Repower 1998 Glastron GS 249

[hackergreg]

Hi there,

We purchased a 1998 glastron GS 249 with a 220HP 5.0L and Volvo Cobra SX outdrive last year. We are getting ready to replace the motor with a 5.7L 300HP and would appreciate any tips or tricks anyone has to offer. We are especially concerned about whether the outdrive will handle the additional HP. Looking forward to a big summer on Lake Erie this year. Thanks in advance !

 

[jimmbo]

The SX drive is a well designed and built outdrive, stronger than the Alpha 1 drive. It should have not trouble with 300 hp, but In a 24 footer, I would be considering a big block. 24 ft is a lot of boat for a small block to accelerate. Of course I'm used to a 5.7 in an 18 footer.

 

[Bondo]

Ayuh,.... Welcome Aboard,...... The drive will handle a 350, No Problem,......

What's the induction yer swappin' over from the dead 5.0l,..??
2bbl. carb,..??
4bbl..??
Efi,..??
Mpi,..??

Everything should be a simple plug, 'n play swap,....
All the bolt holes oughta be right where they oughta be,....
Both motors, if the same latest vintage, are Exactly the same, externally,....

 

[Scott Danforth]

Unbolt old, bolt in new, align, go boating. Make sure your new motor is a 1996-2002 and its plug-g-play

as stated prior, no problem with a 350 or 383

 

[QBhoy]

I’ve made some assumptions about this. Correct me if I’m wrong.
The boat is 98, so assuming the original 5.0 likely a carb or single point injection at best.
You mention you are replacing with a 5.7 300hp ? I don’t think there is a carb 5.7 that will give 300hp. Not sure a VP single point injection will either. Not that I know of. Only a Merc MPI or VP GXI multi point fuel rail fed (I’m sure) will give 300hp and perhaps 310/320hp in VP figures.
So just need to make sure you are swapping like for like...otherwise it will get expensive with the additional ancillaries etc you will need. Not to mention the ecu.
Be good to hear what you have now and what you plan to replace with, in terms of models.
All the best.

 

[Lou C]

http://www.michiganmotorz.com/vortec-marine-gold-package-1967-current-replacement-p-4172.html
one idea, 315 hp

 

[hackergreg]

Thanks for the replies everyone !

The original 5.0 had a 2-barrel carb on it, we're planning on swapping the carb and intake manifold to a 4 barrel, even if we don't get the full 300HP, it's gotta be an improvement over the 5.0 which was 20years old with several hundred hours on it, topping out at about 30mph, with dismal acceleration. We don't want to ski behind the boat or anything crazy, but we'd like it to have enough guts to get out of it's own way...lol. .

As far as the lower unit goes, I'm happy to hear that the consensus is that the lower will handle the HP. I see that the cobra sx has a bunch of different gear ratios depending on the type of motor it's attached to. We we're thinking of keeping the internal gears of the lower unit the same, and making up the difference by changing the prop, is that sane ?

 

[Lou C]

The 4bbl on a normal 350 cu in should give you about 260 hp or so. As far as carbs, you can go with either an Edelbrock 1409 or a Holley 4160. Volvo actually rigged their engines with Holley until the end of the carb era.
The gear ratio that was used for the 5.0 should still be good for the 5.7 given that this is a big heavy boat.

 

[Scott Danforth]

a simple cam change to the motor and you can be running close to 300hp at the prop with a carb'd 5.7

 

[Bondo]

The 4bbl on a normal 350 cu in should give you about 260 hp or so.

Ayuh,.... They were called 260 hp til '96,....

With the Vortec heads, 280 hp is closer to the truth,....

 

[jimmbo]

I put a Holley 650 CFM Spreadbore carb onto my 2002 5.7 VP. A manifold swap was not needed as Volvo used a very good 4bbl intake and adapter with the 500 cfm Holley 2bbl. the swap increased my WOT rpms by about 450, so I had to increase the pitch by 2" to get the rpms back to where they were with the 2bbl.

Holley PART# 0-80552

 

[hackergreg]

Thanks again for the great info guys ! We will take a second look at our manifold, and how exactly do we cam up the motor to get 300HP at the prop Mr. Danforth ?

Also, we've been kicking around trying to re-work the overheat cutoff that was built into the 5.0. I've been told that it's supposed to kill the motor when it get's over 185 degrees, we had an overheat incident at the end of the season with the 5.0, which led us to the motor replacement. I'd like to do whatever is necessary to avoid that happening with the new motor (we will also be replacing the impeller annually). The mechanic at the marina said we seriously overheated our motor, but the cut off did work. Our mechanic said anything over 160 was not good with a fresh water cooled engine. If that's the case, why wouldn't we rig the cutoff at 165 instead of 185 ?....any thought's.

 

[QBhoy]

His advice on the temp is not accurate. There are a few thermostat options for these engines. Some run at 170 and above. Basically he is talking nonesense.

 

[QBhoy]

Are you replacing engine just on this basis ? Is there actually anything wrong with it ? I’m pretty sure the engine would survive temps up to about 185/190 pretty safely. Not recommended but survivable.
If there is no actual damage, I would be questioning the mechanic.

 

[QBhoy]

Also...my 5.0 runs at operating temp of 162 when running fast. But there are Defo engines that run higher temps without fault.

 

[jimmbo]

The engines suffer less wear at 180 - 190 than they do at 140 - 160. The problem is raw water cooling. At temps above approx 140 F the dissolved Salts and Minerals in the water start coming out of suspension, the hotter the water the greater the types and amounts. These salts and minerals have a tenacity for coating the cooling passages. Since new water is always being introduced this becomes a never ending process. Eventually the water passages will look like somebody fill them with concrete. Same thing happens in your auto/truck engine, however the system recirculates the coolant, so once all the salts an minerals have come out of suspension, the accumulation stops growing, but does reoccur when undistilled water is added to the system. Engines that utilize Heat Exchangers, can run higher temps because as mentioned above, new water isn't being introduced

 

[hackergreg]

No...we had water in the #7 cylinder too. That's what ultimately led to the decision to repower.

 

[jimmbo]

Just out of curiosity, where are your acquiring this 300 hp engine?

BTW, a carbed vortec VP 5.7 was rated 260 with a 500 cfm(375 when flow rated like a 4bbl) Holley. It is a tad to small for a 5.7. I was pulling 4 inches of Vacuum at WOT. With the fore mentioned 650, I gained about 6 mph, which was putting me in the 290hp range. I never changed the jets to tweat it. I was going to swap the 1.5:1 rockers for some 1.6:1 ones, that would have altered the effective valve timing and lift enough to get it up to 300hp, even with the stock VP marine cam, but never did

The 4bbl Holleys that Volvo used on the later 5.7s were model 4175s(650 spreadbore)

 

[hackergreg]

Another question came up on this project...does anyone know of a supplier who would provide a full kit of ancillary items: gaskets, hoses, etc. for a full motor swap ?

 

[Bondo]

Nope,.... Not as a "Kit", but as per piece, Sure,......

I believe iboats carries All of the stuff yer lookin' for in the store,....