How To Install A Non-Electronic Transmission Behind An LS Engine

When it comes to the best bang for your buck, the LS engine is hard to beat, and this is why it’s swapped into a variety of cars. These engines are incredibly versatile as parts can be mixed and matched from other engines. And if this isn’t enough of a reason to put one in your project, the aftermarket support is nothing short of incredible.

The early model LS engines came from the factory with a variant of either the 4L60e or 4L80e, and a T56 six-speed manual transmission for those that like to row through the gears. And while modern electronic transmissions are incredible, there are many people who would rather use the less expensive two and three-speed transmission behind the popular LS engine, for various reasons. You will need some information about your combination and possibly a few new parts to make the transplant work, but don’t worry, we will get to all of these details in a moment with the help of PRW Industries.

To help us navigate the ins and outs of these types of transmission swaps, we reached out to Shaun Snow, National Sales Manager of PRW.

As you can imagine, there is a lot of confusion regarding using a non-electronic transmission with an LS engine. “The most common question we receive is, ‘Do I need an adapter.’ There is a fair amount of uncertainty on exactly what needs the adapter and what can work without it,” Snow says.“Guys doing engine swaps are the ones with the most questions since they’re starting from a blank canvas and trying to get parts from multiple sources to work together.”

Gen I VS. Gen III/IV

There are many differences between the Gen I, Gen III, and Gen IV small-block engines. But, let’s talk about the crankshaft and, more specifically, its length.

The Gen I crank protrudes out of the back of the block by .740-inches. Most Gen III and Gen IV cranks extend .340-inches from the block for a difference of .400-inches. This is why you will normally need some additional parts to make up the difference when mating an older transmission to the LS.

In this image, you can see the differences between a Gen I Chevrolet crankshaft length when compared to a Gen III/IV LS.

One of the many great things about the LS engine, especially when bolting on a GM transmission, is the bolt pattern on the back of the engine block. And while we have no idea if GM actually intended this or not, just about any GM transmission can be bolted to the LS. If your old Chevy came equipped with a two-speed Powerglide, TH350, or TH400, you can bolt the more modern LS up to these factory transmissions. However, one bolt in the bellhousing will not be used on the LS.

If you are bolting an early model transmission to an LS engine, you will not use the hole marked by the red arrow. The LS block has a boss but is not drilled and tapped from the factory.

Long Versus Short Cranks

The odds of you needing aftermarket parts for a non-electronic transmission are pretty high. To verify if you need an adapter or flywheel for your LS swap, you will first need to do a little research. If you have an early 4.8- or 6.0-liter engine from 1999-2000, GM used what is called a long crankshaft. This crank projects past the rear cover by .55-inches and these units were only used with 4L80e transmissions. All of the other LS cranks protrude out by only .13-inches and were used with the 4L60e transmission variants. This is very important to note to make sure you get the correct parts for your swap. You’ll also need to decide which transmission you are going to install behind your LS engine.

The 4.8-, 5.3-, and short crank 6.0-liter engines are by far the most popular choice for LS swaps and, with the correct adapter, can utilize any GM two-, three-, or four-speed transmission. However, the long 4.8- `6.0-liter crank is the easiest to deal with in the way of a non-electronic transmission swap. This unit does not require any spacers to install a GM Powerglide, TH350, TH400, 200R4, or 700R4 transmissions if you use a flat flexplate.

Here we used PRW’s adapter sleeve and their High Inertia Quick-Launch flexplate on our 5.3-liter LS.

If you try to run a 4L60e with a long crank 6.0-liter engine, things get interesting. The problem here is that there’s not enough clearance for the torque converter, and it will push it too far in the transmission, causing issues. There’s not a good bolt-in solution for this setup. People have done everything from custom torque convertors to building custom spacers to go between the transmission and engine block for added clearance. Fortunately, this is not the focus of this article since these long crank engines were only produced for two years. And while PRW doesn’t offer an SFI approved unit for this particular application, Snow tells us they are working on one now.

Flexplates

The first piece of this transmission swap puzzle for 4.8-, 5.3-, and 6.0-liter (short crank) engines is the flexplate. And while some enthusiasts will choose to modify the OEM flexplate, this isn’t the best option. Since the torque converter holes won’t line up, the flexplate will need to be drilled out and the existing holes elongated, making them weaker. PRW flexplates are specifically designed for those performing an LS swap.

