Forget two-, three-, four-, or even six-speed automatics – the new hotness in transmissions is the ZF 8HP eight-speed. The 8HP was introduced in V12 BMWs back in 2008, and Chrysler USA builds them under licence as the Torqueflite 8. GM also produces a slightly different version dubbed the 8L, which has been used in Corvettes, Caddys and more.

First published in the January 2025 issue of Street Machine

The alloy-cased, multi-clutch 8HP has been engineered to radically improve fuel economy in modern cars, thanks to advanced computer control and more efficient internals. Compared to a traditional Turbo-Hydramatic, an 8HP shifts faster, offers much better street manners, and can transmit more power to the rear wheels. It can be found in cars like Dodge’s Challenger SRT Demon and Redeye; RAM TRX; A90 Toyota Supra; Audi’s twin-turbo RS6 and RS7; Aston Martin supercars; and even Rolls-Royces.

Andrew Astley from 8speed.au has been at the forefront of 8HP conversions in Australia, and for him, it all comes back to making fast cars nicer to drive on the street and track.

“I was obsessed with making cars fast, particularly 100-200km/h times,” Andrew says. “Back in 2021, I had a Powerglide-equipped car that was fast down the drag strip, but I didn’t like the loose converter around town, so this was where I started researching modern electronic transmissions. Back then, there were no English-speaking people providing public information about these 8HP swaps; it was mainly in Poland and other parts of Europe.”

ZF’s 8HP is a modern evolution of the traditional fluid-controlled, torque converter-equipped automatic. While there are still planetary gears like in a regular auto, the 8HP uses multiple clutches to radically improve shift speed and torque-handling, all controlled by one of the smartest electronic control units used in an automotive setting.

“Inside the 8HP, there are five clutch packs used for gear application, and it uses a combination of three of those clutches in order to give the eight forward gear ratios,” Andrew explains, adding that it’s the size of the clutches that makes a difference. “Not only is the friction surface area of the clutches quite large, but the use of three clutches per gear ratio – compared to a dual-clutch transmission, which only uses one per ratio – helps share the load across the larger clutch surface area. This is one of the reasons the 8HP transmissions have such a high torque-handling capacity for their size.”

Andrew says the 8HP’s eight gear ratios keep an engine in its peak torque band, making it faster than any other gearbox currently on the market, assuming it can handle the engine’s torque. “My first 8HP swap was into a ZF 6HP-equipped car, and changing only the transmission to an 8HP with a Lamik controller improved the vehicle’s 100-200km/h time by half a second,” he says. “This would reflect in the quarter-mile time as well, which is an amazing gain from an extra two gear ratios.”

There are myriad 8HP variants available, with a huge range of power and torque ratings, but Andrew singles out one in particular as the best choice for most street machiners. “An 8HP70 is my pick of all the current options,” he says. “Everyone online talks about 8HP90s, which have a slightly larger clutch pack set-up, but they’re very expensive to buy. We’ve done 50 or 60 built gearboxes, and the majority of parts that go into an 8HP70 build are the same parts you’d use to upgrade an 8HP90. The torque handling capacity of an 8HP70 is very similar to an 8HP90, and if you are building it anyway, it makes sense to start with the more common option.

“These aren’t like a traditional transmission. An 8HP needs to be set up very carefully, similar to setting up a standalone engine ECU”

“The most extreme 8HP70 we have done is a near-standard unit in an 1100rwhp R32 GT-R revving to 9000rpm. Most people say you can’t rev an 8HP that hard, but we do have a customer revving his 900hp SR20 to 9500rpm. But the more you spin them, the more inertia the internals need to cope with.”

When deciding which 8HP to buy for your project, Andrew’s advice is to look at the whole car and how it’s used to ensure the best fit. The transmission’s complexity means attention to detail is key when converting to an 8HP from a traditional auto. “How hard you’re revving the car, how much torque it makes, how it makes that torque, and the weight of the car all come into play when choosing a set-up,” he says.

