Power gains purely from engine position

[shinn497]

Hello.

In the SEMA interview about the 818 Jim mentioned somethings about the 818's engine position that I found particularly interesting.

In particular he mentioned that the intercooler would benefit by not being placed in front of the firewall. This would give increased airflow, better cooling, and less tendency to heat soak. In addition, I've always wondered about the exhausts since they will most certainly have to be provided (they are on FFR's other kits including the mid engine gtm). Given the engines proximity to the rear the exhaust will most certainly be shorter. I can't help but wonder if FFR will take this opportunity to optimize airflow both through the exhaust and intercooler. With an ECU tune this could provide a non-trivial power upgrade. I heard they weren't doing aero testing, but it is being designed on computer. I really hope so, since it is not as if we will be able to purchase aftermarket exhausts on our own.

If they did, just what exactly would be an ideal design? The GTM's loops around the engine bay before it exists the car. I assume this is to fit a cat. Would the 818 exhaust need this too? I'm very curious about this. I know some people have done diagrams of the change in engine position with regards to the design template from the contest. Would the shape of the downpipe/uppipe be affected by this? I forget if the engine actually sits lower...

[BipDBo]

The intercooler will certainly benefit from improved airflow, as the WRX has much difficulty getting air through it. The question is exactly how it will be ducted. This has been discussed at length in previous threads.

The exhaust will almost certainly have be single, unlike the dual exhaust seen on many of the popular designs.

[305mouse]

I would assume in the turbo version the DP will stay OEM and end just behind the wheel, then a new very short cat back exhaust will follow. But who really knows till they make it. As for the intercooler, I plan on using a water/air intercooler. This is due to the fact it will be a summer and track only car. It'll keep it cooler than the OEM air/air intercooler in hotter temps.

[skullandbones]

The water/air intercooler sounds like a good compromise for improving efficiency of the intercooler if FFR has trouble getting air to it. Does that usually involve a separate radiator or piggybacking on to the radiator like a transmission cooler? I'm assuming that the intercooler would have lines running forward in this case. Thanks, WEK.

[Exidous]

A separate radiator is the only way to go for a daily driven car. The engines radiator would heat up or maintain the charge temps high level. I think an air/water setup is a great idea if they cannot get airflow through an air/air enough. The radiator for the intercooler would most certainly have to sit in from of the engines radiator.

[Nuul]

Forgive my ignorance on this subject, I'm having a hard time visualizing how this would work. So you put the intercooler up front like on a EVO and route the tubing to the engine in the back?

[305mouse]

No, the intercooler sits right where it normally would. You then have a seperate water tank of a couple gallons pumping water through a small radiator or oil cooler type setup, then into the water/air intercooler. Some Subaru JDM models in the 90's had water/air intercoolers and you can find them on Ebay from time to time for $100. You would need all the other hardware like pump and radiator to make it work.

[Oppenheimer]

...and the intercooler itself looks very different (air/water vs air/air). Instead of looking like a mini radiator with wide mouth hoses, its more like a solid box with wide mouth hoses and connections for water hoses. No external cooling fins.

[PhyrraM]

The only Subaru models to use the air-to-water intercoolers are the '89-'93 non-North American Legacies. These were the very first of the EJ engine series. The air-to-water intercooler is actually very effective, but it only "bolts on" to the '89-'96 EJ20G series of Impreza and Legacy motors. It *may* fit the '97-'99 Impreza EJ20K and post '96 Impreza and Forester EJ20Gs. Also a small chance it fits the '94+ twin turbo Legacies when converted to single turbo.

The newer '01+ WRX/STI motors have the throttle body move forward in the engine compartment (away from firewall) compared to the early motors, so the air-to-water intercooler is not a bolt on to these motors, but shouldn't be too hard to adapt if desired.

Subaru apparently went away from the air-to-water to simplify the setup and make it a bit more reliable. The electric OEM Subaru pump for the intercooler is known to eat bearings every so often. Many have been replaced with a Ford pump from a supercharged Mustang or Lightning pickup.

At the expense of a few pounds, I see the air-to-water as a good alternative for the 818. Replumbing the system leaves room to add a reservior for added thermal capacity. The OEM Subaru system did not have a reservior and only circulated from the intercooler to the heat exchanger, then directly back. It also sidesteps the air management delimma - the heat exchange can be taken to the airstream instead of forcing the airstream to the traditional Subaru intercooler.

[Twinspool]

I'm really surprised there's talk of dual stage intercooling on a car that's got a serious low mass target to meet. Another water pump, yards of hose, a second heat exchanger, that's at least another 10 kilos and for what? A slight delay in the transient inlet temp rise during acceleration? I don't want to have to start calling this the 828.

