Stall refers to the maximum speed an engine can achieve against the converter when the turbine is locked and prevented from rotating. The rpm achieved (stall speed) will be a function of the engine torque and the converter design. True stall speed is hard to achieve in a street vehicle since it is difficult to hold the transmission input at full engine torque.

---

Performance engines typically have higher torque curves. Allowing the engine to rev up to a higher RPM sooner will get the engine to its “sweet spot” earlier. Also, many performance engines require a higher idle speed RPM and a higher stall converter will allow the engine to idle in gear without pushing through the brakes while idling in gear (at a stop sign or red light for example). However, too high of a stall speed can cause excessive heat, poor fuel economy. It can also lead to a “loose” or “disconnected” feeling at everyday part throttle conditions. Balance is the key.

---

No. The converter starts to drive the input shaft of the transmission well below the stall speed. Most aftermarket industry “advertised” stall speeds are estimates based on an unspecified generic torque input. Most times these numbers are used for simple comparison to show one converter will have a higher or lower stall speed when compared to a different converter.

---

While the bell housing bolt pattern is essentially the same, the positioning of the torque converter nose and rear of the crankshaft flange changed between the older traditional Small Block, Big block, verses the LS style engine. The crankshaft flange was shortened 9.6 mm (about .375”) and the nose of the torque converter was lengthened the same amount when the LS engine was introduced. What this means is that when you bolt an older “non-LS” 4L60 family transmission up to an “LS” engine, the center of the torque converter will not reach the crankshaft. Transmission damage may occur if you do not have the converter piloted into the back of the crankshaft correctly. Use P/N 12621399 6-bolt crankshaft spacer and flexplate assembly to lengthen the crankshaft flange to the proper depth to pilot the torque converter correctly when using an older transmission behind an LS style engine. The 12621399 is a direct bolt on for 4L80 family and TH400 transmissions (see below) however, the torque converter bolt circle diameter (BCD) will need to be modified to use other transmissions (see Torque Converter to Flexplate Bolt Pattern notes below).

---

Use p/n 12621399 spacer assembly for a direct bolt on for this combination.

---

There are basically 3 different torque converter to flexplate bolt circle diameters (BCD) used by GM over the years.

The 4L80 family and TH400 use an 11.5” (292.1mm) BCD.

The early 4L60 (pre-LS engine), TH350, 700R4, 2004R, P/G, etc, use a 10.75” (273.05mm) BCD
Later “LS” style 4L60 family transmissions use an 11.062” (281.0mm) BCD.

Some flexplates have multiple patterns and some do not. Some flexplates may or may not have room to properly modify the bolt circle in every case. You will need to check your application before you bolt everything together.

---

The vertical plane of the flexplate teeth is common between older traditional Small Block, Big Block and LS engines. This means that the starter location and flexplate teeth location are the same in relation to the back of the block. The difference is in the shape of the flexplate. It will either be dished (9.6 mm) or flat depending on the crankshaft flange. The GMPP adapter kits include the correct flexplate for the intended application.

---

The same basic bolt pattern used on all Chevrolet small blocks from the 1950’s and Chevrolet big blocks from the 1960’s is still the same one used today on the Gen III and Gen IV (LS) engines that began production in 1997. The dowel pin location and also at least 5 of the bolt locations are the same. There is one slight change. The top right bolt was eliminated on the production LS engines because it intersected with one of the head bolt locations on the right side cylinder head. Instead of using that location, the top center bolt is used.

GM Performance Parts LSX Cast iron blocks are drilled with a shallow hole in the top right location (which is drilled 16 mm deep and tapped 11.5 mm deep with a 10 mm X 1.5 thread pitch) as well as the top center hole (7 bolt hole locations).

---

Selecting a compatible transmission to use behind our engines is important. GM Performance Parts has adapters to help you mix and match nearly any engine transmission package you may desire. Keep in mind that the transmission you select should meet or exceed the torque and horsepower output of the engine.

---

No. 4L80E family transmissions have never changed any dimensions as they relate to mating to an engine. Current build 4L80 family transmissions will easily fit any older small block or big block and utilize the common flat flexplate. Mounting to the engine is the same as TH400.

---

As noted above, the bell housing pattern is essentially the same, but you will have the opposite converter nose to crankshaft pilot issue. The torque converter pilot on any LS style 4L60 family transmissions will bottom out in the crankshaft before the bell housing touches the block. In this case you need adapter kit p/n 19154766 to space the bell housing back approximately 9.6mm to gain the proper clearance between the converter and crankshaft when using the newer LS style 4L60 family transmission behind a traditional small block.

---

All early Chevrolet Small and Big Block with two piece rear main oil seals used the same 3.580” diameter 6-bolt flange pattern for attaching the flywheel or flexplate to the crankshaft. The Big Block has kept the same 3.580” 6-Bolt pattern regardless of the seal design (one piece or two piece) throughout its history.

