Intake Silencer Removal Dyno Charts

[gypsymoth]

Hi guys,

As I promised long long time ago, I have finally removed the intake silencer this weekend. I have also got measured power and torque data for before and after.

The following are before and after performance charts.

Chieh
--
Chieh's Web - http://Chieh.CameraHacker.com/

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[gypsymoth]

This is the measurement in original vehicle configuration (with the intake silencer).

[gypsymoth]

This chart is based on measurements after intake silencer removal. The measurement is done right after the removal (within 30 minutes) and within 2 miles. No ECU reset.

[gypsymoth]

The measurement was done yesterday, 2002-07-21, between 3:30 PM and 4:30 PM.

Second gear start. The charts above depicts the entire RPM band from 1000 RPM to 6250 RPM in second gear.

Head lights and fogs lights are on (I didn't realize they were on until after the entire test was conducted).

The vehicle (2001 Subaru Impreza 2.5 RS) was assumed to weight 2880 lbs through out the entire test. The only change in weight in the entire test was the intake silencer being removed.

The "after" data is based on measurements after intake silencer removal. The measurement is done right after the removal (within 30 minutes) and within 2 miles. No ECU reset.

Measurement was done using a G-Tech/Pro Competition meter with firmware version 1.0.0. Note that this is not the regular G-Tech/Pro meter. The Competition meter is the new one with the data logging capability. You can get more information about it at http://groups.yahoo.com/groups/gtechpro

Chieh
--
Chieh's Web - http://Chieh.CameraHacker.com/

[Craig W]

Couple questions:

Why is one chart time starting at 8 seconds and the other at 1 second? Maybe it doesn't really matter when comparing the two charts, but I was curious.

The legend on the bottom shows that torque is yellow and hp is red on one and vice-versa on the second.

If that is the case and the colors are correct, that shows a huuuuuge change in power delivery between having the silencer and removing it. I didn't feel near as much of a difference between having and not having the silencer.

Ahh, nevermind on the color thing. They're just shown in opposite order in the legends. Colors are the same.

[WRSport]

What exactly are you calling "the silencer" on the 2.5RS intake?

Just want to be clear here.

[Patrick Olsen]

Also, just to be clear, was the original run done immediately before removing the silencer, or was that on a different day?

I'm sure removing the silencer makes some small difference, but my butt dyno sure as hell didn't notice a 20ft-lb jump in peak torque, a 35ft-lb change in low end torque, a 12-13hp change in peak horsepower, etc etc. That seems awfully optimistic.

Pat Olsen
'97 Legacy 2.5GT sedan

[ATX25RS]

the rs silencer is what is connected from the airbox to the front beam.,...it is a series of boxes and and bowls used to silence the intake....the only opening is a small one positioned behind the headlight......it is very restrictive....

andres

[gypsymoth]

Originally posted by Craig W
Why is one chart time starting at 8 seconds and the other at 1 second? Maybe it doesn't really matter when comparing the two charts, but I was curious.

I was ready to do the first run when a bunch of cars passed me. So I waited . . . and forgot to reset. So the first 7 seconds or so had no data . . . even though the meter was ticking away.

The legend on the bottom shows that torque is yellow and hp is red on one and vice-versa on the second. Ahh, nevermind on the color thing. They're just shown in opposite order in the legends. Colors are the same.

You figured it out. 8-) Apparently Excel orders the legends by the sequence you order the trend-line . . .

Chieh
--
Chieh's Web - http://Chieh.CameraHacker.com/

[gypsymoth]

Originally posted by Patrick Olsen
Also, just to be clear, was the original run done immediately before removing the silencer, or was that on a different day?

This question was answered in my "full disclosure" above:

"The measurement was done yesterday, 2002-07-21, between 3:30 PM and 4:30 PM." (Entire test and removal was done in an hour.)

"The 'after' data is based on measurements after intake silencer removal. The measurement is done right after the removal (within 30 minutes) and within 2 miles. No ECU reset."

I'm sure removing the silencer makes some small difference, but my butt dyno sure as hell didn't notice a 20ft-lb jump in peak torque, a 35ft-lb change in low end torque, a 12-13hp change in peak horsepower, etc etc. That seems awfully optimistic.

To tell you the truth. I didn't feel it at all. I didn't realize there was such a difference until after I saw the data. I did noticed when I drove out to test, the engine wasn't very smooth. But last night, driving my gf out and back (total 100 miles) the engine was very smooth. I am not sure if it was the cold air at night or what, but the engine was and still is amazingly smooth to rev. Since I removed it, it had been very easy to heel-and-toe . . . I have been perfect so far since the removal. I don't know why it has anything to do with heel-and-toe, but I doubt my heel-and-toe skill has improved that much in one day. Anyway . . . I don't believe measurements in butt-dynos or what I felt, so I will spare you. Just interpret the data and provide your own interpretation.

