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Old 05-25-2001, 10:39 PM   #1
BrysImpreza
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Angry Power Loss? Need Advice.

Here's my dilemma.
I have a JCSports intake and an Arospeed 2.25" cat-back exhaust (removed resonator like an ass) on my 1997 2.2 liter Impreza.
My car is now super crappy loud and feels slow as hell. I have little to no low end power and it takes some seriously flooring to feel anything from it.
I wanna put my stock stuff back on my intake to see if it shuts my car up and gets the low end power back.
Since the JCSports, I actually feel like I'm going slower then previously. The exhuast is loud, but I feel some more power gain at mid-range to high range, still nothing low.
What should I do, because all my car is, is loud right now.
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Old 05-26-2001, 07:49 AM   #2
Blindeye_03
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Get youself a ganzflow intake...yourte losing torque with that intake...
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Old 05-26-2001, 08:30 AM   #3
BrysImpreza
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That would be great except I have a 1997 like it says in my description, Larry didn't make one for cars w/ an MAF.
Otherwise I woulda bought his.
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Old 05-26-2001, 09:05 AM   #4
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OIC...hmmm sorry...
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Old 05-26-2001, 11:25 AM   #5
Albert
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The problem is not the intake.

You have no exhaust back pressure. The straight thru exhaust with no resonator is ideal for top end only.

on a 2.2L if you used anything bigger than 2" pipes you've got trouble, even installing a 22" resonator won't help.

Albert

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Old 05-26-2001, 09:21 PM   #6
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I think you might be better off with a 2" Borla catback for a 2.2L motor

Also, a better intake for retaining low end power can be found at www.imprezars.com/product2.htm#filtermaf or you can build your own CAI with my MAF adapters and a PRM racing fillter also found at my site. I am working on a price to sell the extra aluminum tubing to go between the air plenum and the PRM, and from PRM to fender. I have a 97 OBS coming n soon for a test fitting.

Larry
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Old 05-27-2001, 12:59 AM   #7
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i have the ganzflow and a 2.25" cat back and apex'i N1 canister....the ganzflow keeps the low end torque by retaining the airbox...
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Old 05-27-2001, 05:30 PM   #8
BrysImpreza
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Thanx all, sorry to snap at ya Blindeye.. I think it's around that time of the month j/k
I think I'm just gonna do a custom jobby-wobby and put the airbox back on, I seriously think the JCSports intake is a load of crap, at least on the 2.2 liter. Herzy2.5RS seems to be doing good with his JC on his, maybe it's just the 97' L with the 4 Vaccuum tubes.
Oh well, I'm just gonna get an STi in a few years anyway.
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Old 05-27-2001, 07:31 PM   #9
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Its ok...I didnt read that you had a subie with a MAF sensor...my fault .
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Old 05-27-2001, 08:27 PM   #10
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Just out of curiousity, what grade of fuel are you using? if you're using REG (ie 87) try stepping up to 89, do an ECU reset, and you may get the "lost" power back. I have the JCS intake on my '98 Legacy L (2.2L SOHC)and I didn't notice any loss of low end. Also installed is a 2.5" exhaust right now, which will be coming out for a 2.25" Brullen catback. I'm running 91+ octane all the time along with a Superchips Race ICON to advance timing.
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Old 05-27-2001, 10:08 PM   #11
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Albert - not trying to be mean but please stop spreading the old hot-rodding myth that backpressure is necessary requirement for a performance NA engine. It's something I've seen a lot of on this bulletin board and it's simply not true.

VELOCITY of the exhaust gases is a necessary component to help with the scavenging effect. Going ridiculously big, say 3 - 4 inches after the tuned length of the exhaust on a small NA motor, may impede performance because the exhaust gases will slow down in that section (reducing velocity).

BACKPRESSURE, however, regardless of engine type, turbo or NA, hinders performance. Backpressure slows down the gas velocity, which impedes the scavenging effect.

I've seen many articles about this, including one with DYNO sheets of different mid pipes and mufflers on the same car. With each setup, the amount of backpressure was measured. The more backpressure was, the less power and torque there was.

In regard to the original post, a 2.5" exhaust is perfectly fine for a 2.2L motor. It will be especially good if mated to some tuned length headers.

I've tried J-pipes, and personally I thought acceleration from lower revs was smoother and more constant with the original Subaru air box. I'd concentrate on feeding some cold air to it with little restriction. You can test the bad spots in the original intake with a home made manometer. On my NA EJ20, the original intake showed little restriction. That being said, mine's the newer MAP based type.
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Old 05-28-2001, 03:40 AM   #12
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I have a 97 2.2L and for a while I took off the intake plenum (the black box before the throttle body) and I noticed less power too. I also noticed that my MAF quit workin. My suggestion is try cutting the JCsports intake pipe just past that bend, and the connect it to the black box. Just make sure that you get all of the metal filings out after you cut the pipe. As far as the noise goes, I don't know much about it..maybe the Borla headers would help? Or a different muffler? I would put the resonator back on. I am sure it would have some effect.

RX: Are you sure bud? I think you may want to double check your sources. I know some compressible fluid dynamics specialist that would laugh at your theroy. And I have some questions.

1. Why did you say 2.5" pipe for the exhaust? Is there a formula for that?

2. How do you know the flow characteristics of a 2" pipe on a 2.2L car? There might not be a whole lot of "BACKPRESSURE" as you put it. 2.5" my slow the "VELOCITY"

3. Don't you think the engineers at Subaru put that black box ahead of the throttle body for a reason? The black plenum helps smooth out the airflow into the cylinder and dampens the pulses that the engine creates at each intake stroke. It also provided the engine with additional "reserve" air if you accelerate really quickly. It works kinda like a capacitor for a car stereo.

