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4EAT 101 “Best Kept Secret”


 

General Information

4EAT stands for Four-Speed Electronic Automatic Transmission. This simply means that your vehicle is equipped with an automatic transmission with four gears. The gears for the 4EAT are as follows:

Automatic transmission gear ratios:

1st - 2.785

2nd - 1.545

3rd - 1.000

4th - 0.694

Reverse - 2.272

Final drive ratio - 4.11

Each gear can be taken to the following MPH

1st-38

2nd-71

3rd-112

The 4EAT is also equipped with the VTD (Variable Torque Distribution) AWD system. This AWD system adjusts power to wheels depending on driving conditions, making it more technically advanced than the AWD system used in manual-equipped vehicles. The normal driving split is 45% to the front wheels and 55% to the rear wheels.

How does the 4EAT differ from the 5MT? Is it better or worse for performance?

The first difference between the 4EAT and 5MT is the AWD system. 5MT models use a permanent 50/50 split between the front and rear wheels, whereas models equipped with the automatic make use of the technically superior VTD system (mentioned above). The second difference is the gearing. The 4EAT uses 4 gears to make use of its power, where 5MT models make use of 5 gears.

From a stop: The 4EAT (stock) is much different performance-wise than the 5MT. Models equipped with the 5MT are able to achieve their pavement-rippling sub-six second 0-60 and low 14 second mile times thanks to its ability to launch at 4000+ RPM. Models equipped with the 4EAT must use the brake-torque technique (I also take no responsibility for potential damage caused to your car using this technique), however, stock 4EATs using this method can only launch at a maximum 3200 RPM, leading to a 0-60 time in the low 7 second range and a mile in the mid-to-high 15 second range.

From a roll: Judging from the very few 4EAT vs 5MT races that I have studied, a 5MT will have about a 2 car lead on a similarly equipped 4EAT in a race from 40 MPH to 100 MPH. Please note that in the few documented races known, the 4EAT begins to trail after it shifts to 3rd gear, leading me to believe that the 4EAT’s major weakness are it’s gear ratios.

Stock 5MT models dyno at around 170 WHP where 4EAT models dyno at around 150 WHP. From my research, I have noticed about a 20-25 WHP difference between similarly equipped 4EAT and 5MT WRX’s due to the extra driveline loss through the torque converter.

What you need to make the 4EAT comparable to a 5MT in acceleration and mile times.

You need a high stall torque converter. The main purpose of this mod is to raise the stall speed from 3200 RPM to around the 4200 RPM range; allowing the 4EAT to run 0-60 and quarter mile times consistent with 5MT equipped vehicles. This mod is a MUST HAVE if you are planning on consistently drag racing your vehicle. The use of this mod for owners whom do not consistently drag race is debatable. Some argue that it increases daily drivability; others argue that it does not. You’ll have to decide.

I am not interested in 0-60 or mile times, how else can I make my 4EAT a better daily driver?

Although this is highly subjective, the general consensus is that the best method to increase your 4EAT’s drivability is by installing an aftermarket header, uppipe and turbo back exhaust system . This will virtually eliminate turbo-lag and give much better low and mid-range power. You can also add engine management to take full advantage of your modifications to further increase responsiveness and decrease lag.

Best First Mod for the 4EAT

Although the idea of the best first mod is highly subjective, I, along with many others, feel that an aftermarket exhaust system is the best first modification for the money. This modification greatly decreases turbo-lag, causing the car to perform better in all circumstances.

Best New Turbo for the 4EAT

We have found that a GT30R is the best turbo replacement for the 4EAT. Both the VF 34 and 39 have decent spool-up, with good mid-range and top end. If you plan on doing short block upgrades and running higher than 18 psi, then we have found the GT30R to the our favorite.

Of course, you will also need the necessary supporting mods to run a new turbo. A great deal of research must be done if you decide that a new turbo upgrade is right for you.

Using a Blow-Off Valve on a 4EAT

Yes, it can be done, but the difference between using a BOV on a 4EAT is that you will not hear much of the “pssshhh” sound when the transmission shifts. This is because the 4EAT holds its boost during shifts.

I heard that the transmission in the Auto can hold more power than the transmission that is used in the manual. Is this true?

Yes, this is true up to a point. The general consensus is that the 4EAT is a stronger transmission than the 5MT and will last a very long time as long as it is properly maintained and the abuse is kept to the minimum. The 4EAT is an extremely hard transmission to “break,” but it is unable to cope with too much extra power because its shifts are still tuned for stock levels. Once you begin to cross to cross the 250 WHP barrier, you need to consider “beefing up” your transmission with a performance torque converter and valve body upgrade. This need increases if you plan on launching your vehicle or driving it hard on a consistent basis. Very few people have actually broken the "teeth" of the 4EAT, and with a full internal transmission upgrade, the 4EAT will handle over 800WHP.

Can I manually shift the transmission ala Manumatic?

