new lower and gear ratio change?

[hydroViper235]

I've got an 88 xr4 merc 150. Trashed the lower, got a new one in real good shape off an 89 merc 175. I'm run n a 14 1/2 22p ss chopper. The gear ratio must be lower it takes off like a champ but has no top end now. What prop should I run to get my top end back? the spur or big gear in the old one was 21 tooth the new lower had one that has 28 teeth.

[SSIMPALA71]

The xr4 original case was 1.78:1 ratio and the 175 was like 1.86:1. Not sure exactly which prop to say but somewhere around 23-24p

[Jay Smith]

Could also be a 2:1 the way to check ratios is to rotate engine to TDC or "0" at the flywheel mark and line up to the static mark on the flyhweel cover and or block next put a makeshift mark on the propshaft or prop hub and a mark on the gear case ( a static mark ) in exact alignment next rotate the flywheel exactly 1 round and note the ratio of rotation of the propshaft verses how many times the motor rotates in conjuction with the prop shaft that will show if its 2:1 ratio very quickly as one will complete the rotation exactly 2 times for the others 1 time..The others ratios thats not 2:1 might take a degree wheel attached to the propshaft and alittle math;)

Good luck,