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.