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Old 01-15-2004, 02:13 PM   #16
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FMIC vs. TMIC

An FMIC is a Front Mount InterCooler. A TMIC is a Top Mount InterCooler.

TMIC pros:
Shorter piping means less lag
Intercooler is up in a protected location

TMIC cons:
Not as much airflow or space
Heat soak from close proximity to turbo and engine

FMIC pros:
Increased airflow means better cooling
More space to work with

FMIC cons:
Longer piping means more lag
Easily damaged

Which one is best depends on the application. For a lightly modded car, a TMIC may be best because it will cool *enough* to work, but will be less laggy and you won't destroy it if you get in a fender bender. But if you're going for big power numbers, the increased size and airflow an FMIC offer is necessary.

Last edited by ldelaysionl; 01-16-2004 at 02:32 PM.
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Old 01-16-2004, 11:54 PM   #17
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Intakes

Written by MB38

There are three main types of intake "upgrades" you can perform:
1: Cold Air Intakes
2: Short Ram Intakes
3: Drop-in Filters

The first thing to note is that Imprezas do not like to have their intake plumbing fiddled with. Many tuners won't allow a car on their dyno if the intake has been modified. The single best change you can make to your intake tract is the removal of the intake silencer.

1: The concept that drives cold air intakes is simple: colder is better. The piping extends from the MAF down into the fender behind the fog lights where it will, in theory, suck in colder air than it would in the engine compartment. While it's a good theory, there is a problem. The ~5-10 degree intake temperature difference that you will get by sucking in fender air will be thoroughly negated by the 400+ degree temperature inside the turbo. In naturally aspirated Imprezas, the colder intake temperature will not yield greater horsepower either. In fact, in both forced induction and naturally aspirated Imprezas, any cold air intake will merely yield a CEL. There has been no dyno proof that cold air intakes have any positive effects on Imprezas.

2: Short ram intakes stem from a different principle than cold air intakes. The short ram intake sucks in the same air that the factory airbox does, it simply does it in a more efficient manner by reducing restriction. In both naturally aspirated and forced induction Imprezas, this lowered restriction will cause a dangerously lean fuel mixture and a CEL. There is only one [WRX] intake on the market (Perrin Performances) that will not yeild a CEL as the MAF housing is the same diameter as stock and the filter element has enough restriction to keep from causing problems. There has been no dyno proof, however, that this intake increases power.

3: Drop in filters rely on the factory airbox to supply air. The filters are lower restriction than the stock filter which, theoretically, increases power. Unfortunately, there has been no dyno proof to illustrate these power increases. Some drop in filters will cause CELs and lean-mixture problems, some will not. There is no advantage to buying a drop in filter over the stock airbox.

There are only two circumstances when an aftermarket intake of any kind will be required or will increase power. The first is when a front mount intercooler has been installed. Because of the way that FMICs are plumbed, the factory airbox must be removed and replaced with a short ram intake. The setup must then be tuned appropriately.
The other condition is on cars making more than 350awhp on a Dyno Dynamics Dyno. Only at these extreme power levels is the factory airbox's utility expended.

In other words, save yourself the money.
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Old 03-22-2004, 10:08 PM   #18
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Boost Controllers



Manual boost controllers:

Manual boost controllers are pretty basic. They raise the boost, but don't do anything else. They work if you're strapped for cash though. They come in 2 basic types, ball and spring, or screw. A ball and spring controller has a spring with a ball on the end, and once there is enough boost, it compresses the spring, opening the wastegate. The advantage to this type is it opens the wastegate instantly once boost is completely built, so the car will spool up faster than with a screw type and in the end be quicker at the same boost level. Even adding a ball and spring controller to a stock car, without raising the boost at all, can make it quicker because it spools faster, since the stock wastegate opens slowly a little at a time, and the full force of the exhaust isn't used to spool the turbo. The disadvantage to this type is it will be spooled more and boosting more during part throttle driving, and you may get higher than recommended cylinder temps when driving normal. An EGT guage would be recommended so you know if things start to get too hot, though even that isn't instantaneous readout. A screw type is pretty much the opposite, slower spool up, but safer with no part-throttle boosting. This type is generally more accurate too.

