5.0 to 5.7 Rapido rebuilt engine swap

[wil7483]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

You need to buy a new tach. It has to be off... You just spent alot of money a nice shiney engine ... dont you want to make sure it is turning at the right speed so it will last a long time. I bet your put a new tach in and it is turning more then 5000. a 17p is small for that set up.

I will go to West Marine tomorrow and buy a new tach and then see what numbers I get with it once I can get it installed.

My only question is, even if the tach is off, wouldn't the speed still be greater if it was turning higher than what the tach was showing. That is why I feel it isn't the tach. The speed is in line with the numbers that the tach is showing.

 

[krisnowicki]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

I ;thought you had said on the last page that the tach was off.
Are you checking your speed with a gps?

 

[HT32BSX115]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

I ;thought you had said on the last page that the tach was off.
Are you checking your speed with a gps?

And I thought I was the only one that didn't read these posts carefully!!

All of the speeds posted are GPS speeds. I have a Garmin GPSmap 172 in the boat.

D,

Good idea to get another tach. Unless you have a calibrated "shop" tach, you can only try another one and see if they read the "same".

It's unlikely that 2 different tachometers would be off the same amount.

You also could be timed a tad retarded? That would limit your top rpm/power and possibly your distributor isn't advancing completely or enough..... There's any number of "things" that could limit your upper end power.

(I'd run that boat over a scale too.....it would probably be the best $15-20 you'd ever spend.)

Also, are you absolutely sure that you have a 1.5:1 ratio drive?

Turn the engine exactly 3 turns and see if the prop turns 2 complete revolutions.

People have been sent the wrong ratio drives before......... The wrong ratio will make a difference too..... All this stuff will give you weird slip numbers...


HEY! It's going to be 66 today and 71 on Monday. Looks like summer is here early!!!

(After tomorrow we'll be back to FALL and Winter!!)



Cheers,


Rick

 

[QC]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

One thing with the tach issue though is now he is showing between 15 and 20% slip, so I am starting to believe the tach. Prior it was around 5% and we knew something was wrong. Now, I am starting to believe the tach and I also like the 19 . . .

Can you make her porpoise at all? Can you trim all of the way up without losing speed? I'd be starting to play with setup stuff, like weight balance and see if we can get the speed up and the slip down. Again, IF we like the tach . . . The only reason it was suspect was that your original numbers showed slip that was pretty much impossible. If any one of those is wrong (including the ratio) then there is no way to come to any conclusions . . .

 

[wil7483]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

One thing with the tach issue though is now he is showing between 15 and 20% slip, so I am starting to believe the tach. Prior it was around 5% and we knew something was wrong. Now, I am starting to believe the tach and I also like the 19 . . .

Can you make her porpoise at all? Can you trim all of the way up without losing speed? I'd be starting to play with setup stuff, like weight balance and see if we can get the speed up and the slip down. Again, IF we like the tach . . . The only reason it was suspect was that your original numbers showed slip that was pretty much impossible. If any one of those is wrong (including the ratio) then there is no way to come to any conclusions . . .

Yes, I can make her try to porpoise. She be bouncing like a wild bull at a rodeo but she never just sticks her nose in the air and stay there. With the 19p I can trim all the way up and the tach will show 4600 but it is with a loss of speed as you can actually hear the prop chopping the water and not really biting into it. The drive ratio is correct. I checked that last year while it was off when I was diagnosising the previous engines issues. It is definitely a 1.5:1 drive.

So why do you like the 19 as opposed to the 17 which gets me more into the proper rpm range of the engine?

 

[Tail_Gunner]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Okay Rick, heres the results of todays run around the lake. I started off with the 19p prop and the rpms never got above 4200 with a top speed of about 40.3 mph for brief moments. However, the boat shot out of the hole like a bullet and on plane in an instant with very little effort.

I then switched to the 15p prop and I was able to get 4700 rpm's but max speed was 37.2 mph. The holeshot was sluggish but once on plane it cruised out nice.

I finally switched to the 17p prop and I was able to get 4600 rpm's but that was only with the drive trimmed up to the max and you could tell that the prop wasn't biting into enough water to get maximum thrust. When I trimmed down and felt the boat really cruising comfortable the rpms dropped to 4400 and max speed was 39.8 mph. She still came out of the hole quickly and planed out with no effort. Cruising at 3900 rpm she was doing around 32.3mph and the ride was nice.

So I'm tempted to go with the 17p only because it still gives me a decent holeshot and cruising speed. The 15p gets me right up there in the right range for the engine but it is slow coming out of the hole.
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Some confusing issue's here...the 15p has a sluggish hole shot...the 17 and 19 power right out. That is backward's..all of these props what type are they..ss..alum..are they stock...have they had any cupping added.