The low pressure area behind the car should be plenty sufficient. if not, one single electric fan would be all you need. The F5 guys put the GTM in a wind tunnel, you think they'll smack their foreheads and say "Dang, we forgot the intercooler!" one they're all finished?

Have faith man!

[el_jefe]

water/air intercoolers are fine for auto-x or drag racing, but for road racing not so much. Besides the extra weight, it's just not as efficient as an air to air, unless you use some sort of cooling medium like dry ice to bring temps below ambient.

I'm eager to see what F5 has planned for the body and intercooler, this design leaves plenty of options.

As for exhaust, there will be significant gains over the stock triple cat full length design, I'll be running after market up pipes and a larger than stock down pipe to a muffler for street use, and a bypass valve to run straight out for racing and street use.

[Exidous]

Just the lack of drive line losses alone should add a nice chunk of whp. With drastically less restrictive exhaust the 818 will have due to length and fewer/no cats I wouldn't be surprised if a tune is recommenced for an otherwise stock motor.

[shinn497]

I'm really surprised there's talk of dual stage intercooling on a car that's got a serious low mass target to meet. Another water pump, yards of hose, a second heat exchanger, that's at least another 10 kilos and for what? A slight delay in the transient inlet temp rise during acceleration? I don't want to have to start calling this the 828.

The low pressure area behind the car should be plenty sufficient. if not, one single electric fan would be all you need. The F5 guys put the GTM in a wind tunnel, you think they'll smack their foreheads and say "Dang, we forgot the intercooler!" one they're all finished?

Have faith man!

I like that Idea more. I was researching how air dams work when I woke up and I was wondering if you could use a similiar principle (but reversed) to divert air through the intercooler. I.E. something like a ram air scoop to compress the air and create a high pressure zone which vents to a low pressure zone in the back. Bonus points if you could work adiabatic expansion in there.

EDIT I noticed on jim's prototype that there is a little vent just above the rear seats for the intercooler. So maybe this is not planned. Admitedly a big honking scoop on the back would create hella drag.

I wonder how we got into air/water intercooling. I really don't think this is necessary as the new position alone should be more ideal.

[shinn497]

water/air intercoolers are fine for auto-x or drag racing, but for road racing not so much. Besides the extra weight, it's just not as efficient as an air to air, unless you use some sort of cooling medium like dry ice to bring temps below ambient.

I'm eager to see what F5 has planned for the body and intercooler, this design leaves plenty of options.

As for exhaust, there will be significant gains over the stock triple cat full length design, I'll be running after market up pipes and a larger than stock down pipe to a muffler for street use, and a bypass valve to run straight out for racing and street use.

Any Idea if the stock uppipes and down pipes fit. Check out the SEMA video (http://forums.nasioc.com/forums/showthread.php?t=2267300). I ask because word on the street is that the uppipe in particular from the recommended model year is notriously poorly designed.

[PhyrraM]

I'm fairly certain that both stock up-pipe and down-pipe will be retained. The uppipe on the 2.0 WRXs ('02-'05) have a (pre-turbo) cat in them, but are otherwise the same as the non-catted versions.

Unless FFR is going to pay for CARB testing (not likely) the stock up-pipe (w/cat on 2.0s), downpipe (w/cat) and the OEM 3rd cat must all be retained for (by the book) California registration. Possibly for other states too.

The first two are easy with reusing OEM parts. The 3rd can be accomodated (even if relocated) with the FFR provided exhaust.

I'm guessing the exhaust will be something along the lines of:

factory uppipe > factory turbo > factory downpipe w/cat > FFR provided "90" pointed towards driver side > OEM 3rd cat > FFR provided "U" sending back to passenger side > FFR provided muffler > FFR provided "90" pointed out the back > FFR provided tip. With at least two cats and the turbo, the muffler might even be omitted. That would save another "pass" across the car.

[kach22i]

Hello.

In the SEMA interview about the 818 Jim mentioned somethings about the 818's engine position that I found particularly interesting.

In particular he mentioned that the intercooler would benefit by not being placed in front of the firewall. This would give increased airflow, better cooling, and less tendency to heat soak.
Interesting, been a while since I viewed the video but I recall my take being his statements as an explanation for aerodynamic feed.

The intercooler will depend on air flowing coming in from the top, despite the air flow passing over the roof and rear deck lid opening, forming a low pressure or negative pressure pocket.

To counter this, a generous opening at the rear of the car will be provided.

As the body of the car passes though the air, the air passing over, around and under the car will tend to draw or pull air from the rear opening with it, causing air to enter the top rear deck lid opening.

FYI: You can see this same thing put into practice on many mid-engined Ferrari's.

