Repowering with a small block

[little joee]

Okay folks, here's the situation. I currently own a 1998 Searay 180 (18') with a cracked 4 cylinder mercmarine (181 ci), alpha 1 outdrive. I bought the boat with the intention of replacing the engine as the rest of it is absolutely pristene. And the sale price was appropriate for the work needed.

I recently purchased a mercmarine 302 (ford engine obviously) that had a performance rebuild. The 302 is a full engine with exhaust. The flywheel, bell housing and spindle also came with the engine. The engine was run for 1 day and removed from the boat as it didn't deliver as much power as a 383 (go figure, there's no replacement for displacement). This was a very economical purchase.

The question I have is; is it worth while to stuff it in the boat? I have the general concerns of physical dimensions, mounting point locations and ability to handle the weight and power. The drive should be able to handle the additional power without any changes.

I am mechanically inclined (working on a head gasket replacement in vehicle right now), so I'm inclined to go forward and try the conversion. I just need to arm myself with a little knowledge first.

Is this a worthly endevour or am I asking for trouble?

 

[cr2k]

Re: Repowering with a small block

Yea the drive will handle the power, but you will be turning like 7000 rpms to go 40. The 4 banger has a 1.65/1 or maybe a 1.73/1 gear ratio.
The V-8 needs a 1.5/1 ratio. You will need to replace at least the upper drive with the correct ratio.

 

[picklenjim]

Re: Repowering with a small block

Yea the drive will handle the power, but you will be turning like 7000 rpms to go 40. The 4 banger has a 1.65/1 or maybe a 1.73/1 gear ratio.
The V-8 needs a 1.5/1 ratio. You will need to replace at least the upper drive with the correct ratio.

The V-8 will be turning the same RPM as the 4 banger did at it's top end speed. However the V-8 will get you to the 4 cyls. top end speed a lot faster and continue increasing RPM and speed. The V-8 will give you the ability to run a higher gear ratio drive so you will be running a higher speed at a lower RPM than the 4 cyl. did. You would need to see what the max RPM is of the V-8 with the existing drive to be sure your not going to be over revving it. If so then you would need a higher ratio drive or possibly be able to just go with a prop with more pitch.Fast neck snapping acceleration which is what you'll have if you keep the same drive is more exciting than running at top end.

 

[Howard Sterndrive]

Re: Repowering with a small block

I wonder if there's a Y pipe and bellhousing to put a Ford onto a Gen II drive.
Mercruiser didn't mate any Fords to Gen II's
And you'd have something that didn't make sense year-wise.

A 4.3 4V or MPI would be the ticket. The big V6 would probably be a better performer than a small displacement V8 and it probably was available in your 1998 SeaRay

Many marine 302's were rated at less HP than a modern 4.3 4V and weigh much more obviously

 

[wallerus]

Re: Repowering with a small block

With a little patience you can make anything fit. To run the 302 you will need to replace the drive. The 4 cyl. ratio is 1.95:1. The prop shaft speed will be too fast with the 302 if you just get a prop to run the engine in the proper rpm range. No mater what engine you put in the boat other than the 4 banger you will need to change the drive ratio. I think if you do not want the 4 cyl. you would best be served by a late model 4.3. Fuel injected with the balance shaft.

 

[Bondo]

Re: Repowering with a small block

The question I have is; is it worth while to stuff it in the boat? I have the general concerns of physical dimensions, mounting point locations and ability to handle the weight and power. The drive should be able to handle the additional power without any changes.

Nope,.... None of the mounting points will line up...
The gear ratio of your drive is 1.98:1, 'n the V8 needs a 1.50:1...

As noted above,... A V6 would be the Best match for an 18'er, but you'll Still need a different drive ratio....
As the 1.98:1 Only works with the I4 motors...

 

[Gary H NC]

Re: Repowering with a small block

Not to mention finding the Y pipe that will fit and deciding where to beef the stringers up and where to put the motor mounts..
The 4.3 would have been the best choice.

( Bond-O beat me to it )....

 

[BoatingCop]

Re: Repowering with a small block

Also, Check to see what max horsepower is on you boat by checking capacity plate. You don't want to overpower. Good luck

 

[picklenjim]

Re: Repowering with a small block

With a little patience you can make anything fit. To run the 302 you will need to replace the drive. The 4 cyl. ratio is 1.95:1. The prop shaft speed will be too fast with the 302 if you just get a prop to run the engine in the proper rpm range. No mater what engine you put in the boat other than the 4 banger you will need to change the drive ratio. I think if you do not want the 4 cyl. you would best be served by a late model 4.3. Fuel injected with the balance shaft.

If you were to get a larger pitch prop to make the engine run in the same rpm range as the 4 cylinder was running then the prop shaft speed would be the same. However the boat would be going faster due to the increased prop pitch. A 1.5:1 spins faster than a 1.95:1. It's possible you couldn't get a prop with enough pitch though therefore it would be necessary to go to a higher gear ratio. There are boats with V-8's running 2:1 drives for the extra power needed at the prop such as houseboats and cruisers. I do realize the norm would be a 1.5:1 for a V-8 in a boat like this which would have you in the 17-23P range.

