Which OMC 350 Exhaust Manifolds Do I Need?

[BowTieGuy]

I am in the middle of swapping engines and need to know which exhaust manifold I need to buy for my 350 OMC because it didnt come with any. The casting number on the back of the block is 3970010 and the serial on the starboard side below the head is 65000C.
I have been shopping around and there are a few different styles. This is an OMC Stringer style setup. Would it be possible to make my own set using shorty headers and plumbing the water into the headers?

One more thing. This motor has a HEI style distributor on it. I have heard that these are not approved for marine use. Why? Can I simply swap the caps and rotor out to the marine stylet to make it marine grade?


I attached a file that shows where the exhaust from the manifolds are supposed to exit

 

[gbeltran]

Re: Which OMC 350 Exhaust Manifolds Do I Need?

No, do not think about making a set of headers work, that is a recipe for a fire. You will need whatever exhaust was used on the stringer setup, any sbc exhaust will bolt to the heads, I don't know how hard they are to find for that specific application. No cap will make the hei marine friendly. Many people seem to use them but in a covered engine compartment they are not the best choice. If you must stick with it Davis Unified Ignition makes a marine version. If not a marine spec distributor for a small block is easy to fine.

 

[Howard Sterndrive]

Re: Which OMC 350 Exhaust Manifolds Do I Need?

need proper marine exhaust.. not sure the original 350 OMC log style manifolds will clear those valve covers - might have to go with tin...not sure
most center riser manifolds will clear those valve covers

I don't recall any V8's exiting the intermediate on the side like that, so probably have to get creative after the riser with marine exhaust hose and piping/elbows anyways, so center riser manifolds might be the easiest to work with

also can't tell from your pic, but does that intermediate have a second exhaust duct on the starboard side? not all intermediate housings were capable of dual exhaust

if no starboard duct, not going to work for a V8

if it does have the second duct, you need to investigate whether or not they both have exhaust shutters... every 4 banger intermediate I have messed with had the 2 ducts but only one shutter in port side.. you don't want your starboard 4 cylinders hydrolocked full of water first trip out
I guess OMC wanted to save $6 by only putting a starboard shutter in V6/V8 units
marine ignition a must

 

[BowTieGuy]

Re: Which OMC 350 Exhaust Manifolds Do I Need?

No cap will make the hei marine friendly. Many people seem to use them but in a covered engine compartment they are not the best choice. If you must stick with it Davis Unified Ignition makes a marine version.

Why is the HEI not acceptable? Whats the difference? How much are the marine ones?

need proper marine exhaust.. not sure the original 350 OMC log style manifolds will clear those valve covers - might have to go with tin...not sure
most center riser manifolds will clear those valve covers

also can't tell from your pic, but does that intermediate have a second exhaust duct on the starboard side? not all intermediate housings were capable of dual exhaust

if it does have the second duct, you need to investigate whether or not they both have exhaust shutters... every 4 banger intermediate I have messed with had the 2 ducts but only one shutter in port side.. you don't want your starboard 4 cylinders hydrolocked full of water first trip out
I guess OMC wanted to save $6 by only putting a starboard shutter in V6/V8 units
marine ignition a must

Yes I have dual exhaust ports on the intermediate housing. What is this exhaust shutter you speak of? I have been looking at different styles of OMC exhaust manifolds, and I think I need the ones that exhaust straight out the back like these ( http://cgi.ebay.com/ebaymotors/OMC-...6083386QQptZBoatQ5fPartsQ5fAccessoriesQ5fGear ) or can I get these ( http://cgi.ebay.com/ebaymotors/CHEV...4634157QQptZBoatQ5fPartsQ5fAccessoriesQ5fGear ) and turn them upside down?