Next step.
 

Just wondering what y'all think would be the best next step in my project....
It HAS been running flawlessly, but has a few things I'm just not totally satisfied with...

The Boat is a '05 290sc . The engine is a Procharged 555" that made 1000 hp @ 6000 RPM in full marine dress on the dyno.

I'm running an XR drive with an Imco standard length lower. 1.36 Ratio 3.5" prop shaft depth.
The boat accelerates HARD Has NO problem hitting mid 90's everyday loaded with fuel / coolers / people...
and I've seen a best thus far of 99.7 MPH @ 6000 RPM spinning a P5x 25 that was pitched up to a 26 by Hydromotive..
With the HP I'm running I would've though it would have gotten another 5 mph out of it..

I've tried a couple of different Bravo props and none seem as fast on top and take WAY more trim to carry the bow.
My lake is usually rough so I can't run around much at a high trim position without the bow going skyward..

Guess my biggest complaint is the cruise RPM...

1.5 ratio will allow you to run more pitch. I think you'll find your missing speed. The only reason to run a 1.35 ratio drive is if you run out of useable pitch prop with a 1.5 ratio.

That and I would try a one inch shortie drive. The IMCO drive is the best drive for your application. did you try a labbed BRAVO 26 ???
If you can get on plane with a 4 blade prop it should be faster than the 5 blade. Also that 5 blade is causing a lot of transom lift.
One other thing you could try is to cut the bell off of the back of your 5 blade. This should lower the back of the boat so that you don't need to trim as much.
I could not run a 5 blade because it caused too much transom lift even with the bell cut off.

I agree that you should be getting more from it. I ran a 468 Injected and Modified ProCharged M3SC with 7lbs boost 720 HP and 727 TQ 5400 RPM. I ran a B-Max 1.30 with standard length lower with a Bravo 30 Prop and ran 94.8 GPS it was a 98 26' 260 or the later 280.

The 5 blade DOESN'T need as much trim.. It carries the bow perfect with the prop shaft parallel to the hull. (position 5 on my indicator)
With the 4 blade prop, the boat rides wet to the windshield with the prop shaft parallel to the hull ..


It gets on plane just fine with a 4 blade, and I agree, should be faster with it, but it seems I have to trim too much to carry the bow so it loses efficiency


Here are results from a Cutting Edge labbed 4 blade 30 pitch
41 MPH @ 3000 RPM trim 1.5

You have some experiences of this test drive you need to tell us. Way insane ! :)

LOL :boat: 599 mph..


It's the SECOND time I posted that and the board automatically re-formats it without the carriage returns..

I eddditted it again.... :)

That porposing is being caused by that CE prop. My 30p/28p Bravo One props don't do it. I'm really curious how the 30p Bravo One will run.

Running the numbers

1.36 30p 5750rpms = 120mph theoretical speed.

1.36 26p 6050rpms = 110mph theoretical speed.

1.5 32p 6050rpms = 122mph theoretical speed

1.5 34p 5750rpms = 123mph theoretical speed

Dialing in a prop on your current setup is what I would try before changing drives. Are you tied to Cutting Edge props? I have no experience with them. Brett @ bblades has treated me awesome and his props have impressed me. Might give him a call.

A lil more thinking... My bblades labbed 30p B1 needs 6 to 6.5 on my Livorsi indicator at WOT. The 28p bblades labbed B1 likes 5.5 to 6.

If you are trimming to 9 that's way too much. I would check and make sure the drive is not out of the gimbal ring ears at that position. The 5 blades lift the stern as mentioned and push the bow down. This keeps you from having to trim out as high. Not good for top end though. These Velocity's seem to run best speed with the nose in the air and high on the pad vs parallel to the water.

I'm still of the opinion you have alot to gain with the current setup by dialing in the prop.

Spoke with Max Machine Worx..

He brought up that my Imco anti cavitation plate may be part of the issue of it not carrying the bow decent with a 4 blade...


He suggested I try a stock 1.5 ratio lower and go from there... GOOD news is, I just happen to have one laying in the garage... :)

That's a quick and easy test to verify. Is that an Imco SC lower?

Keep in mind, Bravo props are figured to run 1 pitch smaller than stamped....