[StatGSR]

water/air intercoolers are fine for auto-x or drag racing, but for road racing not so much. Besides the extra weight, it's just not as efficient as an air to air, unless you use some sort of cooling medium like dry ice to bring temps below ambient.


what? water/air can be great for road racing to. water to air is actually much MORE efficient than air to air, as water does a much better job of transferring heat than air. granted air to air intercoolers work their best during road racing (because of the constant movement of air across the fins) but that doesn't make a water to air inadequate or less efficient. Also front mount air to airs can prevent your radiator from keeping the car cool as it essentially blocks and heats the air that needs to go through that.

its all give and take, and from a packaging stand point, i don't doubt that water to air may be the best overall choice for a mid engine car like the 818...

good source for water to air kits...
http://www.frozenboost.com/index.php?osCsid=cb3a83310e7eb4bae221edf03cd1433b




I'm really surprised there's talk of dual stage intercooling on a car that's got a serious low mass target to meet. Another water pump, yards of hose, a second heat exchanger, that's at least another 10 kilos and for what? A slight delay in the transient inlet temp rise during acceleration? I don't want to have to start calling this the 828.

The low pressure area behind the car should be plenty sufficient. if not, one single electric fan would be all you need. The F5 guys put the GTM in a wind tunnel, you think they'll smack their foreheads and say "Dang, we forgot the intercooler!" one they're all finished?

Have faith man!


Low mass has nothing to do with intake temp... as for weight, the stock seats will weigh substantially more than a water to air setup.

this isn't a cookie cutter car and everybody is more than welcome to build it as they see fit, i would say its F5s job to make it as efficient as possible given their constraints, but every builder is not going to have the same constraints as F5 when building their car. also, I'm pretty sure that it has been mentioned that the 818 wont see a wind tunnel pre-production.

[skullandbones]

Well, following the direction of the thread, I think engine position translated loosely could mean engine component placement which in this case would be the intercooler radiator. Not taking weight or cost into account and if the companies claims are accurate from your link (x20 reduction in AP) then a mod like this would be very attractive for power gain or lack of power loss depending how you look at it. Placing the heat exchanger in front of the primary radiator would not be my first choice. It would be nice to place them (I would use two small ones) on either side of the radiator with their own dedicated electric fan. I think an engineering solution to calculate the most efficient system would be in order. Another added feature would be a clean up of the engine bay. Some may not want to tackle such a project but I think it would be very interesting especially if you had a consortium of users working on it together. IMO WEK.

[BipDBo]

The intercooler has been discussed at length, but I'll weigh in again. I'm not a car builder, so my practical knowledge there is limited, but I'm an HVAC mechanical engineer, so I know some things about heat exchangers. An air to air heat exchanger transfers heat directly from one air stream to another, which are only separated by a thin sheet of aluminum. A fluid intercooler places a medium of water between that two air streams. The heat is transfer from air stream to water, and then to the other air stream. Whenever you introduce a medium in a heat exchanger system, you will loose some efficiency. Given the same surface area touching each air steams, and the same air velocity, a direct heat exchanger will be more efficient than one with a water loop. A fluid intercooler will also be more complex, heavier, has a small parasitic loss from the pump and is surely more expensive. The big advantage, however, is that you can absorb heat coming off of the turbo and discharge that heat in different locations. You want your duct run from the turbo to the cylinders to be as short as possible because any length will add lag. That's why Subaru puts the intercooler on the top; to reduce duct length. Unfortunately, that's not the best place to discharge the heat. To discharge the heat efficiently, lots of cool air is highly desirable, but for a few reasons, the top of the hood isn't the best place to find lots of cool air. For one, hot air rises, so heat coming from the engine and the radiator will rise in the engine bay and tend to soak the intercooler. Also, it's very difficult to get air to flow over the intercooler at the top of the hood. The big radiator intake on the front of a WRX tends to positively pressurize the engine bay. The intercooler scoop has to work against this pressurization to get cool air down through the intercooler. The airflow is slow, and I've heard can even be in reverse, which would cause hotter air to flow slowly up through it. If someone installed a fluid intercooler on a WRX, they could probably see a significant advantage. This is because they could reject the heat next to or in front of the radiator, where there is plenty of cool air.

The 818, however, will not have a positively pressurized engine bay, so with little effort in ducting and aerodynamics, it should be easy to get lots of air to the intercooler. Also, the radiator (which rejects most of the engine heat) will be on the other end of the car, so there's no danger that this air will be pre-heated by the radiator. Therefore, the top-mount, direct air-to-air intercooler straight off of the WRX is pretty optimum for the 818. I would, however, make one modification. The WRX design pushes air downward through the intercooler. Since hot air rises, this is working against gravity. When at a stoplight (without the help of a fan) convection will make the air reverse direction, and flow upward, drawing from the engine bay, which is hotter because of the engine (not such a huge issue though, since the engine itself generates much less heat than the radiator). It would be best, to duct from a low intake with relatively high aerodynamic pressure (like just in front of the rear wheels) to the bottom of the intercooler, and then duct out to a high, low pressure discharge. I'm not sure if it would be practical to duct it this way, but if it could be done with big enough duct to provide good airflow, this would be optimal.

