Subaru Engine Conversion Wiki, Let's compile all the knowledge into one thread... Options

[Britain Smith]

I have been going thru several of the threads regarding Subaru engine conversions to learn about the different ways people are performing the installation. From radiators to CV adaptors, there are several paths to take. Lets try to compile all that information into one thread. Anyone can contribute and I will take the information in the thread and update the top few posts with the details.

Here is a list of 914 Subaru related Threads:

Out with the old...in with the new...Britain's Racecar Development, Subaru Engine, Lotus Suspension! Time to go racing!

The Project Anklebiter Build Thread

Tony's Subaru Conversion Thread

Suby-engined rustoration

Zaney's Suby Rustoration Adventure

PorSTi Project Thread

It's official, Subaru EJ25 progress thread

Subaru 6 Cylinder EZ30R Conversion

My 914 EZ30R Twin Turbo Conversion

914 SVX swap, subaru 3.3 conversion

914 Subaru EG33 engine and WRX transaxle conversion, Finally finishing up

Subaru Engine w/Boxster transaxle, Perfect fix for 914???

Subaru Transmission into 914, DAMN that turned out good!!

Orange 75 project, Engine is in!

VOX Subaru Swap build

914 Subaru EG33 engine and WRX transaxle conversion

[thenewwazoo]

(bloody hell those smilies to the left are distracting)

Here's some quick info regarding suby transmissions and clutch assemblies.

There are two main types of suby clutches - "push" and "pull". Relative to the stock configuration, a "push" clutch has the slave cylinder mounted on the engine side of the clutch fork and actuates toward the driveshaft end. The "pull" clutch has the slave cylinder mounted near the center of the transmission and actuates toward the engine. The type of clutch actuation is dictated by the combination of the flywheel, clutch, pressure plate, throwout bearing, clutch actuation fork, and the slave cylinder. All of these items must be matched in terms of fork actuation direction. A transmission can be converted from pull to push by flipping the pull slave cylinder and using a kit - some bellhousings may have bolt holes for using either type, but I don't believe this to be the case. Note that cable-actuated clutches actuate in the "push" direction.

So here's a quick cheat sheet for transmissions and clutch actuation direction. From the factory on cars sold in the USA,
1.8, 2.2L engines came with cable-actuated clutches (Impreza -'01, Legacy -99?)
2.5L non-turbo engines came with push-style hydraulic clutches (Legacy 96+, Impreza 98+, Forester all years)
2.0L turbo engines came with pull-style clutches (02-05)
2.5L turbo engines in the WRX came with push-style clutches (06-09)
2.5L turbo engines in the STi came with pull-style clutches (04+)

You cannot mix and match flywheels with clutches across these (e.g. no WRX clutch on an N/A flywheel, no push WRX clutch with a pull WRX flywheel, etc). You also cannot use an STi fw/clutch/pp in a non-STi bellhousing without some grinding, and you still must use a pull-style clutch fork actuation. Why does this matter? Two reason: power and packaging.

Due to the proliferation of WRXes and the relative scarcity of high-power N/A cars, there are basically no cheap or livable options for N/A clutches that will handle real power. If you're not going to be making more than realistic power for a 2.5L N/A (say, about 200 lb-ft), you can use any clutch combination you want. If you are going make more power, you can either shell out BIG bucks ($800+) for an N/A clutch/fw/pp kit, or you can find a way to make a WRX or STi clutch work.

So why not just grab a WRX clutch/fw/pp and stick it on any old gearbox? The gearbox might not have the bosses required to mount a pull-style slave cylinder. Why not just use a WRX transmission? The pull-style clutch actuation mechanism is physically large, and it's on the top of the transmission, right where the 914 has lots of metal. The push clutch cylinder is smaller, lives closer to the engine where there's space, and can be more easily made to fit inside the 914 transmission tunnel without cutting. The solution, then, is simple - you need a WRX clutch with a push-style clutch actuator. Luckily, that's what Subaru moved to with the WRX in '06+. You can use a stock N/A slave cylinder and clutch fork with an 06+ WRX flywheel, clutch disk, pressure plate, and throwout bearing!

This matters because WRX boxes are expensive (easily twice the cost of an N/A box of the same year), rarer since the N/A transmissions have been around since the early '90s, and basically identical in terms of capability when used in a 914. 06+ WRX flywheels aren't terribly cheap yet, but prices are coming down all the time. '06+ transmissions, however, are still really expensive.

What this means is that, when you're doing shopping, you must consider the transmission, that transmission's clutch actuation direction, and then what flywheel/clutch/pp combos match that direction. You can work backwards or forwards, but they must necessarily follow in that direction unless you want a headache. (IMG:style_emoticons/default/smile.gif)