First off, I changed the lower unit to the 1.5 ratio off my stock "x" drive and put it on my XR instead of the 1.35 Imco lower I've been running

So, if an "XZ" drive is an x upper with an xr lower, what would THIS be ? an RX ? lol

https://cimg6.ibsrv.net/gimg/www.off...e2affafa66.jpg

It was ROUGH and BUSY on the lake today.. getting numbers was difficult so not as complete as before.....

SO... Spinning a Bravo 30 1.5 Ratio stock lower...

40 MPH @ 3000 RPM trim 1
48 MPH @ 3500 RPM trim 2
57 MPH @ 4000 RPM trim 5
94.7 MPH @ 6085 RPM trim 6.5 (pulled out of the throttle)

Boat ran good on the pad. bow seemed to carry pretty good overall...

Bravo 34 LH (By the way.. the boat comes off the trailer WAY easier if you put the shifter in forward when backing up with a LH prop LOL)

45 MPH @ 3000 RPM
56 MPH @ 3500 RPM
65 MPH @ 4000 RPM
93 MPH @ 5500 RPM (couldn't get any more RPM out of it )


I'd try to find a 32 but that'll likely just get me to 99 mph which is where I've been stuck at anyways.....

Thinking maybe a -1 shorty and go back to 5 blade props ?

-2 shorty with 1" spacer installed and ready for testing.. :evilb:
Went back to the 1.35:1 ratio.. the 1.5 didn't show much of an advantage and 1.35:1 is SUPPOSED to be stronger anyways...



https://cimg7.ibsrv.net/gimg/www.off...528986ca1d.jpg

Pullin for ya to hit that magic number... Good Luck!!!

https://www.offshoreonly.com/forums/...-outdrive.html

Looking forward to your results. I considered a shorty when I first bought the VR1. Always wondered about how it would run. On my 21 Challenger a 2.5" shorty Alpha SS netted 5 mph & 500rpms with no prop change vs before. The shorty resulted in a propshaft 3.5" below hull, which is what my VR1 is with a stock Bravo lower. Keep us updated!!

So... They shorty did not help..

I first tried the 26 p5x I've been running.. Drive trim had little effect on the attitude of the boat now. Trimming above neutral would create a rooster tail instead of lifting the bow.
Prop slip was about the same through the midrange but went up a little on the top end.. lost 3 MPH for 96 MPH @ 6000 RPM..

Tried a bigger prop (28 P5X) midrange numbers looked promising. (76MPH @ 4500 RPM :) )..
boat accelerated decent but could only spin it 5200 RPM @ 92 mph..

So, once again, it looks like I need a prop in between the two I have.. LOL

InsaneMan: Didn't you raise the X when you redid the transom ? Or was that the last boat ?

That was the last boat.. A 26' Corsa ended up with the prop shaft 3.25" below the bottom and worked well..

This one was at 3.5" below from the Factory and I went to 2.5" below. may work with a 6 blade prop but don't really want to go there..

NEXT !


I picked up an HD transom assembly.. Puts me one step closer to an SCX upper..
and should prolly be running one anyways with the power and speed I'm at..

https://cimg3.ibsrv.net/gimg/www.off...6930ada45d.jpg


I ALSO Picked up an Imco extension box.. :D
Seems a 12" box and a -2 shorty works well on this hull ... I'm going to find out....

https://cimg1.ibsrv.net/gimg/www.off...73c3e3486c.jpg

You may want to check with George at All American Drive before you spend money for SCX. I had him go through my drive and rebuild it, he gives a 24 month warranty. I have a 280 with an old Bravo drive at stock height that runs pretty good. I had a B1 4 blade 28P labbed by BBlades and it only made it worse. Porpoises like crazy, determined the prop now has to much rake. I had an old Hydromotive QIV 27P without a bell, tough to keep on plane with a load in rough water, but it likes speed. I have to go easy on the throttle up to half and wait for the nose to start coming down and then I hit the trim and hammer down. I was in 1.5' waves so had to go easy on the trim, had to keep the boat flat to the water, but it ran great, just a slight bit of chine walk that was easy to sort out. I'm running an NA 524 and I hit 85 before things got to rough. I know I need a lot more pitch as I hit my 6k rev limiter pretty easy when the water is calm. My next prop will be a Hydromotive no question, will try a 30P next summer. No question the B1 is more efficient at low speeds, I think a QIV with a little bell will help that. But the way the QIV runs above 60 is night and day different.

Did you try the -2 IMCO shortie without the spacer and the big prop?

