The Turbo Conundrum
 

I've noticed alot of people feel that the 12.5:1 compression ratio in the new 2.0L engine the BRZ will own, makes a turbo setup impossible. This is something I don't really understand.

When it comes to the world of N/A performanced based engines now a days, the compression ratio is almost always too high to allow for any decent application of forced induction. But as far as the subaru engine goes, lowing the compression ratio is a piece of cake compared to most engines. And swapping in 9.0 or 9.5:1 compression pistons could easily allow for a 300-400whp turbo setup with little modification to the rest of the vehicle. This is assuming of course that Subaru continues to use forged rods along with their forged crank and the 6 speed trans is beefy enough to take it. Which based on the other applications of it, I would assume that the trans wouldn't be a huge issue at that level, minus maybe a clutch job.

I guess my question is why the 12.5:1 compression ratio has scared so many people off. As far as i'm concerned its not a huge job. Yes you'll have to tear the heads off, but if you plan on installing a system yourself, you probably have no problem doing that.

Note: Personally I plan to get a 2.5L in there somehow whether it be a complete swap or just a shortblock swap (to keep DI) because i'd rather have the extra torque. And have no intention of doing this, but I know alot of others are very interested in a high reving 2.0L turbo in this car, and feel like its impossible due to the CR, something I just don't understand.

i suspect most people dont want to go "all in" and replace the internals. also the engine will most likely use a modified version of stratified charge with dished pistons for cold start. so you would have to get rid of stratified charge with ecu tuning or get aftermarket dished pistons.

But if you're going with a turbo system, aftermarket tuning is a must anyways. And likely Cobb tuning will be the system of choice for ecu, which allows easy access to all perameters within the ECU. Cobb might even offer a standard map on their system that you can just load and go.

As for the pistons, with a boxer engine, you wouldn't even have to remove the shortblock to swap the pistons out. Its not much more involved than replacing the head gaskets. I guess to me it doesn't seem that involved, anyone going 300hp+ should be prepared for this type of work anyways.

To me the cost of all the parts and possibly labor for the install, likely needing complicated routing for the piping, would be the biggest issue for the average user.

Well it just depends on how my hp you want... with a compression ratio of 11.5:1 mahle pistons and better rod bearings us celica guys were seeing 300hp with no problems... daily beaten too with no problems for thousands of miles.....

Because we want to put the turbo on a stock motor, not have to build it for a turbo. And stock at 12:5.1 is to high for comfortability with a turbo for most people. Sure you can install lower compression pistons, but that would mean the initial cost for running a turbo, equates to having to build the motor (i.e. install lower compression pistons).

Aside from that, It probably will have the first turbo setup out, before it has a set of low compression available for it.

Goes back to people looking for cheap and easy again huh? Which just isn't smart. Just slapping a turbo on 90% of n/a only engines is a terrible idea.

yup most people who slap a turbo on dont look for more than 50 hp, those who do learn not to do it again unless they wanna beef up the motor...

at 300 rwhp this thing will be faster than a 5.0 mustang GT and in a car like this it more than necessary... lol

Has nothing to do with being cheap. You don't need to build every N/A engine just to run a turbo.

I.E. Scion tC...2az comes stock 9:6.1 compression. Runs 350-400whp before needing internals. At 10psi you make 300whp/300wtq.

Plenty of N/A motors out there can have a turbo on them and not fear of detonation with the proper tuning. But most of them are not running 12:5.1 compression either. Anything over 11 in compression is considered high compression to me. Great for N/A, but not for boost, creating the higher initial cost to run turbo because you have to drop the compression.

Dragonitti is right, and most N/A tuners look for more compression anyhow. The legacy and impreza N/A guys have a tough time finding a road for more compression. Which is why Frankenstein motors with EJ22 heads on EJ25blocks are had..or getting head-gaskets to raise compression.

You current turbo owners are a bit spoiled because of boost. high performance N/As are pretty fucking hardcore, and not many have experienced when and how to use that kind of power when boost junkies hype up turbos like its the best and only thing you need in motorsports.

There is no reason to automatically assume that the compression will be too high for boosting -- DI systems are VERY good at quenching knock.

You just assume that I'm a turbo only guy... When it comes to the small car game, I and many others, prefer a 4 cylinder turbo to keep weight down and even moreso the subaru motor for its low center of gravity. Honestly I'd prefer a H8 or an H6 with a screw type eaton supercharger on it for the torque factor while still keeping it a lightweight car, but both are a bit of a pipe dream.

At this point, that is what I'm counting on. 8 injectors should aid in that quite a bit.

A DI system is just a way of more fine tuning a engine for fuel quantity. Its not a miricle worker by any means tho. The amounts of pressure this high compression motor will produce combined with a turbo will likely lead to the motor dieseling.

If a certain motor under a certain amount of boost with standard injection started knocking at 9.5:1 CR, Direct Injection might allow the CR to be raised to 10.2 or 10.5:1 without knock occuring, but its not going to help much when you start trying to add any real sort of boost to a 12.5:1 motor.