As for "awfully optimistic" . . . I didn't make any predictions or any claim. The data are what I extracted out of the G-Tech meter . . . nothing more . . . nothing less. I didn't manipulated it, that's for sure.

I don't think the meter can be optimisitic if you have already base-lined it with itself in the "before" case. Plus we are not comparing it with data that are generated by something else.

Chieh
--
Chieh's Web - http://Chieh.CameraHacker.com/

[Patrick Olsen]

Originally posted by gypsymoth
This question was answered in my "full disclosure" above:

"The measurement was done yesterday, 2002-07-21, between 3:30 PM and 4:30 PM." (Entire test and removal was done in an hour.)"

I was just confused by the fact you said "the" measurement, which implies one measurement. Just semantics...

Originally posted by gypsymoth
As for "awfully optimistic" . . . I didn't make any predictions or any claim. The data are what I extracted out of the G-Tech meter . . . nothing more . . . nothing less. I didn't manipulated it, that's for sure.

I don't think the meter can be optimisitic if you have already base-lined it with itself in the "before" case. Plus we are not comparing it with data that are generated by something else.

I'm not accusing you of being optimistic, I'm accusing the G-Tech of being optimistic (or inaccurate). I'll admit, I don't know how, since as you pointed out you used the same instrument for both tests, so how could it be optimistic on one but not the other. I can't explain that.

As an engineer, I tend to distrust things that don't make sense. These numbers don't make sense. You yourself stated, "To tell you the truth. I didn't feel it at all. I didn't realize there was such a difference until after I saw the data." Unless you were sleeping, there's no way you wouldn't feel a nearly 50% increase in low end torque - that's a huge change.

Here's a bit of quantitative analysis to back up my qualitative feeling that the numbers don't make sense - look how long it takes to go from 1000rpm to the rev limiter for each run. It actually took slightly longer during the "after" run - about 7.4sec compared to maybe 7.2sec for the "before" run. (Just visually guesstimating those numbers). With all that extra area under the torque curve in the "after" graph, how could it possibly take longer to accelerate the same amount? That doesn't make sense.

I'm not attacking you, Chieh, I'm just saying something doesn't jive with those graphs. Did you do more than one run? If not, I would try that - see if you can get an average based on a few runs. If that doesn't generate some more realistic numbers, I'd send that meter back to G-Tech and tell them to try again.

Pat

[beethoven]

50%? That's almost a 100% increase in low-end torque along with a 25% increase in peak torque.

I would do a few more runs to make sure that isn't an anomoly in the data.

[gypsymoth]

Originally posted by Patrick Olsen

I was just confused by the fact you said "the" measurement, which implies one measurement. Just semantics...

Ahh . . . yes . . . sorry for the grammar error.

Here's a bit of quantitative analysis to back up my qualitative feeling that the numbers don't make sense - look how long it takes to go from 1000rpm to the rev limiter for each run. It actually took slightly longer during the "after" run - about 7.4sec compared to maybe 7.2sec for the "before" run. (Just visually guesstimating those numbers). With all that extra area under the torque curve in the "after" graph, how could it possibly take longer to accelerate the same amount? That doesn't make sense.

Good point. I haven't spotted that. But I have all the data. So I will look at it some more to see if I can validate what you are saying. Would you care to analyze the real data? It has several thousand data points.

I'm not attacking you, Chieh, I'm just saying something doesn't jive with those graphs. Did you do more than one run? If not, I would try that - see if you can get an average based on a few runs. If that doesn't generate some more realistic numbers, I'd send that meter back to G-Tech and tell them to try again.

No problem, Patrick. I am not saying you are attacking me. Just seems like you are saying "awefully optimistic" without saying why you felt it was so. I am an engineer also, Patrick, so more quantative and logical rebuttal works better with me than talking about feelings. Thanks.

Chieh
--
Chieh's Web - http://Chieh.CameraHacker.com/

[gypsymoth]

Originally posted by beethoven
50%? That's almost a 100% increase in low-end torque along with a 25% increase in peak torque. I would do a few more runs to make sure that isn't an anomoly in the data.

I have done a lot of runs in the past with the stock configuration. The number were very consistant. I have been using the same type of launches and using second or third gear pulls. The number look very much like the before case (in the same range). I believe the first set of data is correct. I did launch twice to get the first set of data. I did not feel (there I go with my feelings again) I pulled the first run consistantly so I threw away the data without even looking at it.

I feel I pull the before and after case consistantly with each other. So I am more comfortable that the after set of data is correct. However, as many of you engineers know, when a human is involved nothing is consistant.

That being said, beethoven, I am planning on measuring again after the ECU has had a chance to learn the new curve (assuming ECU has continuous learning). I wanted to measure again with 100 miles on my car, but I have 200 miles on my car now and I have been busy. But let see if my next run has similar numbers to the after case.

