Logo

more power from my mercruiser 260

barrylee66

New member
I am about to begin building another motor for my boat 84 searay sundancer 245 5.7 I want 300 hp. and I have a few questions like can I run an aluminum intake or heads? boat run mostly in salt water and does not have a closed loop cooling system. but I will be flushing it out. also I would like to convert to roller cam. or buy a newer roller cam motor. can that be done and if so do you have to run a different flywheel?
 
Can you say 383 sbc..?
That should put you in the 320 + hp range...all accesories will bolt on. Get a slight high rise cast ieon manifold if possible and a bigger marine carb. 650 cfm to 750 cfm depending on cam choice.

That is my opinion. Several remanufactures sell 383 blocks of varying horse power
.

Now understand that the alpha 1 gen 1 based outdrive is marginally good to about 350 hp BUT with small block touque NOT big block torque. In the mid to late '80's they put 454's with alphas and they were blowing the upper gear appart due to the high torque of the big block....
 
I have been running a 6.2 MAG MPI (383) rated at 320 shp now for 5 seasons with an Alpha Gen II and a High-Five 21" pitch prop.
Works really well and makes great power. In cruise it uses no more gas than a 4.3.
YOu get the power of a big block with the weight of a small block. Good way to go IMO.

Rod
 
I again don't wish to step on any ones toes. However, alphas did have 2 different sets of gears, the hd duty uppers gear set can still be bought. Here is the part # for the 1.50 heavy duty gear set.....43-1841OA4 1.50R. About 350 dollars. Glm makes a set about 175 dollars Glm 11210 1.50R
If you had the standard set and the hd set side by side you would see the difference, also the bearings are different.
 
Last edited:
I again don't wish to step on any ones toes. However, alphas did have 2 different sets of gears, the hd duty uppers gear set can still be bought. Here is the part # for the 1.50 heavy duty gear set.....43-1841OA4 1.50R. About 350 dollars. Glm makes a set about 175 dollars Glm 11210 1.50R
If you had the standard set and the hd set side by side you would see the difference, also the bearings are different.

great suggestion to handle the extra grunt of powe....
 
I am about to begin building another motor for my boat 84 searay sundancer 245 5.7 I want 300 hp. and I have a few questions like can I run an aluminum intake or heads? boat run mostly in salt water and does not have a closed loop cooling system. but I will be flushing it out. also I would like to convert to roller cam. or buy a newer roller cam motor. can that be done and if so do you have to run a different flywheel?
You will eventually have issues if not equipped with the Closed Cooling system.
This has everything to do with the ph balance of the cooling water, and the resulting corrosion that will take place between iron and aluminum.
There is a Marine bronze lined dual plane intake manifold that can be purchased.... but does not help in the area of aluminum cylinder heads.

If building a fresh engine, now is the time to add the closed system, and you will be able to use your aluminum components.
Otherwise, they may live a short life.



Can you say 383 sbc..?
That should put you in the 320 + hp range...all accesories will bolt on. Get a slight high rise cast ieon manifold if possible and a bigger marine carb. 650 cfm to 750 cfm depending on cam choice.
..........

Now understand that the alpha 1 gen 1 based outdrive is marginally good to about 350 hp ...................
Many will suggest that the A drive limit is closer to 300 hp MAX.... and a MAX hull length of 26 foot or so.

**************************

Which ever SBC engine you build, just say NO to any of the "full dished" pistons!
(see image below)
There are much better piston selections for a more true Marine build..... and in particular, for the 377/383 version!
We want to create a "squish" or "quench" area within the combustion chamber. The full dished piston cannot do this! :mad: :mad:
In fact, it works against us in this aspect! :mad:

For a few dollars more, you can purchase the correct piston in a Low Comp Q/E, Reverse Dome, or D-dish, etc.
The partial dish volume selection (along with your combustion chamber volume) controls C/R..... so C/R can remain correct for Marine use, etc.
Nothing else needs to be changed, other than the correct head gasket for the quench dimension.
Any good piston supplier can help you with your selection..... they just need to know your Marine application.
It's actually that simple!
 

