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Old December 15th, 2017, 17:43   #5
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PickleRick's Avatar
Join Date: Nov 2017
Location: Greenville sc

There is no direct drive for a stern drive that i am aware of and that includes factory yanmar, mercruiser and volvo small 1.7 to 2.5 diesel motors. I have tried to find what ratios were used with no luck so far.

The alpha comes in only these gear ratios
120 & 140 4 cylinder 1991 thru present 1.93 / 20-24
175 & 4.3 V-6 1991 thru present 1.81 / 17-19
198 V-8 1991 thru present 1.62 / 24-24
198 thru 260
1991 thru present 1.47 / 20-22

The only other converted diesel carver i know of uses a little 50 or so hp isuzu 2.2 i believe with max 2800 or so hp. No turbo. He is a long range hull speed cruiser around 1800 rpms. 10 mph max. He is using the 1.98 ratio

The other user here with a 1.9 tdi in his 25 ft sea ray (similar weight as well as hull design) is using the same gear ratio as i am which is stock for the v8

The stock v8 is at about 23 mph at 3200 rpms. At around 4000 to 4250 you'll hit maybe 32 empty.

Keep in mind all my goals and info is in mph not knots. I want comfortable on plane crusing around 3000 rpms at @ 20 mph.

I hope the torque plateau will allow me to plane closer to 16 to 18 mph at 2800 rpms. Im not holding my breath here.

Direct drive would not be possible in this boat and it's also power robing, takes up more space and makes low speed maneuvering harder. Not to mention harder to trailer. Direct drive = full inboard. My boat is a inboard/outboard.

I dont care to reach 30mph or even 25 mph. I just want to comfortably get on plane and cruise without having to run the motor at her redline. Id like crusing rpms to be as close to 3000 rpms or lower as possible. The purpose of this swap is fuel economy

The v8 would get 2 miles to a gallon on a good day. I hope to double that
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