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Old 10-30-2018, 10:19 PM   #1
Chipbreak
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Default All around gains from a down pipe

Now I know this has been talked about alot, but I have a more personal questions.
So I am currently running a 04 WRX with the jdm ej205 w/Avcs. I had the car protuned in Toronto on 94 octane gas. The car was tuned for 17.5 psi and makes 210 whp on a dyno jet. Everything else in the car is stock (catless up pipe). My tuner said if I went with a downpipe he would tune the car for 18.5psi, I was also think about upgrading:
-Sti tmic
-3 port ebcs
-oil to air separator
-q300 cat back

Now would I really be looking at that much more hp gains with these upgrade, mid range and top end. or am I just throwing my money away?
I plan to install an Air to Oil separator amd still tmic regardless of if I do the downpipe
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Last edited by Chipbreak; 10-30-2018 at 10:25 PM.
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Old 10-30-2018, 10:29 PM   #2
CarmelValleyWRX
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i think the downpipe will give you way more bang for buck than an intercooler.
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Old 10-30-2018, 10:45 PM   #3
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Yeah, the downpipe is a big one and is worth adding. Having a 3" downpipe outlet and 3" exhaust also makes a measurable difference over the ones that neck down to a stock sized donut gasket. An invidia downpipe to match the q300 would be a good setup.
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Old 10-30-2018, 11:04 PM   #4
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plus the DP sounds cool inside the car even without a muffler replacement. you can hear the turbo spooling bigger intercooler is meant for bigger turbos or if your going to be doing tons of WOT pulls back to back that would heat soak the stock TMIC. on the street the TMIC has plenty of time to cool off between WOT spurts.
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Old 10-30-2018, 11:14 PM   #5
carlos.danger
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Dp will do wonders.
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Old 10-31-2018, 05:22 PM   #6
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Make sure you get a tune or it will over boost like crazy
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Old 10-31-2018, 05:51 PM   #7
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The downpipe alone is a game changer. Honestly best bang for your buck power mod!
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Old 11-07-2018, 10:18 AM   #8
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DP is a necessity to many any more power. Gains are large for the money and labor involved. Highly recommended. Plus, there's actually been claims by MRT Performance that running a stock downpipe and pushing a car hard over time puts more strain on the engine and other parts. Adding an open downpipe and tuning for it releases the exhausts gasses better, putting less strain on things.

As far as your other mods, the STI TMIC looks cool, but is not necessary. You won't net anything more from it with the stock intercooler.

The AOS is a good choice for any vehicle, even stock. However again, it's not really needed. If you had a larger turbo, much more boost, etc... it would be more beneficial.

3 port EBCS... eh, again, a little upgrade that would not help with power, but with boost regulation. Not needed, but cheap.

Catback - they always sound good, so I'd put this up there again with, not needed, but the enjoyment level is going to be way up there in comparison to the other items on the list.
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Old 11-07-2018, 02:04 PM   #9
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performance wise the bang for buck goes (IMO), DP, 3 port, AOS, TMIC, cat back.

DP gives you the most performance gain. 3 port adds on top of that by extending your torque curve over both ways. AOS will keep the motor clean and help reduce detonation which = slightly more safe power. TMIC will allow you to make even a tiny bit more power safely. cat back is personal preference mostly. you probably wont see gains from it. stock muffler will help keep the coppers at bay.
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Old 11-07-2018, 04:20 PM   #10
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Quote:
Originally Posted by CarmelValleyWRX View Post
performance wise the bang for buck goes (IMO), DP, 3 port, AOS, TMIC, cat back.

DP gives you the most performance gain. 3 port adds on top of that by extending your torque curve over both ways. AOS will keep the motor clean and help reduce detonation which = slightly more safe power. TMIC will allow you to make even a tiny bit more power safely. cat back is personal preference mostly. you probably wont see gains from it. stock muffler will help keep the coppers at bay.
An AOS and TMIC being listed above fuel or the intake/exhaust manifolds of the motor? Surely you jest...

Even the 3-port is questionable... it's good to wring the high RPM torque out of the turbo but only if you're running the OEM turbo so far outside of it's efficiency range that you need to.

Opening the exhaust is the number one thing you can do for improving output on a factory turbo motor. Period. This includes everything from the exhaust valves back, but generally covers the exhaust beyond the turbo, more than anything (given emissions laws).

