is the intake .......will the 305 intake fit on the 350?
If so, how would the 2 bbl carb perform on the 350 or would that even work?
Would it defeat the purpose? putting the 305 intake and carb on the 350.

Would it be simpler just sticking to a 305 instead.

Any input would be appreciated.....thanks.

 

[redjmp]

Re: Concerns, swapping cracked 305 for 350

Yes everything will swap over as long as you get a post '86 block.
It should make more hp even with the 2 bbl.
If you really want more hp get the right size vortec heads and a new intake manifold and 4bbl carb on either the 305 0r 350.
A stock roller cam setup can be had cheap as well and will give you even more power.
If you want the most you can get then you need a 350 stroked to a 383 and you need the electronic fuel injection but it gets pricey.
It will get you around 400 ponies which is almost twice what you have now.

 

[krisnowicki]

Re: Concerns, swapping cracked 305 for 350

if you do this you will need a outdrive stronger then an alpha which is what you have right? That out drive shouldn't use more then 300 hp .... So if you get a 350 all the tin will work and your outdrive will be ok however, if you get a hyped up 350 300hp or more you may want to consider a new outdirve or a shower for your current one.

 

[eztiger12]

Re: Concerns, swapping cracked 305 for 350

To answer the question about the outdrive, yes it's an alpha one with a 165 ratio.

I'm not looking to really sup-up the 350......nothing over 300hp,just the stock 230 hp or 290 hp ...I don't want to change the out drive.

Like I mentioned before, my major concern is swapping the intake from the 305 onto the 350............

Will I encounter any problems.....will the 2 bbl carb provide the 350 demands.

Where can I get another intake with a 4 bbl carb for this application?
What can this run me .....price wise?

Thanks once again......

 

[John_S]

Re: Concerns, swapping cracked 305 for 350

Options:

1) 305 non-vortec longblock - easiest to swap, lowest cost, but no gain in hp
2) 305 vortec longblock - need new intake and 4brl carb - 250hp at prop
3) 350 non-vortec 2brl - 35mm (305) vs 43mm (350) different 2brl - 210hp at prop
4) 350 non-vortec 4brl - need new intake and carb - 250hp at prop
5) 350 vortec 4brl - need new intake and carb - 280hp at prop

All the 350 options will give you more torque at lower rpms - more important if we are talking a heavy boat or cruiser, which I think your 2355 would qualify at.

New intake/carb/arrestor: assuming you are not raw water cooled in salt or brackish water : $500-$700.

Options 1 & 3: your current prop and gear ratio can remain same.
Options 2 & 4: you will probably need to change prop or gear ratio.
Option 5: you will probably have to change both prop and gear ratio.

If your Alpha is long in the tooth, and you would be replacing it soon (consider a SEI replacement) you can get the ratio you want, which would make #5 probably your best bet.

 

[eztiger12]

Re: Concerns, swapping cracked 305 for 350

Thanks a lot Imported_John_S

That's a great explantation, I don't think it could be any clearer, it really helped.

Yes, The boat is only in fresh water (No salt).

I'll probably stick to options #1 & #3 and look into option #4 since I have a few months to do the work.

When you explain option #3......"need to mod carb -venturies and jets different - 210hp at prop".......would it be possible to give more information on how to go about this........

Thanks

 

[John_S]

Re: Concerns, swapping cracked 305 for 350

"When you explain option #3......"need to mod carb -venturies and jets different - 210hp at prop".......would it be possible to give more information on how to go about this........"

I just checked the online, earlier version of my #17 service manual, and see that the 305 carb is 35mm vs 43mm of the 350. That tells me you would need to change carbs, not just parts. The venturie and jet change might be between 2brl vortec and non-vortec 350's, but would want to check that.

Once you are into buying a new or rebuilt carb, you might as well go 4brl.

Here is the online service manual. Its 20+meg, so you want a high-speed connection. Look at section 5B.

http://www-alt.mercurymarine.com/mnetdata/Service/Cruiser/Servmanl/17/17covr2.pdf

 

[erikgreen]

Re: Concerns, swapping cracked 305 for 350

I just went through this same swap - I'd go with a 350, preferably vortec, if you can.

I already had a four barrel and intake, but I looked around and there are lots of them available. Most people here recommend an edelbrock intake and carb. Make sure you get one that favors the 0-1500RPM range at least, or the entire 0-5000 range. Most car intakes are designed for high rpms.

Other than the RPM range, there's not a lot of difference between the marine and car intakes and carbs, so most chevy small block intakes/carbs will work for you. Edit: most intakes will, but you do need a MARINE carb. Didn't mean to make it sound otherwise.

Also, did you guys all know that SEI is going to offer a Bravo replacement sometime soon? They're testing the early production units now according to their web forum.

Erik

 

[John_S]

Re: Concerns, swapping cracked 305 for 350

Just be careful, you do need a marine approved/rated carb. While the differences are minor, they are VERY important. The Edelbrock 1409 600cfm Marine carb is highly recommended on this site, especially when it comes to being calibrated out of the box for sbc. and if it isn't perfect, it is easy to tune, and $300 or so, price tag doesn't hurt.

 

[krisnowicki]

Re: Concerns, swapping cracked 305 for 350

i have an a used intake and four barrel carb off my boat. It is an e-brock carb and intake. It is used but i am getting rid of it pm me .... It is off a 350

 

[eztiger12]

Re: Concerns, swapping cracked 305 for 350

Hey Thanks erikgreen & Imported John

This tread is a hell of a lot better than any manual........
I going to be on the look out for a Edelbrock 1409 600cfm Marine carb.......
What kind and make intake would you people recommend?

I got to check what Krisnowicki is offering....

 

[John_S]

Re: Concerns, swapping cracked 305 for 350

Need to know if you are staying with 87-95 heads (Edelbrock model 2104) or 96-up vortec heads (Edelbrock models 2716 or 2116). Given your larger boat, would stay with Performer series of Edelbrock.

 

[eztiger12]

Re: Concerns, swapping cracked 305 for 350

Yes, I do want to stay with 87 - 95 heads......otherwise it will get too complicated with the alpha One ....(don't want to change the gears).

I'll be extremely happy just getting a couple of horses more with the 350..........I know of boats like mine that even have 4.3L in them.

At the sametime, I would like to keep the cost down as much as possible...

Imagine, when I bought this boat (1st boat), it was to be in tip top working order.

 

[John_S]

Re: Concerns, swapping cracked 305 for 350

A couple of horses you would never know the difference. The 350/4brl will be noticable, but not earth shattering. Enjoy.