Chieh
--
Chieh's Web - http://Chieh.CameraHacker.com/

[gypsymoth]

Here's a bit of quantitative analysis to back up my qualitative feeling that the numbers don't make sense - look how long it takes to go from 1000rpm to the rev limiter for each run. It actually took slightly longer during the "after" run - about 7.4sec compared to maybe 7.2sec for the "before" run. (Just visually guesstimating those numbers). With all that extra area under the torque curve in the "after" graph, how could it possibly take longer to accelerate the same amount? That doesn't make sense.

Patrick, I found the answer for you in the next two charts of Engine Speed (RPM).

Here is the before case:

[gypsymoth]

This is the after case:

[gypsymoth]

Hi Patrick,

If you look at the "after" engine speed chart, you can see that I screwed up the initial launch and it was smooth with a peak and then a valley as the transmission brings the engine speed back down to close to 1000 RPM. I knew that had been the case during launch, but forgotten to eliminate that part from the power and torque charts.

So, if you look at the "after" chart, you can see the rev. band should really start at about 1.4 seconds . . . which is equivalent to about 8 seconds in the "before" chart.

"before" case: ~15 seconds - 8 seconds = ~7 seconds
"after" case: ~8 seconds - 1.4 seconds = ~6.6 seconds

Note these are approximations, since I am eye-balling the numbers on the two charts that I have presented above. Since I have the full set of data, let me know if you want real numbers.

Throw away the first 1.8 seconds (due to the 50 point moving average trendline) in the "after" case power and torque chart, and you will have comparable data.

Thanks for pointing it out, Patrick. I hope this new disclosure makes it less confusing. Please point out anything else. I am trying to analyze this data as much as you are.

Chieh
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Chieh's Web - http://Chieh.CameraHacker.com/

[gypsymoth]

Here are some more disclosures:

Before Case:
0-60 MPH: 11.456 seconds
1/4 mile: 19.128 seconds at 70.39 MPH

After Case:
0-60 MPH: 10.265 seconds
1/4 mile: 18.061s at 82.58 MPH

In the before case above, the time is the result of subtracting 7.395 seconds (due to "So the first 7 seconds or so had no data . . ." that I mentioned earlier).

In the after case, I had not subtracted the 1.4 seconds that Patrick pointed out. If we subtract 1.4 seconds, we will have the following numbers:

After Case:
0-60 MPH: 8.865 seconds
1/4 mile: 16.661 seconds @ 82.58 MPH

By the way, you need to read the 1/4 mile time and MPH in the "before" case with a grain of salt. If you look at the Engine Speed chart, you will have realized that I let the RPM trail off slightly before the quarter mile. So the quarter mile time and speed is probably slightly faster than I indicated here.

Chieh
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Chieh's Web - http://Chieh.CameraHacker.com/

[SubaFastR]

Why not just redo the test? Sounds like the launches were not identical, making the data worthless.
Kevin

[Patrick Olsen]

Thanks for the additional data, Chieh.

Here's a thought for second-checking the numbers the G-tech generated. It'll take a little bit of math and physics, but you're an engineer, so you're all over that, right? Just figure out what the speed of the car is at, say, 1500rpm (since in both cases you started a bit over 1000rpm) and at the rev limiter (or maybe 6000rpm just to make it a bit easier). So, now you've got velocity. Combine that with the mass of the vehicle and you can figure out the kinetic energy at 1500rpm and 6000rpm. You changed that kinetic energy over a known period of time, so working some unit conversions and stuff you can figure out the average power for the given time period. I did this once after installing an MRT exhaust on my car - unfortunately, I don't remember what results I came up with, so I can't say how well they compared (or didn't compare, as the case may be) to the dyno numbers I got later.

Oh, and are you launching in 2nd gear? Or are you doing this from a 2nd gear roll? (I hope it's the latter).

Pat

[gypsymoth]

Originally posted by SubaFastR
Why not just redo the test? Sounds like the launches were not identical, making the data worthless.
Kevin

I don't believe the data is worthless. I have had this logging tool for two entire months now. And I have, in the past, seen data of launches that are inconsistant. However, the result data were very consistant, and did not deviate 15 to 20 HP as these two data sets have indicated. In fact the only difference is the elapsed time.

This is due to the fact that the data is calculated between two sample points, not averaged through out the entire measurement. So as soon as the pedal to the floor, human inconsistancies are pretty much out of the factor. So even if the data close to the launch is off, I believe data during the second half of the rev. band is valid. And data at the magical cross point 5252 RPM is way pass the point my feet went to the floor.

