ST1200 6 Speed with Reverse | Shifter

ST1200 6 Speed with Reverse | Shifter

Lenco ST1200 Transmissions

For more specific information on any of these Lenco transmissions please refer to the Tabs below, or call our tech line at (909) 673-9080. Lenco Parts and Price List is available here.

The Lenco Racing ST1200 6 Speed Transmission has been specifically designed and engineered for severe duty street/strip applications.

The ST1200 gives you the advantage of Lenco brute strength at a lesser price than our full race units.  

All ST1200 Street units now come with low drag bearings and a billet case.

The ST1200 transmission is pure Lenco through and through and is ideally suited for nitrous, blown, injected and carbureted engines producing up to 1200 HP and 900 lb ft of torque.  As with all Lenco transmissions the ST1200 is a planetary design and comes with up to 6 forward speeds.  Shift with either our patented multi lever system or with the optional, more compact CO2 setup.

Multiple speeds are achieved through utilization of multiple cases.  

The ST1200 is available with all popular bellhousing patterns - Ford, GM, MoPar and our own five-bolt design. You may choose any conventional input shaft spline.

We are able to offer the ST1200 Street/Strip at lower cost than our pure race CS1, CS2, CS3 and CS4 designs since we use 8620 steel instead of 9310 material for the ST1200 gears. 8620 is a premium quality material that will provide excellent service for 1200 HP hot rods. 9310 steel would be used in Pro Stock, Pro Mod and other similar applications where substantially more HP, torque and tire plant is generated.

We supply premium grade bearings in the ST1200 instead of the much more expensive aerospace-spec bearings as used in our race transmissions. The ST1200 comes with aluminum cases instead of the magnesium style race units.

Engineered for 1200 HP.
Air or Lever Shift.
Reverse Lockout.

Ford. GM, Mopar Patterns.
Aluminum Housing.
Neutral Position
5 First Gear Ratios.
Low Shift Pressure.
32 Spline Output

3/4" Gear Set.
Light weight components.
Light weight ring gears (units w/27 and 32 spline shafts only).
Low drag (angluar contact and needle bearings).
Choice of ratio.
Choice of standard or new generation reverses.
Air servos or max-adjust shift towers.
Input shaft.
Throwout bearing collar (4 & 5-speed only).
Shifters and lockouts can be either style.

ST1200 Gears 3/4"

1.25% ratio uses 32 tooth planet gears, a 22 tooth sun gear and an 86 thooth ring gear.
1.31% ratio uses 27 tooth planet gears, a 25 tooth sun gear and an 80 tooth ring gear.
1.38% ratio uses 23 tooth planet gears, a 28 tooth sun gear and a 74 ytooth ring gear.
1.44% ratio uses 22 tooth planet gears, a 35 tooth sun gear and a 79 tooth ring gear.
1.48% ratio uses 22 tooth planet gears, a 40 tooth sun gear and an 83 tooth ring gear.

In general, all LENCO transmissions are a planetary design. Planetary transmissions rely on a central sun gear to provide a 1:1 direct drive ratio once shifted from the launch ratio.

In order to achieve an underdrive first gear launch ratio the LENCO transmission relys on planet gears which rotate around the sun gear.

Each sun and planet gearset provides two speeds. Those two speeds are (1) the lower underdrive ratio and (2) the direct 1:1 final lock-up drive ratio.


Each LENCO transmission is thus a two speed and is housed in one dedicated two speed.

We acheive more than two speeds by combining multiple cases.

For example, a three speed requires two cases.
A four speed requires three cases.

A five speed requires four cases, and a six speed requires five cases.



Since each case contains one gearset and provides both underdrive and direct drive, multiple cases (gearsets) provide multiple underdrive ratios.


You must multiply each cases underdrive ratio in order to determine the first gear ratio.

In the example of a four speed, the case nearest the engine would contain a 1.37 ratio planet gear set. The middle case would also contain a 1.37 planet gear set.
The rear case a 1.31 ratio gearset.



By multiplying these three ratios you come up with a 2.46 first gear ratio. Second gear ratio is 1.80 and third gear is a 1.31 ratio. Final drive ratio is 1:1.


Multiply all three gearset ratios to determine the first gear ratio of 2.46:1. Multiply the two rear case gearset ratios to determine the second gear ratio of 1.80:1. The gearset in the third case alone, 1.31:1, determines the third gear ratio. All three units shifted equal final drive ratio of 1:1.


The internal action of a LENCO is such that when the transmission is in first gear the dedicated planet gear assembly provides the launch ratio. The planet gears are driven by an encompassing ring gear.


When the transmission is shifted a clutch pack compresses the rotating sun gear assembly to the direct drive central sun gear. Thus a 1:1 ratio is achieved.


Each case in succession, with its particular underdrive ratio, determines the immediate drive ratio.


Once all cases have been shifted the entire transmission assembly is locked in the final 1:1 direct drive ratio.


It is not necessary for the driver to disengage the clutch when shifting from ratio to ratio since all shifting is done with the engines clutch fully engaged.

(909) 673-9080

Please call for ordering or technical information.

  • Views: 33512
  • Brand: Lenco Racing
  • Product Code: ST1200-6-R-S
  • Availability: In Stock

Tags: sr1200, transmissions, street transmission, drag racing, 6 speed

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