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Old 02-03-2007, 04:25 PM   #1
keaniegenie
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Default 2.0l to 2.5l swap, and what AVCS means to you

It seems every time somebody does a swap from a 2.0l to a 2.5l, they are looking for some improvement in their power band. I found myself writing long posts over and over again telling the story of my swap, so I thought I'd start my own post, even though people will rarely search for it anyways

It's obvious that people who swap to a 2.5l EJ257 wants an improvement in power/torque in some fashion. How you go about your build should be relative to your total goals. I think one thing most people planning a motor swap think of is what kind of power they ultimately want and what kind of power band they're looking for.

This is the combination of engine/turbo setups I've had in the order I had them.

EJ205 w/ stock turbo
EJ205 w/ stock turbo + TBE, TMIC, EWG, and EL header
EJ257 w/ stock turbo +TBE, TMIC, EWG, EL header and no AVCS
EJ257 w/ stock turbo + TBE, TMIC, EWG, EL header + AVCS
EJ257 w/ Element GT52 turbo + TBE, TMIC, EWG, EL header and AVCS

The main purpose of this post to explain the differences I've noticed during my build, since it was done in stages. Let me start with my goals, and why I chose to go this route.

The biggest thing I found lacking of the EJ205 motor was the bottom end. Having driven several STI's, I desired the bottom-end torque and responsiveness the STI's had. This said, I also wanted to improve my top-end power as well. So in a sense, I wanted to improve my entire power band from bottom-end to top-end power with a final goal of 375+whp on pump gas and 450whp with water injection.

My original assumption regarding the bottom-end torque of the STI was that the increased displacement provided all of the low-end grunt I was shooting for. Having had a 2.5l EJ257 (longblock) with no AVCS wired, I soon learned the responsiveness of the EJ257 relied heavily also on the AVCS. There was no doubt there was an increase in torque and responsiveness with the 2.5l, but it was no where near the level of the STI's I've driven. Keep in mind that I had a TD04 turbo (stock WRX turbo) which spools faster than the factory STI VF39.

Later, I wired in AVCS control, which requires either a STI ECU, or a Hydra. Voila! Now it felt like an STI. The power was not only much better in the lower end, but the power range was also much more linear. Lag is not only reduced, but the power is smoother. WRX guys are very familiar with the boost on/off feel(this is the sudden torque you feel when the turbo is spooling up). This feel is dramatically reduced making the car feel more like a big NA motor.

Not long after, I installed the larger turbo. We modded the stock injectors , installed a fuel pump and new inlet pipe and got a new base map for my GT52 turbo from Phil. I was amazed how well such a large turbo mated to my 2.5l AVCS motor in terms of linear response and fast turbo spool up.

After my build, I had the luxury riding in a 2.5l hybrid with an FP Green turbo. For people who don't know, the FP Green uses the same housing as my GT52 turbo but utilizes a smaller turbine and compressor wheel.

This hybrid utilized the proper gaskets so the compression ratio would be safe and was using complete stock WRX heads including WRX cams. Even though the displacement of our cars was the same, it was very obvious that my setup was still much more responsive on the bottom-end power range. The hybrid had better bottom end power than an EJ205, but the boost on/off feel was still there and the Green felt laggy compared to my GT52 even though the Green is a smaller turbocharger. The only real explanation for this was the AVCS. Even though my STI heads uses more aggressive cam profiles, the bottom-end was still much better.

I find many 2.5l hybrid owners planning on non-AVCS setups with upgraded cams. When I speak to these users, often they're telling me they want more bottom-end torque and more overall power too including top-end. What many of them don't realize is they're taking 2 steps forward, one step back. Yes, the 2.5l will improve torque/power, and yes, the cams will improve top-end, but what they don't realize is how much higher lift/duration cams effect bottom-end power. The end result is a car with marginally improved bottom-end and much better top-end power. This combo doesn't even make sense to me unless your power goals exceed 500whp since you don't have to sacrifice the bottom end to get any power level less than this. On the other hand, a EJ257 longblock w/ AVCS is capable of hitting 500whp while having much improved bottom-end. The slightly more aggressive cams still provide great daily driving response, and the AVCS more than makes up for the profile.

