Is my SX-M outdrive correct for my boat/ motor??

[spoonek]

Greetings, new boat owner here, first time posting.

I recently bought a 2000 Chaparral Sunesta 233 deck boat with a 5.0GI PWTR engine. The metal plate on the out drive says the gear ratio is 1.97. The lake I use is at 1071' above sea level. The boat weighs 3832, fuel tank is 58 gals.

I'm wondering if the outdrive is original to the boat. Is the gear ratio optimized for a 4000+ pound boat with a 5.0v8?

Many thanks!

 

[evantful]

I believe the ratio normally used on the SX of that era for a V8 application was 1.60. The 1.97 I believe was for the 4cyl engines.

The 1.97 tend to be more commonly found used and cheaper than the other ratios so its very possible that the original owner needed an outdrive and purchased the cheapest but incorrect option.

 

[garbageguy]

My 1998 Wellcraft 240 SE (pretty heavy boat) with carb'd 5.7 has a VP SX-M 1.6

 

[spoonek]

Thanks for the quick responses. Would I need to change just the lower unit or is the final ratio a combination of the upper and lower? Thanks again!

 

[Assassin3F]

Going to preface this with "I don't know anything regarding changing the gear ratio..." You can get the drive service manual from the Boatinfo link in the adults only sticky at the top of the forum. There is little to no info regarding changing gear ratios in the manual on boat info however...it appears that you will need the workshop manual (which supposedly covers upper and lower gear overhaul procedures) P/N 7731624-8 (and just to be clear that manual is circa 1995 so there may be some different info in more current versions)...that's the bad news...the worse news is there is a list of Drive units and gear ratios that appear to use different part numbers for Penta SX drives with different gear ratios.

The 5.0 Liter Fi models have two different possibilities 3868077 (1.60:1) or 3868068 (1.60:1)...not sure if this means you need a different drive or if your existing housing can be converted by changing out the gears. I can tell from reading the service manual however that the procedure for disassembly and reassembly is pretty extensive and you will need some specialized tools, gauges and materials (gear shims etc) to get it all put together right. This looks like an off season project to be honest but for all I know you are a super whiz mechanic...in which case I hope you are in southern Michigan cause that would be fantastic.

Sorry I can't be of more help I just couldn't find anything regarding a change in drive ratio online.

 

[wkb2460]

My 2000 Larson with a 5.0 PEFS has the 1:60:1 drive also.

 

[Fishhead-1]

Have you taken the boat out and checked for max rpm?

 

[Poco2]

My 1998 Four Winns H200 with a 5.0Gi SX Cobra is 1.6. My sons 2006 H200 with a 5.0 GXi has the SX-M with 1.6 ratio. They are 20' and weigh about 3600 lbs. I think the higher ratios are for smaller engines. Your altitude is not significant. We run at 2500 feet. What is your prop size. What is your wot RPM? Top speed?

The gearing is in the upper drive. The gears are expensive and the labor to change them is too. I would try to adjust speed and wot rpm to specs with the prop rather than re-gear.

 

[bruceb58]

The gearing is a combo of both but you can change just the lower to get it down to 1.79.

Before you go and change anything, need to verify that the drive is what the tag says as the lower could have already been changed,

Using a helper, rotate the input shaft the number of times it takes the prop shaft to rotate 10 times and divide the input shaft number by 10.

If you do indeed have a 1.95, you may just want to sell it and get the correct drive assuming a real high pitch prop can't get you into the correct RPM range...which I doubt.

 

[Maclin]

Is it a DuoProp? What RPM's do you see on the tach for any given MPH?