I may re-test. However, that will be very hard to do anytime soon . . . considering that the ECU continuously learns:
http://forums.nasioc.com/forums/show...hreadid=219101

However, I do encourage others (yes, you) to do your own objective test with some type of measurement device or method . . . not butt dynos . . . so that we can compare the results. Taking off the intake silencer is 5 minutes of work on my car. Doesn't require taking off the wheel and stuff as mentioned on www.ScoobyMods.com (probably for previous years). And best of all it's free . . . nothing to buy.

For now, as I mentioned to beethoven, I will measure again in this configuration. The reason I haven't yet is because I need to find time. I want to measure during the same time of day to eliminate as much environmental factor as possible and that time happens to conflict with my work hours. I will not measure during night time due to safety reasons.

Chieh
--
Chieh's Web - http://Chieh.CameraHacker.com/

[gypsymoth]

Originally posted by Patrick Olsen
Thanks for the additional data, Chieh.

You are quite welcome. 8-)

Here's a thought for second-checking the numbers the G-tech generated. It'll take a little bit of math and physics, but you're an

Thanks for the direction, Patrick. I will give it some thought and do something like that when I have time. It might be even easier than that, since the G-Tech calculates the MPH with each sample point. It does it from the only two data it has: time and acceleration. With the method you mentioned, theoritically I can cross check it's calculation.

But first, I want to get pictures of the intake silencer for those people who asked, "what is the intake silencer?" By the way, I noticed that you have a 1997 Legacy 2.5GT. What does the intake silencer look like on that? Is it the same as the 2001 Subaru Impreza 2.5RS I have? Do you have a picture of it?

Oh, and are you launching in 2nd gear? Or are you doing this from a 2nd gear roll? (I hope it's the latter).

I am launching from 2nd gear. I do this whenever I want to do a measurement and I want the data for entire rev band. Plus, if I do this every time, over time, my launches will be very consistant. I don't use any special launching technique. Basically my right foot goes on the gas, my left foot is off the clutch.

What is your definition of 2nd gear roll? What does that mean? How do you do it? Why do you prefer a 2nd gear roll?

Chieh
--
Chieh's Web - http://Chieh.CameraHacker.com/

[gypsymoth]

Thanks for the direction, Patrick. I will give it some thought and do something like that when I have time. It might be even easier than that, since the G-Tech calculates the MPH with each sample point. It does it from the only two data it has: time and acceleration. With the method you mentioned, theoritically I can cross check it's calculation.

Hi Patrick,

Thank to your clear thinking and your suggestion, I think I may have found a source of error in the data. However, I need to do some research before I can say whether this source of error is justifiable.

If it is justifiable, then Kevin may be right that consistant launches does make a difference. However, the data will not be wasted, because the error can be easily corrected.

It's 2:30 AM now . . . I ran out of time 2:30 hours ago. So I'll let you guys know the answer in a few days.

Chieh
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Chieh's Web - http://Chieh.CameraHacker.com/

[tonytiger]

Nice idea about the average power Patrick.
Correct me if I'm wrong, but you should take the rolling energy of the rotating pieces of your (wheels, tires and the energy of the engine etc.) Subie to your equations.

The power is still proportional to 1/(dt) so this doesn't change anything fundamentally.



tony

[Patrick Olsen]

Originally posted by gypsymoth
But first, I want to get pictures of the intake silencer for those people who asked, "what is the intake silencer?" By the way, I noticed that you have a 1997 Legacy 2.5GT. What does the intake silencer look like on that? Is it the same as the 2001 Subaru Impreza 2.5RS I have? Do you have a picture of it?

No, I don't have a picture of it, nor have I seen what the 2001 RS' silencer looks like. However, they're all functionally the same, and I'm sure present about the same restriction to the engine. They're just some sort of resonator box with an inlet and an outlet. My '89 Mustang GT had one on it, too - different size and shape, but basically the exact same thing that came off the Legacy. About the same inlet size, too, which isn't a good thing when you figure it's trying to suck in enough air for an engine twice as large as the Legacy's.

Originally posted by gypsymoth
I am launching from 2nd gear. I do this whenever I want to do a measurement and I want the data for entire rev band. Plus, if I do this every time, over time, my launches will be very consistant. I don't use any special launching technique. Basically my right foot goes on the gas, my left foot is off the clutch.

What is your definition of 2nd gear roll? What does that mean? How do you do it? Why do you prefer a 2nd gear roll?

When I said "2nd gear roll" I just meant a rolling start. Rather than launching from 2nd gear, just get yourself going in 1st, as you normally would, shift to 2nd and let your speed drop to 10mph (or whatever speed correlates to 1000rpm or so). Start data-logging and go to WOT. I don't know if the G-Tech will allow you to datalog that way. Does it need to know that you're starting from a dead stop? I guess since it's just an accelerometer it wouldn't have any way of knowing you were actually at 10mph (or 5mph or whatever), and that might monkey up the data. Hmmmm.....

The only reason I suggest it is to make it easier on your car - 2nd gear launches probably don't make the clutch very happy.

Pat