3.0l swap to high performance 350

[nofear1132]

I recently accumulated a jet boat with a 350 in it completly gone through double hump heads 202 valves, cam driven waterpump all that good stuff.....I have a 21 foot larson with a 3.0l 4 cylinder mercruiser in it, and it had a 4.3 in it so its capable of the v motor with the side mounts. So I'm assuming I can put the 350 in the larson with some conversion like the upper unit .....does anyone wana help me with this and give me a brief run through of how and what it would take to get this done....thanks

 

[nofear1132]

350 motor need exhaust and carb

350 motor need exhaust and carb

I just bought a 350 out of a jet boat and am slowly converting it over to go in my i/o larson
So I know ill need new exhaust manifolds question, this motor had a lot of upgrades like double hump heads 202 valves, water pump driven off cam.....is it still possibel for me to go cheap for now and use stock manifolds? Will I stress motor? Will burn something up, what will happen?
Also the motor has no carb any idea on cheapest way to go for this type of motor and still get good performance? Any helps appreciated thanks

 

[HT32BSX115]

Re: 350 motor need exhaust and carb

Re: 350 motor need exhaust and carb

Howdy,


Well, where do I start?

First of all, you didn't indicate whether a Volvo, Mercruiser or OMC drive is going behind this "350"

Also, since it came out of a jetbote, did it have dry stacks on it?

If it did, you may not be able to use it (safely) in any I/O application without having a rather severe reversion problem (unless you're also going to use drystacks)


If the cam is ok, you'll need whatever manifolds and risers that will match up with your Y-pipe or thru-hull exhaust setup.

In an I/O there's NO cheap exhaust system if you want performance. You can get a good marine carb from Holley. They're not cheap either.

A restrictive exhaust won't "hurt" the engine but it will limit performance. Stock I/O (thru-prop) exhaust is not known for REALLY good performance.........but if you're going to use thru-hull exhaust, there's a lot of (expensive) choices out there.

There's Impco, Gill, Corsa, etc.......bring $$$


Cheers,


Rick

 

[Bondo]

Re: 3.0l swap to high performance 350

Ayuh,... You'll need a Pile of Merc parts to do it...
None of the jetboat parts on the 350 are gonna work, tryin' to hook it to an Alpha drive...

 

[nofear1132]

Re: 350 motor need exhaust and carb

Re: 350 motor need exhaust and carb

Thanks, I have a mercruiser aplha 1....how do I tell if it was dry stack?

 

[QC]

Re: 3.0l swap to high performance 350

Ok, I merged the two threads to keep this all in one place.

Welcome aboard nofear!!! Good luck with this. Sounds like a lot of fun and a lot of work . . .

 

[Flysfloatsor]

Re: 3.0l swap to high performance 350

Here's What Id do:

1. Buy a Marine I/O cam that Doesent cause reversion. Just bought Comp Cams Xtremem Marine 262.

2. Install

3. search Your local craigs list for used SBC manifolds w/ risers. Always a ton on there this time of year because of all the cracked blocks/boat scrapping folks.

4. Buy a Ypipe block off plate for $20.

5. Get some wet exhaust hose 3" or 4" depending on what manifolds you get along with some stainless Exhaust tips

6. Install the block off plate, then the engine, then the thru hull exhaust.

7. Get someone to change the 1.84 gears in the upper Alpha to 1.5...

8. Get a new prop

9. Go fast-ish...

PS, dont forget the 1000 little steps in between those 9 main steps either.

 

[HT32BSX115]

Re: 350 motor need exhaust and carb

Re: 350 motor need exhaust and carb

Thanks, I have a mercruiser aplha 1....how do I tell if it was dry stack?

Well,


Like Bondo indicated, at the minimum you'll need a Mercruiser flywheel housing, engine mounts, brackets and accessories etc.....


The other "stuff" like which camshaft it has inside, well if you cannot speak to the guy that sold it to you the only way to know would be to pull the cam and have it measured.

Jet boats do not usually operate in the same RPM & torque/HP range as an I/O. YOU *may* need to, at the minimum, replace the cam.

If it's a rather high compression, high RPM (to get the peak HP) engine, you may have an additional problem with detonation trying to run it at the RPM (5000 or so max) that most I/O's like to run.......

Engines that run well in front of a jet pump may not work well in front of an I/O.......

 

[nofear1132]

Re: 350 motor need exhaust and carb

Re: 350 motor need exhaust and carb

Thanks guys, man I can really get used to this forum lol
Alos the motor had a "transmission" on it in the jet boat taking that off ,would that make anything different in the motor? Also I have that trans and the over the stern basset headers for sale if anyones interested

 

[QC]

Re: 350 motor need exhaust and carb

Re: 350 motor need exhaust and carb

Alos the motor had a "transmission" on it in the jet boat taking that off ,would that make anything different in the motor?

Maybe, but only if it wasn't a jet, and jets don't have transmissions . . . Sumpin' a little fishy here. Describe your "jet" drive. I'm thinking this might be a V-drive.

 

[Bondo]

Re: 350 motor need exhaust and carb

Re: 350 motor need exhaust and carb

Maybe, but only if it wasn't a jet, and jets don't have transmissions . . . Sumpin' a little fishy here. Describe your "jet" drive. I'm thinking this might be a V-drive.

Ayuh,... I ain't never seen a Jet, with a tranny either...

'n I also agree, Jetboat motors are usually put together Alot differently than I/O motors, Right from the Get-go...
Sell it, 'n buy a Pickup motor,...
It's closer to an I/O motor, than a Jetboat motor....