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What mods to do first?


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Ok, between the holidays and my birthday, ive put aside about 700 dollars that I want to spend on my car. I already have rims, sway bar, and cat back exhaust. Im not too sure what would be the best way to spend my money, I was originally thinking of going with the access port, but after seeing that Dyno im not too sure. Who would still rccomend going with this? Also what kind of gains are seen after running stage 2 will satge 2 make it really worth it? Any Ideas or help? Thank you.

 

-NSaglibene

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I was in the same boat. Im going with an Up/Down and highflow cat rather than an AP (and saving some $ too! http://www.legacygt.com/forums/showthread.php?t=6218 ). I know everyone that has a REX loved the AP but I didn’t have a WRX and I am reading very mixed reviews on the AP.

 

 

If figure this was I will get some hp and give the AP a few more weeks/ months to tweak. If I still don’t like it im going with a EUCTEK.

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Add $300 to that $700 and sign up for a Skip Barber two-day driving school, unless you've already done performance driving training. It's the way to get the most from your Legacy GT...mod the driver.

 

Kevin

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I was wondering the same thing. What to do dirst. I am thinking about up pipe, down pipe, cold air intake, and some sort of pcm programming. Is this a bad route to go for starters. This is my first turbocharged car and don't know where to start.
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Hmmm yeah im still lost, I think im leaning back towards the AP, because it seems to benefit a lot in stage 2. Also, Im in NY so if I ran a catless uppipe, and a low resistance cat DP, would I pass emissions? Is an UP and DP all I need to run stage 2?

To get the most from stage 2 you need a full TBE. Also the uppipe cat is only good for the first 5-10mins the car running. The STi comes with no cat in the up.

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If I had a GT I'd definately go with exhaust mods first...

 

Down pipe hiflo cat full exhaust... the less backpressure on that turbo the better.

 

Then work on increasing the volume of piping going into the engine or increasing the efficiency of the intercooler...

 

That or ecu tuning... those are where you're going to find the most increase.

 

CAI isn't going to do much for a turbo car till the turbo can spool freely... at least not much more than putting a drop in hiflo filter and removing the silencer.

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What about the drop in torque from more free flowing exhaust? Anyone have any dyno from up/dp?

I would think due to the turbo spooling quicker, this shouldn't be much of an issue. But then again, this is my first turbo car.

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:rolleyes::rolleyes: Here we go again.

 

LOL....ok here's a repost from a write up I did a while back.

 

A lot of people have different thoughts on backpressure, and often confuse it with Velocity and Delta Pressure...…is probably the most widely misunderstood concept in engine tuning. IMO, the reason this concept is so hard to get around lies in the engineering terms surrounding gas flow. Here's the most impotant ones you need to be aware of to understand the things I'm about to say:

 

BACKPRESSURE: Resistance to air flow; usually stated in inches H2O or PSI.

DELTA PRESSURE (aka delta P): Describes the pressure drop through a component and is the difference in pressure between two points.

 

One other concept needs to be covered too, and that's the idea of air pressure vs. velocity. When a moving air column picks up speed, one of the weird things that happens is it’s pressure drops. So remember through all this that the higher the air velocity for a given volume of gas, the lower it's internal pressure becomes. And remember throughout all of this that I’m no mechanical engineer, simply an enthusiast who done all the reading he can. I don’t claim that this information is the absolute truth, just that it makes sense in my eyes.

 

Ok, so as you can see, backpressure is actually defined as the resistance to flow. So how can backpressure help power production at any RPM? IT CAN'T. I think the reason people began to think that pressure was in important thing to have at low RPM is because of the term delta pressure. Delta pressure is what you need to produce good power at any RPM, which means that you need to have a pressure DROP when measuring pressures from the cylinder to the exhaust tract (the term "pressure" is what I think continually confuses things). The larger the delta P measurement is, the higher this pressure drop becomes. And as earlier stated, you can understand that this pressure drop means the exhaust gas velocity is increasing as it travels from the cylinder to the exhaust system. Put simply, the higher the delta P value, the faster the exhaust gasses end up traveling. So what does all this mean? It means that it's important to have gas velocity reach a certain point in order to have good power production at any RPM (traditional engine techs sited 240 ft/sec as the magic number, but this is likely outdated by now).

 

The effect of having larger exhaust pipe diameters (in the primary, secondary, collector and cat-back exhaust tubes) has a direct effect on gas velocity and therefore delta P (as well as backpressure levels). The larger the exhaust diameter, the slower the exhaust gasses end up going for a given amount of airflow. Now the ***** of all this tech is that one exhaust size will not work over a large RPM range, so we are left with trying to find the best compromise in sizing for good low RPM velocity without hindering higher RPM flow ability. It doesn't take a rocket scientist to understand that an engine flows a whole lot more air at 6000 RPM than at 1000 RPM, and so it also makes sense that one single pipe diameter isn't going to acheive optiaml gas velocity and pressure at both these RPM points, given the need to flow such varying volumes.