Now, if a person said they wanted a top-end monster and they wanted the 2.5l just to help spool up their giant rotated turbo, a hybrid w/ aggressive non-avcs cams makes a ton of sense. The upgraded cams on a 2.5l hybrid will yield more top-end power than a stock STI longblock w/ AVCS. If you're shooting for 600whp on race gas, then you should be prepared to lose some bottom-end power for the ultimate top-end goal. The aggressive cam profile is then not an option, it's absolutely necessary.

So if you want the best improvement of bottom-end with an ultimate HP goal less than 500whp, AVCS makes the most sense. Not only that, but you also have the piece of mind that you're reaching your ultimate goal with an OEM motor. This, of course, is not taking into consideration any motor building you may want to do on the shortblock, IE pistons, rods, etc.

Many people think the cost of wiring an AVCS setup is super expensive. However, many people don't consider the ENTIRE cost of the build. If you follow a couple, small tricks to your build, you will save hundreds of dollars and get your ultimate goal at a reasonable cost. This post is long enough, so I won't go into details here. PM me if you want details.
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Old 02-03-2007, 05:38 PM   #2
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Dear lord....go grab yourself a beer for that
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Old 02-03-2007, 06:09 PM   #3
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Informative....To say the least.
I am a newb aquiring information but what if you built your block (pistons,rods blah blah blah) and decided to increase flow on existing wrx heads?
To flow more than those avcs heads with better cams than the stock WRX has?
Is AVCS all hype or can WRX heads ported/polished + better cams beat them?
I too am looking for something with power across the entire band but really dont mind a little lag down low as I am used to it with my rex.
This would be on some sort of stoker motor of course.
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Old 02-03-2007, 07:50 PM   #4
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Have beer, now reading...
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Old 02-03-2007, 08:45 PM   #5
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golf clap... excellent writeup
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Old 02-03-2007, 09:31 PM   #6
keaniegenie
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Quote:
Originally Posted by Imprezav View Post
Informative....To say the least.
I am a newb aquiring information but what if you built your block (pistons,rods blah blah blah) and decided to increase flow on existing wrx heads?
To flow more than those avcs heads with better cams than the stock WRX has?
Is AVCS all hype or can WRX heads ported/polished + better cams beat them?
I too am looking for something with power across the entire band but really dont mind a little lag down low as I am used to it with my rex.
This would be on some sort of stoker motor of course.
my own experience has shown me avcs is no hype. Ask any sti owner with a hydra. With a hydra, you can simply turn the avcs on and off by a couple of clicks on the laptop.

set your goal of what power you want, and the answer to your questions can be easily determined.
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Old 02-04-2007, 01:45 AM   #7
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Thanks for the very nice writeup. I am definitely going to do a 2.5l short block eventually and this is very informative.

So what's needed in order to utilize AVCS when using the 2.5l short block? STi head, Sti ecu, engine wiring harness? Am I missing anything?

Can you PM your "tricks to a build" knowing as much as possible is going to help tremendously. Thanks
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Old 02-04-2007, 02:27 AM   #8
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can someone explaine what AVCS is exactly?
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Old 02-04-2007, 03:31 AM   #9
keaniegenie
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AVCS is subaru's adjustable cam timing name. Basically, their version of vtec.

One thing I don't want to do is make it sound like AVCS is going to make your car pull like a semi truck. The difference is definitely notable, as is the 2.5 block. The combination of the two together is what makes the sti motor so much better than the ej205 wrx motor.
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Old 02-04-2007, 03:48 AM   #10
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Man I totally know the painfully feeling of no bottom end and no AVCS...but not for long.
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Old 02-04-2007, 10:35 AM   #11
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very...slow....deliberate...clapping.
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Old 02-05-2007, 06:03 PM   #12
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Thanks everybody...

Here's a good description of AVCS

http://www.drive.subaru.com/Win05_WhatsInside.htm
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Old 02-06-2007, 10:53 AM   #13
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Here's a link on AVCS in the 2.5l forum too.

http://forums.nasioc.com/forums/showthread.php?t=699107
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Old 02-06-2007, 01:29 PM   #14
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Thanks KG, knowing how much better you seem to have it with AVCS I am convinced I should go that route eventually. I have an EJ255 with no AVCS and an EWG VF39. Is it really going to make a ton of difference on my setup? I know you had a TD04 and not the VF39 but I'm hoping you can still shed some light. My "build" is complete and just awaiting a retune so it would cost a great deal of money to get AVCS going and get a tune.
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Old 02-06-2007, 02:19 PM   #15
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The EJ255 is an AVCS motor, right?