 

[little joee]

Re: Repowering with a small block

Thanks for all the help! You all helped bring up some things I wasn't aware of.

It sounds like I still have a ton of work to do.

But in terms of going with a V6 (Better fit size and it was an option on this model) what does the forum think my chances are? I would need a complete engine from the carb to the flywheel and I bet I could match the prop to make up for the different gearing. At this point I would have a 4 cylinder with a cracked block and a good 302 to trade (plus some cash as always). Am I looking at a ton of extra cash or could I trade straight across?

 

[proshadetree]

Re: Repowering with a small block

Dout anyone would do an even swap. Check prices for parts to put the ford in and compare to a different engine. Even with the six I would swap drive. V/8 and v/6 drives I will swap back and forth a 4 cylinder drive is just to low for use on the larger engines. Just my opinion though

 

[wire2]

Re: Repowering with a small block

..... and I bet I could match the prop to make up for the different gearing. ....

Maybe. Going from 1.5:1 to 1.98:1 is a 33% jump. Starting out with a typical prop of say, 19", and bumping it up 33% to compensate, lands you in 25-26" pitch.
Plus, I believe the 4 cyl drive might be physically smaller than a 6 or 8.

 

[NHGuy]

Re: Repowering with a small block

If you are determined to do the Ford motor get the gears to change the drive to a 1.5. As prop pitch goes up diameter & behavior changes. You might not be able to get a 25 or 27 pitch for that drive without going big dollars. As far as the exhaust, skip fabricating a through prop y-pipe and go out through the hull. Through hull allows the motor to breath best and they are easily fabbed up. If you don't want the loud sound you can muffle the through hull exhaust.
You will also need to search out motor mounts and a coupler that will fit the Ford where a Chevy would normally be. Unless that is what you mean by bellhousing & spindle. The rear mounts on Mercruisers are part of the engine bellhousing. If I understand you right you might have the hard stuff handled up front. I'd suggest a posting on Speedwake.com. Those guys like to play with motor changes etc.
I'm going to PM you some other info too.
Sounds like a fun project. You might want trim tabs when you are done since that motor & exhaust will be a few hundred extra pounds over original.

 

[metalwizard]

Re: Repowering with a small block

If you are determined to do it I have an upper and a bellhousing that might work from you. it came off a ford v8 motor.
But its for an OMC stringer with electric shift. all in decent shape.

 

[picklenjim]

Re: Repowering with a small block

Thanks for all the help! You all helped bring up some things I wasn't aware of.

It sounds like I still have a ton of work to do.

But in terms of going with a V6 (Better fit size and it was an option on this model) what does the forum think my chances are? I would need a complete engine from the carb to the flywheel and I bet I could match the prop to make up for the different gearing. At this point I would have a 4 cylinder with a cracked block and a good 302 to trade (plus some cash as always). Am I looking at a ton of extra cash or could I trade straight across?

This sounds like a more feasible idea. Don't know about the trading part though. You could always just sell the 302 outright and then find a good 4.3 V-6 marine motor. Then see how it works with the drive. You can always change the drive, that would be the easiest part of this whole deal. Then again you could just get a new 4 cylinder short block.

 

[Bondo]

Re: Repowering with a small block

Thanks for all the help! You all helped bring up some things I wasn't aware of.

It sounds like I still have a ton of work to do.

But in terms of going with a V6 (Better fit size and it was an option on this model) what does the forum think my chances are? I would need a complete engine from the carb to the flywheel and I bet I could match the prop to make up for the different gearing. At this point I would have a 4 cylinder with a cracked block and a good 302 to trade (plus some cash as always). Am I looking at a ton of extra cash or could I trade straight across?

Ayuh,... What you need is the Complete driveline, from the Pulleys to the Prop....

I can tell you from actual experince that you can'y buy a prop Big enough to make that ratio work...
A 26" heavily cupped SSteel wheel Blows out, 'n Over-revs wildly....

I suggest sellin' all yer junk Outright, then take the funds, 'n buy a running Donor boat....
$3500. or less should get you ALL the pieces Necessary....

 

[HPTGreyGhost]

Re: Repowering with a small block

Bond-o,
I've considered this in the past. How do you junk a boat once you've stripped it? Does a normal junk yard take something like that? Do they pay you or do you have to pay them for a fiberglass boat hull?

 

[Bondo]

Re: Repowering with a small block

Do they pay you or do you have to pay them for a fiberglass boat hull?

Ayuh,... There's No value in the hull...

My county transfer site takes it for $60. a ton....

Last 1 cost me $40. after I filled it with Trash for the trip up the road...

 

[HPTGreyGhost]

Re: Repowering with a small block

Thanks. That's not really that bad. Can you recover the trailer too or do you have to leave it with it?

 

[Bondo]

Re: Repowering with a small block

Ayuh,... I just scale in, run around back, 'n the guy with a frontend loader get's a hook onta the hull, 'n I drive away to scale out, With the trailer....

It's a Trash site,... I ain't leavin' 'em a perfectly Good trailer....