Ext box you have pictured is a +3. You probably already know that. If the box is known to wrk good on your hull go for it, seems rare they don’t work good. Have you tried a full diameter Maximus? My Baja actually likes the long tubes, lifts the whole boat out of the water. I’d also give a bblades 4 speed a try, long tube big diameter. If your boat doesn’t like the tubes they’re easy to remove. Most say a higher pitched prop spinning slower results in a little more speed vs a lower pitch spinning faster.

Either way good stuff and keep posting your findings

Same issues with all my props (3) that had the bell cut off. I blocked off the exhaust cavity in the drive to keep air from going thru it and the props grabbed water like you wouldn't believe. Planing and staying on plane at lower speeds no issues anymore. Was like magic.:)

I have through hull exhaust and the exhaust tunnel is blocked. I think my prop shaft is only about 4" below the bottom and that may be some of the problem as well. I am also pushing about 700hp with a 0-60 time of about 8 seconds going easy. I had a long talk with Tom the owner of Hydromotive when I was in town. He and Steve Stepp are old buddies and Tom really understands what the Velocity's like. Hydromotive's forging source was bought out by Yamaha so he's had to find a new source and get them dialed in. I can't wait to try a QIV 30P, I should be in the mid-nineties.

SB brings up a very good point. With the water rising 1” for every 10-12” behind the boat, your prop is probably closer to 5.5” below the water line, assuming the leading edge of your prop blades are 24”or so from the edge of the pad. So in theory that should be plenty of water for a four blade to hook up good, unless the air is traveling through the exhaust passge in the drive aerating the prop.

For comparison sake the leading edge of the prop blades on my setup are 43.5” from the edge of the pad. When I mounted my go pro in the notch of the boat it appears that the water is rising about 3-4”. So my .25” below the bottom is more like 4.25” at the prop

SB - I did the same thing with my -3 IMCO shortie lower. I used a piece of lexon to seal off the exhaust passageway in the lower. This Mod made a noticeable improvement in planning.

ummm... NO.. I did NOT.. was sold to me as a "neutral" box..
I don't have room to raise the engine ANY...

Guess I need to dig up a merc inner transom plate and see where it lines up... :eek:

I'm not sure what the exhaust tunnel is. Transom assembly or at/in the drive itself ?

Y pipe ?

You can always mount the box lower on the transom as long as the hole in the transom is covered or lowered.

Boatally Insane,

have ve you tried LH ve RH of same pitch to see if handling/porpoising is any different? They say different characteristics for each.

Close... I was running a RH 25 P5X and now have a LH 28 P5X.
Only difference is the direction the boat lists when I'm by myself..
Have yet to try the LH with a passenger to see if it'll be level now...

I only tried it as a -1 and a 28 P5X and it didn't work well..

Don't really want to try bigger diameter props with the XR and 1000hp..

It all depends on the boat and how far your prop shaft is below the running surface at speed.
The closer the prop shaft is to the surface of the water or the more blades the prop has increases the transom lift.
On my boat the drive rides on top of the water going under the boat. ( the bullet sits on top of the water )
The bullet and the flare at the back of the prop act as a ski and causes transom lift. The higher the bullet is but yet not fully surfaced the more transom lift.
Transom lift counteracts trim for bow lift. This will cause you to trim more than is safe and can cause an ill handling boat at speed.

Boatally insane
You say that you are using a lot of trim.- but from what you have listed you are not.
If 5 is neutral than any trim setting below 5 is negative trim.
Any number above 5 is positive trim.
Once I am on plane I always trim to neutral for best speed at a certain RPM.
A setting of 5.5 to 6 is probably still parallel to the water surface due to the angle of the hull to the water because the bow has risen.
My drive is fully surfaced and at top speed I run only 5.5 to 6 with 5 being neutral on my boat also.
If that is all that you are trimming that is less than most V bottom boats.

When you separate the top and bottom halves of the drive You will see a huge hole that goes down the back of the drive. I just cut a piece of Lexan and used 5300 to seal it in place. No air flow trough prop now.
This will help the prop hook up to get on plane.
There are a lot of little things that can be done for few $ and little time that will help a boat get on plane.
My Daytona wouldn't begin to get on plane with a 4 blade prop and barely get on plane with the 5 blade.
I shortened the trim rams 3/4 inch and modified other parts to allow the drive to tuck under more. ( more negative trim ) This allows the prop to be deeper in the water and also causes the prop to push up on the back of the boat more than with the normal trim level.