Although available as a true manumatic in Japan, the American version of the automatic WRX does not contain that feature. You may manually select the gears, although there is little purpose as A) manually shifting from a stop will not net you better acceleration and B) it does put extra stress on your transmission. I manually shift the automatic from a stop frequently and through the gears without any issues.

However, the manual functionality of the 4EAT can be useful for proper power delivery when cornering, it can also be used to place the car in a better gear when racing from a roll.

4EAT Idiosyncrasies

The automatic in the WRX is a lot different than any other automatic that I have driven. The 5MT guys can choose the gear that they want their car to be in, keeping the car in it’s optimal power band. We can do that as well, it just takes knowing how to fully use the automatic to take advantage of the car’s power band. Lets review the different gear selections on the automatic gear shifter. (please note that the following information is intended towards stock vehicles. The rules are completely different for modded or even lightly modded cars).

1: This is a special situation gear (explained further in the manual) It should be used rarely, if never. Some owners like to start out in 1 to ‘manually shift” the gears. Please note that the transmission will not automatically upshift while in 1, so when you shift into the next gear, make sure to do so at least 1000 RPMs early because of the shifting delay.

2: This is also a special situation gear (explained further in your manual). Starting off in 2 will start your car in 2nd gear, not first, making it perfect for dyno tuning, but doesn’t make much sense for daily driving. Please note that the transmission will not automatically upshift, so make sure to shift at least 1000 RPM early because of the shifting delay.

3rd gear is sometimes referred to in other cars as “D.” By selecting 3, the car will drive normally but will not upshift into 4. Selecting 3 is ideal when you are driving in any situation where you will not be maintaining a constant speed (while driving in the city, for example, or climbing a steep grade). By selecting 3, your car will also be much more willing to downshift into 2 when extra power is required, making 3 the Power Gear of the WRX. Interestingly enough, there have been some reports of a .2 second better time at the track thanks to the more aggressive torque split while in 3.

D is sometimes referred to in other cars as “OD.” By selecting D, the car will drive normally and shift into 4th gear as soon as it can. This is only ideal while maintaining a constant speed (Highway, freeway driving). While in D, the car does not like to downshift into 2nd gear, making it a poor gear selection for times when quick passing response is necessary.

Why the 4EAT is better then the 5MT.

All of us are forgetting the main advantage of the Auto-WRX: the AWD system itself. When we talk of "Rally Proven", the "proof" is actually missing in the Manual-WRX. Here is the reason why:

The VTD-AWD system of the Auto-WRX is the most advanced AWD system of Subaru, with a true torsen (torque sensing) planetary gear center differential, which works in association with electronically controlled continuously variable multi-plate clutch-packs. The torque split is at 45/55, with a slight rear bias in power, in normal driving, unless more is needed front or back. This system equals in sophistication and effectiveness, the best AWD systems currently available in the market including the Audi Quattro (not the "Quattro" present in the Audi TT, which is inferior to the VTD-AWD). The VTD-AWD system is conceptually identical to the AWD systems present in the World Rally Conquering Subarus, the significant difference being that the WRC cars have driver adjustable torque splits and are much more of a heavy-duty kind. The hardware otherwise is identical in design. The Rally Subarus also have a true auto-manual transmission, which is actually a clutch-less manual, but the underlying AWD system is better adaptable to the Auto-WRX, not the manual-WRX, due to which the manual-WRX soldiers on with an AWD system that is essentially tractor-technology. "Gets the job done" but nothing to write home about.

The other Auto-Subarus do not have the torque-sensing center differential and drive more like a FWD car in normal driving.

The manual WRX on the other hand, has the same Viscous coupling AWD system present in all other manual Subarus, which is a reactive system, as opposed to the proactive nature of the VTD-AWD system of the Auto-WRX. The viscous fluid which is used to transfer torque front/back needs slippage before it can react and transfer torque. Also, since differential lock is achieved due to the viscous fluid being twisted (unlike the torque sensing incredibly sturdy planetary gear differential in the Auto-WRX), the torque-transfer is both slow and in efficient. The AWD system of the manual WRX cannot be compared with the Audi Quattro or any other sophisticated AWD system. It does not have the breadth of operation (cannot transfer the amount of torque front/back like the VTD-AWD), the reactiveness (reacts slowly due to its very Viscous coupling nature) or the rapid torque transfer characteristics (due to the "reactive" nature of the system) of the VTD-AWD equipped Auto-WRX. With the Viscous coupling AWD system present in the manual-WRX, Subaru certainly would not be winning many rallies....just a heads-up.

Everything else remaining the same, I would have preferred a manual in the WRX. But in this particular case, everything else is not the same. Far from it! Let’s face it - we love these cars for their AWD systems and not for their "manual gear shift capability".

4EAT_Phase_II_Automatic_Transmission

4EAT Transmissions

So on that criteria,

the Manual-WRX has a huge and glaring deficit and the 4EAT is the “Best Kept Secret”.



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