After that, you turn up the boost while minding the mechanical limits of the motor (knock limitations and knock tolerance, usually) AND fueling system capacity. Stock fuel systems are engineered to operate at ~80% under the OEM motor output. Period. This generally covers injectors and fuel pump (and that's it). You don't need bigger lines, you don't need an aftermarket regulator.

So with that road map in mind (and that isn't just for Subaru or boxer motors, but rather all mass-produced OEM turbo motors I can think of), I guarantee I can find 5 parts that don't include an AOS or TMIC, which are two of the WORST bangs-for-the-buck I can think of.

This is now specific to Subaru motors (2.5 liter primarily, given it is the norm. in this market now):

#1 Downpipe - the stock Subaru part sucks. One without a cat. is even better for performance, but the bang-for-the-buck is probably worse, when you look at the details; reason being, catted pipes are usually a small premium in price when the actual cat. is an expensive part, so a catless downpipe has a higher margin for the manufacturer. I digress - get catless if you only want performance and can pass an OBD-only test for registration.

#2 AP or open source tools - I shouldn't need to explain this, but to take advantage of anything affecting airflow or boost control, you need one of the two (minimum - a standalone system will serve you better in the long run).

#3 Turbo-back exhaust (not inc. DP) - far down the list from the 1 and 2, the rest of the exhaust still matters and you'll pick up power here for marginal cost.

#4 Fuel injectors - even at factory boost levels, you will be able to max out 565 cc injectors on a 2.5 liter motor with the exhaust uncorked. Turning up the boost *will* raise your fuel pressure under load, but you're riding the ragged edge of injector capacity at peak torque (not sustained).

#5 Fuel pump - the factory pump is more capable than the injectors, but you will put additional wear and tear on it by stressing the output. Easy to replace and relatively cheap. Even if it doesn't add output to the motor, that output becomes zero if the stock pump fails all at once under load (not common, but the stockers DO wear out).

Bonus #6 - if you have a WRX or other platform with the plastic intercooler... making an OEM metal intercooler (usually STI) fit is highly recommended. This is the one concession I'll make on the TMIC recommendation. If you do not know your post-IC IAT values, you should not be upgrading the intercooler to something aftermarket, ever. The factory plastic part is still efficient... but this is more of a reliability upgrade. On a MAF-based fueling system, if you get a leak at the IC, your car is dead in the water. A welded metal IC is just cheap insurance (even cheaper if you buy the take-off from a moron that 'upgraded' his STI top-mount).

So where to go from here? An exhaust manifold or removing the TGVs can help a bit, but I would honestly suggest making plans for a better turbo at this point. If you're dead set on keeping within the IHI family for OEM fit, then the exhaust manifold and intake manifold (TGV delete or full manifold) options become more attractive.

The factory boost control on Subaru cars is very, very good - especially for stock turbos. A 3-port really isn't necessary but it will help hold your torque a little higher into the RPM band. These motors really shine in the mid-range so you should really ask yourself want you want before you try to make a EJ25 family motor perform as a high-strung, high-HP project.

An AOS is the worse bang for the buck there is. For 99% of people, it is a way to keep high load oil blowby out of the intake system for 100x the price it takes to do this safely with a few hoses and fittings. It adds no power and only starts being worth the money when you've outpaced the OEM PCV system.

High boost (say 25+ psi) and/or high RPM (over 8000 RPM on the 2.5) are milestones to note that may benefit from a quality AOS. If you're hitting either of these without upgraded internals or a non-OEM turbo, you should probably be saving your pennies for a new motor rather than buying a fancy catch-can.
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Old 11-07-2018, 05:33 PM   #11
CarmelValleyWRX
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ok i was talking about the list this guy had put down for upgrades. your right... fuel system should be added well before a cat back... if you are pushing the stock turbo the TMIC can help and leaves room for a bigger turbo. the AOS is not a bad idea no matter what but is expensive. EBCS only costs $50 and if tuned right adds quite a lot of low end torque and can extend the power band a little on the top end so i think its a good bang for $50 bucks. if we were to make a list of best to worst of ALL mods that exist then my hierarchy above would obviously change.

if i were to make a list of my favorite/most effective to least favorite engine mods I have done so far...
1: tactrix/ gong speed density... and not only for tuning but is #1 tool for troubleshooting.
2: DP
3: silicone IC hose to make working on the car much easier.
4: 3 port solenoid
5/6: vf48 (injectors kinda have to go with this.)
7: TMIC helps alot in the hot months of 100+f
8: helper spring on the vf made a huge difference in spool
9: AVCS
10/11/12: bowl blend/deshroud head, high CR piston, 2.1 stroke
13: porting inlet and exhaust manifolds/tgv's
14: silicone inlet/maf hose
soon to come external wastegate and GS cross pipe, and tuning methanol injection. we will see how these mods stack up.

im choosing external wastegate over a cat back because it should increase VE more than an exhaust. plus it will be stealth until it gets some throttle
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Old 11-07-2018, 06:25 PM   #12
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Silicone I/C hose? You mean the elbow or the throttle connector? The stock elbow is already silicone (and costs $600, new), and the throttle connection lasts a LOT longer if you use the heavy duty rubber part.