The biggest disadvantage to all manual controllers is you can't adjust the boost on the fly. You have to make a pass, watch your boost guage, pull over, get out, adjust the controller, get back in, make another pass and check the guage again, and keep doing this till you get it right. Then if you want to turn it down cuz you're done racing and time to drive home, you have to start the process all over again. Come back to the track next weekend you gotta set it back to high boost. It's a pain in the ass. Some, like the TurboXS controller (I forget what it's called) allow you to switch between 2 different boost levels with the flip of a switch, one for low boost daily driving, and one for high boost racing. This is certainly a lot easier once it's set, but still the same old process to get it set, and it's not near the adjustability of an electronic one. Also, manual boost controllers can be affected by the weather conditions. You might set it during the afternoon to get ready for the race that night, then nightfall comes it could be off again, and you have to go through the same old deal again. The biggest advantage of manual boost controllers is they are cheap.



Electronic and electric boost controllers:

Electronic and electric mean the same thing when taken literally, but this is a catch phrase used to distinguish between 2 different types of electronic controllers. Actually I don't even know if this is a common phrase, or just local slang, but that's beside the point.



Electric boost controllers:

Electric boost controllers are a lot like manual boost controllers, but with a motor or solonoid to do the adjusting for you. You generally have a dial of some sort, and you need a boost guage of some kind too. You make a pass and watch the guage, if it's too much boost, just turn the dial down some, if it's not enough, turn it up some. No getting out and turning the little wrench hassle of the manual controller, and you can actually do it without pulling over and stopping every time if you have a long stretch of road to test on. Much easier. However, they are also affected by the weather problem the manual controllers have, although it's not nearly as big of a problem here because you can adjust it with a simple turn of a dial/push of a button. They come in 2 types, Solonoid and screw. The screw type is just a screw that opens and closes in the path of the air. This kind is more accurate, but less resposive as it may take a moment for the screw to turn to it's new position after you turn the knob. The solonoid type has a solonoid that opens and closes, letting more and less air through to the wastegate. This type is instant response, but generally less accurate.



Electronic "learning" boost controllers:

These are pretty much the same as regular electrics, but they have a built in boost guage and a computer that attempts to "learn" your cars boost characteristics so it can make all adjustments automatically. They can be time consuming to set as you need to make several passes to give them time to learn, but once they're programmed themselves everything else is a breeze. If you want 15 psi, just dial it to 15 psi and it does the rest, no watching the boost guage as you fine tune the dial. This type also compensates for the weather conditions automatically. However, they can be confused with cars that have boost creep or other strange boost characteristics, causing them not to perform up to par. They are also the most expensive type.

Both electric and electronic controllers usually come with other features you can't get on a manual, such as push button instant preset boost levels, integrated timing controllers, etc... This depends on the model.



Here is a test from several of the more popular controllers on the market to help see how they perform - http://www.arimport.com/forum/index.php?showtopic=490
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Old 07-12-2004, 07:14 PM   #19
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Will "X" modification void my warranty?

Yes and no. Your warranty can not be completely "voided" due to modification. However, if your mod caused something to break, then the broken part will not be covered under warranty. The rest of the car is still under warranty though. For example, I'm running a nitrous kit on my car. My entire engine and drivetrain warranty is out the window. If I broke something like an axle, it would be said the extra power from the nitrous is what caused the axle to snap and it would not be covered. But if one of my windows broke or my speedometer stopped working or something else like that which has nothing to do with the nitrous happened, it could still be covered under warranty.

As the saying goes, "you gotta pay to play".
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Old 10-18-2004, 12:46 AM   #20
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Which is better, the SOHC or DOHC 2.5RS?

In stock to medium modified vehicles, it's my opinion that the SOHC is a better motor. It makes more power earlier in the RPM range, and is more reliable since it lacks the infamous "head gasket failure" of the DOHC. In a heavily modded vehicle, however, the extra control of DOHC can be a big advantage. Here is a dyno comparison between a stock SOHC and a stock DOHC 2.5RS:



Obviously by looking you can see the SOHC has better midrange torque and power, but the DOHC holds power to redline a little better.

A little background on this graph:

Quote:
A little while back a group of us NESIC types got together for a dyno day at Adrenalin Motorsports in Massachusetts. I dyno'd my '97 Legacy 2.5GT 5-speed sedan in stock configuration (well, stock + K&N drop-in filter and synthetic fluids), and Marc Sawaya dyno'd his '00 2.5RS 5-speed also in stock configuration.

