120hp merc i/o upgrade

[drgaul]

i am restoring a 1969 rienell 16ft i/o merc. i am a capable with autos but- i want to replace my locked up 120 4 banger with a 305cid chevy. i here all kinds of things,will the out drive fit? is the gearing different and will not work? any ideas on engine mounts? what about through the hull exhaust or non water cooled headers? thinking cheep here guys, if my drive will work and only limit speed can this be fixed with prop pitch? thanks drg.

 

[Boatist]

Re: 120hp merc i/o upgrade

Dwain<br />Will that big an engine be legal in your 16 foot boat?? What is your boat's max HP??

 

[Bondo]

Re: 120hp merc i/o upgrade

What you are proposing is Not feasible....<br />Your outdrive is a 1.98/1.. V8s require a 1.50/1.... I Doubt you'll Prop it Up to where it will run Right...<br />Dry-Exhaust will Burn your boat to Dust...<br /><br />Can It Be Done ?? Maybe, or Yes....<br />Can It be Done Cheaply ?? NO Way In H-ll !!<br />Before you try this, Junk this boat,+ Go Find something Closer to what you Really Want....

 

[drgaul]

Re: 120hp merc i/o upgrade

boatist- they offered a v8 option in this boat.

 

[Trent]

Re: 120hp merc i/o upgrade

Cost lots of money to convert. Manfolds, risers, brackets, change gear ratios. Cost more than that puppys worth. Cheaper to fix the 120.

 

[drgaul]

Re: 120hp merc i/o upgrade

bondo i know about the different gearing ie l4-1.98, l6-1.65, v8-1.50, and i think they made a 1.30 also. am i lead to believe this is like the gearing of a car, 1.98-4.0,1.50-3.0 ect? if so the boat would accel faster with a slower top speed and i would have to watch my rpms? in most cases i know you are right but i have the boat,v8 and the stick flywheel and the time. i could change the upper unit at a latter date if say a 27 degree prop would not fix the problem. what about over the hull headers are these water cooled as well on say a jet boat if not i could use auto headers turned up for a while. can you say load. just looking for a way to get the boat in the water till i can get $ to buy a different boat or correct upper unit of the merc. if i understand correctly this setup would have 25% less speed and fuel ecom or is there something i dont understand about the relationship of? i am use to being insane,it comes with having little money and thinking to much or to little, in the car field we call it hot rodding.your input is helpfull in helping me understand how boats put the power to the water.

 

[drgaul]

Re: 120hp merc i/o upgrade

you may be right trent, but if i am right, and i dont know yet if i am, i am hoping all i will have to buy is a couple hose, bolts and the mounts, i may be able to get these from the local boat grave yard just down the road. what i really need is to understand the relationship of putting the power to the water, cavatation ( i hope i spelled that right ) ect. and if there is any real diff-from my drive and a v8 other than gearing. thanks drg

 

[Trent]

Re: 120hp merc i/o upgrade

Drive of that year will be the same (pre Alpha) or "R" drive except the gears in the upper. Guess you could try it but as you know you will not get "top" preformance. Try different props. Hope your not disappointed and dont overev or lug the engine too much.

 

[drgaul]

Re: 120hp merc i/o upgrade

trent from all i have read so far i think i am going to have to watch my rpms and i dont think it will run any faster than the l4, unless the fact that it will have more power will let it rev higher for short distances. any coments on the auto headers? are jet boat headers water cooled? and is there any other thing i have not thought of yet except i am insane haha? i like the boat it is a deep v-hull, plenty of room for people ect. any good books that i should read?drg.

 

[Bondo]

Re: 120hp merc i/o upgrade

Yes, this Can be done....<br />NO, You Ain't going to like it....<br />Yes, Jet Headers Are Wet.....<br />NO, Auto Headers are a Fire, And Saftey Hazard....<br /><br />If you Want a Boat..... Sell this 1 off for parts... Take the money,+ go Buy a boat more suited to your Needs...

 

[drgaul]

Re: 120hp merc i/o upgrade

thanks bondo for the info on the headers, i thought they were wet headers but i was not positive if it was to help heat the cold water comming in or to cool the exhaust. and i also understand that jet boats and hydros have open engine bays so nothing gets to close to the f-glass or wood, and the heat can't build up to bad. not to mention that you can see all the chrome.any good books to read on how boats transfer power. I can't buy a boat for a few hundred bucks. it would be nice though. ill check on a set of used manifolds and run them through the hull if i have to for now. up the road there is over 200 junk boats that have lots of spare parts. i just needed to know what to get and why that is the reason i am writting.drg

 

[horndog]

Re: 120hp merc i/o upgrade

a 305? I don't think so. a 3.0L is a perfect match for it if you can get one used for cheap. It will bolt up to it without a prob! I am sure you can find a used one in that boneyard by you

 

[drgaul]

Re: 120hp merc i/o upgrade

horndog is that an l4? if so sounds like a good possibilty (if i can get it cheep). thanks.drg

 

[horndog]

Re: 120hp merc i/o upgrade

yes, a 3.0L is an I4. What is nice is that it is still in production so finding parts would be easy.<br /><br />I have the 2.5L 120hp and am kinda waiting till she won't run anymore, but hopefully she does it when I have the $$$$ to do so

 

[iwldntli2u]

Re: 120hp merc i/o upgrade

Horndog-<br />DId you just say that a new Mercruiser 3.0 can replace the old I4 such as a 1981 120 with out any mods? I have been asking about this for a year and everyone told me it would not bolt up to the stern drive. They say i have to replace the hole drive system to install a newer 3.0??<br />Help!!

 

[mlslocks]

Re: 120hp merc i/o upgrade

The 2.5 and 3.0 are the same engine. The difference is the bore and stroke. I just replaced my 2.5 with a 3.0 and used all my 2.5 accessories and manifold. I also notice a small power increase. Up on plane faster.

 

[drgaul]

Re: 120hp merc i/o upgrade

horndog and mlslocks thanks for the info,looks like you are helping several people at once.drg

 

[FatBack]

Re: 120hp merc i/o upgrade

Add a Mercarb run exhaust thru hull with inboard riser on Mercarb manifold. 14 more horses.

 

[drgaul]

Re: 120hp merc i/o upgrade

thanks fatback ill check it out, i figured there would be a lot of gain there.drg

 

[horndog]

Re: 120hp merc i/o upgrade

as mlslocks said, bolts right up. I have been checking out that option just in case this one takes a digger since I have the 2.5L as well. And as we both know, parts are hard to find.<br /><br />Look on e-bay motors for a motor, I know I have seen some in the past with all accessories for dirt cheap, brand spanking new sometimes.