How Subaru Made Their Most Powerful Engine Ever - STI S209

hello everyone and welcome in this video we are talking about the Subaru STi s 209 finally the US market gets one of the good ones so this is the first time an S line product has been made exclusively for the US market there's going to be about 200 of these made for the US market Subaru STi s 209 so in this video we're gonna be talking about how the engine works what changes they've made with it and also getting into its water injection system for the intercooler which is a pretty neat little thing that they did and it's also something that they did in the 2004 to 2007 Subaru STi so cool that they have brought it back for this special edition s line s 209 also a huge thank you to Matt Maria motoring for hooking me up with some footage of the engine from the Detroit Auto Show so the engine is based on the same ej20 v platform you've likely formed an opinion about it the engine has been around for quite some time but of course it is that 2.5 liter boxer engine and so you've got your four cylinders right here as you can see but they have made some significant changes to this engine so up at the front you've got a conical air filter and a new induction box that leads you back to a compressor which is now eight percent larger you also have a six percent larger turbine and out the exhaust the mufflers have a seventeen percent reduction in air flow restriction and they've also of course added this water injection system and of course after passing through that intercooler the air is distributed in the intake manifold between the four cylinders alright so comparing the specs between the base 2019 STI and the s 209 the 2019 STI both of them of course having the 2.5 liter boxer four-cylinder engine however the 2019 STI at 310 horsepower at 6,000 rpm the S 209 with 341 horsepower an additional 10% or 31 horsepower they have not yet provided at what rpm that will be at I will get into that in just a second and then the 2019 STI is that 290-pound feet from 4,000 rpm to 5200 rpm and the only thing we have learned so far about the S 209 is that it has an increase in the mid range of about 10% at 3600 rpm now Car and Driver has said that Subaru estimates the peak torque for the 2:09 will be 315 pound-feet and if we were to assume that this was at 4000 RPM that'd be an increase of about eight point six percent so somewhat in line with what Subaru has stated up ten percent at 3,600 rpm and then of course the 341 horsepower / the 310 giving us an increase of 10% power so I might guess that you know if the torque does taper off towards that higher rpm then we may see this 341 horsepower at a slightly higher rpm than 6000 now how is it creating this additional power well part of it is through using this larger turbocharger and having more boost so it's running at 18 psi versus 16 point - for the 2019 STI and another big benefit that the S 209 has is that it has forged pistons and forged connecting rods so not only are they lighter but they are also significantly stronger all right so let's chat about the intercooler water spray because this is quite neat so the process goes you've got your air comes in that filter up front it's then compressed by the turbocharger adds 18 psi of pressure to that air / atmospheric that air is of course then heated up as it has been compressed from that compressor and then travels into your intercooler so you know an interesting thing that Subaru does with their intercooler is placing them up top and it's an air-to-air intercooler so they kind of get some of the benefits of an air to water intercooler and some of the benefits of an air-to-air intercooler in that you know placement for air to water intercoolers is very good because you could put it back in the engine and as you can see the air just comes in through this intake passes into the turbocharger and then immediately can be directed into that inner cooler which is above the engine rather than routing that air all the way back to the front so you can help reduce some of that turbo lag by shortening the path that that air has to travel you also have the efficiency benefits of an air-to-air intercooler so even though it's you know not at the front of the engine which would be ideal from an efficiency standpoint you're still reliant on ambient air to cool that so you know the minimum air temperature you that you could get would be ambient air versus an air to water intercooler system which your minimum temperature would of course be dependent on the water temperature and so that would be slightly higher than ambient so that compressed air is cooled as it travels through this inner cooler and then you have the option a driver controlled option so there's a panel on the steering wheel to spray this water onto the inner cooler and use evaporative cooling to help bring down that intake temperature even lower and so you know if you're looking at your hot air that's going into the intercooler then you have cool ambient air going across the intercooler which is then being heated up and then you also have these two water injectors which are spraying water on to the intercooler so through evaporative cooling the heat of that intake charge is going to heat up that water and evaporate it away and in doing so it's going to cool the air even further so you bring down that air temperature and then of course distribute it into the intake manifold between the cylinders sending in a nice cool dense oxygen-rich because you've you know improved the density by dropping down the temperature us you can inject more fuel and thus make more power now I had a few questions about this system so I reached out to Subaru to