Anyways, yes I know I am being a smart @ss but its nothing to get angry about...nothing personal.

-Andy
Function over Form
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Old 05-28-2001, 03:46 PM   #13
Albert
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rx- In layman terms WE understand it as a lack of backpressure, maybe using the words scavenging and velocity are more discriptive, but as the length of your response clearly shows the use of either word in this situation is overkill.

Real life test with no white coats involved yielded the following results for us.

-99 Impreza 2.2L
-same driver
-3 passes with each setup
-oe intake
-oe exhaust mainflod and cat
-3 different diameter exhaust pipes (oe, 2", 2.5")
-no resonator, 2 oe 2.2L exhaust systems were hacked to get pipe length for muffler.
-used same 2.5" in/out magnaflow muffler.

Real world butt dyno results:
OE and 2": Off idle response and low end response(torque) felt the same.The driver couldn't feel any difference.

2.5": Off idle required more throttle, and riding the clutch longer to get a quick acceleration. When accelerating normal he said it felt like the car was going to stall.

Unscientific, however our conclusion was that the 2.5" exhaust pipe was too big, and it was letting the exhaust gases out too quickly. I feel comfortable using the term "lack of back pressure".

For normal everday use and driving a 2.5" exhaust is too big for a subaru 2.2L engine.

Edit: I have the Tanabe Hype Medallion cat- back system on my 2.5RS which has 60mm (2.37")pipes, and even this is too large for stop and go daily driving, however when I'm out for some fun I have no complaints.

Albert

[This message has been edited by Albert (edited May 28, 2001).]
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Old 05-31-2001, 06:38 PM   #14
rx
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RallyImprezive - My sources are fine.

Laughable, really? I invite your compressible fluid dynamics specialist friend to offer theorys on why backpressure is good in a performance vehicles exhaust system.

I have no formulae to offer you. However there is backpressure in my 2.0 litre EJ with 2" full system, incl cat, resonator and headers. If I were to put a more restrictive muffler (more backpressure) on the end of my exhaust system, the car will not perform as well - simple as that.

I'm not sure if it's member only access, but try a search on "backpressure" in Autospeed. www.autospeed.com - you will find all of the info, dyno results etc that you need to come to a concrete conclusion on the matter.

I know very well the benefits of the OEM plenum box, and I agree with your thoughts on it. Please point out where I speak adversly of it? I'm using it at the moment. I've tried j-pipes, cone filters on the t/b etc and found the OEM plenum box to be the best.

Albert - I come from the school of 'backpressure is a very naughty word'. What ever you want to use is fine, it's just whenever I see the b word I go into backpressure slaying mode.

I'd recommend checking out the articles I spoke of above - should be some interesting stuff in there for you. I'll come back with a proper link.

Real dynos talk business, butt dynos tend to be biased towards what you think works. I thought I had the fastest car in the world when I had a j-pipe, however back to back testing with a g-tech disproved this.
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Old 06-01-2001, 10:23 AM   #15
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RX is correct, backpressure is not good for any engine. However, every exhaust system must strike a balance between reducing backpressure, and maintaining exhaust velocity.

There is a period of time in the piston stroke in which both the exhaust valve, and the intake valve are both open. Proper exhaust velocity creates a vacuum at the exhaust valve which both draws exhaust out of the piston, and sucks air/fuel into the piston for the next stroke. This vacuum induction is what allows small engines to maintain torque at low RPM's.

However, I still think 2.5" is too large for the 2.5, and definitely too big for the 2.2. 2.25" should be about right for a n/a motor of this size.
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Old 06-01-2001, 01:49 PM   #16
RallyImprezive
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I didn't mean that more backpressure equals more horsepower, that would be stupid. I meant that a certain amount of back pressure is necessary. I couldn't think of how to word it right, but what Gavin said is what I meant. About needing backpressure for velocity. I suppose we would need to really dive into the characteristics of thwe EJ series motors to find out exactly what diam. is best. And of course, that can also change depending on where the owner wants the power band to be. So I guess I am going to shut up about it. There are to many variables. I know I sound like I am trying to be a smart-ass when I write, but don't take it personally, I just get "excited." I would be a lot more passive in person.

-Andy
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Old 06-01-2001, 02:08 PM   #17
BrysImpreza
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damn, an argument over my post, I'm sorry.
I'm stuck with the exhaust, it was welded on and it's here for a while. It's a really nice one (Arospeed) it looks great, sounds great (a little loud but I'm putting in a resontaor)
My car is just a little slow off the line, but nasty in the upper range.
I'm going to put my stock intake setup back on and try it for a few days after resetting the ECU.
If I feel that the intake really cut down on torque, I'm going to do a set-up like Peatys and mold a custom pipe into my set-up, drop in a K&N panel filter and then expand the pipe going into the stock box to 3" being pulled from the front of my engine.
Then we'll see, hopefully my car will have nice take off and top end response.
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Old 06-01-2001, 06:06 PM   #18
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Andy, that's not the same thing as backpressure. The basic theory is that you need some restriction in your exhaust to keep it from cooling too quickly and slowing down, thus eliminating the low pressure vacuum at the exhaust valve. Backpressure is just a side effect of this restriction. The two come as a package, but they are not related.

Too much backpressure, from bends in the pipe, will also eliminate the vacuum, regardless of diameter.
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Old 06-02-2001, 11:36 AM   #19
RallyImprezive
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Cool, thank you for the technical explaination. I love technical stuff. Now next time I argue about exhaust stuff, I will have more technical ammo! I am heading towards a career in computers, but sometimes I wonder if I should be working on getting ASE certification or something. I can't decide which I like better.
-Andy
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