“We offer several different part numbers for the LS. The main difference is what converter patterns are on the flexplate, the thickness, and if it is a solid plate or has holes to lighten it like the factory versions,” Snow explains.

PRW offers a couple of different flexplates for the LS engine. The High Inertia Quick-Launch on the right, and the Quick Rev design on the left.

PRW offers a couple of different flexplates for swapping in a non-electronic transmission which includes the High Inertia Quick-Launch design (PN 1834620), and the Quick Rev design (PN 1834610) a lightened version with large holes for less rotating mass. These are both high-performance units that offer multiple holes for different torque converters and are designed to take the punishment of today’s high horsepower engines. A 4mm thick center plate provides a robust infrastructure for these flexplates and is robotically cold-welded to meet SFI 29.1 certification. These units are a direct bolt-on design with a forged one-piece steel ring gear. PRW’s flexplates are constructed of cold-rolled premium steel and feature a double-welded ring gear for added durability.

Adapters and Options

Now that you know what flexplate you need, let’s talk about the PRW adapters and when to use one.

“Any transmission that uses a dished LS flexplate and an old-style torque converter (TH350/400, 700R4, non-LS 4L60E, 4L80E, etc.) will require an adapter to work correctly, Snow explains “Some companies are now building custom torque converters for these transmissions to work without an adapter, but those are the minority in my experience.”

And while a custom-built converter is an option, you may not want to purchase a new converter for your application. Plus, the adapters are super affordable and easy to install.

This crank adapter sleeve (PN 1800346) is designed to slide into the crankshaft when using a dished flywheel and is needed for non-electronic transmissions and the 4l80e.

Crank Adapter Sleeve

When it comes to adapters, PRW offers two different types. The crank adapter sleeve (PN 1800346) is designed to slide into the crankshaft when using a dished flywheel and is needed for non-electronic transmissions and the 4l80e. Before bolting up the transmission, the adapter will be inserted at the end of the crankshaft. The torque converter will then slide into this adapter, keeping it centered and allowing it to function correctly.

The adapter sleeve keeps the torque convertor centered and allows it to function correctly.

Crankshaft Adapter

The second adapter (PN 1803533) is needed if you plan to run a flat flexplate with a non-electronic transmission or a 4L80e. This piece fits on the crankshaft, and then the flexplate will bolt on top of it, making a short crankshaft a long one. We should also note that this part can be used on a short crank engine with a dished flexplate as well. But, instead of bolting it to the crankshaft with the flex plate behind it, you will put the flexplate on the crank and then the adapter.

PRW’s crankshaft adapter is needed if you plan to run a flat flexplate with a non-electronic transmission or a 4L80e.

Summary

If you have a long crank LS engine and want to run a GM non-electronic transmission or a 4L80E, no adapters are required, but you will need a flat LS flexplate. And while PRW doesn’t offer an SFI approved unit for this particular application, Snow tells us they are working on one now.

If you have a short crank LS engine and plan on using a non-electronic transmission or a 4L80E, you will need the dished flexplate like PRW’s High Inertia Quick-Launch Design (PN 1834620) or Quick Rev Design (PN 1834610). You will also need PRW’s crank adapter sleeve (PN 1800346) or the crankshaft adapter (PN 1803533).

The crankshaft adapter can also be used on a short crank engine with a dished flexplate. But, instead of bolting it to the crankshaft with the flex plate behind it, you will put the flexplate on the crank and then the adapter.

If you are planning on running a flat flexplate on a short crank LS engine with a non-electronic GM transmission or a 4L80e you have one option, PRW’s crankshaft adapter (PN 1803533).

Conclusion

Bolting on an early non-electronic transmission is a simple process as long as you know your engine is a long or short crank design. After that, you will need to order the right components. If you still have questions, the experts at PRW are certainly willing to help you out. You can give them a call or shoot them an email, and they will make sure you get the parts you need.

Article Sources

About the author

Brian Havins

A gearhead for life, Brian is obsessed with all things fast. Banging gears, turning wrenches, and praying while spraying are just a few of his favorite things.
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