 

These concepts are why larger exhaust piping works well for high RPM power but hurts low RPM power; becuase is hurts gas velocity and therefore delta P at low RPM. At higher RPM however, the larger piping lets the engine breath well without having the exhuast gasses get bundled up in the system, which would produce high levels of backpressure and therefore hurt flow. Remember, managing airflow in engines is mainly about three things; maintaining laminar flow and good charge velocity, and doing both of those with varying volumes of air. Ok, so now that all this has been explained, let's cover one last concept (sorry this is getting so long, but it takes time to explain things in straight text!).

 

This last concept is why low velocity gas flow and backpressure hurt power production. Understand that during the exhaust stroke of a 4 stroke engine, it's not only important to get as much of the spent air/fuel mixture out of the chamber (to make room for the unburnt mixture in the intake system), it's also important that these exhaust gasses never turn around and start flowing back into the cylinder. Why would this happen? Because of valve overlap, that's why. At the end of the exhaust stroke, not only does the piston start moving back down the bore to ingest the fresh mixture, but the intake valve also opens to expose the fresh air charge to this event. In modern automotive 4 stroke engines valve overlap occurs at all RPM, so for a short period of time the exhaust system is open to these low pressure influences which can suck things back towards the cylinder. if the exhaust gas velocity is low and pressure is high in the system, this will make everything turn around and go the opposite direction it's supposed to. If these gasses reach the cylinder they will dilute the incoming mixture with unburnable gasses and take up valuable space within the combustion chamber, thus lowering power output (and potentially pushing the intake charge temp beyond the fuel’s knock resistance). So having good velocity and therefore low pressure in the system is absolutely imperative to good power production at any RPM, you just have to remember that these concepts are also dependent on total flow volume. The overall volume of flow is important because it is entirely possible to have both high velocity and high pressure in the system, if there is simply not enough exhaust piping to handle the needed airflow.

 

It’s all about finding a compromise to work at both high and low RPM on most cars, but that’s a bit beyond the scope of this post. All I am trying to show here is how the term backpressure is in reference to a bad exhaust system, not one that creates good low RPM torque. You can just as easily have backpressure at low RPM too, which would also hurt low RPM cylinder scavenging and increase the potential for gas reversion. And understand that these tuning concepts will also affect cam timing, though that is again probably beyond the scope of this post. At any rate, hope this helps, peace. "

 

The goal of any exhaust system is to efficiently remove burnt gases from the combustion chamber, prevent reversion at overlap, and by enhancing exhaust gas velocity leaving the chamber, create a vacuum to help draw or scavenge in more intake charge volume at cam overlap.

 

The key is maintaining exhaust gas velocity or energy as the gases leave the exhaust port when the exhaust valve opens.

 

So as the exhaust gas leaves the exhaust port in a 4 stroke engine , it creates a series of pressure waves travelling at the speed of sound that move towards the exhaust tip (or forwards) and then some reflects back. Like the water waves coming onto the beach, forward and back, forward and back. The main overall direction is forwards but there is some reflection back to the exhaust port (reversion).

 

Simple enough...everyone knows this. So what's new and groovy?

 

The problem is at cam overlap (when both the exhaust valve and intake valve are both partially open and when the pressure in the chamber is greater than in the intake port).

 

If a high pressure wave is reflecting back and arrives at the exhaust port at the wrong time (i.e. when burnt gases still need to leave), it blocks the flow out. You see these instances when a high pressure wave is reflected back at the wrong time as dips in the torque curve AT REGULAR INTERVALS (usually in the midrange rpms).

 

If a low pressure wave is reflecting back at the correct time at the exhaust port it actually helps pull burnt gases out of the chamber and also helps pull in more intake air/fuel at overlap. You see these favourable low pressure reflected waves occurring on your torque curve as small torque increases AT REGULAR INTERVALS.

 

Now here's the first bone of contention and a source of debate between exhaust makers.

 

1. Is a reflected high pressure wave always bad?

 

Most of the experienced people I speak to and read on the various boards say YES! You never want backpressure and you want it as low as possible for as long as possible. The low backpressure assists in maintaining that high exhaust gas velocity. They then design anti-reversion chambers and/or place steps (increases in diameter at various proprietary points along the length of the header) to prevent the reflected waves from travelling back to the head.

 

There are also some pretty smart people who believe slightly differently ...They believe that if you have a high pressure reflected wave arriving a few milliseconds before exhaust valve closure, you prevent the loss of intake air:fuel out the exhaust valve at cam overlap. The exhaust backpressure at this crankshaft degree in the exhaust stroke prevents leaking out or bleeding out of you intake charge into the header and ensures all of it goes into the chamber for combustion.

 

However, these people do NOT use the exhaust diameter as a way to create this backpressure. That would be too crude or less precise, since the backpressure would exist at all times and they only want this backpressure over the few crankshaft degrees when the exhaust valve is just about to close ,when the intake valve is opening further, and the piston has reached TDC and starts downward for the intake stroke. Using an exhaust just to have backpressure then is like cutting butter with a chain saw.