[Oppenheimer]

This ^^^ makes a lot of sense.

Top mount, air-air, ducted low2high. Add a fan if lots of stop & go, keep engine heat from heating air in duct when sitting.

[skullandbones]

I'm all for KISS. And it sounds like BipDBo has good points. I hope FFR uses some of the existing engineering from the GTM and uses some system that would work like you suggest. I'm referring to the side air scoops which allow for the cold air ducts. Whether the exhaust air was directed up or out the back (low pressure gradient), it would be better than the system as is if there is a high pressure air source. If the intercooler had an insulated barrier to keep hot air away or redirect it, that might be OK, too. WEK.

[Nuul]

This ^^^ makes a lot of sense.

Top mount, air-air, ducted low2high. Add a fan if lots of stop & go, keep engine heat from heating air in duct when sitting.

Hmmm, so something roof mounted like Hugo did on his GTM?

8358

[bromikl]

I'm surprised no one mentioned an intercooler sprayer system. They're cheap, simple, and as I understand it, effective.

[apexanimal]

^ only moderately effective... water injection is much more efficient...

[el_jefe]

What he said. Plus, most tracks get annoyed if ANY fluids are leaking from your car lol

I have found they help a bit with heat soak in between hard runs (auto-x or drag racing), but a really efficient IC won't notice it much at speed. On the other hand, the STI came with one from the factory, so it would look clean. But I'd rather do water/meth/alcohol injection.

[flexer]

Forgive my ignorance on this subject, I'm having a hard time visualizing how this would work. So you put the intercooler up front like on a EVO and route the tubing to the engine in the back?

Here is a good article on it. Its hard to keep them efficient though when used for longer periods....THINK ROAD COURSE:

http://www.enginebasics.com/Advanced%20Engine%20Tuning/Water%20vs%20Air%20Intercooler.html

Or this on setting an efficient one:

http://www.enginebasics.com/Advanced%20Engine%20Tuning/Air%20to%20Water%20Intercooler%20Design.html

[bugeye_fever]

I think that either setup would work well with this car, just depends on your power output goals and intended use. I don't see the added weight of an a/w setup being a big problem as you'd have the heat exchanger in the rear of the car and should you choose to put the radiator in the front you'd spread that weight out over almost the entire length of the car. The weight for the most part would be low in the car and all together forward of the cg which wouldn't hurt the chassis, might actually get it closer to 50/50.

I figure they guys who want to keep it the absolute lightest probably won't worry to much about max power, so the stock top mount located in its stock position with proper ducting and adequate heat shielding will be perfect. I'll link a couple threads i've been following that may be able to generate some new ideas or otherwise stir creative juices.

For the a/w guys or those looking for more information, this guy is pretty smart. Got all the stuff from frozenboost.com which has already been linked in this thread, and in addition to water/meth injection is seeing sub ambient temps.
http://www.iwsti.com/forums/water-meth-injection-nitrous-intercooler-cooling/199117-t-gs-air-water-ic-build.html

Here is one that's a/a for above stock hp, this would take a little more fabrication, but I think shows the rear mounted a/a is feasible.
http://forums.nasioc.com/forums/showthread.php?t=2047734&page=16
Plus there's a video on pg 20 that shows what the 818 could sound like, i.e. pure sex!

[metalmaker12]

I agree, this car is going to fly with the stock wrx 227hp engine, or be a complete rocket with an Sti. we are talking about heat soak and adding water-air intercoolers. I have owned 4 wrx/sti's and they don't even experience heat soak and lag that often even when beating them in 90 degree heat. With about half the weight the engine is not pushing much around. Everything FFR they make is "butter"They will wind tunnel this masterpiece

Can't wait to build my 818

[pipe_dream]

Indeed, the 818 is going to be a performer even with a 227hp engine. About the tune... I live near Seattle and a local shop here (Outback Automotive) does custom Subaru tunes for $325 to perfect the A/F ratio map. On bone stock turbo Subarus the shop commonly sees a 10% gain in power and a 20% increase in fuel mileage.
My wife drives a '11 WRX and I've been dreaming of how fast one of these cars could be if you removed 1400 lbs! W...O...W.

