Logo
FULL SITE MENU

Alpha one gears

D

ddabal

New member
someone told me that mercury m

someone told me that mercury makes a heavy duty gear set for the alpha drives which will allow them to handle more hp. anybody know anything about it? I have one of the big block 454/330 /apla one combinations mercury used for a few years(before they knew better). the combination scares me.
 
"I think the big block Alpha u

"I think the big block Alpha uses a 1.32 ratio upper gear set, which helps to carry the heavier torque. This is because the vertical shaft is turning faster relative to the engine RPM, than for say a 1.47 ratio small block gearset. (HP=torqueftlbs X RPM / 5250) The higher vertical shaft speed also means the water pump pushes more water as needed for the additional cooling requiremnts of the big block.
But the book rated max hp for the Alpha remains at 300, so you need to be sensible about the throttle.
I am faced with the same problem, as I just swapped a 350 hp 6.2 MPI engine in my boat, still with the Alpha. So far so good.
I don't beleive there is a stronger gear set available, but maybe someone else here knows differently.
Rod"
 
I would see that the unit has

I would see that the unit has a drive shower on it for cooling the upper drive shaft gears.
 
"No, there are two different 1

"No, there are two different 1.50 gear profiles. During the MR and up to Alpha they developed a heavy duty set. Your year had the better gear sets. Actually its the engine torque that hurts the drive. Run some high perf oil, put a drive oil monitor on it. Change the oil yearly and drive it. Screw the shower, they are so not right for stock situations."
 
"Ayuh,.......
Rod is On the M

"Ayuh,.......
Rod is On the Money,.......

The 1.32/1 Gear Set was Merc's answer to their misguided BBC/ Alpha Problems........"
 
"No, There were other 1.32 app

"No, There were other 1.32 applications years before that BBC/Alpha combo. Its all hull and power package dependent.

Rod, I must debate your 1.32 theory. The ratio of the gears do not give them the ability to "carry" torque. If you look at all the combinations the design is such that the lower half rpm is the constant. Meaning a 4cly with 1.98 and a v8 454 1.32, the lower is spinning the same rpm, the rest is done with the prop pitch which determines the wot rpm. Therefore the verticle shaft rpm and water pump rpm is the same for all.

Torque kills, that is what eats an Alpha drive not the HP."
 
"Yes, Followup,

Its theore

"Yes, Followup,

Its theoretically the same or the constant. Slight variability will exist through the range of all the drive ratios and prop pitch combinations. I did find some data about water output testing to diagnos a water pump problem and the vertical shaft rpm will be within 1 qt per 1/4 min of delivery on all models."
 
"Harve;
I don't want to c

"Harve;
I don't want to create a huge issue, but I do have the following comments.

Firstly I think the engine RPM needs to be the reference constant, as most marine engines operate in the range of 650 idle to 4800 WOT; whether they are 4, 6, or 8 cylinders; 100 or 500 hp. Moreover they create hp more or less in proportion to RPM.
Heat generated is also basically proportional to hp generated, and therefor varies as engine RPM. The pump speed varies directly as the engine speed and this matches nicely the cooling requirements.
Agreed the lower gear set throughout is the same. The variable is the upper gearset.
A 135 hp 3.0L running a 1.94 gearset has a 20 tooth drive gear turning a 24 tooth driven gear, and the vertical shaft turns .833 rev per crank revolution.
A 330 hp 7.4L running a 1.32 gearset has a 20 tooth drive gear turning a 16 tooth driven gear, and the vertical shaft turns 1.25 rev per crank revolution; some 50% faster.
There is no way a 4 cyl 1.98 and a 7.4 L 1.32 lower shaft and gearset/prop is turning the same speed.
And would you mind telling me how the 7.4 pump is NOT going to be capable of pumping more water than the 3.0 at any similar RPM??

The fact is at any comparable engine RPM the 7.4 prop will be spinning about 50% faster than the 4 cyl, and it will likely be a 23, 25 or higher pitch prop due to the higher hp available, whereas the 1.98 will likely be a 17 or 19 pitch. This is all relative of course to the 7.4's much higher top end on similar size and class of boats.

In my post I mistakenly said the 1.32 will carry higher "torque"; I meant higher "horsepower". Any given shaft can of course handle only so much torque, no matter it's rotating speed. A faster turning shaft will carry more hp at the same torque since hp is torque times RPM divided by 5250. My apologies for this confusion.

But the fact is the 330 hp 7.4 simply makes too much torque for the Alpha regardless of ratio, and there have been lots of failures.
This much we can agree on.

Peace.
Rod"
 
Back
Top