We all know that the SOHC is supposed to have better mid-range than the DOHC, and I wanted to see how true that was. So, I finally got around to reading the numbers off of my graph and off of Marc's graph to create a combined DOHC vs. SOHC graph. I did actually cheat a bit on my graph - the day that Marc dyno'd his car (and hit 104.x hp) my car dyno'd at 100.6hp or something like that. On a previous day, also in stock configuration, and on the same dyno, I had dyno'd at 104.x hp. Knowing that (theoretically) the peak power should be the same on the two engines, I used my graph from an earlier day so that the graphs would "match". Who knows, maybe in real life the SOHC cars actually do make a few more HP than the DOHC engines, as was indicated on the day we dyno'd at the same time. Or, perhaps the few extra HP that Marc's car laid to the rollers was due to the fact that my engine has twice (?) the mileage and hence is a bit tired? I dunno. I just figured for a "neater" comparison I'd use the graphs that had virtually matching peak power outputs.

Last edited by LjasonL; 10-20-2004 at 10:51 PM.
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Old 11-04-2007, 02:05 PM   #21
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Re: FAQ's regarding the Impreza

Swaybars

To deal with sway bars, you need to understand that everything is compromise, nothing you change on your car is wholly good, there will be a compromise of good effects and bad effects. If you know what the compromise is, you can make a more intelligent decision on what parts you want.

First, what is understeer and oversteer? It simply refers to the tendency of the front end to lose traction before the rear end (understeer) or vice versa. The technical term for this is TLLTD. Taken from another site:
Quote:
Originally Posted by http://www.teamscr.com/sway.html
TLLTD stands for Tire Lateral Load Transfer Distribution. While this term may sound complex, it simply measures the front-to-rear balance of how lateral load is transferred in a cornering maneuver and is commonly used to compare the rate of lateral traction loss between the front and rear tires. You probably understand this already as the concept of "understeer" and "oversteer."
If you're reducing oversteer, then by definition you're increasing understeer. I see people say they did something to decrease oversteer, then immediately add that they did this without increasing understeer. This is impossible, as they are just words for opposite values of TLLTD. You can visualize this by a number line with oversteer at the right and understeer at the left. Understeer is just negative oversteer. When this person 'reduced oversteer' they indeed added understeer, it's just that in this case that added understeer canceled out too much oversteer and brought them closer to neutral. I think the confusion here is a result of the 'understeer is a bad word and we don't want anything to do with it' mentality. Again, it's all a compromise.

Okay let's get to the point. Sway bars do three things:
1. Increase weight on outside tires
2. Reduce body roll which reduces camber change when cornering
3. Change front to rear weight distribution (changing oversteer and understeer)

I'll copy this from another site since they do a better job of explaining these effects clearly than I do:
Quote:
Originally Posted by http://www.nsxprime.com/FAQ/Performance/swaystrutbars.htm
Effect 1) is not a good thing for handling. The coefficient of friction for your tires decreases as more weight is applied. Read that twice to make sure you got it. If your car weighs 2000 lbs and 1000 is in front and 1000 in back (500 each corner), your cf might be .8 for illustration purposes. Your total grip in front is 500 * .8 + 500 * .8 which is 800. As you go into a turn, some of the weight in front transfers to the side so you may have 600 on one front corner and 400 on the other. However, at 600lbs, the cf may be only .7 and at 400, the cf may increase to .85. (Each tire has different values here.) Your total grip now is 600 * .7 + 400 * .85 which is 760. This is a decrease in total front grip. When you add stiffer sway bars, you increase the weight transfer to the outside which further decreases the cf for that outer tire and, therefore, for that end of the car.

Effect 2) is usually the primary reason for sway bars. When the body of the car rolls over, it takes the suspension with it. This causes the tires to ride on the outside edge of the tire and not get a flat contact patch. NSXs are very good in this area, but can still be improved (I suppose).

