repowering

[mh11]

Hello there, I have the '78 galaxie 22xl that you all have been so gracious in helping me with.

Question, if I wanted to build a chevy 350 motor to make it scream, what do I need to look out for with regards to the engine. Do I need to stay with the same block for instance that is in there now?

Also, I believe the last owner replaced the upper housing looks like an alpha one, not the pre alpha, or MR that has the little fin on the top cap.

How much horsepower can these drives handle? I don't want to build something that is gonna blow the drive.

My aim is to get around 350 horsepower, is this gonna be ok with the drive?

Thanks!!!

 

[TilliamWe]

Re: repowering

...Question, if I wanted to build a chevy 350 motor to make it scream, what do I need to look out for with regards to the engine.

First thing to do is forget almost everything you know about building a small block Chevy for the street. In a boat you need to build for low to mid range torque. Also, a Mercruiser Alpha drive will probably handle 350hp from a 5.7, as it's the torque that can kill them... but they don't like to spin much over 5000rpm. As i said, it's not like building a 1/4 mile car.
Other will post specifics. But if you could somehow get a copy or read Dennis Moore's Small Block Power book, it'll explain things in some pretty good detail.

Good luck.

 

[mh11]

Re: repowering

I am at anywhere from 3500-maybe 6000 feet elevation at lake tahoe.

I wanted to build around 350hp since I will be losing a bunch of hp at altitude here.

What can I do to the drive to allow it to handle more horsepower?

Thanks

 

[TilliamWe]

Re: repowering

What can I do to the drive to allow it to handle more horsepower?

Thanks

Nothing really. Upgrade to an Alpha 1 Gen 2, maybe, but that's a big project. And not worth it, really. (see below in the Bravo comment)

What you can do to make the drive stay together is
1.) Do not hammer the throttle wide open from a standing start.
2.) Do not get the boat airborne when jumping a wave.
3.) If you do get the boat far enough out of the water to let the motor speed up, cut the throttle before you re-enter.

Bubba's prediction of doom is not accurate. Mercruiser put 330 horsepower 454s in front of Alpha Ones for a couple model years in the 80's. They didn't break them right away. And I personally know one that was in a Sea Ray 268 Sundancer (VERY heavy cabin cruiser) that the drive lasted 4 years and over 400 hours without breaking or failing at all. So it can be done, you just have to be careful.
Of course a Bravo drive would be better, but that's a big project.

 

[mh11]

Re: repowering

Well that stinks if I have to replace it, what will it entail if I want to put the bravo outdrive on it, and can I even do that.

Basically if I want to go fast 55-65mph, should I sell this boat and buy another one?

I really like the shape and look of these old boats, I just want to go fast!!!

Thanks

 

[dubs283]

Re: repowering

Yeah, the old alphas behind the 454's. Crazy, but they did handle it if the boater was responsible with the throttle but they were generally in larger cuddy boats so speed was not the concern there. It's all in the gear ratio too. My suggestion to you is if money is not an issue, look into bravo. otherwise you will be having headaches and continual repair issues.

 

[mh11]

Re: repowering

Well considering the fact that I just bought it around 4-5 months ago maybe, and the fact that I only paid 2500.00 for it including the trailer, and it runs pretty darn well, and the fact that I like the shape.............

Should I just run it the way it is? I am going thru the boat in few weeks to get it to run tip top

This boat is gonna be used for cruising, hopefully fast, towing my little kids around on a tube, and maybe a bit of fishing.

I just like to go fast.

Thanks

 

[mh11]

Re: repowering

So if I build the motor to put out 300-350hp, I should be ok if I don't mash the throttle down, and be stupid right?

What HP did the 454's put out that Merc ran with the Alpha drives?

Also, I cannot see getting this boat out of the water when running, it's one heavy azz boat.

What about taking the gears and driveshaft out, and cryogenically treating everything, would this help.

I really really like this boat, I want to really go thru it and tune everything up.

Thanks!!

 

[HT32BSX115]

Re: repowering

You're pretty limited on what you can do to an engine to make it run at 5000 MSL.

A friend of mine with a 26 bayliner put a GM 400 cu-in small block in front of an Alpha. He also put a Procharger on it..

I think it's gonna break that Alpha. He set it up to run at Tahoe.

I told him not to "straight-arm" the throttle and he probably will be ok. He hasn't had it on the water yet.

Just about all the Merc carb'd 454's were rated at about 330 crankshaft at around 4700 rpm.

My brother had my boat before and ran it at Tahoe (when it had the 460 King Kobra inside)

He had to remove the 20p prop and go to a 17p prop to get it to plane quickly and run halfway decent. Of course with the 17p prop it was pretty slow.

I have 26p props on it now and I'm probably going to try it in Tahoe next Aug. I'll bring my 24p props to put on it there...

 

[mh11]

Re: repowering

Thanks HT32BSX115, take it you are a pilot? MSL, guess I will look for you at Tahoe when I fly my glider out of Truckee

So basically I should get the motor to pull steady 4200-4600 with the motor in it now, and just enjoy it. I figure if I get it running smooth, maybe get 45-50mph out of it.

