Here are a few of the mods available for Cessna twins.
Prices shown are estimated- many do not include installation.

* RAM Aircraft Corp. refused our request to review this data for accuracy.
As a result, some information on RAM conversions may be incorrect.

AIRCRAFT

MOD

COMPANY

REMARKS

EST. COST

310 &
T-310

STOL

Sierra
Industries

Full STOL conversion
(including droop tips).

$27,000

310F-
310Q

Executive ll

Colemill
Enterprises

New IO-520's (300HP),
3-blade props, higher gross.

$87,000

310F-
310Q

Colemill
Enterprises

New IO-520's (300HP),
3-blade props, higher gross.

$76,500

310R &
T-310

Power-Pac spoilers (Hydraulic)

Spoilers Inc.

Increased descent,
less shock-cooling.

$6,995
to
$8,995

310R

Bearcat

Colemill
Enterprises

New IO-550's,
3-blade props.

$67,000

310 &
T-310

Vortex
Generators

Micro Aero-
Dynamics

Reduced stall
speed and Vmc.

$2,500-
$3,500

T-310,320

300 hp, new props,
increased GTOW.*

$101,000 *
+ airframe

T-310,320

325 HP, new Q-tip props,
increased GTOW.*

$112,000 *
+ airframe

320 A,
B & C

Colemill
Enterprises

New Cont. IO-520's (300HP)
3-blade props, higher gross.

$76,500
+ airframe

340

Intercoolers

American
Aviation

10-12 Knot increase, better
single engine performance.

$13,475

340 &
340A

Vortex
Generators

V/G Systems

Reduced stall speed
and Vmc, lower drag.

$2,250

340 &
340A

Vortex
Generators

Micro Aero-
Dynamics

Reduced stall speed and
Vmc, increased gross.

$3,450

340 &
340A

Power-Pac spoilers (Hydraulic)

Spoilers Inc.

Increased descent,
less shock-cooling.

$7,995

340 &
340A

STOL

Sierra
Industries

Full STOL conversion
including droop tips.

$25,000
+ airframe

340/340A
(Series II )

Engine /
Prop Upgrade

Reman TSIO 520-NB, 310hp
new prop,s +150 lbs useful *

$65,000 *
+ airframe

340/340A
(Series IV )

Engine /
Prop Upgrade

Ram
Aircraft Corp.*

325 HP, new Qtip props
+300 lbs useful load.*

$87,000 *
+ airframe

340/340A
(Series VI )

Engine /
Prop Upgrade

335 HP, new props, VGs,
intercooler scoops.*

$91,000 *
+ airframe

340/340A
(Series VII )

Engine /
Prop Upgrade

335 HP, new Qtip props
+300 lbs useful load

$101,000
+ airframe

401, 402,
414, 421

STOL

Sierra
Industries

Full STOL conversion
including droop tips.

$45,000
+ airframe

414

Vortex
Generators

Micro Aero-
Dynamics

Reduced stall
speed and Vmc.

$3,450

414,
414A

Power-pac
spoilers (Hydraulic)

Increased descent,
less shock-cooling.

$7,995

414,
 414A

Intercoolers

American
Aviation

10-12 Knot increase, better
single engine performance.

$13,475

414 / 414A
(Series II)

Engine /
Prop Upgrade

310 HP, new props,
+160 lbs useful load

$65,000
+ airframe

414
(Series IV)

Engine /
Prop Upgrade

325 HP, new props
+160 lbs useful load

$87,500
+ airframe

414A
(Series IV)

Engine /
Prop Upgrade

325HP, new props VGs,
+355 lbs useful load.

$87,000
+ airframe

414A
(Series V)

Engine /
Prop Upgrade

Liquid-cooled 350HP engines,
(2000 hr TBO), VGs, +150 useful.

$242,000
+ airframe

414
(Series VI)

Engine /
Prop Upgrade

335 hp; new props, IC scoops,
VGs, +415lbs useful load.

$91,500
+ airframe

414
(Series VII )

Engine /
Prop Upgrade

335 hp; new Qtip props,
VGs, +395 lbs useful load

$101,000
+ airframe

414A
(Series VII)

Engine /
Prop Upgrade

335 HP, new Qtip props,
VGs,+320 lbs useful load.

$116,500
+ airframe

414A

STOL

Sierra
Industries

Full STOL conversion
including droop tips.

$45,000
+ airframe

421

Vortex
Generators

Micro Aero-
Dynamics

Reduced stall speed
and Vmc, higher GWT.

$3,450

421 B

Engine Upgrade

Reman 375 hp GTSIO-520-H
(1200 hr TBO), reuse props

$83,300
+ airframe

421 C

Engine / Prop Upgrade

Reman 375 hp GTSIO-520-L/N, new props, increased useful.

$87,600
+ airframe

421B

Vortex Generators

V/G Systems

Reduced stall speed
and Vmc, lower drag.

$2,250

421B-C

Power-pac
spoilers (Hydraulic)

Spoilers Inc

Increased descent,
less shock-cooling.

$7,995

421C

STOL

Sierra
Industries

Full STOL conversion
including droop tips.

$50,000
+ airframe