Effect 3) is neither a positive or negative absolutely. It depends on your car. If your car understeers, it may be due to effect 1) on your front suspension. Too much weight is transferred to the front outside tire which reduces its cf and may be causing it to break loose from grip. A way to prevent this is to increase roll resistance in the rear with a stiffer rear sway bar. The stiffer rear sway bar would resist body roll and apply more force to the outside rear tire instead of applying so much to the outside front tire. Obviously, you can go too far (too stiff in rear) which would transfer too much weight to the rear outside tire and cause it to decrease cf too much and eventually break loose.
So to make it short, the positive effect of sway bars are that they can reduce camber change due to body roll. The negative is a stiffer sway bar will decrease traction on the wheels it's applied to. And an effect that can be either positive or negative is they change the handling balance of the car. This is probably going to be your biggest concern when picking a bar. To put it simple, if you want to reduce understeer (change to more rear % TLLTD) then you can either add a bigger rear bar or a smaller front bar. Usually the bigger rear bar is preferable to a smaller front. The opposite is also true, if you want to reduce oversteer (more % front TLLTD) then you either add a bigger front bar or a smaller rear bar. Again, adding the bigger front bar is usually preferable.
For some reason there's a myth running around the Subaru community that this isn't the case - that adding a bigger front bar will reduce understeer some how. This of course does not agree with the physics of how sway bars work, but you don't have to take my word on it. Whiteline, one of the most respected manufacturers of sway bars for Subarus, had this to say:
Quote:
Originally Posted by http://www.whiteline.com.au/default.asp?page=/faqswaybars.htm
As most factory vehicles are biased towards understeer, fitting of the larger rear swaybar will help in providing a more neutral characteristic in the handling at the limit. This is due to the increase in roll stiffness at the rear, which loads the rear wheels more unevenly and provides slightly less grip at the rear than previous.

At first this may sound sacrificial, however, as the rear end is resisting more of the roll, the front end resists less in proportion, leaving the front wheels more evenly loaded, therefore more available front end grip. In the end an increase in overall grip can be achieved by balancing the vehicle. A WRX or other front torque biased all wheel drive vehicle will benefit even more due to combined front end steering/traction demand.
...
The balance (and grip increase) of the car could also be achieved by reducing the front swaybar stiffness, however its roll stiffness would be reduced and roll camber would suffer. This would lead to large amounts of positive camber being gained on the outside wheels/tyres when cornering. This would result in a wheel/tyre that would not be at its optimal camber setting at the limit of handling.
A tidbit often pointed out is that the serious auto-x Subarus often use big front bars. Many misinterpret this as evidence that the bigger front bar really does reduce oversteer. The real reason this is done on serious race cars is because of something called motive traction, which we haven't discussed yet. When you put that big rear bar on your car to reduce understeer, the way it does this is by linking the two rear wheels together; as the outside corner is compressed in a turn, the bar rotates and compresses the inside tire too. If the effect is extreme enough, the inside rear tire will actually lift off the ground, and when you go to accelerate out of the corner, you'll just get wheelspin due to the lack of motive traction at the rear end. So what do you do? Add a bigger front bar to increase motive traction at the rear, and then you can accelerate out of the corner sooner. As you probably know by now, this comes at the price of more understeer bias. For the race cars, it's worth a little more understeer to be able to get on the power sooner coming out of a corner. Again, compromise...



So now that you know how it works, the next question is probably 'What will work best for me?' Well, that's not a simple question to answer. This has a great deal to do with the rest of your suspension setup (other factors that increase stiffness such as stiffer springs), your driving style, what you intend to do with the car, and just what feels best to you. You're going to be faster with a setup you feel more comfortable/confident in than a setup that has more overall grip but makes you nervous. Most of the time you actually want a bit of understeer bias, and not true 'neutral' handling that's often claimed to be the holy grail.
What do I use? Adjustable rear sway (22-24mm), stock front sway, STi front strut tops, front strut bar, and a set of springs meant for a sedan which, due to the extra 80 pounds in the back of a wagon, gives me a slightly stiffer rear spring rate than similar wagon-specific springs. This part wasn't really by design but just because nobody was making wagon-specific springs at the time I bought them. How does it feel? A bit of understeer on throttle with smooth lift-throttle oversteer. I do have that rear motive traction issue we discussed, but it's not an issue for me because I don't competitively race my car. This will only be an issue at the absolute limit, which you will almost never (or should almost never) reach on the street. I only know of one road where I can actually get that back inside tire spinning coming out of corners, and the car is AWD so I still have the front end pulling anyways. The balance is more important to me than the motive traction issue so I leave it be. If I were to try and competitively race the car I would add a bigger front sway to combat it; in fact, I've been thinking about adding a *slightly* bigger front bar to get quicker turn in at the expense of a little more understeer. Compromise...

I encourage you to read the articles I quoted, especially the first one which includes a controlled real-world test of sway bar effects on TLLTD.

http://www.teamscr.com/sway.html
http://www.nsxprime.com/FAQ/Performa...ystrutbars.htm
http://www.whiteline.com.au/default....aqswaybars.htm

Last edited by LjasonL; 11-04-2007 at 06:04 PM.
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