From what i just seen on merc site the 20 four stroke looks a little bit smaller. But defiantly noticeable
www.mercurymarine.com/engines/outboards/fourstrokes/enginesetfour_specs.php?ID=69 take a look
25 EFI FourStroke Specifications
HP @ Prop
25
kW @ Prop
18.6
Max RPM (WOT)
5000-6000
Cylinder/Configuration
3 (in-line)
Displacement (CID/cc)
32.1/526
Bore & Stroke (in)
2.40 x 2.36
Bore & Stroke (mm)
61 x 60
Cooling System
Water-cooled w/thermostat
Ignition System
CDI w/electric spark advance
Starting
Manual or Electric
Gear Ratio
1.92:1
Gear Shift
F-N-R
Steering
Tiller or remote
Alternator Amp
15
Alternator Watt
186
Trim System
Manual or power trim
Shallow Water Drive
Available
Exhaust System
Through prop
Lubrication System
Wet sump
Recommended Oil
Mercury 4-Stroke Outboard Oil
Oil Capacity
1.8 L / 2 Qt.
Fuel Induction System
2-valve single overhead cam
Remote Fuel Tank
Standard
Remote Fuel Tank (US Gal)
6.6
Remote Fuel Tank (L)
25
Shaft Length (inches)
15/20
Shaft Length (mm)
381/508
Dry Weight (lbs.)
157
Dry Weight (kg.)
71
Operator Warning System
Low oil pressure, overrev, overheat
Available Propellers
Consult current dealer propeller guide
CARB Star Rating
3
Warranty
3 years 20 FourStroke Specifications
HP @ Prop
20
kW @ Prop
14.9
Max RPM (WOT)
5400-6100
Cylinders
2 (in-line)
Displacement (CID/cc)
21.4/351
Bore & Stroke (in)
2.40 x 2.36
Bore & Stroke (mm)
61 x 60
Cooling System
Water-cooled w/thermostat
Ignition System
CDI w/ electric spark advance
Starting
Manual or electric
Gear Ratio
2.15:1
Gear Shift
F-N-R (Shift-in-Handle Tiller or Remote Control)
Steering
Tiller or remote
Alternator Amp
2 Volt / 11 Amp
Alternator Watt
139
Trim Positions
6
Shallow Water Drive
Standard
Exhaust System
Through prop
Lubrication System
Wet sump
Recommended Oil
Mercury 4-Stroke Outboard Oil
Oil Capacity
1.0 L / 1.1 Qt.
Fuel Induction System
2-valve single overhead cam
Remote Fuel Tank
Standard
Remote Fuel Tank (US Gal)
6.6
Remote Fuel Tank (L)
25
Shaft Length (inches)
15/20
Shaft Length (mm)
381/508
Dry Weight (lbs.)
115
Dry Weight (kg.)
52
Operator Warning System
Low oil pressure / Over--rev
Available Propellers
Standard equipment
CARB Star Rating
3
Warranty
3 Year Limited and 3 Year Limited Corrosion
This should help dave