Full Function: APS Turbo Manifold

Home Catalog Services Company Customer Cars Tech Contact Information [ Contact Us: (510) 475-5855 ]

Select Vehicle

		DSM


		Evolution

		Evolution X

Manufacturers

FFTec Racing
FFTec Accessories
ACT
ACT/Fidanza
AEM
ARP
ATP
BBK
Brian Crower
Bride
Crower
Defi
Eagle
ECMTuning (DSMLink)
Eibach
Exedy
Fluidampr
Forced Performance
Garrett
Gram Lights
GReddy
Ground Control
HKS
Hotchkis
Innovate
JUN
K&N
Koni
Koyo
Magnaflow
Mitsubishi
Momo
Mr. Gasket
Nagisa
Power Enterprise
Precision
RC
RMR
Sard
Simpson
Slimline
Snow Performance
Sparco
Tanabe
TiAL Sport
Tokico
Turbonetics
TurboXS
Volk Racing
Walbro
Wiseco

Special Deals

Gift certificates

Help

"Hey everyone I would like you all to know that there are some real nice and knowledgeable guys at
Full Function Performance. I was just there getting injectors and a tune. I got a smoking deal on the
injectors, got them installed in under an hour."

-NorCalEvo Member

FULL FUNCTION - APS TURBO MANIFOLD AND UP-PIPE WITH INVIDIA TURBO BACK EXHAUST TUNED ON 2004 STI

So you have a Subaru STI and have been flooded with choices of performance parts. Where do you start and what is worth the money and what isn't. Well this Full Function tech article will hopefully help you make some of those decisions by starting with the basics. Intake, exhaust and turbo manifold followed up with some good tuning.

Reducing exhaust back pressure eases the flow for exhaust gases exiting the combustion chamber, reducing the amount of work the engine has to do to expel the gasses netting gains in efficiency. Reducing backpressure on most turbocharged engines has the additional benefit of better turbine efficiency, which aids in boost response. All of this means more power.

For the Turbo Manifold we choose APS. We chose this particular manifold due to it's unique 4-2-1 equal length design. The exhaust manifold section is the 4-2 and the up-pipe is a 2-1. APS is known for making high quality parts for modern performance vehicles. APS products are of the highest quality materials, fit, finish and most importantly PERFORMANCE!!

For the Exhaust we choose an Invidia turbo back, which is also made from high grade stainless steel and is TIG Welded. This setup does not have any catalytic converters and has smooth mandrel bends to ensure a turbulent free exhaust exit. Accompanied with this free flow is an exhaust note is that smoother when paired up with the APS turbo manifold.

The test vehicle rolled into Full Function with an AEM Cold Air Intake system already Installed. When we performed a baseline dyno test the STI netted 231 peak horsepower and 235 peak torque on our AWD Mustang dyno. That's close to 10 more horsepower and torque than we usually see on stock STI's. We also noticed the Air Fuel Ratio was about a half point leaner than stock STI's. The Horsepower gains, Torque gains and leaner air fuel ratio are a direct results from the AEM Cold Air Intake system. With an intake system already installed all we had to do now was the Equal length turbo manifold and turbo back exhaust.

	Shown to the left is the drivers side exhaust manifold which quickly joins the cylinders exhaust flow into one single cross-pipe. This cross-pipe carries the exhaust under the front of the engine and joins the other pair of exhaust runners. The heat shield of the merged section of the exhaust manifold was removed prior to picture taking.
	The exhaust system severely bottlenecks at this junction on the passenger side of the exhaust manifold. Here is where the cross-pipe from the drivers side two cylinders (above white oil filter) crams exhaust into the passenger side cylinders' exhaust flow creating a Los Angeles traffic jam effect of exhaust. All this traffic is now routed through the up-pipe and into the turbocharger.
	Once the exhaust has passed through the turbochargers turbine housing and wheel it then flows into the down pipe and passes through the factory primary catalytic converter. All 2.0 turbo have 3 catalytic converters, one before the turbo and 2 after. All the 2.5 turbo models only have 2 after the turbo. Pictured left is the first of the two catalytic converters on the 2.5 STI.
	As mentioned earlier the STI has two catalytic converters after the turbocharger. Pictured left is the second of the two.
	The APS Manifold keeps the exhaust flow separated for a long distance then smoothly transitions them together. Shown to the left is a picture of the drivers side exhaust manifold runners merging with the passenger side runners.
	Pictured left is the passenger side of the APS Turbo Manifold system. Here you can get a better look at exactly how smooth the merge of exhaust flow really is. This type of equal length manifold design tends to smooth out the choppy helicopter like exhaust tune of the Subaru's.
	The Invidia down pipe does not have a catalytic converter in it's design. This allows the turbo to spool faster reducing turbo lag. The factory exhaust was very small and limited the amount of power the engine could produce. The Invidia Exhaust removes this restriction allow for future horsepower enhancements. The down pipe fit very well without any of the issues that we have seen with other down pipes.
	Notice how much smoother the exhaust flow is with the Invidia exhaust in place. Along with featuring larger diameter piping the Invidia Exhaust eliminates Secondary catalytic converter; no longer creating another horsepower restriction.

The Red lines represent the horsepower and torque with only the AEM Cold Air Intake Installed. As stated earlier in the article this car produced almost 10 more HP and TQ than a factory STI most likely due to the AEM Intake.

The Green lines represent the horsepower and torque with the AEM Cold Air, APS Turbo Manifold and Invidia Exhaust. The car made tremendous gains in horsepower and torque. With the new parts the Subaru made more torque by 3700 RPM than the car did at peak torque before. Not only did it make more torque by 3700 RPM but it carried more torque all the way till redline. By 4700 RPM the car made more horsepower than the it had before at peak and also carried these gains until redline. Before any tuning of we saw peak gains of 38 lb tq and 45 hp. Very impressive for just bolting on parts and not even raising the boost. Now lets see what happens when we add a little more boost and tune the car.

The Blue lines represent the horsepower and torque with the AEM Cold Air, APS Turbo Manifold, Invidia Exhaust after we custom dyno tuned it. We started tuning by bringing the Air Fuel Ratio to 11.2:1 and raised the peak boost to 17PSI. Due to the size of the factory turbo, boost fell off to around 15psi by redline. Once we were happy with the Air Fuel ratio we carefully started adding timing closely monitoring the engines vital sensors. Once our tuning was complete we were able to net an impressive 61 lbs of Torque and 48 Horsepower over the original configuration. With an upgraded turbocharger clearing 300 wheel torque and 300hp would be fairly easy. When comparing all the area between the Red Horsepower and Torque and the Blue ones its very easy to see just how effective this setup proved to be. When we compare these results to other STI's without the Manifold we see performance gains starting from peak torque all the way up to redline, improving the entire midrange and top end performance.