5.0 to 5.7 Rapido rebuilt engine swap

[krisnowicki]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

When its all said and done you will need to do a WOT run and see if you are in the WOT range. I bet your prop is to small and you are wasting revs right now. From your data it seems your are running a 15 or 17" i bet a 21 or 19 would be right for you boat and out drive ratio.

 

[sschefer]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Glad to hear it was just a lifter that wasn't pumping up. Probably just a piece of dirt in the oil galley that finally washed through. Keep an ear open, if it starts to click and then clear on first starts then it's a leaker. You can replace that next winter so just have fun this summer! Great job.

 

[coastalcruiser]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

My redneck drive stand puts the shaft at the exact height of the boats coupler. adjustable by raising or lowering the front of the trailer. 4 screws attach it to the hand truck-cart. also got rid of some scrap lumber, total cost $0

 

[wil7483]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

When its all said and done you will need to do a WOT run and see if you are in the WOT range. I bet your prop is to small and you are wasting revs right now. From your data it seems your are running a 15 or 17" i bet a 21 or 19 would be right for you boat and out drive ratio.

What would be the right range for this motor. 4200 - 4800 rpms I'm presuming. If that is correct I was at 3800 a few times and it got to 33.6 mph on the gps with the 6 of us on board and full 60 gallon tank of fuel. I think that I was btwn 1/2 and 3/4 throttle then. Right now it has a 15 or 17 on it but I don't know which exactly. Actually it has the 15 on it. I dropped down a pitch last year with the old engine trying to get to WOT range and never put the larger prop back on. The next time I'm in Eufaula I will put the 17 back on and borrow a 21 from the shop there and see what difference they both make before buying another one.

Just a hypothetical (and I know I'm in the wrong forum for this) but what type of numbers should I expect with a 21p prop? I will admit, I'm not a speed guy. I don't ski or pull skiers. Just go back and forth to the fishing spots.

 

[FreeBeeTony]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Just curious.............how much does the boat weight?

 

[krisnowicki]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

I had a liberator which is close to weight and shape. I ran a 21p prop with a 1.5 ratio and got 4600 rpms which was perfect. And I got about 52 you should expect something close. I would bet you are going to get at least 50 and will need a 21p or at the smallest 19. But, I would bet 21 or 23

 

[wil7483]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Just curious.............how much does the boat weight?

3900 lbs empty. So if you add up 360lbs for the weight of 60 gallons of fuel, 700 lbs for the 6 people, and maybe another 100 lbs for gear and it gets up there pretty quick. I'd put it at about 5000 lbs give or take a few pounds here and there.

 

[sschefer]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

On a stock 350 you should be setting the red line at about 5000 RPM's. That's a safe number if you're not running it for long periods of time. The power curve with a stock cam is over at that point and anything beyond that is just wasted gas. 3800-4200 should be the top end of the power curve. I'll bet this is where you find the sweet spot. Call that your crusing speed and save the red lines for the hole shots and races to the courtesy docks at the ramp.

 

[betayv]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Just won't take the old lady next time that's all, then I can stay out as long as I want


yes is time to enjoy the boat and do some fishing GREAT JOB!!!

 

[wil7483]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Hey guys, just to follow up. I took boat to lake today to try her out with the 17p prop but the lake was flooded. I decided that I would just drive down to Destin and put her in the bay. Here are my numbers and a few pictures. With the 17p prop I was able to get to 4300 rpm WOT. Top speed at those rpms was 43.6 mph on the gps. There was a mild chop on the water but otherwise a good day for boating (in the bay). I have a 19p prop on order and should be here tomorrow actually. Do you guys think it is going to make much of a difference? I am even looking to pick up a 21p just in case the numbers are better with the 19p. From the data above what should I expect with the 19p or higher prop? Today there was just 3 of us in the boat and one of us only weigh 24lbs. 270 lbs for myself and 120 lbs for my daughter. So there wasn't a lot of weight in the boat.