Like any hardware, the 8HP has a few potential traps for new players. “We’ve sold around 450 controllers now, and people who think it’s just another transmission can get caught out,” Andrew says. “These aren’t like a traditional transmission; they need to be set up very carefully, similar to setting up a standalone engine ECU on a conversion. If you approach it like doing an engine conversion with an aftermarket ECU, you’re in the ballpark.”

The benefit to all the technology in the 8HP is that it makes the transmission far more versatile. In the past, you’d often have a stock ’box that can’t handle the power of your combo, or a race trans that isn’t great to drive on the street, but the 8HP can do both.

The 8HP’s eight gear ratios keep an engine in its peak torque band, making it faster than any other gearbox currently on the market

“With different drive modes, you can bang gears in an 8HP like a sequential, or flick a switch and make it Rolls-Royce smooth for the cruise to cars-and-coffee,” Andrew says. “The key to getting them to drive nicely is road tuning. The TurboLamik base maps are pretty close to perfect if you have a car that makes similar power and weighs similar amounts to the chassis and engine combo they were based on, but variations from there will need to be tuned in.”

When it comes time to buy an 8HP, source a variant that works with the available adapter plates for the engine in your project. “The 8HPs should always be identified by the original engine they were fitted to,” Andrew cautions. “There are different bellhousings and different converter bolt patterns. It gets really tricky; for example, the BMW N47 and N57 are very similar engines, but although the N47 8HP has the same bellhousing as an N57 8HP, they use different torque converters. This means that swap adapter kits won’t work with both versions, even though they are very similar set-ups.”

While that might all sound scary, it simply highlights the benefit of doing your research to learn the 8HP’s intricacies. With the right knowledge on board, you’ll be well placed to swap one into your street machine and enjoy all the perks these advanced modern transmissions bring. Less parasitic drivetrain power loss, faster shifts, and the ability to tune in smooth shifts for the street all sound like big wins to us.

IN DETAIL:

1. The 8HP mechatronics unit (in the foreground) is the component that turns the trans controller’s brains into forward motion. Here, it is connected to the valvebody. The HIS (hydraulic impulse oil storage) pump on the right is used on some 8HP variants for stop-start emissions technology.

2. It doesn’t take too much work to get an 8HP70 or 90 to handle the load of, say, a blown LS Commodore or turbo Barra Falcon making 1000-plus horsepower. However, the transmission needs to be completely stripped to perform that work, which takes a day to pull down and a day to refit.

3. All the tech and hardware in the 8HP comes at a cost, both in terms of expense and weight. “These things normally weigh around 90kg, so they’re much heavier than a Powerglide or TH400,” Andrew says.

4. Most 8HP transmissions come equipped with a plastic oil pan, but there are aftermarket billet pans available that are better for cooling and preventing damage. “We fit thermostats to many of our swaps, as we actually find it difficult to get some 8HPs up to operating temperature,” Andrew says.

5. There are several controllers available for the 8HP. As with ECUs and VCUs, there are budget options, and more expensive controllers that can increase the functionality of the hardware. Some brainiacs have taken to unlocking certain OEM transmission control units to make budget 8HP swaps possible.

6. It’s important to fill an 8HP with the right amount of fluid. “You can destroy an 8HP fast if it doesn’t have enough oil in it,” Andrew says. “It can’t apply enough pressure to the clutches and can burn them out if the oil is low”.

VARIETY PACK

While Turbo-Hydramatic, Tremec, and ZF 8HP transmissions are all available in a range of sizes and specifications, the chart below gives an overview of the basic differences between each ’box. However, the breadth of design variations among 8HP fitments makes this only a very loose guide.

“Picking an 8HP transmission to compare in size to other transmissions is difficult, as even 8HP90s will differ depending on their application,” Andrew says. “There are too many variances in all the different cases to give any useful dimensions to readers, but they have similar clearance issues to a 6L80.

“They are often longer than a 6L80E, and the very rear section of all 8HPs is quite large compared to older transmissions,” Andrew continues. “However, a BMW N57-fitment, AWD 8HP70 with a rear-drive adapter will go into a VE Commodore without any clearancing. The Jeep and Dodge ’boxes are completely different again, and tend to be longer than BMW ZFs, narrower around the output shaft on rear-drive versions, and much larger on all-wheel-drive versions.”