is it a 350 or a 305?

[jsmith3102]

I have a sea ray mercruiser engine and the party I bought the boat from said they replaced the block but what I don't know is if they replaced it with a 350 or a 305. How can I tell. I do have the head off. Can I measure the size of the cylinder? The top end suggests a 305 but that is no guarranty.

 

[45Auto]

Re: is it a 350 or a 305?

350 has a 4.000" bore, 305 has a 3.736" bore.

 

[jsmith3102]

Re: is it a 350 or a 305?

Went and checked and it is a 350....
Thank you a bunch!!!
Based on that what is my Hp?? with a 2 bl carb (mercarb)..
If I switched to a holy 4bl carb what would the gain be?
1994 engine components..

 

[45Auto]

Re: is it a 350 or a 305?

The early 90's 350 2 barrels were 210 HP. Swapping to a 4 barrel carb and manifold without doing anything else to the motor might gain you 20 HP. That would be about a 2 MPH gain in top speed. I doubt if you could tell the difference if you had 2 equal boats side by side, one with a 2 bbl and 1 with a 4bbl.

Lots of threads on here about hopping up the 350, do a search and you can read for days! Hopefully WCA_TIM will see this and give you a little input. He's a straight shooter and will have some good info on modifying a small block.

 

[chiefalen]

Re: is it a 350 or a 305?

The 4 barrel will suck alot more gas.

Depends on the size of the boat, and pitch of the prop how mush faster the top end will be.

20 hp in my boat made a world of difference, i went from a 120 to a 140.

 

[Bondo]

Re: is it a 350 or a 305?

Ayuh,....

I can't quite agree with ya on this 1 45auto,....

The 350 with the rottenchester 4bbl. was 260hp....
Same with the Merc./ Weber/ carter clone 4bbl. carbs,....

I Know you'll see an Honest Improvement in both acceleration,+ topend by swapping up to a 4bbl. from a 2bbl. carb.....
But,....
A Holley would be my Last choice to go with....
Mercruiser has Never used 1 before, so you'd be fabbing Everything for it.....

I've got a couple copies of the Merc./ Weber carter clones,....
If I were to have to Buy a new carb,...
It would be the Edlebrock Performer, just because it is Also a carter clone....
Ayuh,.. I Love the simplicity of'em....

 

[MikDee]

Re: is it a 350 or a 305?

I agree with Bond-o, The stock 350 4bbl has been 260hp for as long as I can remember, the newer engines might be rated lower, just because it's prop hp, but I'm sure they're the same net hp, if not even more hp then that.

 

[Mkos1980]

Re: is it a 350 or a 305?

I agree with the posts above. Edelbrock carb all the way. Run that with a Merc Magnum Bowtie 4bbl intake and your all set!

 

[John_S]

Re: is it a 350 or a 305?

From Merc Service Manual #17 which covers the early 90's SBC V8's: (all hp rated at prop)

5.7L 2brl: 210
5.7L 4brl: 235
5.7LX/350Mag 4brl: 250

 

[45Auto]

Re: is it a 350 or a 305?

Knew it was less than 260 HP, probably mixed up the 210 from the V6. From Merc Manual #17, the mid 90's 2 bbl and 4bbl base motors (5.7L) were 235 HP. Doesn't even list a 2 bbl for 94 though.

Shows the '96 2bbl at 235 HP and the 4 bbl at 250 HP.

Be interesting to look up some old test data if it's still out there.

If you have the $500 or so for a new manifold and carb it definitly won't hurt anything to put it on! Depends on how much you want to spend on a 15 year old Searay and what you expect to gain from it. You could probably make more difference leaving 1 cooler or 1 fat chick out of the boat ....

 

[45Auto]

Re: is it a 350 or a 305?

LMAO!! Looks like we were typing at the same time, Imported_John_S!!! I didn't bother to look past the first couple of pages of the manual, figured I just remembered the 210 wrong. Looks like you looked a little deeper into it than I did.

Anyway, looks like about a 15 HP difference.

 

[John_S]

Re: is it a 350 or a 305?

The Online version of the SM is not as current as the printed manual I own. The 2brl version is indeed 210hp. The 4brl L version appears to be a low-profile intake with a 600cfm Weber, while the LX and Mag had the high-rise dual plane and 750cfm Weber.

Note: I thought the LX had a low-profile intake, but have seen posts from a number of owners that indicate the high-rise version was used. ???

 

[MikDee]

Re: is it a 350 or a 305?

IMO, Switching to a 4bbl carb would make a nice boost in power. It's all a big numbers game "It's 6 of 1, or half a dozen of another" as the expression goes. My 79' SeaRay 350/260hp must have been crank rated hp, and the later model 350/235hp, are prop rated hp. In fact, that's probably a conservative rating, because the later model engines had 4" risers, instead of 3", and hotter electronic ignition, instead of points, plus it looks like a (hard to believe 9.3:1?) comp. ratio, compared to the then common standard 8.5:1 ratio.

In fact, I believe the old style 350 2bbl was rated at 230hp.
Plus the 351 Ford (Merc.) was rated at 225hp 2bbl, & 250hp 4bbl back then.

 

[krisnowicki]

Re: is it a 350 or a 305?

What is the difference between the 5.0l and 5.0lx that is 15 hp? is it the 4bbl v 2bbl?

 

[Limited-Time]

Re: is it a 350 or a 305?

What is the difference between the 5.0l and 5.0lx that is 15 hp? is it the 4bbl v 2bbl?

Short answer is yes. L= 2bbl, LX= 4 bbl. at least in 96 when I bought my current boat.

 

[Fishermark]

Re: is it a 350 or a 305?

I have a crate engine from Mercruiser in my boat - granted, it is a 2003 model, but just out of curiosity I checked - it is a MCM5.7liter and is rated at 250 HP. It only has a two barrel carb on it. It makes me wonder where they get some of these numbers. (THEY being the factory - not the above posters. )

 

[MikDee]

Re: is it a 350 or a 305?

I have a crate engine from Mercruiser in my boat - granted, it is a 2003 model, but just out of curiosity I checked - it is a MCM5.7liter and is rated at 250 HP. It only has a two barrel carb on it. It makes me wonder where they get some of these numbers. (THEY being the factory - not the above posters. )

I doubt the heads, valve sizes, or cam design (except being a newer roller type cam) changed, from the early 350/260hp motors, to the 1990's series 350's. Or if they did, they only got better, but I'm guessing that your 2003 engine is a Vortec design Mark, with late model (better) Vortec heads, and probably factory roller rocker arms as well, even if nothing else changed, I bet that's why you have that much hp with a 2bbl.

 

[John_S]

Re: is it a 350 or a 305?

In '98 and above the 5.7L 2brl is rated for 250hp at prop. As Mikdee mentions, the additional hp is in the heads (vortec).

 

[180shabah]

Re: is it a 350 or a 305?

Ditto - the vortec heads made the power difference(approx. 30php).
FWIW - they were introduced in '96, but not all '96's have them.