How many impellers do I have to change ?
 

Just converted my RWC 87 250 SD 454 with Alpha O/D, to a volvo crank driven raw water pump. With a 1 1/4" high speed thru hull pickup and a 1 1/4" raw water strainer, so I no longer need the alpha cooling water. Do I still need to keep a good impeller in the sterndrive for cooling the outdrive ? Or can I just put an Alpha sterndrive shower in place of the impeller. Are there other ways that will cool the outdrive without an impeller.

Any ideas ??

Interesting question. You DO need all the cooling that you can get if you have a big block into an Alpha. I guess I'd remove the external cooling hose (from drive to transom assmb.), remove the impeller (but not pump housing), plug off the fitting where the cooling hose went into the transom assmb., and let forward motion force feed water through the outdrive and dump out in the cavity where the hose was. You only need that water circulation when you are under load anyway. And, being a BB/Alpha combo, I guess I'd do the drive shower thing too. --- Jer

No you do not need the impellor. My first boat was rigged exactly like jp described and I never had a problem. No drive shower either, alpha, sbc.

Dave

Outdrive impeller AND crank pump cooling
 

The problem was, if I had a SBC, I wouldn't have to go with an external water supply.

Will I do damage to the outdrive if I simply remove the impeller in the Alpha, cut the water hose coming from the outdrive, and plug the line going to the transom ?

I thought I covered all that in my earlier post. But, since it is a BB (more cubes-more torque) I would spend the C note for the shower. Also, Merc has forged, HD upper gears for that Alpha. Since it's winter, I'd make that upgrade now if you don't have them in there already. --- Jer

I've seen the l/h side of the upper unit
(outside the water inlet cavity)
drilled and tapped, and a flexable hose
ran to the top cap where it is discharged
just like a drive shower.

The water inlet fitting on the bell housing
must be plugged too.

jt

I like that plan, jt! --- Jer