Tech Specs Indiana Outboard AssociationSeason 2014

In outboard boat racing, there are two main categories of motor, stock and modified. In addition, there are two main types of hull, hydroplanes and runabouts.


Modified classes

200cc Modified Hydroplane/Runabout (Formula A)

AXSR (cropped)Displacement: 13.2 c.i.
Permitted engines:
• OMC 13.2 c.i., 2 cylinder

Straightway speed range: 55-60 mph

250cc Modified Hydroplane/Runabout (A Mod)

Displacement: 15 c.i.
Permitted engines:
• Swanson Champion-American Hot Rod, 15 c.i.
• Mercury KG4H, 2 cylinder
• Mercury Mark 15, 2 cylinder
• Mercury Mark 20H, 2 cylinder

Straightway speed range: 55-60 mph

350cc Modified Hydroplane/Runabout (B Mod)

7-M 350MHDisplacement: 20 c.i.
Permitted engines:
• Swanson Champion-American Hot Rod, 20 c.i.
• Yamato Model 80, 2 cylinder
• Mercury Mark 20/25-20H, 2 cylinder
• Mercury KG7, 2 cylinder

Straightway speed range: 65-70 mph

400cc Modified Hydroplane (25 Mod)

400MH motorDisplacement: 22.0 & 22.1 c.i.
Permitted engines:
• Mercury 25SS racing powerhead
• Mercury 200, 22.0 c.i. powerhead, 1970 to date
• OMC 22.1 c.i. powerhead, 1970 to date

Straightway speed range: 65-70 mph

500cc Modified Hydroplane/Runabout (C Mod)

Displacement: 30 c.i.
Permitted engines:
• Mercury Mark 30H, 30 c.i. 4 cylinder
• Wizard WA25 30 c.i. 4 cylinder
• Yamato Model 102/302 24.5 c.i. 2 cylinder

Straightway speed range: 70-75 mph


Stock classes

A Stock Hydroplane/Runabout

Displacement: 13.2 c.i.
Permitted engines:
• OMC 13.2 c.i., 2 cylinder
• Mercury “A” motor
• Sidewinder 15S

Straightway speed range: 55-60 mph

B Stock Hydroplane

Permitted motors:
• Yamato Model 80, 2 cylinder
• Yamato Model 102/302, 2 cylinder with 7/16″ carburator restrictor plate
• Sidewinder 20S (probationary)

B Stock Runabout

Permitted motors:
• Mercury/25SS
• Mercury/Mariner 25XS without restrictor plate
• Hot Rod 20 CID
• Yamato Model 80, 2 cylinder
• Yamato Model 102/302, 2 cylinder with 9/16″ or 1/2″ carburator restrictor plate
• Sidewinder 20S (probationary)

C Stock Hydroplane/Runabout

Permitted motors:
• Yamato Model 102 or 302

D Stock Hydroplane/Runabout

Permitted motors:
• Mercury Mark 55-H
• Mercury/Mariner 44XS
• 402XS
• Bass/Tohatsu


Junior classes

J Hydroplane/Runabout

AXSH (cropped)Displacement: 13.2 c.i. or 15.9 c.i.
Permitted engines:
• OMC 13.2 c.i., 2 cylinder with 0.5″ carburator restrictor plate
• OMC 15.9 c.i., 2 cylinder with 0.5″ carburator restrictor plate
• Mercury 60-J 15.9 c.i., 2 cylinder

Straightway speed range: 35-40 mph

AX Stock Hydroplane/Runabout

Displacement: 13.2 c.i. or 15.9 c.i.
Permitted engines:
• OMC 13.2 c.i., 2 cylinder with 0.65″ carburator restrictor plate
• OMC 15.9 c.i., 2 cylinder with no carburator restrictor plate
• Mercury 60-J 15.9 c.i., 2 cylinder

Straightway speed range: 40-45 mph