In the mid 1980s the small block changed the rear main oil seal to a one piece design using a 3.000” diameter 6 bolt flange pattern. The main reason was that the one piece seal crankshafts now required an external balance weight that was attached to the flexplate/flywheel. By changing the pattern this prevents any imbalance from occurring by using the wrong flexplate /flywheel.

All Gen III and Gen IV LS design small blocks use a 3.110” (79 mm) diameter 6-bolt crankshaft flange pattern with some exceptions. The Supercharged LS9 6.2L Corvette engine has a unique 9-bolt crankshaft flange and has only been offered with a manual transmission from Chevrolet. The Supercharged LSA 6.2L Cadillac CTS-V and also the GM Performance Parts LSX454 both share the same 8-bolt crankshaft flange.

---

Trailblazer SS Cool Brakes If you own one of the impressive 2006 Trailblazer SS hot rods, then you’ll want to maximize your brake system capability by installing the GM Performance engineered front brake cooling system (pn 19154753). This kit installs easily and makes a dramatic improvement in brake rotor and pad temperatures during extreme brake situations—which improves stopping distances, brake pedal feel and component life.

---

When shifting through the gears of a manual transmission under hard acceleration, the fast guys never completely take their foot off the accelerator-they back off, but not fully, to keep the engine turning enough rpm to mesh the gears and keep the car accelerating with as little lost time as possible.

---

While it’s best to powder-coat or professionally paint parts for maximum appearance and durability, covering parts with semi-gloss black spray can paint is a good way to make everything look great while keeping a down-to-the-wire project moving forward.

---

When starting the build of their ‘dream car’, many enthusiasts have a tough time springing for the initial dollars to commission an artists ‘sketch’ of their dream. Big mistake. These sketches are great for keeping you on your original mission, inspiring you to keep working through the tough times and helping others to get behind your efforts.

---

When building a rollcage, it’s best to mate the rollcage tubes as tight as possible before welding them to maximize the strength of the weld and the overall strength and appearance of the rollcage. A tip to help you make these tight fits is to create a cardboard template (inset) that mates tightly, then replicate that on the end of the tube. (Refer to Cobalt Roll Cage Article in “Performance Pulse” Section)

---

The weight of the suspension ‘corners’ on your performance car make a dramatic impact on how the vehicle handles bumps, cornering, acceleration and braking. In general, the lighter the components hanging out in the breeze, the quicker the spring, swaybar, bushings and shock absorber can control the motion of the wheel/tire combination. This land speed racing setup is the extreme in lightweight, but it shows how important keeping these components light and strong, is to vehicle performance.

---

One of the great lessons of racing is that some relatively inexpensive testing goes a long way once you are at the racetrack and want to go fast. With that in mind, it is a good idea to take your performance vehicle to a chassis dyno facility to do power and simulation runs. While this can be costly, it is almost always much cheaper than the actual tow/race/return cost—and just helps you have a better time once you do go racing!

---

If you own a Saturn Red Line Ion or Chevrolet Cobalt SS-supercharged vehicle, now is the time to consider upgrading your 2.0 L Supercharged Ecotec (RPO LSJ) engine with a GM Performance Stage 1 or Stage 2 performance package. The Stage 1 (pn 17801947) or Stage 2 (pn 17803229) kits install easily and produce a substantial increase in power. And if you want to ‘step up’ from Stage 1 to Stage 2 later on, there is a Stage 1 Upgrade to Stage 2 kit (pn 17803230).

---

A rollcage that is being installed in an existing subframe vehicle needs to be welded to the floor in many places, as there isn’t a separate frame to weld to in these vehicles and the sheetmetal floor is usually too thin to apply the proper level of heat for a strong weld. A way to maximize the strength of this weld point is to build a plate out of 1/8 inch mild steel that closely matches the shape of the floor. Stitch weld this plate to the floor and then weld the rollcage tube to this mounting plate. (Refer to Cobalt Roll Cage Article in “Performance Pulse” Section)

---

An anonymous race quote says, “Worry about the ounces and the pounds will come.” So all performance enthusiasts should be working to shave weight where you can. Your lighter vehicle will show real results in performance that are often better than tons more horsepower!

---

Always carry a fire extinguisher in a performance vehicle and if you’re racing, it’s best to install an on-board fire suppression system that can be activated from the driver’s compartment.

---

If you add aftermarket gauges to your vehicle, consider installing them ‘clocked’ to have the gauge needles pointing straight up when everything is operating to plan. That way, you can tell at a glance if everything is working properly.

---

The fast drivers will always tell you, ‘Smooth is Fast’. Smoking tires and sideways cornering might look cool, but it’s not fast. This is best attained by imagining you have a raw egg between your right foot and the throttle—apply it carefully, but aggressively, to minimize tire spin and loss of traction but maximize acceleration.

---

While it seems some drivers are ‘gifted’ with speed, usually they’ve just got more experience than their competitors. If you want to go fast, take your time, carefully discover the limits of your driving capability and car, get good coaching and keep good notes about your experiences. While it will seem to take a long time to get fast, pretty soon you’ll be considered one of the ‘gifted’ speed demons.

---