Hey guys i have a 92 chaparral 2500sx with a yamaha outdrive. I replaced the engine with mercruiser and changed accesories to mercruiser. I've got everything tuned in on the engine now and im trying to figure out my prop slip to figure out what i need to try on this thing.
Anybody know the ratio of a 7.4 yamaha outdrive?
Also a quick formula to figure out my slip would help.
Thanks in advance for any help!

I think the 7.4 is the same as on my Yamaha diesels, the Hydradrive leg. It looks different to the leg found on V6's and small blocks, it also shifts a lot smoother.

If it is a Hydradrive, the ratio is 1.5:1.

See the photos in the link to see if your is a Hydradrive. http://www.redfinnboats.com/pdf/Yama...chure-2010.pdf

You are correct about the gear ratio and the Hydradrive. Yamaha for I/O sterndrives do not supply parts to USA anymore. Some places (very few) will have stuff still sitting on the shelf but very hard to find anything for the Yama gas I/O and the outdrive related parts. Yamaha did not offer a duoprop outdrive for the sterndrives ever in the USA but does for the outboards engines for the past x amount of years.

Also I have the service manuals for these anddouble check about what was standard gear ratio for the 7.4 L. Also Yamaha has not made an I/O gas app since 1993 for the USA markets and I think they never made a diesel app for the USA market..

Specs for the 7.4L Yamaha

300hp at prop

8.5:1 compression Ratio

4 bbl carb

RPM range 4200 - 4600

weight engine and all drive components total package is 1153

Standard drive ratio 1.50:1

Outdrive hydraulic clutch system

drive cap. 2.5 qts of gear oil

recommend a GL4 gear oil spec for the outdrive

engine oil straight 40 wt & showing 6 qt capacity with oil filter change

oil pressure at 2000 RPM's spec is 49.3 psi ( funny how they say .3)

timing at idle speed - 750 to 800 rpms is 13 degrees BTDC with timing jumper attached set into base timing mode

FYI worth.