BoatBuddy

I know on the 500EFI you can run regular gas, but can you on the 500HP carb?

Scott

yes 87 min I run 89 to avoid getting less than 87 but if you trust the station and supplier your all set. Waste of money to burn anything higher.

Hydrocruiser

Here's the specs for both the engines in question:

The "Bulldog" and Hp 525 show 87 Octane as well and Merc jumps it to 92 Octane recommendations in the 575 and above.

HP500 Specifications :
Propshaft Horsepower: 470/350
Displacement (Liter/CID): 8.2/502
Cylinders: V-8
Bore (in/mm): 4.47/113
Stroke (in/mm): 4.00/102
Compression Ratio: 8.75:1
Fuel Requirements: 87 Posted Octane (R+M)/2
Full Throttle RPM Range: 4800-5200
Ignition Type: Thunderbolt V
Alternator (amps/watts): 55/776
Length (in/mm): 38.3125 /973
Width (in/mm): 32.75/832
Height (in/mm): 23.5/597
Weight (lbs/kg): 1305/592
Warranty: 1-year limited, 3-year limited corrosion


HP500EFI Specifications

Propshaft Horsepower: 470/350
Displacement (Liter/CID): 8.2/502
Cylinders: V-8
Bore (in/mm): 4.47/113
Stroke (in/mm): 4.00/102
Compression Ratio: 8.75:1
Fuel Requirements: 87 Posted Octane (R+M)/2
Full Throttle RPM Range: 4800-5200
Ignition Type: Digital
Alternator (amps/watts): 60/847
Length (in/mm): 34.3125/872
Width (in/mm): 33.75/857
Height (in/mm): 22.0625/560
Weight (lbs/kg): 1305/592
Warranty: 1-year limited, 3-year limited corrosion

FYI

HP525 EFI - 525 HP
Specifications
HP: 525
kW: 410
Full Throttle RPM Range: 4800-5200
Displacement Liter/CID: 8.2/502
Bore & Stroke (in): 4.47/4.00
Bore & Stroke (mm): 114/102
Compression Ratio: 8.75:1
Cylinders: V-8
Alternator Amp: 65
Alternator Watt: 917
Fuel System: MPI
Ignition System: PCM 038 distributorless
Fuel Requirements: 87 Posted Octane (R+M)/2, (92 RON) International
Transmission: (Six) w/Huber 600 Series
Drive Options: Bravo One XR, Bravo One XR w/ITS, Bravo One XR Sport Master (Standard or Short), and Bravo One XR Sport Master (Standard or Short) w/ITS. Dry-Sump Six w/Huber 600
Length (in/mm): 39.5/1003
Width (in/mm): 34/864
Height (in/mm): 24/610
Weight (lbs / kg): 1201/545
Warranty: 1-Year Ltd. for Recreational Boating/3-Year Ltd. Corrosion
SmartCraft: Yes


Definately true about variance in brands and stations. I had a knock and switched brands in the same octane rating and the problem went away.