Watching your vid i noticed you are not getting much lift aka your wake show's the full 8' hull print..were you at wot..in those pics???Your boat has 20 degrees of dead rise and at 40 mph it should cut waves up to 1' like butter....I noticed you didnt like the ride quality when you trimmed her out...

If you nose her in the ride will be a bit smoother but create lots of drag.aka i have a 19' Wellcraft 2800 20 degree v and nosed in it does 49 nose up or trimmed out 57 makes a bigg difference.

I would think at 40 with a a good lifting prop that boat would ride like glass on a 1' chop or maybe even 2..trimmed way out. But that 15vs19 hole shot is way off the beatin path...A few years ago a person here had a 350 with similar problems turned out to be lifter issue.

I really think that boat would turn 50 and youd be thrilled with how well it cuts a chop.

 

[wil7483]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Well when I had the boat in Eufaula, AL with my wife and all my nephews and daughter on board I was running the 17p that day with her trimmed all the way up and the front end was really jumping in and out of the water. That is why my wife wanted to go back to land. I tried to recreate that while in Destin, FL and I was only able to make it do it sporadically. I guess then it was really riding high. At Lake Jackson I was able to make it porpoise I guess but it didn't like it. The prop just wasn't catching any water in my opinion. Next time out I am going to take my daughters camera, it has sound so that way everyone can hear and see as well.

I can say this, the front end is getting lifted well out of the water when I trim it out to a spot that I find comfortable. The next time I go out I will experiment with the full range of the trim and really get a clear picture of how well she rides at each different setting and take detailed notes and pictures of everything.

 

[Tail_Gunner]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Sounds like yo have a bow lifter..Is that a 3blade ss or alum...Id bet when all the bugs get worked out a good 4 blade ss stern lifter would get you the ride and speed your looking for..Actually any stilletto is a great overall lifting prop..but there Bay Pro 11 are the dynomite..Lifts that stern up more allow the v to cut the chop...smoother ride and at Wot if propped right the hull print you see would be reduced by 60-70 %..less wetted area ...higher speeds .

But as the others have said...i thing your having a timing advance issue above 2500 rpm..aka your coming strong out of the hole...but all the props dont hit 4900..15 should hit 5000 in a blink.

 

[coastalcruiser]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

went to http://www.volvo.com engine configurator yeah I know you have a merc
anyway typed in your boat weight and length it spat out this data for a gi that's throttle body injected but brand new! results are
Engine 5,7/350
Speed 43.730 mph I converted from knots
@ 5000 rpm
Anyway if your doing close to 40 mph, not too shabby!! imo

 

[captmello]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

It does sound like you've got a heavy boat. I don't understand why the prop calc. doesn't take weight into account. Is it because the slip % just goes up? Or, should the engine just not be able to reach the proper RPM with the larger pitch?

We're trying to find an additional 9-10 mph here! That could add up to 100+ missing horse power!!

IF the motor can spin a 19 inch prop at 4500ish RPM, your not going to find another 100 HP from the 5.7.

By the way, that is a great looking boat!

 

[sschefer]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Just my two cents about the stock 350 chevy engine. They love to run in the 3800-4200 rpm range. If your 19 is putting you there then that's what I would stick with. Trying to get 5000 rpm out of it is possible but I think you'll only get there through sacrifice as you've noted with the 15. Keep the 17 in case you decide to run at high altitudes it will be your best prop then.

What you need to remember is that the powerband on the 350 is short, 3200-4200 rpm. 5000 rpm is out of the power band and running there really does nothing more than shorten the life of the engine.

The next big change you can investigate is getting rid of that Rochester Quadrajet carberator. However, I hesitate to make that recommendation without other modifications. The volumetric efficency of a stock 350 chevy is about 600cfm. So without some head modifications you won't acutally be able to suck in any more air.

 

[Cptkid570]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Just my .02 cents. Your boat is running great. 40mph in a boat that heavy is fine. I wouldn't worry about trying to hit the 49 mph that the factory claimed it would go. That is under optimum conditions with everything brand new and the boat as light as possible.

Your best prop range is the 17 to 19. Maybe instead of getting top rpm, try them out at the typical cruising speed that you like to go. If you usually cruise at say 30mph, whichever prop gives you the lowest rpm at 30 could be the best one for you. Both get you out of the hole fine, but are putting you at a high rpm. Just go with whatever feels best for you in your typical situation.

I know that's not the "by the book approach", but seems to me that you are running good and you may be starting to over-analyize it a little too much.

Just my opinion.. I've loved this thread, you've done a great job. Be proud!

