305 or 350 How to tell the difference?

[PitchFork]

As I have learned to question everything with my used 1994 boat. It has a Mercruiser Alpha Gen 1 not the Gen 2 it is suppose to have. I now believe it has a 350 / 5.7L instead of the 305 or 5.0L I thought it had. The reason I question it is I found a number behind the port valve cover that reads 3970010 which I believe it translates to a 1970-1980 350 / 5.7L.

Is there any other way besides pulling the heads or valve covers to determine 5.0 or 5.7? The Mercruiser tag on the Starboard side next to the starter is partially missing I can only read the last 6 digits 425436. Also from what I have read the 305 and 350 use the same external components like Fuel Pump, Spark Plugs, Distributor cap rotor, coil, starter, so on......

 

[ken_23434]

Re: 305 or 350 How to tell the difference?

Look for the casting numbers on the block itself. They will be towards the bottom of the block on the side. Look between the exhaust manifold and the top of the oil pan.

Also, some blocks have a number just in front of the head (port side one).

 

[Isaacm1986]

Re: 305 or 350 How to tell the difference?

almost everything on 305 and 350's are compatible with each other. really the only way to tell the difference is to run the block number online. That will tell you what you have.

 

[Isaacm1986]

Re: 305 or 350 How to tell the difference?

According to the number 3970010. You have a 1970-1980 4bolt main 350 5.7 liter.

that is what i came up with.

 

[Matt89GT]

Re: 305 or 350 How to tell the difference?

my block has the same casting number and is a 350 with a 2 bolt main, I just r&r my motor due to loss of oil pressure at 3000 rpm's and above to find the pickup layin in the bottom of the pan and mine is a 2 bolt main. The book my buddy has, stated that the 3790010 casting numbers are used on the 302, 327 and 350's and use both 2 or 4 bolt mains, just sayin

 

[PitchFork]

Re: 305 or 350 How to tell the difference?

I have been using Adult Sticky Service Manual #17 which covers 1993 - 1997 305 / 350. Everything has matched up and been right so far. Is their any other manual that I should be using? Also is the timing the same on 305 / 350 at 8? BTDC no matter the year of the engine?

The reason I ask is because before I first put a timing light on the engine it was at 10? BTDC so I adjusted it back to 8? BTDC and it seems it is a little bit sluggish than it was at 10?? At 10? the boat fired right out of the hole and put a smile on my face at 8? not so much.

 

[Matt89GT]

Re: 305 or 350 How to tell the difference?

people say every engine is different as to what it likes such as 8? or 10? of timing I've heard people say set it where it runs best, but bondo or Don can best answer that for you as to where to set it. Hopefully they will chime in and give you the correct information, just sayin

 

[ken_23434]

Re: 305 or 350 How to tell the difference?

my block has the same casting number and is a 350 with a 2 bolt main, I just r&r my motor due to loss of oil pressure at 3000 rpm's and above to find the pickup layin in the bottom of the pan and mine is a 2 bolt main. The book my buddy has, stated that the 3790010 casting numbers are used on the 302, 327 and 350's and use both 2 or 4 bolt mains, just sayin

That's because the 302, 327 and 350 all use the 4" bore block.

 

[chriscraft31]

Re: 305 or 350 How to tell the difference?

The 305 has a bore of 3.50" I believe, and the 350 has bore of 4.00" if you don't trust castings then you will need to pull a head.

 

[Bondo]

Re: 305 or 350 How to tell the difference?

The reason I ask is because before I first put a timing light on the engine it was at 10? BTDC so I adjusted it back to 8? BTDC and it seems it is a little bit sluggish than it was at 10?? At 10? the boat fired right out of the hole and put a smile on my face at 8? not so much.

Ayuh,... Your motor might support 10?, rather than 8?,...
But, it'll be more susceptible to Detonation....
Especially if the fuel filter loads up, or some other fuel restriction occurs...

It's a SBC,... You can tune it "by the Book",... or use your Own parameters... Your call....
The Hotter you time it, the Quicker it Burns...for awhile anyways....

Buyin' a 305,+ gettin' "Stuck" with a 350,..?? I fail to see a Problem with that...

 

[zbnutcase]

Re: 305 or 350 How to tell the difference?

The 305 has a bore of 3.50" I believe, and the 350 has bore of 4.00" if you don't trust castings then you will need to pull a head.

305's have a 3.750 bore. NO need to pull a head the block casting number WILL tell you what you have.

 

[PitchFork]

Re: 305 or 350 How to tell the difference?

Buyin' a 305,+ gettin' "Stuck" with a 350,..?? I fail to see a Problem with that...

Hope this is the case still searching but it looking more like I got a 350.

Above the Oil Filter the stampings are:
137 N
WR
010

010 is also on both sides of the block behind the engine mounts.

I found I think WR stands for 1969 350 a lot older engine than I tought I bought but at least its well maybe a 350. Not sure how to translate 137N?

 

[Bondo]

Re: 305 or 350 How to tell the difference?

Hope this is the case still searching but it looking more like I got a 350.

Above the Oil Filter the stampings are:
137 N
WR
010

010 is also on both sides of the block behind the engine mounts.

I found I think WR stands for 1969 350 a lot older engine than I tought I bought but at least its well maybe a 350. Not sure how to translate 137N?

3970010

Ayuh,... It's a 350cid, 5.7l motor...

 

[deves3000gt]

Re: 305 or 350 How to tell the difference?

Not to hijack this thread but what sites are you guys looking at to find this info. Only resone i ask i to would like to find out this info on my engine but dont know were to look online for it.

ps not bad buying a 305 and getting a 350

 

[Bondo]

Re: 305 or 350 How to tell the difference?

Not to hijack this thread but what sites are you guys looking at to find this info. Only resone i ask i to would like to find out this info on my engine but dont know were to look online for it.

ps not bad buying a 305 and getting a 350

Ayuh,.... Chevy casting #s,...