Attachments

  • Dished Piston.jpg
    Dished Piston.jpg
    4 KB · Views: 13,789
Last edited:
I really dont want to build a stroker motor. I am building the motor myself. it should not be hard to get 300 hp from 350 inches. but if I cant use aluminum I will find iron parts. but I dont really understand, my entire outdrive is made of aluminum. the heads do not contact iron because the gasket seperates them. same with the intake. I should be able to do it with all iron parts. I am also trying to do it as cheap as possible. thats why I was asking about the newer roller blocks.I really cant afford aluminum heads but was going to try an aluminum intake.
 
I again don't wish to step on any ones toes. However, alphas did have 2 different sets of gears, the hd duty uppers gear set can still be bought. Here is the part # for the 1.50 heavy duty gear set.....43-1841OA4 1.50R. About 350 dollars. Glm makes a set about 175 dollars Glm 11210 1.50R
If you had the standard set and the hd set side by side you would see the difference, also the bearings are different.

MM; no worries. You're not stepping on any toes around here!
And that is great information regarding the HD gear sets. Thanks for posting.

Rod
 
it should not be hard to get 300 hp from 350 inches.
it is hard if you want to stay under 5000 rpm
383 is the easy way,,, I have to think cheaper or same $ as building a 350 with enough torque at low rpm to make 300HP under 5K
you can do it yourself. There are 383 "kits" out there for good value. Just listen to Rick on the pistons.
 
300 hp should be easily had by adding a set gm cast iron vortec heads and suitable intake for those heads and a mild cam. Comp cams make few marine grinds and the gm lt4 hot cam is also an option IF you are setup for a roller cam
 
300 hp should be easily had by adding a set gm cast iron vortec heads and suitable intake for those heads and a mild cam. Comp cams make few marine grinds and the gm lt4 hot cam is also an option IF you are setup for a roller cam
Well, that's what many think to be the case.
Look at the RPM whereby the horse power rating is taken.
How many of us operate our cruiser engines at 5,200 rpm? :eek:

Fact is, the Vortec cylinder head still offers a "wedge" area, and is where we want the "quench" or "squish" to occur.
A full dished piston underneath the wedge, can not offer this.
Unfortunately, that's what we'll most commonly find being used in the GM SBC........., that silly, stupid, no good, worthless full dished piston! :mad: :mad: :mad:


Here is an interesting article by Jeff Smith on the Q/E.
It pertains mainly to H
P Automotive, but the Q/E or S/E applies to Marine just as easily and effectively....., in fact, more so.

Since the Vortec chamber is only 64cc, we still need a piston dish volume in order to control C/R.
However, we can create a squish area by broadening the ring landing area, allowing it to "mirror" the wedge area......, as shown below.

Something similar to this piston can be used.

images


Now we can end up with both the correct C/R, and a Q/E, and take real advantage of the Vortec design!

On a technical note..... a proper quench will allow for a point or two higher on C/R and without further risk of Detonation.
This build equates to a performance gain, all due to one simple change to our piston selection.
Cost difference is minimal......, machine work and set up time should remain close to the same!

Let your camshaft supplier know of your piston/cylinder head selection.



Edit:
No offense to any of you full dished piston lovers!
This is simply my take on this based on some 45 years involvement witht the SBC!

Read articles by Dennis Moore, Jeff Smith, John Erb, Mike Nixon or even some of the Mopar experts!
The Mopar guys also know about the "Wedge" Head and what to do with it.

.
 
Last edited:
[QUOTE the heads do not contact iron because the gasket seperates them. same with the intake. ][/QUOTE]

You must understand that the steel bolts connecting aluminum heads to a cast iron block means the two dissimlar metals are connected electrically. An additional connection between the two in done by the steel cylinder gasket seals.
 
Well, that's what many think to be the case.
Look at the RPM whereby the horse power rating is taken.
How many of us operate our cruiser engines at 5,200?

turn mine to 5400 all the time, bottom is stock gm except for the forged flat top pistons, it will hold without a problem, mine is balanced tho
 
turn mine to 5400 all the time, bottom is stock gm except for the forged flat top pistons, it will hold without a problem, mine is balanced tho
It's one thing to spin her up to 5k rpm in a small boat such as yours.....,
avatar576_1.gif


.... but try doing that in a cruiser, or even with the OP's searay sundancer 245 !!!!!!

