390 HP500's Prop
07-17-2025 | 02:45 PM
#1
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Joined: Nov 2022
Posts: 17
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From: Turks & Caicos
390 HP500's Prop
Hello everyone. I purchased a 2000 390 with HP500's and Bravo 1 drives about 2 months ago. Just got done replacing the exhaust manifolds and valve springs. Finally got to water testing see below
With 28p Bravo 1, 1.5 Gear, 5400RPM @ 74 MPH.
This puts me at 21% slip which is way to high. I'm thinking maybe some 30p Bravos? I see other older post mention 29p Hydromotives but don't mention any specific model. I'm assuming the Quad IV.
The shop that has the boat will be trying for s^%ts and giggles because they have them laying around, pair of XR's with -2 shorty lowers to see how the boat will react, not sure what props as yet. Anyone run a 390 with -2 lowers that can also provide feedback?
Last question is there any specific application or time when you'd switch from 4 to 5 blade? For example xyz HP or xyz prop height or xyz slippage.
Eventually (summer 2026) I'll be putting TBS blowers on the engines and whatever it produces it produces. Money isn't endless so after that I'm done with the build. Not interested in motor swaps. Maybe the -2 lowers would be more beneficial at this increased power level vs now??
Any general feedback to all of the above is truly appreciated.
With 28p Bravo 1, 1.5 Gear, 5400RPM @ 74 MPH.
This puts me at 21% slip which is way to high. I'm thinking maybe some 30p Bravos? I see other older post mention 29p Hydromotives but don't mention any specific model. I'm assuming the Quad IV.
The shop that has the boat will be trying for s^%ts and giggles because they have them laying around, pair of XR's with -2 shorty lowers to see how the boat will react, not sure what props as yet. Anyone run a 390 with -2 lowers that can also provide feedback?
Last question is there any specific application or time when you'd switch from 4 to 5 blade? For example xyz HP or xyz prop height or xyz slippage.
Eventually (summer 2026) I'll be putting TBS blowers on the engines and whatever it produces it produces. Money isn't endless so after that I'm done with the build. Not interested in motor swaps. Maybe the -2 lowers would be more beneficial at this increased power level vs now??
Any general feedback to all of the above is truly appreciated.
07-18-2025 | 07:32 AM
#2
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Joined: Feb 2001
Posts: 695
Likes: 58
From: Warwick, MD USA
Congrats on the 390 puchase. I've enjoyed mine for 20+ years now!
21% slip is way too much - your props probably need some work. You are also likely hitting your rev limiter at ~5,400. I run Mercury Racing labbed 30" Bravo's for my HP500 EFI.
I also have run Hydro Q4 28" but the plane off is really difficult as the props struggle to hook up. They sometimes slip while underway as well. The top end is slightly better than the labbed Bravos but I still greatly prefer the Bravos. I feel the Hydros lack sufficient blade area for 390 - they worked great on my prior 320. On the single engine Velocities some prefer Hydros and other Bravos (I prefer Bravo on mine due to handling).
If you go shorties you will need 5-blade props. I believe Steve Stepp told me 1" shorties will work on the 390 but 2" will be too much. I saw this as a lot of expense and compromised handling for a couple MPH gain. The 5 blades are harder on your drives as well.
Lastly I don't believe you'll ever need 5 blades on standard x-dim 390. Steve dialed it in very well for 4 blade props and you won't see speed gain or much handling gain. That said he used 5 blades on the single engine race boats - not because they had better top end but because the handling got them around the race course faster!
Best of luck!
21% slip is way too much - your props probably need some work. You are also likely hitting your rev limiter at ~5,400. I run Mercury Racing labbed 30" Bravo's for my HP500 EFI.
I also have run Hydro Q4 28" but the plane off is really difficult as the props struggle to hook up. They sometimes slip while underway as well. The top end is slightly better than the labbed Bravos but I still greatly prefer the Bravos. I feel the Hydros lack sufficient blade area for 390 - they worked great on my prior 320. On the single engine Velocities some prefer Hydros and other Bravos (I prefer Bravo on mine due to handling).
If you go shorties you will need 5-blade props. I believe Steve Stepp told me 1" shorties will work on the 390 but 2" will be too much. I saw this as a lot of expense and compromised handling for a couple MPH gain. The 5 blades are harder on your drives as well.
Lastly I don't believe you'll ever need 5 blades on standard x-dim 390. Steve dialed it in very well for 4 blade props and you won't see speed gain or much handling gain. That said he used 5 blades on the single engine race boats - not because they had better top end but because the handling got them around the race course faster!
Best of luck!