[Etos]

The intercooler will certainly benefit from improved airflow, as the WRX has much difficulty getting air through it. The question is exactly how it will be ducted. This has been discussed at length in previous threads.

The exhaust will almost certainly have be single, unlike the dual exhaust seen on many of the popular designs.

The WRX/STi never have an issue with getting air to the intercooler. They have a hoodscoop for a reason. Heatsoak is a complete non issue with subarus with the only extreme being from drag racers on a very hot day who have been sitting in idle waiting to get to the line.

As silly as it may look, having a hoodscoop on the back trunk looks to be the best way. It would definitely be unique.


Yes the exhaust will be single since it's a single turbo setup. I think the only thing FFR would needs to supply is a catback. I'm not quite sure how they will pull it off with the tranny in the way though. I could see some people saying screw it and just straight pipe out back from the downpipe. However they plan on doing it I think it's important to keep the OEM designed downpipe and not an FFR one as that would start to limit peoples options on non-stock location turbos.

[Slatt]

Heatsoak is a complete non issue with subarus with the only extreme being from drag racers on a very hot day who have been sitting in idle waiting to get to the line.

I beg to differ. There is no doubt intake temperatures in a WRX climb quickly when stopped, engine running or not. And keep in mind that the MAF sensor, where that temperature reading comes from, is less heat soak sensitive than the intercooler itself. There is also no doubt that, when stopped, hot air rises from the engine bay through the intercooler and out of the hood scoop.

When auto crossing I must sit at idle waiting for a run and I routinely spray down the intercooler with a hand-held water bottle before a run and many other WRX drivers at least open the hood. The but-dyno says there is no doubt that makes a difference at launch (yes, even with water injection). Sadly, it also means the pilot has not been strapped in and thinking calmly about his upcoming run...

I'm not suggesting that FFR should take steps to address this issue themselves, but it is an issue with the WRX power plant and warrants discussion.

Personally, I consider drag racing silly, but auto crossing fits nicely with the design and the target market for this Venom/818 thing and is not 'extreme'. Folks who intend to hot foot away from a stop light are on their own, though!

[autostang]

The only two reasons I can see to keep the stock downpipe are engine tuning and emissions restrictions(I don't know how these apply to a car like this) . In the end the cars should be much better off with a custom pipe. I can't see a reason it should need to go down. A straight pipe out the back would be less restrictive,weigh less, and if its straight really shouldn't cost much too fabricate. Another benefit to a shorter exhaust pipe is that the hot gas spends less time in the engine bay and everything stays that much cooler.

[PhyrraM]

The only two reasons I can see to keep the stock downpipe are engine tuning and emissions restrictions...........

Cost is another.

FFR has a reputation for complete kits - and the projected cost of the kit is only $10,000. A good way for FFR to keep about $100 in the budget AND keep the car registerable in many states is to reuse the OEM downpipe w/all factory cats. I'm 99% confident that the base kit will.

[autostang]

Cost is another.

FFR has a reputation for complete kits - and the projected cost of the kit is only $10,000. A good way for FFR to keep about $100 in the budget AND keep the car registerable in many states is to reuse the OEM downpipe w/all factory cats. I'm 99% confident that the base kit will.

Agreed, the cost goes hand in hand with the emission requirements which I admittedly don't know the requirements of for kit cars.

[Nuul]

I'm 99% confident that the base kit will.

This is my assumption as well. Since I'm in Indiana and we don't have emissions tests that's one of the mods I'll probably do. I can't help but think those pipes are going to be a mess back there.

[skullandbones]

I think FFR will need to make an aftermarket performance exhaust available for the 818 like in the GTM. It probably won't be included in the basic kit but it could be part of a complete kit pkg or performance pkg. It's also possible to make the performance tubes larger and better flowing (more room) and still have necessary emission and tuning component application. My performance intake still allows for all the sensors and emission connections for my 5.0. I think it would depend on the state to state requirements for those who want a street legal car: emissions required or not. Also, since this is planned to be exported extensively, it could be even more difficult for those guys. WEK.

[Nelff]

In Cali there may be a problem with an exhaust pipe not having a CARB number. But, since it is a specialty/manufactured car there may be an easy way around this. Most other states that have just a visual inspection and not 'CARB' numbered parts just look to see if there is a cat. If these are OBD II engine management systems the inspection station just plugs in to the under dash and tells the inspection station that all is well in the emissions equipment. Sooo, if the engine management system is stock and all the sensors are plugged in and working, there is a cat, there shouldn't be a problem.

[Oppenheimer]

I think FFR will need to make an aftermarket performance exhaust available for the 818 like in the GTM. It probably won't be included in the basic kit but .....

They have to supply an exhaust, and it has to be part of the basic kit. The stock Cat back exhaust just won't fit in a mid-engine application like the 818.

