Since I can't Get help on the Donzi Forum
 

Fellas, I need some help here. 2000 ZX with the 377's. I have a set of 3bl 25p lab mirage boat runs 72 gps 5000 rpm.
Also have a set of 4bl 26p lab Bravo I 74 gps 5000 rpm.

What am I doing wrong? Thought this should be an 82 mph boat with the twin step hull? Fuel levels were approx half. 1-4 persons did not matter.

2nd question. I have been getting a lot of cavitation when getting to plane. I have backed up on the K planes and has since helped. Thanks for any and all help.

Magic Good to see you out and loved eating up the Velocity the other day, we'll run next time

What HP ar ethe Scorpions rated???

Pretty sure the 28 with 6.2/320hp's is a 70-72mph boat max.

In order to see 82 in a 28ZX with Scorpions, you will need to put the boat back on the trailer. Hook it up to a FAST truck and FLOOR IT!!!!:evilb:

I think 72-75 is about the top end of that boat.

aired out and just you and about 10 gal's of gas might push 75.

The easiest way for a boat to pick up 10-15 mph is to list it with a broker. ;)



(sorry for all the smarta$$ comments- realistically though, the boat is hitting just about what it's capable of doing. Once GPS was introduced, everyone's boats magically got alot slower)

Those are great quotes, its amazing how fast our boats go when we're talking about speed, late at night, over many beers:ernaehrung004:

A customers 28ZX with 5.7's was supposed to go 75mph. Everybody on the net told him that's how fast their's was.. It went exactly 65. We got it to 69 with a bit of tweaking, 1/8 of a tank, two guys, light chop, maybe a bit of current... Damn GPS.. :rolleyes:

My friend ordered a 29' from Fountain brand new with the similar motors. It came from Fountain with 1.35 gears in the drives and I believe a 28 pitch bravo. It ran 80 light fuel with 2 people. speed report from fountain was 82. It only was a single step and it was not the real deep step like in the single engine boats. What drive ratio are you running. Also it took some water to get to 80!!

I see Scorpions rated at 340 or 350 pshp depending on which mercruiser literature you read. That would be like having around 400 flywheel Hp per motor.

Performance Engines - Scorpion 377
Propshaft Horsepower: 350 (273 kW)1
Full Throttle RPM Range: 4800-5200
Displacement (Liter/CID): 6.2/377
Bore (in/mm): 4.00/102
Stroke (in/mm): 3.75/95
Compression Ratio: 9:1
Cylinders: V-8
Alternator (amps/watts): 65/917
Ignition Type: Digital
Fuel System: MPI
Fuel Requirements: 92 Posted Octane (R+M)/2 (98 RON)
Drive Unit: Bravo One XZ/XR
Gear Ratio: 1.36:1 or 1.5:1 Left- or right-hand
Length (in/mm): 37/940 2
Width (in/mm): 29 /737
Height (in/mm): 20/508 3
Weight (lbs/kg): 969/4414

If your 28ZX is not a scorpion edition you are only running 72 top end. The Scorpion 377 did run the boat 78-80 mph and the props turned out for more stability. The 28ZX likes either a neutral tab or slight more then neutral. Now if you do have 377s How many hours? Did you do a leak down compression check? The Scorpion 377s are blue in color and the Regular 377s are MerCruiser black.

Boat is a Scorpion ed, I have seen it, on second thought I have never been under the hatch.

IU sharp boat, we will be at the beach all weekend.

Ya fellas appreciate the help, the boat indeed is a Scorpion edition 377 HP I do a little homework. Yes engines are blue it really is a scorpion. I have inward rotation I know the ideal conditions and have had the screaming out, out on lake michigan I have all the room I need so space is not a problem either. Like I stated 1/2 tank of fuel and 2-4 ppl did not matter to the GPS 74 was what I hit multi lake, multi water condition. I have 380 hrs on engines... Any other questions or reiterations I can state for some info? and Magic I am back In Iraq

Doesn't anybody else question how he can only turn the 25" 3 blade props 5,000 RPMs...then try a set of 4 blade with MORE pitch and still hit 5,000? Something isn't right here.