learn more about it and the first one was you know what type of fluid can you use with this system and Subaru plans for you to be able to use just any old regular water so I asked about this and they said STI is looking into the fact that of course every state has differing water quality it seems like they do want to be able to let you just use whatever water you want though if you do go back and look at the 2007 STI owner's manual it does specify that you only use pure water my next question was what happens to the system when you have temperatures below freezing and so the convenient thing about this if you're driving in temperatures below freezing you don't need the thing to work because your ambient air is going to be so cold that your intercooler is going to be very efficient so that cold ambient air is going to be able to drop that intake charge temperature quite a bit so you don't need to rely on this water cooling system in order for that to happen in order for that peak performance and so that's the good news about it as far as precautions that you want to take Subaru says that you'll want to keep the tank half empty half full for the optimists out there but keep that tank half empty so that there's plenty of room for that water to expand they said that if you use more than a half full tank of water in there then you're you could actually crack that case that the water is sitting in so you want to make sure it's that just half-full if temperatures are getting very cold and also the lines for the water injectors are rubber so they do have the ability to expand if that water within them or to freeze now how much cooler will the inner cooler spray actually cool down that intake charge well unfortunately I don't have a definite answer on this but I was told by Sumer that they were targeting a drop of 10 degrees Celsius so if the water was on they would expect to see this temperature right here exiting the inner cooler to be 10 degrees celsius cooler than if you were not using the inner cooler water spray system next will the car be rated for 341 horsepower without the intercooler spray and the answer is no and this is pretty interesting and it comes down to how the testing is done in certifying an engine for its horsepower rating and so you might be thinking wait a minute if the thing in cold temperatures can make you know peak power because ambient temperatures are low enough such that the air coming out means that you don't need the water spray system then why would you actually see an increase in performance using the intercooler spray for the published numbers of how much power this engine makes well when engines are certified for their power using sae standard j 1349 this means that the testing is going to be done at 77 degrees Fahrenheit or 25 degrees Celsius and at this temperature the intercooler spray will actually have a meaningful effect in increasing horsepower and so based on how the standard works out it will actually play a role in increasing horsepower Subaru did not say how much but they said without the intercooler spray it would be rated for slightly less horsepower and finally how long it does the water spray lasts so Subaru said that there is a three point four liter tank which is placed in the trunk and then you've got a water pump to send that up to the injectors and they said it will last five point five minutes 330 seconds maximum operational duration for this system so if you kind of do the math and assume that that five point five minutes drains the entire tank that means you're injecting a liter of water about every 100 seconds so on the car you've got little paddle shifters of course it's a manual transmission so these little shifters aren't shifters they're actually for controlling the intercooler water spray so these little paddles I think that is such a cool thing you know anytime you can push a button on your steering wheel that then provides more power is quite neat in my book even you know even though I don't think the overall difference in power is going to be all that significant if I were to take a guess based on the fact that that car has 341 horsepower based on the fact that they're targeting you know a 10 degree Celsius reduction in air temperature I would say the system's probably not going to give them any more than 10 horsepower when it's being used so not something honestly you would end up feeling but still a very real actual difference that would be made you would actually produce more power so it is a cool thing it's kind of an engaging thing with the driver and a throwback to the oaf or 207 sti's which i think is very cool and you know let's say you're going out on a track day you could perhaps put some ice water in that tank so you had some ice-cold water that you're spraying on the intercooler bring temperatures down even more and make even more power doing so so quite cool you know kind of playing around with the system the driver engagement involved with it thank you all so much for watching and a big thanks to Matt Rand motoring for hooking me up with some footage I'll include a link to his video on the s 209 if you'd like to check that out where he got to walk around it at the Detroit Auto Show thank you all so much for watching

Channel: Engineering Explained

Views: 503,370

Rating: 4.9158401 out of 5

Keywords: Subaru, subaru wrx, subaru wrx sti, subaru sti, subaru s209, subaru sti s209, subaru impreza, subaru outback, subaru boxer engine, subaru awd, symmetrical awd, awd, all wheel drive, subaru sti type ra, subaru sti s line, japan, jdm, america, new car, buy new car, buy subaru

Id: xTvfpiqz8Ug

Length: 10min 8sec (608 seconds)

Published: Wed Jan 16 2019