DRIVE RATIO

[BUY_B]

I HAVE AN 86 290XF WITH 270 CRUSADERS, I WONDERED IF ANYONE WOULD HAVE A ORIGINAL SPEC SHEET THAT GIVES THE DRIVE RATIO
WHEN THE BOAT WAS BUILT, ASSUMING THAT THEY ARE ALL THE SAME.
SOMEHOW THE DRIVES GOT CHANGED DURING AN ENGINE SWAP BY THE LOCAL MARINA ABOUT 8 YEARS AGO AND NOW THE ENGINES WILL NOT GET PAST 4000 RPM, WITH THE SAME PROPS. 17 KNOTS AND 1/2 MILE TO A GALLON OF GAS DOESN'T WORK FOR ME. ANY HELP WOULD BE GREAT, THANKS.

[GoneFission]

Is there any chance they went from a reduction gear to direct drive?  That might explain it...

[BUY_B]

THATS WHAT I'M TRYING TO FIGURE OUT. FOR SOME REASON I THE TAG IS NOT ON THE PORT DRIVE  AND THE STARBOARD IS IMPOSABLE TO SEE WITHOUT REMOVING THE AFT DECK.

[GoneFission]

Can you see one of the props?  If so, you can see how many turns the prop makes for 1 revolution on the engine.  Turn the engine over one full revolution with either a wrench or the starter - if the prop turns one full rev, you got direct drive.  If the prop turns half a turn, you've got a 2:1, but I doubt it based on your numbers.  

You could re-prop to a lower pitch, but a smaller prop turning higher RPMs is not as efficient as a bigger prop turning lower RPMs.  2:1 drives on boats in the 28-30 foot range usually work well with V-8 gas inboards and somewhere around a 16x17 prop.  

See ya one the water - soon I hope...   Need to get that tank installed...

[BUY_B]

I'VE GOT ACCESS TO A STOBE TACH. I'M GOIN TO CHECK THE CURRENT RATIO WITH. THE DRIVE WILL NOT TURN THE SAME AMOUNT WITH THE ENGINE NOT RUNNING. NO HYDRAULIC PRESSURE. I DO NOT WANT TO RE-PITCH, THE BOAT RAN 25-28 KNOTS BEFORE THE DRIVES WERE SWAPED. THE PROPS ARE DO DOUGHT THE RIGHT DIAMETER AND PITCH.
THANKS FOR THE FEADBACK.

[GoneFission]

oops, sorry - did not realize you had Velvetdrives.  Got to have the mains running to make the trannys work...   Strobe tach should work, or try a borescope to find the tag on the tranny...