302 to 351 upgrade for Donzi 16

[donzidan007]

I'm thinking of rebuilding my 302 why the leg and bell housing are off is it worth up grading to 351 will it make much difference at the moment I'm getting 54 mph with gps with a not so good prop and bell housing shaft that's getting fixed

[Donzi_Dude]

your exhaust location will not be the same(not to say it wont work). if i was going to the trouble i would use a 408 stroker.


i think a 400HP 347 would be a gas in a 16.

[mattyboy]

the 351 is taller and as dd said exhaust is one issue hatch clearance is another. the 351 fits but you might need change things like flame arrestor, and the distributor cap. the front motors mounts may need to be address mainly how they attach to the motor. i think they used a different setup on the 351, I know they used a few different setups on the 289/302. my 302 has a plate/stand that bolt to the timing chain cover i didn't want to take a chance and have to mess with the mounts in the boat so I stayed with the 302 and had it worked on.

[wrussellw]

I changed my '67 16 from a 302 to a 351. The height difference required a hatch modification because of the exhaust. I put tear drops in to accommodate it. I see low sixties on GPS.

[mattyboy]

my 351w fit without any hatch mods but it was rigged by Holman Moody

[ClassicFanatic]

I consider doing the same thing to my C16 93'.

It has a OMC Cobra 5.0 (302) and as far as i know all the "marine-parts" are interchangeable with a 351w. I am tempted to stroke it up to 408, but i think the little Donzi will work good enough with a 351w with 650 Edelbrock and a Edelbrock Performer.

Hope I don't have to space out the engine hatch...

[mattyboy]

yes most parts can be reused , new intake and dist. maybe some new exhaust hose the 351 is wider and taller so you will need to see how much clearance you have now with the hatch . the 351 is 2 1/4 inches wider and 1 1/2 inches or so taller same length so motor mounts should not be an issue. will probably need a bigger prop not sure if they made a different gear ratio for the 5.0 and the 5.8 the ratio in the omc was determined by a combo of the upper and lower gears so when all is said and done you might need to jump an inch of pitch or two .

good luck keep us posted

[ClassicFanatic]

yes most parts can be reused , new intake and dist. maybe some new exhaust hose the 351 is wider and taller so you will need to see how much clearance you have now with the hatch . the 351 is 2 1/4 inches wider and 1 1/2 inches or so taller same length so motor mounts should not be an issue. will probably need a bigger prop not sure if they made a different gear ratio for the 5.0 and the 5.8 the ratio in the omc was determined by a combo of the upper and lower gears so when all is said and done you might need to jump an inch of pitch or two .

good luck keep us posted

Thanks, Mattyboy.

Yesterday I bought a complete OMC 5.8 1989 engine. The carb is out of tune and I will order a Edelbrock 1409 600 and Edelbrock Performer intake. I also consider buing gt40 heads, but I'm not sure if I'm better of with the P's (will there be a sparkplugg-clearence-issue with GT40 og GT40P?). What about using the 5.0 head? The valves have the same diameter and it looks like it would ad some needed CR to the 351w?

I also consider new Pertronix ignition, but I will wait to see if it will clear the hatch.

[mattyboy]

Thanks, Mattyboy.

Yesterday I bought a complete OMC 5.8 1989 engine. The carb is out of tune and I will order a Edelbrock 1409 600 and Edelbrock Performer intake. I also consider buing gt40 heads, but I'm not sure if I'm better of with the P's (will there be a sparkplugg-clearence-issue with GT40 og GT40P?). What about using the 5.0 head? The valves have the same diameter and it looks like it would ad some needed CR to the 351w?

I also consider new Pertronix ignition, but I will wait to see if it will clear the hatch.

I used a breakerless electronic mallory dist. on mine. any ford powered donzi I have seen the spark plugs are a bitch. The gt40 heads will have a thermactor holes that need to be plugged

[mattyboy]

the P have straight plugs not angled which may cause clearance issues with the risers

[ClassicFanatic]

the P have straight plugs not angled which may cause clearance issues with the risers

In my head it sounds great that the plugs sit straight. With angled plugs (like it is today) it's hard to change the plugs.

[ClassicFanatic]

http://www.correctcraftfan.com/forum...0p-valve-train

Check out the second picture from TRBenj. Looks very good with the GT40P's.

[mattyboy]

Yes that looks better on a boat where you can get get in and take a pic like that Just remembering my 16 with my short stubby arms any thing lower was an issue the runners on the PCM are part of the body of the riser wonder if that makes a difference too

Do you have all that other omc stuff on your risers the harness plug and electronic stuff?

[mattyboy]

been looking at the different designs for Ford SB manifolds each are a bit different as far as water channel and runner config

osco are different from PCM from Barrs the one that may be an issue with the P heads would be the GLMs they have a water bar under the runners so I guess you have to take a look at your risers and see what kind of clearance you have under the runners

[ClassicFanatic]

Update on my 302 to 351w upgrade.

Next week I will drop the engine. Based on a 1989 OMC Cobra 5.8 (351w). Edelbrok Perfoermer intake. Edelbrok 1409 Marine carb. BARR exhaustmanifold and risers.

I will make this setup work properly before I install GT40P's.

Estimated HP?

Will upload pictures after engine install.