Correct prop for 43 cobra

"New member
Username: nowunn

"New member
Username: nowunn

Post Number: 1
Registered: 09-2008
Posted on Friday, September 05, 2008 - 08:42 pm:

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I am trying to rehab a 1986 thunder craft it has a 4.3 liter omc with a cobra outdrive it did not come with a prop so i bought one at a boat shop i also got the thrust washer and a splined washer the thrust washer and the prop slide onto the shaft ok but there is not enough spline for the splined washer i have a feeling i got the wrong prop it is 15x17 the only other marking on it is 391200 it is steel could anyone tell me what they have, or if some props are deeper than others .how to find the correct one? thanks"

"391200 is an aluminum prop, n

"391200 is an aluminum prop, not steel.

Prop selection is done largely by trial and error. We don't know what your boat, passengers and gear weigh so there is no book or reference that says what prop goes on a Thundercraft of unknown length.

The correct prop for your boat is one that lets the engine rev to between 4200 and 4600 rpm while underway with the throttle at full "wide open" position. The engine must be running right, and properly tuned up for this test.

Try your 391200 17P with typical gear and people aboard...if the engine wants to exceed 4600 rpm before you reach full throttle, you will want a 19P. If the engine is lugging below 4200 with the throttle at full, you need a 15P"

"On the OMC's you have to

"On the OMC's you have to make sure that the thrust washer sits right down inside the lip on the front of the hub, if it doesn't then the prop won't go all the way on and you won't get the spline washer on."