Drive for a year or two, and maybe think about new boat? Maybe get an older boat like this with V-drive? Those should handle more hp correct?

Thanks!!

 

[mh11]

Re: repowering

Well, my old brother in law works at a supercharger company, should I just cryo the gears, put the blower on, and go easy on the throttle?

Maybe get real 330hp at altitude out of the motor, and just go easy?

Or am I just asking for trouble??

Thanks!!

 

[Bondo]

Re: repowering

Or am I just asking for trouble??

Ayuh,..... Without a Doubt...

 

[TilliamWe]

Re: repowering

Sorry Bubba, I have personal experience with a 454/Alpha combo. Do you? Ours didn't break, and it was doing a fine job. And I also have personal experience with a 350 ZZ3 (allegedly 340hp) in front of a pre Alpha (1979 model boat) that I did all of the things I listed above and didn't break it. And that drive was over 12 years old at the time. It can be done.

That said, a Small Block even at 350 crankshaft HP is not going to explode an Alpha all by itself. And with an SEI replacement drive sold right here on iboats for $1200, with a 3 year no fault warranty, what have you got to lose?

mh11, the other thing to consider is the ability of your hull to run at the speeds you want. It may not be condusive (sp?) to that at all. If it carries it's deadrise back to the transom and doesn't have a keel pad, it may take 500hp to hit 60mph. It takes gobs and gobs of power to make a boat run just a little faster.
Then, is your floor, stringers, and transom solid, with no rot? Are you sure???

I recommend keeping your boat the way it is and use it as is. Buy a real speed boat (such as the v-drive type you mentioned) if you want to go fast. It'll be much easier in the long run.

 

[mh11]

Re: repowering

Ok, well here goes................

The boat is basically solid. I have taken it out three times since buying it.

The previous owner had $8k worth of receipts that had been put in to the boat. Everything, gel coat, paint, interior, etc.

Chevy 350 crate motor with 100 hrs on it. I will post pics, I bought this for only 2500.00 with the trailer!!!!!!

When I started, it wouldn't pull over 3k rpms. About 37 mph. 5 blade stainless 23 pitch prop.

Changed to 17p 3 blade aluminum, got up to 3900 rpm. 35 mph on speedo.

Some soft spots forward of the motor, and around the two rear seats on side of motor. Seems to be solid though. Seems like some deck needs to be replaced.

Seems to me that I have a lean condition looking at the plugs, and that there may be water in the tanks from sitting for a while. I am going to change the water seperating fuel filter, and replace the filter at the carb, and tune her up a little.

I already had new points and condenser put in, and the timing and everything set to stock specs.

I need to get up around 4200-4600 rpm to see what she will do. I have a feeling once I get that, I will gain some top speed.

Figured that I would run two different props, one low when we tow, and one high when we want to cruise. What do you all think?

Other boats from this era claim to hit 55-60 mph on speedo, so I would assume this boat can do the same. That is why I am on this forum.

My need for speed has partly to do with my 08 Suzuki GSXR 1000. It hits 104mph in first gear!!!!!!!!!!!!!!!!!!

I want my boat to haul azz!!!!! Any further thoughts are appreciated!!

Thanks!!

 

[TilliamWe]

Re: repowering

Ok, well here goes................

When I started, it wouldn't pull over 3k rpms. About 37 mph. 5 blade stainless 23 pitch prop.

Changed to 17p 3 blade aluminum, got up to 3900 rpm. 35 mph on speedo.

Some soft spots forward of the motor, and around the two rear seats on side of motor. Seems to be solid though. Seems like some deck needs to be replaced.


I need to get up around 4200-4600 rpm to see what she will do.

Other boats from this era claim to hit 55-60 mph on speedo, so I would assume this boat can do the same. That is why I am on this forum.

1. Check your tach to make sure it's working properly. That prop change should have made a HUGE difference in rpms.

2. Uh-oh... that is not good. You have a rotten floor. And when you cut the floor out, there is a decent chance that you will have rotten stringers. They may be fine, but I wouldn't bet on it.

3. What rpms is your engine supposed to run at WOT? This is very important to know.

4. 55-60 on the speedo doesn't mean diddly. Speedos are inaccurate to say the least.

5. "Other boats of that era" can mean a lot of things. What is your boat capable of?

 

[Bondo]

Re: repowering

I want my boat to haul azz!!!!! Any further thoughts are appreciated!!

Ayuh,.... You've got the Wrong Boat......

If you're turnng a 17" prop to 3900rpms at 35mph,....
You're never going to see 60mph with that package....No Way in 'ell....

 

[Ridemywideglide]

Re: repowering

My need for speed has partly to do with my 08 Suzuki GSXR 1000. It hits 104mph in first gear!!!!!!!!!!!!!!!!!!

ROFLMAO... That's funny right there..