engine coupler or wrong prop -5.7 with sx outdrive

hello, i recently bought a 1998 regal 242 and took it out for a test drive.the engine is a new 5.7 upgrade on the 5.0 with a cobra sx outdrive i believ to be a 1.66 ratio.it runs great however it will only do about 10 mph.i can give it gas from 1500 rpms to 3000 and it just does not want to react other than rev up.i do not smell or see the black smoke as described in a coupler failer.and it is a new prop that does not appear to be spun out.i looked in between the engine and could not find any rubber pices of the coupler either.it makes a lot of water flop around but doesnt speed up.i measured the prop and it appears to be a 13" with 17 pitch.i can put it in gear without the engine running spin the prop and i will turn the engine but i would expect that as it will push the boat at low speed.can someone please tell me that all i need is ablankady blank prop with a pitch of something and this will fix it.if not what else is there to determin a coupler failing.many thanks in advance

Re: engine coupler or wrong prop -5.7 with sx outdrive

Sounds like the prop has a spun hub in it.

Re: engine coupler or wrong prop -5.7 with sx outdrive

thanks for getting back,i will try that this weekend.i did go back out and look at the prop.it does not have any rubber to slip,it has a square tube that slides in the prop and a metal sleeve that slides in it and lockes the two to the prop shaft.wouldnt i see signs of rounded plastic tube if it was slipping.i would sure be glad if thats it and not the coupling.thanks again

Re: engine coupler or wrong prop -5.7 with sx outdrive

I seen where someone said they had a cavitation problem from exhaust gases.i took a picture to show where there is a hole at the bottom of my exhaust tube just past my boot.i thought it was a drain hole.also where my outdrive and pinion housiong come together there is a considerable gap all around it.i made sure the raw water tube was sealed good between them when i put it back together but had not put seam sealer back(i think it was seam sealer they used to seal between the two)and there was a lot of exhaust coming straight up and not out the prop area.i would think since the prop is about 12" lower that it wouldnt cause a problem.anyhow here is a picture and i would like any advice you could give.i bought the boat and was told it was water ready.im hoping that when it took it apart for bellows and didnt put the sealer back that i changed something.otherwise i believe i was lied to because 8 mph isnt going to cut it.thanks in advance

Re: engine coupler or wrong prop -5.7 with sx outdrive

Cavitation won't stop you moving like you report. What you're seeing is not a cavitation problem.

Forget what you think you can see in the prop, and no you wouldn't necessarily see a problem from the outside of the prop... that's why people are recommending you make a mark then take it out.

Do that test, and probably you'll find that your prop hub is spun.

That prop with that pitch on a 5.7 should get you on plane ok in a 24 foot boat, probably in less than 15 seconds depending on weight.

On a 24 foot boat, I'd expect that swapping a 5.7 in for a 5.0 liter engine would get you maybe 4-5 miles per hour more, max of about 10 more, over the 5.0 once your prop is fixed. You're fairly high up on the drag vs. horsepower scale, where you're paying 10 hp for 1 mile an hour of speed. In a 24 footer it's more usual to have twin engines or a dual prop drive because you need the extra prop in the water for good performance.

Right now though, check the prop for a spun hub, it's 99 percent certain that's the problem.

No one can tell you what the right pitch should be until you get that fixed then report your top speed with a correct tachometer reading. Without that it's just guessing, and probably getting it wrong.

Erik

Re: engine coupler or wrong prop -5.7 with sx outdrive

Oh, and that's probably a relief hole for exhaust to come out of when at idle. It's supposed to be there, and it's not causing problems for you.

Erik

Re: engine coupler or wrong prop -5.7 with sx outdrive

Thanks ericgreen.i wasnt trying to avoid the test its just that the water on the ohio is up and i have to drive 50 miles to get to a lake to test it.will be going later this weekend and i was trying to be thurough enough in explaining what all is actually going on,and done to it to help you- help me.i would absolutly love it to be a prop issue and not the coupling (which i still dont see evidence of).will try the marking of and a different prop later.you mentioned duel prop,you cant see it in the picture but there is a 1 1/2 outline around the outdrive where it bolts to the transom that looks like something had been there(bigger outdrive)dont know if i had a switch done to me or if it was just the way it was built.once again i thank you!

Re: engine coupler or wrong prop -5.7 with sx outdrive

That's one of those things you kinda have to find out from the previous owner

I don't see the pic you're referring to, but it's possible there was an older model of OMC or other drive on there before, or it may just be an area of the boat that didn't get polished or painted for some reason.

If there was a DP290 drive on there the transom would have been cut out larger, not just mounted with the larger transom plate.

Good luck on the testing, let us know how it goes.

Erik

Re: engine coupler or wrong prop -5.7 with sx outdrive ! UPDATE!

Re: engine coupler or wrong prop -5.7 with sx outdrive ! UPDATE!

Hi, after trying out my boat again,i unhooked the cable to the outdrive all together and shifted by hand,apparently it was not engaging all the way up and since it has a cone clutch it was not grabbing good enough to keep it from slipping.i swear it couldnt have been more than 3/8" out but it was enough to prevent me from moving right.now i can do 35 mph at 4100 rpms..yes im happy!maybe this will help someone down the road,thanks to all who helped.