But the question of the moment is if the downpipe will be stock or not. This is part of the exhaust that is prior to the Cat. FFR could relocate the turbo, and supply a custom downpipe (which might not flow 'down' anymore) if they wanted to, which would allow them to locate the turbo wherever they wanted.

As much of an advantage as that could be, there are good reasons to think they won't do this. Besides being one more part they have to fabricate and include in the kit (increasing cost or reducing profit), it could make the 818 illegal to register in many locals. Not just in Cali, but in other countries (818 = worldcar aspirations).

Leaving turbo in stock location, and reusing the stock downpipe (which still allows builder to replace with any of the performance downpipes on the market), seems like the solution FFR will provide, along with a custom Cat back exahust to fit the new engine location of the 818.

[skullandbones]

Sorry, I was not familiar with the plumbing of the WRX (should have checked the donor list!) but if FFR is true to their word about keeping the cost below 9.9K then they would have to provide a solution similar to the "J" pipes on the roadsters and coupes (included in basic kit). Those even have the O2 sensor bungs. That would be a very affordable route for FFR (inhouse fabrication). If it allowed for relocation of the turbo, that would be even better. Thanks for the clarification. WEK.

[Etos]

I beg to differ. There is no doubt intake temperatures in a WRX climb quickly when stopped, engine running or not.

And the moment you pass 50 feet from a stop it's mostly gone. Just cause some people go crazy over a none issue doesn't make it a real issue. Fact is idle doesn't create that much heat. WOT creates infinites amount more heat yet is none issue at all since you are constantly moving keeping the heat out. Instead of spraying water all over the place you're much better off coating/wrapping the header/up-pipe/first half downpipe and putting a turbo blanket on. More performance and pretty much 0 heat at all.

I just always find it funny people making such a big deal about something like heat soak. I can't tell if it's genuine concern or just an attempt to look like they know something.

[bugeye_fever]

As an autoXer, I have noticed some heat soak, but only during autoX, and only on the hottest of days. I also ruined my heat shield when installing my exhaust, and dont have one installed. That doesn't help, lol.

Far as I've seen the donor list has a big "subject to change" disclaimer at the bottom, so as far as exhaust I would expect Factory Five to reuse the stock down pipe in the basic kit. For those not familiar with the subie exhaust, all the donor car wrx's have 3 cats from the factory, 1 in the up pipe, and 2 in the down pipe along with the rear O2 bung. There isn't actually a catted section of pipe you can simply remove and replace with a "test" or "race pipe". I think this actually helps the situation, FFR would only need to fab an exhaust section with a muffler to attach to the stock Subie down pipe exit location, which is right near the rear end of the trans. If you wanna get rid of the cats, the subie aftermarket has you covered with a large amount of downpipes that end at the stock location.

Only thing I can think of is how much bodywork will be at the rear of the car? I don't think it would be enough to put the muffler straight behind the dp exit, it would be super short, super loud, and probably super awesome to most of us. I anticipate a 90 under the trans and a muffler on the other side. Regardless, I get more excited about this car everyday! And totally unrelated, what does WEK stand for!?

[skullandbones]

They have to supply an exhaust, and it has to be part of the basic kit. The stock Cat back exhaust just won't fit in a mid-engine application like the 818.

But the question of the moment is if the downpipe will be stock or not. This is part of the exhaust that is prior to the Cat. FFR could relocate the turbo, and supply a custom downpipe (which might not flow 'down' anymore) if they wanted to, which would allow them to locate the turbo wherever they wanted.

As much of an advantage as that could be, there are good reasons to think they won't do this. Besides being one more part they have to fabricate and include in the kit (increasing cost or reducing profit), it could make the 818 illegal to register in many locals. Not just in Cali, but in other countries (818 = worldcar aspirations).

Leaving turbo in stock location, and reusing the stock downpipe (which still allows builder to replace with any of the performance downpipes on the market), seems like the solution FFR will provide, along with a custom Cat back exahust to fit the new engine location of the 818.

So if I'm hearing you correctly, then FFR would build a short custom pipe to change the direction of the down pipe to make it fit in the new engine bay (is there an artist's conception of the proposed plumbing?). Bugeye said the down pipe could be used but that is with a modification by FFR as well. Right? I'm not a big fan of the tube wrapping and blanket but in this situation it sounds like a very good idea (lower engine bay temp and increased energy for the turbo).

Sorry for the confusion. WEK is not a new acronym: just my initials. WEK.

[bugeye_fever]

No worries, thought I'd seen a few other posters put the same thing.

I think they'd be able to use an unmodified stock down pipe, I'm working on a picture to illustrate.