 

The people who agree with this will often tell you that combustion chamber and intake port pressures are higher than the pressure in the exhaust just before exhaust valve closure . So some intake flow into the chamber can get pushed out the closing exhaust valve by the higher combustion chamber pressures.

 

So all you guys that say backpressure is a good thing...I don't believe so...not at all crankshaft degrees which is what you get with a restrictive diameter exhaust. You don't want to have too big a diameter (actually it's cross-sectional area) that will slow or kill velocity or energy. But no backpressure most (99%) of the time is good.

 

2. How do we get low pressure waves and high pressure wave to arrive at the correct time?

 

The conventional way to get the exhaust gas harmonic to do this dance of low pressure to pull in more intake charge and high pressure to prevent bleeding off all at the right time is by changing the tube layout on the header: using lengths, diameters, collectors with various merge angles. But these are limited to one harmonic or exhaust gas speed.

 

So some Japanese engineers at Yamaha (figures, it's always some genius engineer at some bike manufacturer that comes up with these wild ideas) thought: "What if you have an exhaust throttle valve (located in the header collector or at the entrance to the secondary tubes in the first merge collector) that could control the pressure wave behaviour?".

 

The throttle valve angle would vary as the speed of the exhaust gases changed to control the reflected waves. In an 11,000 rpm bike, the valve opens progressively as the rpms climb as the tubes are "in step" with the engine harmonics and less reflected waves occur but at around 7000 rpm, the valve is closed down to 40-60% of wide open when the harmonic is "out of step" with the engine and at 8500 rpm the exhaust throttle valve is progressively opened. How much to change the throttle angle is based on crankshaft angle input or ignition signal input to an ECU with then controls the throttle valve angle knowing the harmonics of the engine.

 

We see these in the Mercedes McLaren F1 car. If you think this is somebody's Frankenstein pipe dream then guess again. The new Suzuki GSXR1000, Honda Fireblade, and Yamaha R1 already have these. And those are today's street bikes! Can the new RSX and Civic Si be that far away from the next stage forward for more power? The impetus will not be performance oriented but the drive to bring this to the market place will likely be more practical, as this throttle valve (the first one was called the Exup or Exhaust Ultimate Power by Yamaha in the late 80's) gains better emissions and lower exhaust noise.

 

So the new toy for exhaust makers will be like variable valve timing and variable cam timing...the mating of electronics to optimise exhaust harmonics at each rpm as the harmonics change with the rpms climbing. It won't be just cut and try any longer...it will be cut try and reprogram.

OBAMA......One Big Ass Mistake America!
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Actually, I would like to bring up another reason people feel that they lose some torque with high-flow exhaust systems. That is usually because they throw an exhaust system on without making any changes to the air/flow ratios, thus usually creating a very rich condition. You really do not want to change the parameters of the intake/exhaust flow too much from stock if you are running a stock ecu, for todays modern setups won't make allowances for large changes.

 

Another area that gets hit is the exhaust side of the turbocharger. Frequently they are a bit on the small side these days, and when you put a big exhaust system on you start getting boost creep and other issues.

 

All in all, when properly tuned and with all your i's dotted and t's crossed, you will make the most power, everywhere, with a high-flow exhaust.

 

Cheers,

 

Paul Hansen

http://www.avoturboworld.com

http://www.apexjapan.com

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Guest *Jedimaster*
Does all this mean the loudest car has the most HP?

I guess that would be me right now (those who were at the meat know what I'm sayin') :lol:

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EXHAUST...EXHAUST...EXHAUST. Turbos need a free-flowing exhaust. That is the best way to unleash hp. With that, also add a free-flowing intake. Such as a simple K&N or a cold air intake. Air needs to enter and exit, the easiest way possible.

Only problem is a really good exhaust will cost money, especially keeping it legal with a high-flow cat.

 

-KevinH

KevinH
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Sooo if one could buy a stock STI uppipe for lets say around 75-100 dollars would this be worthy mod to compliment a panel airfilter on a stock LGT?

The STi uppipe is cat free so it’s a great bolt on. It will decrease spool time and give a few hp. But when installing this you are only 2 or so bolts away from installing a down pipe.

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I need to ask a real noob question here but where does the uppipe take up residence? Down pipe? I would think from their names the up pipe connects the engine to the turbo and the down pipe the turbo to the exhuast system? Gimme some ABC's here thanks for the heads up on the relationship of the downpipe install it would sure seem a waste of time to do one at a time.
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I need to ask a real noob question here but where does the uppipe take up residence? Down pipe? I would think from their names the up pipe connects the engine to the turbo and the down pipe the turbo to the exhuast system? Gimme some ABC's here thanks for the heads up on the relationship of the downpipe install it would sure seem a waste of time to do one at a time.

http://www.legacygt.com/forums/showthread.php?t=572 1/2 way down. ;)

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