 

[wil7483]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

I agree with you all. I am extremely satisfied with the way the boat is running. I actually love my boat now that I am actually able to use it instead of fixing it. I am not looking for more speed myself, I just want to be sure that it is running within it's recommended rpm range and that I have the best possible prop on her. She is getting me on the water and soon to the fish so I can't be happier. She has sat in the driveway for the better part of the past two years so this in itself a major achievement. I can finally start to enjoy the boat. If everyone thinks that I should run the 19 then I will run the 19 the next time I am out and experiment with trim settings to find the best configuration. Thanks to everyone. I have really learned a lot through this experience.

 

[QC]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Although some of the data is confusing, I like the 19 because it is fastest which tells me that the horsepower, prop and load are coming together there. It is important to note that comparing different props (type/model) with different pitches is definitely not the same thing as different pitches of the same prop design . . .

Also, stock carbed 350s were most often rated at 4200 - 4600 WOT. Why I asked about the porpoise is that boats are usually fastest at the point they just start to porpoise, so I wanted to understand if there was maybe 1 or 2 MPH available by playing with trim and weight balance. If so, RPM would rise slightly. This is how trim tabs can be used to increase speed. Trim to the point of slight porpoising, then control the porpoise with the tabs. Once the boat finds that sweet spot and is allowed to settle, U might find that elusive couple of MPHs . . . If she porpoises as soon as you start to trim out, then she needs some weight shifted forward. If she won't porpoise trimmed all of the way out then she needs some weight shifted aft . . . These points and balance can change with different prop types etc. as TG has noted (bow lift vs. stern lift etc.). In all cases, if you want more speed, then get as much weight out of her as possible.

I don't believe she is very far off, and I don't think there is a chance of seeing 49 . . .

 

[wil7483]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Ok, last post to this thread. I took the boat to the lake today and tried all three props again. 1st I checked the timing and found that it was at 12 degrees BTDC so I adjusted it until it read 8 degrees BTDC. Then I took off across the lake a few times at WOT playing with the trim settings all the while. The 17 was on the boat and I was able to make the boat porpoise with it and the rpms actually got up to 4700. The speed was consistent with previous outings however. Top speed on the 17 with the trim set for the rpms to spin at 4500 was 39.3 mph. The lake was rough today with high winds. I turned to the 19 and went back out. The boat really do not want to turn that 19. RPM's only got to 4300 and that was with it fully trimmed out and the prop not biting the water. After adjusting the trim the rpms dropped to 4100 and the boats top speed was still only slightly better than the 17 at 41.6 mph on the gps. Lastly, I put the 15 on and was able to actually spin it up to 5000 rpms with her trimmed all the way out but the speed on the 15 was lousy. The best top speed I was able to obtain was 35.6 mph with the trim in the spot where it sounded and felt the best. So I am still dead set on the 17. It is within the rpm range, decent hole shot, and speed is acceptable for my purposes. Too bad I bent it up backing out after beaching the boat. Hit something underwater and when I took the boat out of the water the prop was really beat up. The price to repair is only slightly better than a new one. Any suggestions?

 

[Tail_Gunner]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Yes of course... Get your self a stilletto bay pro 2 16 pitch. I can see from that first pic you have a lot of thrust, but you prop is a 3 blade alum..id bet a few dollar's on that. Is that boat a open bow or cuddy

A good 4 blade will lift that stern heavy boat you have up a few inches making the ride far more "Wateralbe"..smooother and probably faster. You have a lot of azz... err boat draggin there. let me PM some one who really would know...

That ignition is it electronic... dist that is


Did a little browsing....looks like a cuddy

 

[wil7483]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Yep it is a cuddy. I believe it is points type ignition. It is the Thunderbolt V mercruiser ignition.

 

[HT32BSX115]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Hey sounds like you got it running pretty good!

If you haven't tried a SS prop you might give one a try.

btw, if you have Thunderbolt-5, it's electronic (no points)....same one I have on the 454......you do know you have to put it in "BASE Mode" to time it right?

There should also be a knock sensor connected too I think.

 

[Don S]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

Yep it is a cuddy. I believe it is points type ignition. It is the Thunderbolt V mercruiser ignition.

No wonder this thread is over 200 replies long. You don't have a clue what you have or how it all works together.
Let me guess, you doen't have an OEM manual either. DO you?

 

[Tail_Gunner]

Re: 5.0 to 5.7 Rapido rebuilt engine swap

No wonder this thread is over 200 replies long. You don't have a clue what you have or how it all works together.
Let me guess, you doen't have an OEM manual either. DO you?

calm down Don...ive just figured out ive had enough of mefi-3 programming...And i am going to ask you how just how to manually set up my dist..... I hope you have some asprin handy...

Wil all thing's are good if Don is getting envolved...You just need to check your ego a bit.....But if you listen closely. It will get done right...no question...