I don't have the other two part no. on hand, but Subaru actually makes three throttle connections - rubber, reinforced rubber, and STI/Samco silicone (red). 21869AA030 is the HD rubber one and easily the best of the three.
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Old 11-07-2018, 07:22 PM   #13
CarmelValleyWRX
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i mean replacing the stock plastic POS y pipe that is nearly impossible to pop back onto the turbo with a silicone version y pipe. makes life 1000x better when working on the car taking IC on and off. what silicone elbow comes stock and cost $600? part#? maybe some jdm silicone pipe or something? my silicone pipe came with the throttle body one too but the stock one works. my stock one was 12Yo and dried up and cracked so im running the "new" (now 2 years old) silicone one.
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Old 11-07-2018, 08:22 PM   #14
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With a td04 a 3 free flowing exhaust is probably counterproductive. I prefer a 2.5 catback, the stock donut gasket setup is also not going to hurt flow considering the power level. I also prefer a twin dump down pipe for better low end and midrange torque, with a td04 that is. A bell mouth down pipe is fine too with the td04. A 3 port boost controller is beneficial when custom tuning, the tuner can setup for faster spooling response.
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Old 11-08-2018, 01:02 AM   #15
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Quote:
Originally Posted by CarmelValleyWRX View Post
i mean replacing the stock plastic POS y pipe that is nearly impossible to pop back onto the turbo with a silicone version y pipe. makes life 1000x better when working on the car taking IC on and off. what silicone elbow comes stock and cost $600? part#? maybe some jdm silicone pipe or something? my silicone pipe came with the throttle body one too but the stock one works. my stock one was 12Yo and dried up and cracked so im running the "new" (now 2 years old) silicone one.
The stock elbow that connects the turbo to the intercooler is reinforced silicone, red in color, and costs $600. There are 2 variants, one for the cable throttle and one for the DBW throttle models.

US (DBW) part no. 2004-2007 - 14462AA354; looks like the new part no. dropped in price... only $300 ish now.
JDM (Cable) part no. - 14462AA244; still $750 at today's exchange rate.



The Y-pipe is a different story - both the metal and plastic parts suck, but I'd rather replace that red hose with a cheaper, more flexible silicone one than replace the metal Y.
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Old 11-08-2018, 01:43 AM   #16
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Quote:
Originally Posted by mrsaturn7085 View Post
The stock elbow that connects the turbo to the intercooler is reinforced silicone, red in color, and costs $600. There are 2 variants, one for the cable throttle and one for the DBW throttle models.

US (DBW) part no. 2004-2007 - 14462AA354; looks like the new part no. dropped in price... only $300 ish now.
JDM (Cable) part no. - 14462AA244; still $750 at today's exchange rate.



The Y-pipe is a different story - both the metal and plastic parts suck, but I'd rather replace that red hose with a cheaper, more flexible silicone one than replace the metal Y.
Holy crap! I didn't believe it until I looked up that price myself. JP-carparts has it for $860 USD at the moment! What the hell? lol

I just had my intercooler off today (JDM EJ207) and was looking at that piece, thinking it looked unusually stout for a factory piece. Never would have imagined it would be so expensive!
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Old 11-08-2018, 01:42 PM   #17
CarmelValleyWRX
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that must be an STI piece. my EJ205 wrx had this. https://www.ebay.com/itm/2002-2005-S...4383.l4275.c10

the silicone replaces the whole y pipe thing and you reuse the aluminum ends. this plastic one is virtually impossible to get back one once you take it off
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Old 11-08-2018, 03:13 PM   #18
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Yes, you are correct. The more common upgrade was to replace the 3-piece design of the WRX model with the cast STI part and an aftermarket elbow similar to (but infinitely less expensive than) the red part above. Either way works, but the latter is a little more resilient to collapsing the hoses against wires, BPV hose, throttle coolant hoses, etc.
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