Apples/Oranges!

.
 
what about just buying a vortec core motor with a factory roller cam to start with. what year motor would I be looking for ? and will the flywheel that I have with the original set up work? also I am not wanting to run my boat at 5200 all day,really would like more power and torque at cruising rpm so I can run more prop for gas mileage.
 
Last edited:
One piece rear main seal blocks and two piece rear main seal blocks use different flywheels, couplers and bell housings. The later model one piece rear seal uses a different bolt pattern on the flywheel which requires you to use a bravo style bell housing and triangular style coupler. The bell housings between the two are very close but a triangular coupler won't clear inside the older bell housing (ask me how I know this, lol). Other than that everything else will change over. Except for the circulating water pump, you will need the new style with longer necks to clear newer style composite timing cover
 
I used the block, heads, crank and rods from a 1997 Chevrolet truck. If I'm not mistaken most blocks 87 and later will accept a roller cam. If you use vortec heads make sure you get the correct style intake manifold because the bolt pattern for the vortecs are different than other gm heads. And don't go crazy with a cam because they will inhale water if you have to much lift and duration or if your lobe separation angle is to little. Most folks will safely say 114* LSA is safe. 112* is ok if the rest of the specs will allow it.
 
Last edited:
Before you sink another dime on a new engine buy, beg, borrow or conive your way to a moisture meter and test the moisture levels in the transom, stringers and floor. If you can get at the flotation foam test it also. Since it is a 1984 there is a high probability the aforementioned structural parts are wet if not waterlogged and rotting, especially the floatation foam.

Gutting a hull and rebuilding it better than it came from the factory is a challenge but very rewarding. I did it on a 19' Baretta in 2003. It took about 8 long weekends from Fri. eve until 11 p.m. Sun. I drank my share of cold beeer and iced tea and lost 20 pounds, from the heat. I used several 4'x8' sheets of exterior grade plywood w/one side sanded. These sheets were cut to fit the new floor and others were cut into stringers,

Front part of the stringer was made from 4'X8' sheets of 1/2" plywood while rear stringers were 2"X8"X6' and reinforced w/blocks of hardwood for enginemounts and cross members were made from 2"X6"X6'. The transom is made of layers of 2"X12"X 10' boards cut to fit the transom from the inside. After all of the wood is cut to fit it gets treated w/ 2 coats of clear penetrating epoxy sealer CXPES. All of the fitted wood gets epoxied and glassed into place. Polyesther compounds cannot stick to epoxy. Install a new rear fill fueltank so the fill/vent lines are not buried under CLOSED CELL floatation foam. Epoxy is not cheap but is a stronger adhesive. I have a plant that the owner got to know about my project and sold epoxy to me at wholesale for $50/gallon. It is located in Lebanon, OHIO. I have pics in progress rebuild. The reason I did the rebuild was the engine was nearly new.

The finished boat will be lighter, stronger and much faster w/a new complete Vortec drop-in 350 CI 260 HP.
 
Last edited:
what about just buying a vortec core motor with a factory roller cam to start with. what year motor would I be looking for ? and will the flywheel that I have with the original set up work? also I am not wanting to run my boat at 5200 all day,really would like more power and torque at cruising rpm so I can run more prop for gas mileage.
Perhaps reread post #6 again.


The 1984 crankshaft flange is different from the post 1987 crank flange.
IOW, the flywheels will not interchange.

The early SBC will not accept the OEM roller cam system until approx 1991 or so. Check me on this!
The earlier blocks are not machined for the cam follower keepers, nor for the hold down tray mounting, nor will they be machined for the cam sprocket thrust control.


If you really want to see a performance gain in this hull......, and without going crazy on an engine build (of which will likely cause A drive issues anyway), consider removing the A drive, and install a V/P Duo Prop drive system.
The V/P Duo Prop (not the Merc BIII) will be similar to adding 80+ HP to this hull.

You'd have two choices/routes to go if you were to do this:

1... the DP-C or C1 of which is an AQ series drive (my preference).