[Nuul]

Sorry for the confusion. WEK is not a new acronym: just my initials. WEK.

I had been wondering that. I thought it meant: "whatever, everyone knows" until now lol.

[PhyrraM]

Not a 90 under the transmission, a 90 OVER it. The muffler will be in the cross section ver the rear of the transmission, then it will drop to a tip on the drivers side.

The *general* rule is that if FFR leaves the catalytic converters in "stock" location (in relation to the motor) any "cat-back" exhaust will not need to go through CARB approvial for an E.O. number. I don't know how FFR has traditionally dealt with CARB approvials, but bypassing them period would be a big sigh of relief for all.

[bugeye_fever]

http://i1118.photobucket.com/albums/k609/bugeye_fever/random/SubieExhaust.png

Here's a pic of the underside of a Subie, keen eyes will see its an STI and the down pipe has been partially modified already, but it works for this purpose.

Red line represents the back end of the trans once it has been modified for front wheel drive. You can see how far back the stock down pipe extends past the trans so dependent on how much body work is at the rear of the car, FFR my have to provide an exhaust, and I will retract my previous statements about there being no mid pipe, there is. However in the Subie aftermarket the 2 sections of pipe with cats are commonly replaced by a one piece pipe. Found this on Perrin's website, and its the first time I've actually seen a partial mod of the down pipe. Learn something new everyday!

[JAubin]

Hey, just joined the forum as I'm really stoked about this car! I used to drive an '02 WRX Wagon and spent a lot of time playing with the motor/suspension/brakes so really excited to work on one again.

FYI, here's a pretty helpful diagram of what the exhaust layout is on a WRX. http://www.wrxtuners.com/forums/attachments/f52/5133d1299165736-spt-catback-exhaust-wrx-exhaust-diagram.gif

[BipDBo]

FYI, here's a pretty helpful diagram of what the exhaust layout is on a WRX. http://www.wrxtuners.com/forums/attachments/f52/5133d1299165736-spt-catback-exhaust-wrx-exhaust-diagram.gif

Wow it looks like their would be a lot of performance to be gained not just from hp increase but also weight savings if you ignore CARB and remove all of the cats and silencers. I wonder how feasable it would be to build your exhaust system with a standard muffler and all of the cats, but make it easy to unbolt and remove. This way, you could replace it with a lighter, smoother straight pipe on track day. Would that screw up the turbo tuning? This is an area in which I have no expertise.

[JAubin]

The Pre-cat in the Up-pipe is usually removed primarily so you don't throw pieces of it into the turbo. It's only useful during warmup anyway. The two cats behind the turbo are a pretty large restriction but the biggest is the flat flange the stock downpipe has. It doesn't have a smooth inlet from the turbo, so a bell-mouth can make a really big difference. From what I've heard other people say, going for a super free-flowing exhaust (ie 3" all the way) isn't necessary unless you're doing other things like going with a big turbo, etc. With only replacing Uppipe and Downpipe and a tune it's easy to approach 300 hp at the crank. Always good to retune when you change parts, but how different the two exhausts were might make those changes really small.

[PhyrraM]

IIRC, 2.5 liter WRXs do not have the up-pipe cat, leaving only the two after the turbo.

ALL STIs do not have the up-pipe cat, at least in North American markets.

Here are pre-'02 (never sold in Norht America) and post '02 downpipes. All of the donor WRXs (and STIs, ('02-'07)) have the 2 piece downpipe. The older ones are slightly shorter also.

http://farm6.staticflickr.com/5297/5533614607_946d99a692_o.jpg (http://www.flickr.com/photos/23291496@N04/5533614607/)

[skullandbones]

I am enjoying the pics and diagrams especially since they are very well labelled. It helps explain some of the discussion points by referring back. Thanks alot from me and probably a lot of people who are less familiar with the technology. I was wondering if there are any renderings of the possible layout in the 818 engine bay. I know there are a lot of unknowns but someone did mention such a rendering. Has anyone done a drawing?

Note: One of the things I have noticed in the literature about tuning is that if you maintain similar geometry in the plumbing and component placement, there is less disruption in the way the computer interprets data from the sensors. However, this may not be the case since we are looking at a turbo boosted system. It may be more sensitive to changes that the computer just can't adjust for.

Thanks again, WEK.

[StatGSR]

^ the computer wont care whats going on post turbo for the most part. IMO everyone should plan on tuning there car after this swap anyway, the factory maps are garbage for power and even fuel economy, and with open ecu being such a dirty cheap way to tune, there's just no excuse!

[skullandbones]

^ the computer wont care whats going on post turbo for the most part. IMO everyone should plan on tuning there car after this swap anyway, the factory maps are garbage for power and even fuel economy, and with open ecu being such a dirty cheap way to tune, there's just no excuse!

