Sm-dp question

[Fishhead-1]

I bought a complete takeout 5.7 Gxi with sm-dp 1.78 ratio with set of f4 props a year ago complete fresh water half system exhaust gimbal trim pump everything. I run a 5.7 Gsi with same duoprop but a 1.95 ratio with a set of f3 props. The Gxi was on a smaller 21 foot boat, is that a common ratio to be bolted to a sbc engine not a big block? I'm going to build the Gxi as a swing engine as mine has 1600 hours and want to swap it out in two years. I would like to have a swing set of drives ready in the future so my question is are both uppers the same ratio and the lowers are not? Am I looking at $1500 just for a gear set lower to turn it into a 1.95? Do I sell the lower only and buy a used 1.95 ratio that ends up to be a basket case? My current drive is in great shape I'm just thinking down the road. What would you do, thanks

 

[evantful]

The 1.78 does seem alittle odd for the 5.7GXI, especially on a 21ft boat. I think I would atleast try the 1.78 DP-SM as is, and play with some different prop sets to see if you can get it in the right range. It may not be terrible.

Just out of curiosity where did you find the takeout engine and drive?

 

[Fishhead-1]

I'm dialed in perfect with my existing ratio and prop set at wot at just under 5000 rpm. It was in a almar and the guy had a bracket put on it and a 300 suzuki

 

[Fishhead-1]

I found this chart so it looks like the 1.95 and 1.78 uppers both use the same trans ratio correct? Upper (SX and DP-S):

3857007 BRP HSG AY,GEAR 22:23 (1.43, 1.51, 1.60, 1.66, 1.68, 1.78, 1.95)
3857010 BRP HSG AY,GEAR 21:26 (1.79, 1.89, 1.97, 2.18, 2.32)

Lower (SX):

3855692 BRP G'CASE AY,SX 19:26 (1.43)
3855693 BRP G'CASE AY,SX 18:26 (1.51 and 1.79)
3855694 BRP G'CASE AY,SX 17:26 (1.60 and 1.89 )
3855695 BRP G'CASE AY,SX 17:27 (1.66 and 1.97 )
3855696 BRP G'CASE AY,SX 17:30 (2.18 only )

To get the final ratio value, multiply both ratios together. So , e.g. for 1.79

Upper 21:26 and
Lower 18:26.

So the final ratio is (26*26)/(21*18) = 1.79