87 Stinger 260 Speed and gear ratio
 

I have an 87 Stinger 260 running twin 350's and OMC Cobras.

Why does the boat run 9mph on one engine and 50+mph on two?
Also while running only one engine the prop seems to cavitate and have no power, but when you fire the other engine up, hold on ! ! It simply does not make sense to me.

The only thing I can make of it is that they are working in multiples, concerning the power. Sort of like two horses can pull 4 times the load of one horse.

I burned the upper on one of the outdrives. I have been looking at gears for the OMC and have found that the V6 versions run 21/19 and the V8 runs 21/16.

Will my boat go faster if I run a higher ratio like 21/19 or will the engines simply destroy the gears?

Any thought on these questions will be greatly appreciated.

You are draging one gear case like an anchor with only one motor running. the v6 gear ratio will stand up just fine, but you will need to prop up to not over rev the v8 . your speed will not change. just the prop size.

also your props are pitched to run with 2 engines,when running on just one prop is way too big and the 350 wont have enough power to spin it. Its always a good idea to carry an extra prop with much less pitch in case you do have to come home on one engine you dont have to go 9mph.

Thank you for the advice.

To help me understand correctly:

The 9mph is due to the prop being the wrong pitch.

(I can get higher RPM's just no speed). It seems to cavitate running on one prop. I do understand the part about dragging an anchor and I do not remember if I trimmed up or not.

The gears will hold up but will not create more prop spin and faster speeds. I would have to change the props also if I change the gears. I understand.

Sucks, now I have to spend more money on more HP ! !

You can not trim up high enough to not drag one gear case. with only one eng. running. P.S. you do not want to run differant gear ratios in only one drive you will not be able to
even out r.p.m. exactily with the prop change.:bsflag:

Think in a different way to answer your 9mph Question.
Your 7-8000lb boat is running on one 250 hp engine that is (without both motors running pushing together), WAY over propped and underpowered with extra drag from the dead outdrive.
Too much prop. Too much weight. Not enough Ponies.

I must be missing something here but, running on one engine would be just to get back into the dock. why would you care how fast that was? and also why would that indicate a gear ratio change rather than just repairing the wounded drive? confused