Do the WRX/STI computers allow you to have the ECU reflashed? Is it a real overwrite of the existing program? Also, have you any ideas on what a tuning session like that would cost? When I have checked with one of my performance shops in this area, it was $100 for basic tune and shop time plus extra for any overrun (open ended). And that was for N/A only. Maybe that's a good price.

Thanks, WEK

[RossLH]

Do the WRX/STI computers allow you to have the ECU reflashed? Is it a real overwrite of the existing program? Also, have you any ideas on what a tuning session like that would cost?

Yes, and there are a few ways of going about it. Open source is the most frugal direction ($200 for the hardware, software is free, OTS tunes run anywhere from $50-$150, and remote tuning generally costs around $200), or you can go with a Cobb Accessport, which is about $700 and includes a few OTS tunes. A dyno tuning session usually goes for $400-500.

[Etos]

^ the computer wont care whats going on post turbo for the most part. IMO everyone should plan on tuning there car after this swap anyway, the factory maps are garbage for power and even fuel economy, and with open ecu being such a dirty cheap way to tune, there's just no excuse!

Not true. The OEM downpipe is very restrictive for the wastegate. Changing the downpipe without doing some kind of a tune, OTS or dyno, will cause overboost issues. Add that to the lean OEM maps and you get tons of detonation.


Do the WRX/STI computers allow you to have the ECU reflashed? Is it a real overwrite of the existing program? Also, have you any ideas on what a tuning session like that would cost? When I have checked with one of my performance shops in this area, it was $100 for basic tune and shop time plus extra for any overrun (open ended). And that was for N/A only. Maybe that's a good price.

Thanks, WEK

Yes the OEM ECU can be rewritten. It's not like the old days where you need to replace ECU or 'chip' the car. Dyno tunes range alot, typically in the 300-600 range depending on CobbAP, Opensource or aftermarket ECU(always costs a tune for those).



Yes, and there are a few ways of going about it. Open source is the most frugal direction ($200 for the hardware, software is free, OTS tunes run anywhere from $50-$150, and remote tuning generally costs around $200), or you can go with a Cobb Accessport, which is about $700 and includes a few OTS tunes. A dyno tuning session usually goes for $400-500.

Opensource cables are $120(125?) brand new and you can get them used for about $80. Cobb AP2 does run $700 new and used should be bought with caution. The AP marries to an ECU and must be unmarried before it can be used on another car. Plenty of people have bought them used to find out they were just paperweights. Having cobb reset them costs ALOT, almost as much as what they cost used.

[RossLH]

Opensource cables are $120(125?) brand new and you can get them used for about $80.

Tactrix 1.3 cables aren't sold anymore, and the 2.0 is $170 plus shipping. If you add a reflash connector, its another 8 bucks. It all comes out to be pretty close to 200 bucks new. 1.3 cables do pop up used from time to time, but they sell fast.

[bugeye_fever]

Off the Cobb tuning website, brand new AP's are $595. Well worth it, I bought mine back in '08, been tuning with it ever since. Especially if your donor used the 32bit ECU with i believe the 06-07 wrx's have.

[apexanimal]

the tactrix 2.0 cables do the same things as the 1.3 but cover more models, correct?

[Nuul]

Off the Cobb tuning website, brand new AP's are $595. Well worth it, I bought mine back in '08, been tuning with it ever since. Especially if your donor used the 32bit ECU with i believe the 06-07 wrx's have.

I'm leaning Cobb because I want multiple maps. I'll probably run 93 most of the time but I'd like to do an E85 map for shiggles. My understanding of the opensource tuning is that I'd have keep a laptop in the car to flash the E85 map whenever I wanted to use it.

[PhyrraM]

....... if your donor used the 32bit ECU with i believe the 06-07 wrx's have.

For North American spec cars:

16 bit ECU - 2.0 liter, Cable throttle, '02-'05 WRX.

32 bit ECU - 2.5 liter, Drive by wire throttle, '06-'07 WRX, '04-'07 STI, any '04+ turbo Legacy, Outback, Forester, or Baja.

[RossLH]

the tactrix 2.0 cables do the same things as the 1.3 but cover more models, correct?

Correct. Plus you can set up logging to an SD card so you don't need to carry around a laptop to take data logs.

[Etos]

Tactrix 1.3 cables aren't sold anymore, and the 2.0 is $170 plus shipping. If you add a reflash connector, its another 8 bucks. It all comes out to be pretty close to 200 bucks new. 1.3 cables do pop up used from time to time, but they sell fast.

You're right, it's been a while since I bought mine that I confused the 1.3 and 2.0 pricing.