2... the DP-S style Gimbal system drive.


1.... Before you sink another dime on a new engine buy, beg, borrow or conive your way to a moisture meter and test the moisture levels in the transom, stringers and floor. If you can get at the flotation foam test it also. Since it is a 1984 there is a high probability the aforementioned structural parts are wet if not waterlogged and rotting, especially the floatation foam.

2.... The finished boat will be lighter, stronger and much faster w/a new complete Vortec drop-in 350 CI 260 HP.
1... Excellent suggestion!

2... Remember..... anything that you get from GM will be using these below!
Doesn't matter who you debate this with, who you argue this with, who you speak with..... this is a poor choice for a SBC Marine Engine piston! :mad:
To avoid this, you must build your own, or talk to the guys at MichiganMotors.
 

Attachments

  • Dished Piston.jpg
    Dished Piston.jpg
    4 KB · Views: 13,555
The early SBC will not accept the OEM roller cam system until approx 1991 or so. Check me on this!
The earlier blocks are not machined for the cam follower keepers, nor for the hold down tray mounting, nor will they be machined for the cam sprocket thrust control.

Ayuh,... The block castings changed to roller cam compatable castings in '87....
though the machinin' may, or may not have been done, depending on it's original configuration...
 
Bill, you may be correct.
Like said, I'd want to be double checked on my comment.

I do know that the block must accommodate this equipement, which involves the machining for the tray, keepers and thrust plate.
If this has been done...., there should be no issues.

SBC Hyd Roller Kit.jpg



Note the piston selection here.

rollerlifters4213.jpg


.
 
Last edited:
Ayuh,... The Perfect pistons for a Vortec headed motor,... ;)
Yes, much better than the full dished, Bill.


The Vortec wedge has a widow peak shape in the center of it.

0405cct_head06_z.jpg


This may be a better piston selection.

p173611_image_large.jpg


Or one of these with the correct dish volume.

images




.
 
Ayuh,... No doubt Rick,....


Where'd ya find the pistons that mirror the head, with the heart shaped dish,..??

With a big enough dish to keep the comp ratio down, with the squish at .043", those should be Sweet pistons...
 
Bill, just do a search for SBC Low Compression Quench, D-Dish, or Reverse Dome pistons.
The supplies can offer you an array of pistons that will be suitable with an array of combustion chambers and bores/strokes.
Just give them the C/R desired, and they'll suggest the piston style and part number.... and in most all materials and process.
Cast aluminum, Forged aluminum, Hypereutectic process/alloy, pin offset position and height, skirt length, ring landing configuration, etc.

As for the quench dimension, HP Auto and Marine can each use a different ideal quench dimension.
.038" is prefered for Marine, due to the lower RPM -vs- the higher RPM of the Performance Auto engine.

.
 
That is one sweet looking motor Ricardo! I would like to build one of these. (Of course as a long term project due to the economy at the moment! lol). Anyways what bare block should I use for the build? 350 or 400? Is there less machining with the 400 vs. the 350? I know about the problems 400's had with overheating issues in stock heads. I guess the aftermarkets have overcome these issues? Sorry to ask so many questions but I am very interested in this particular build because of the low rpm torque it produces. That's what it's all about, Right? Oh yeah, anything else I should pay attention to with block selection? thanks, Tom
 
One piece rear main seal blocks and two piece rear main seal blocks use different flywheels, couplers and bell housings. The later model one piece rear seal uses a different bolt pattern on the flywheel which requires you to use a bravo style bell housing and triangular style coupler. The bell housings between the two are very close but a triangular coupler won't clear inside the older bell housing (ask me how I know this, lol). Other than that everything else will change over. Except for the circulating water pump, you will need the new style with longer necks to clear newer style composite timing cover
ok that answers that question. so can I use vortec heads and intake on the older 2 peice blocks with the correct pistons
 
where do I find a moisture meter. I live on the west coast of fl so plenty of marinas and boat mechanics around here. no evidence of leakage around the gimbal unit I have that out. but I dont have x ray vision either. also the bottom looks great about 30 coats of bottom paint.
 
Back
Top