380 hours on small blocks, they will be getting tired, time for a leakdown test.

Well come out on the boat cause it happened, I tested in two lakes, with both sets of props... The Diameter is not exact but close enough that it shouldn't make a difference. I don't understand it either, but that is what happened on both occasions. Thinking of going to 5 blade to see what happens.

Just went through something similar on my friend's Cig 35. The motors are over-cammed (midrange sucks) and it was under-propped. The only thing we had were 4 blades 3 pitches up. Same rpm, same top speed. They were just slipping like SOB's. No logic, but I saw it happen. In this case, being labbed may be dropping the pitch. The extra blade may be compensating for some lack of bite.

My advice would be to talk to a prop pro. Hydromotive, bbblades, Throttle up, etc. Let them make a reccomendation, then they can swap demo props back & forth until you have it dialled in.

Good luck over there and come back safely and soon!!!!!!!!!

My single 26ZX dines on a steady diet of Scorpions:party-smiley-004:

I can't believe what nobody responded on the donzi net. I never saw a post relating to that topic.

I believe he ment the OSO Donzi Forum ........ Don't recall seeing it on Donzi.net either ..........

Be careful in Iraq and a big Thank You for serving the greatest Country in the world.
Now back to your boat, the best blade for your boat ia the 3 Blade Mirage, Now that I know were you boat you are almost on the money The Donzi 28ZX Scorpion ran 82 MPH in Sarasota Optimum conditions light fuel and heavy concentrate of Saltwater, Saltwater ads about 5-7 mph in speed. Here in NJ the Scorpions all run about 78 same boat trailered to 1000 Islands NY, boating Lake Ontario that same boat will run 72-74 mph.

Thanks for Serving!

The prop RPM difference is not surprising, I have found many prop oddities in my own boat.

Example I can spin 25 3 blade 5900 RPM
I also have a 26P 4 blade I can spin 6000. RPM and the boat is 1mph slower??? Doesn't make sense- but it is what it is.

As for your rig, low to mid 70's sounds about right.

Someone said earlier your mills may be getting tired - do a leakdown test and see what they are holding. With fresh blocks and some bblades worked props you may see 80.



Uncle Dave

Laveycraft 2750 Ilmor 710
Laveycraft 20.8 Sebring 406 SB
Fleetwod nitrous toy hauler
Yamaha raptor 700/Kawi KFX 450
Nissan Titan

Thanks for serving too!

From what I have heard Shang is right on the money. I have seen a few Scorps in persons. Nice looking boat.

How to get small blocks to go 80+
 

Sounds like you might need to change those iron small blocks over to a pair of our LSM550's and really see some real 80-90 mph speeds!

Regards,
Ray @ Raylar

Don't you mean 90-92+??

Go to Donzi.net and PM "Mr X". I don't recall what his was running but I know for sure he walked away from me at 76 mph :angry-smiley-038: Ted knows Donzi's in and out and will get you pointed in the right direction.

Dan

Might make 88-90mph, I am not so sure that hull would see 92mph even with 1400 hp.!

Best Regards,
Ray @ Raylar

Oh it would and has seen 90+ with Procharged 350 mags (ok so they were also worked over).

My 26 has a pretty similar running surface and it runs in the 90's and does it with authority. But hey, its a single.

You are correct your 26ZX has the same running surface but the big difference is one engine verses 2. The 26ZX will un with big power the boat is made for one engine big block. The 28ZX runs 2 small blocks weight to hull ratio. Big blocks will not work in a 28ZX to dangerous.

I could see that weight being a pretty big difference. I could also see the big blocks being a very bad idea.

I would like to see some more folks do stuff to the twin ZX. I think that some cool things could be done. A couple of Ray's light screamers might be the ticket. That would be a strong package that you could beat on pretty good. If I had to run in rough water I would have looked pretty hard into that idea.

At least until you learn how to drive... Baby steps man, baby steps... :drink: :party-smiley-004: :p

I have a 2000 28 ZX Scorpion boat and I have seen 79.5 on GPS. stock so far.

I have been in another one that went 82.

Email sent to Tim Be safe in Iraq.