Are you eventually going with a larger turbo? It's obvious that AVCS does something even with small turbos, but the difference isn't as dramatic as a large turbo setup.
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Old 02-06-2007, 11:43 PM   #16
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I would like to go AVCS but I have been told to avoid the STI LB by someone very knowledgeable. I didn't get all the details but suffice it to say that the EMS I wanted to go with (autronic) can't do it. I have heard that the Hydra can but not sure what/if there are any issues. Everyone I ask doesn't seem to have a whole lot of input on the issue.
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Old 02-07-2007, 12:22 AM   #17
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Quote:
Originally Posted by thejean View Post
I would like to go AVCS but I have been told to avoid the STI LB by someone very knowledgeable. I didn't get all the details but suffice it to say that the EMS I wanted to go with (autronic) can't do it. I have heard that the Hydra can but not sure what/if there are any issues. Everyone I ask doesn't seem to have a whole lot of input on the issue.
You're not asking the right people.

There is a buffet of stand alone's that can control variable cam timing. The Hydra is one of them. The main reason the Hydra is so popular with the Subie community is Phil Grabow of Element Tuning. His help and knowledge is priceless.

That said, if you have a question, ask him.
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Old 02-07-2007, 02:21 AM   #18
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Yeah, he told me that hydra can do it but all of the good tuners local to me use Autronic.

Last edited by thejean; 02-07-2007 at 02:49 AM.
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Old 02-07-2007, 02:40 AM   #19
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Quote:
Originally Posted by wrx360 View Post
Thanks for the very nice writeup. I am definitely going to do a 2.5l short block eventually and this is very informative.

So what's needed in order to utilize AVCS when using the 2.5l short block? STi head, Sti ecu, engine wiring harness? Am I missing anything?

Can you PM your "tricks to a build" knowing as much as possible is going to help tremendously. Thanks
Thanks for the informative writeup KG.
Can you please cc me on this PM
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Old 02-07-2007, 02:54 AM   #20
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Quote:
Originally Posted by thejean View Post
Yeah, he told me that hydra can do it but all of the good tuners local to me use Autronic.
To follow up, I spoke to Ray Hall (Autronic developer) and here is his direct quote:

Quote:
JC,

The 2.5L STI engine has different cam triggers. The current plug-in ECU does not support these. Others have fitted the 2L STi cam trigger wheels when doing this conversion.

Ray Hall.
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Old 02-07-2007, 10:31 AM   #21
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Quote:
Originally Posted by keaniegenie View Post
Later, I wired in AVCS control, which requires either a STI ECU, or a Hydra. Voila! Now it felt like an STI.
Kind of a n00b question here but...

If I already have an STi, but plan on switching to a stand alone EMS, will I loose AVCS if I choose something other than Hydra? Say like, AEM EMS?

Or is this something strictly for non-avcs motors to begin with?
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Old 02-07-2007, 10:34 AM   #22
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AEM will not control avcs or your drive-by-wire system, so it's out of the question for you.
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Old 02-07-2007, 11:00 AM   #23
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Quote:
Originally Posted by keaniegenie View Post
AEM will not control avcs or your drive-by-wire system, so it's out of the question for you.
Oh o.k. thanks for clarifying, I was not aware of that...
So Hydra is pretty much the best way to go in terms of stand alones for suby owners?
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Old 02-07-2007, 01:11 PM   #24
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*subscribed* this will be good info in a month!
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Old 02-07-2007, 02:59 PM   #25
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Quote:
Originally Posted by -auSTIn- View Post
So Hydra is pretty much the best way to go in terms of stand alones for suby owners?
Either that, the Link, or one of the uber expensive units like Motec are the only options you have. Hydra you have good US support. Link is more for the easterners/southerners but can still be made to work just fine in the hands of someone who knows what they are doing.
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