After taking her out of the water I flushed the engine at the dock for about 10 minutes with fresh water. Then I rinsed the boat, drive, and trailer real good. When I got home I flushed the engine again for another 10 minutes on the muffs and rerinsed everything. Then I opened the drain plugs and let the water drain into the bilge. You'll think this is sufficient to remove the salt water from the inside of the engine?

 

[HT32BSX115]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Sound like you got it running pretty good!

4300 is a bit low for that engine I would think. 4800-5000 might be closer for it. You might check your total timing advance.

If it was doing 4300 with a 17.....it will be severely over-propped with a 19.

I think it should turn a 17p prop faster than you're getting. Otherwise you might have to try a 15.



Or maybe even a 16 4 blade (if you could borrow one to try). I know you're not trying for a really high top speed but you do want to prop any boat so it turns max rated RPM at WOT .....(loaded near the average weight where you run it all the time)...that will usually give you the best all around performance.

Cheers,


Rick

 

[wil7483]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Hey Rick,

I had the 15 on it but I never did any WOT runs so I didn't have any numbers to post. Hopefully the lake will be back within it's banks this weekend and I can get out there with all three props and see what type of numbers I can get wit each.

 

[rad1026]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

great thread. Thanks for all the documentation.

 

[sschefer]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Humm, 4300 RPM, that's just outside the power curve. Dropping to a 15 would cause you to cruise through the power band and up to higher RPM's but it wouldn't get you any better MPH numbers.

I think you're right in trying the 19. You definitely have the HP to turn it and if it will keep you in the 3800-4200 rpm range at WOT you should see a better top end while keep the engine loaded like it needs to be.

 

[Cptkid570]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Earlier in the thread, you had some photos where you were redoing some of your interior... next time you are taking photos for the thread, could you get some photos of the boat too? I really like that boat.

 

[wil7483]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Not much to look at really but serves a purpose.

 

[Cptkid570]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Very good. Thank you for sharing.

Do you have much clearance between the top of the spark arrestor/carb and the bottom of the engine cover? Too bad it can't come down a foot or so more and you could make a bench seat across the back.

I like the design of that boat though..and it's good to have a porta pottie. I'm surprised your wife doesn't like to go out on it more (probably because you are testing WOT and screaming along at 43mph! hahaha Just kidding)..

 

[QC]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

4300 RPM, 17P, 1.5 ratio, 43.6 MPH = 5% slip . . . too good. Something is wrong and I always suspect the tach. At 15% slip you're turning 4800 RPM Could be the pitch is wrong, or the gear ratio. Everything has to be dead nuts to make good decisions. If my guesses are correct the 19P could be perfect, but need to confirm your numbers!!

 

[wil7483]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

4300 RPM, 17P, 1.5 ratio, 43.6 MPH = 5% slip . . . too good. Something is wrong and I always suspect the tach. At 15% slip you're turning 4800 RPM Could be the pitch is wrong, or the gear ratio. Everything has to be dead nuts to make good decisions. If my guesses are correct the 19P could be perfect, but need to confirm your numbers!!

You may be right. I am going to the lake this weekend with all three props in hand, 15p, 17p, and 19p and do a series of runs at WOT with all of them and record the numbers (hopefully in pictures) and then post them and see what I come up with. I really had to play with my trim settings with the boat in the ocean and the chop. A few times she came clear out of the water. It's really hard to make this boat porpoise due to its weight but it came close a few times with the trim all the way to it's upper limit.

Here are the props I am using:

48-16314-17 14.5 dia x 17 pitch RH rotation. Stainless steel
48-78116-15 (Not sure if aluminum or stainless.)
48-78120-A40 19 14 x 19 Quicksilver Aluminum RH rotation

 

[wil7483]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Very good. Thank you for sharing.

Do you have much clearance between the top of the spark arrestor/carb and the bottom of the engine cover? Too bad it can't come down a foot or so more and you could make a bench seat across the back.

Originally it had a bench seat but I redesigned it so that it was more condusive to stand up bottom fishing.