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Old 07-16-2009, 11:07 AM   #1
Dom Terreto
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Default Akuma Testing, Chapter 1:Wideband Readings

Hey everyone, Evan here from Akuma Motorsports. We've had a busy opening week at our new location, but have found time for a little research that I think many of you will find interesting!

As long as I've been in the industry, there has always been a debate surrounding air/fuel readings and the effect that catalytic converters have on them. As we were setting the test up we continued to speculate the outcome, and we were excited to be able to share the findings with the tuning world!

The Test:
Our goal was to find out the difference between pre and post-cat afr readings.
The Setup:
The team used my personal 2005 sti as the test mule. My setup is: stock airbox, VF48, STOCK DOWNPIPE (with bung welded in pre-cats), and a cat-back exhaust fabricated by myself with a greddy muffler.
Equipment:
We used Akuma Motorsports' brand new Mustang Dynamometer which has the ability to read multiple inputs, including dual wideband O2 sensors, dual boost inputs, etc, etc. We put O2 sensor #1 in the downpipe, just after the turbo. O2 sensor #2 was installed out back in the tailpipe.
Results:
Let the graph speak for itself!!












Final Thought:
There absolutely is a difference between pre and post-cat afr readings... BUT they are completely predictable. The post-cat afr curve DIRECTLY follows the pre-cat reading, except it is about a third of a point leaner in our test.

Feel free to discuss

Cheers,
Evan, and the team at Akuma Motorsports

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Old 07-16-2009, 11:16 AM   #2
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Below 3.4k rpm, there is far more than .3:1 AFR difference.

Nearly 2 point difference at 3k rpm...

So half of the rpm range isn't all that predictable...

This supports my position that post cat measurements aren't good enough...unless your motor only runs at 3.5k+ rpm.
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Old 07-16-2009, 12:27 PM   #3
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The difference you see is open loop and closed loop. Obviously you wouldn't want a post-cat reading for your closed loop fueling. But our testing was clearly pertaining to open loop. So you are partially correct, but that would be a completely different test, and definitely not half of the rpm range.

Cheers,
Evan @ Akuma
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Old 07-16-2009, 12:33 PM   #4
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Are you guys Street Fighter nuts? I see the word Akuma and I have to ask
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Old 07-16-2009, 12:46 PM   #5
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Nice. It is a bit of coincidence...the Street Fighter reference.

As far as the vastly different readings before the CL/OL transition, that has a lot to do with the position of the sensor and the exhaust flow during the run. The sensor in the tail pipe has its limitations as to accuracy when flow is limited. Remember it is in an open environment and that will skew the readings.

The main point of this test was o show there is a slight enleanment(this is a word for our purposes...lol) in post cat/tail pipe readings. Most tuners expect this, but the data was never quantified. The hypothesis of post cat enleanment is proven true. However with a few notes. The curve is very accurate. You can reliably tune the cars with cats from the tail pipe sensor when there is enough exhaust flow and the cats are at operating temps. Keep in mind this is an OEM cat, not a hi-flow cat. The efficiency of the cat will determine the differing AFRs'. If a cat is inefficient, we would expect to see a much closer AFR curve between the two sensors.

Sorry for the long explanation..lol

John
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Old 07-16-2009, 02:29 PM   #6
kevinh211
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nice test. we need more of these on nasioc.
i'd like to see the same test with out a cat.
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Old 07-16-2009, 02:32 PM   #7
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Even on catless cars the difference is about the same between tailpipe and downpipe. Also, outside of 14.7ish AFR, the cat isn't catalyzing anything (especially @ 11.6 AFR) so it isn't affecting the AFR.
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Old 07-16-2009, 03:00 PM   #8
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I did the same test a while back with Cobb catted downpipe and didn't see any significant difference in the AFR readings.

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Old 07-16-2009, 05:12 PM   #9
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Quote:
Originally Posted by Airboy View Post
I did the same test a while back with Cobb catted downpipe and didn't see any significant difference in the AFR readings.
I've done the same test with my TXS catted stealthback, and saw a difference of around 0.75 AFR.
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Old 07-16-2009, 05:34 PM   #10
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I dont think all of the fueling compensations are unconvered in the rom.

I think you could get results that show leaner pre-cat, same pre-cat and richer pre-cat depending on IAT, coolant temp, etc.

My AFR's can fluctuate 0.3 from run to run with the LC-1 in the same spot.

However, I think the convention "leaner further from motor" always stands whether you have cats or not.......i just dont believe that you can nail it down to 0.xxx AFR since the AFR will fluctuate from run to run in both spots.

Last edited by Phatron; 07-16-2009 at 05:42 PM.
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Old 07-16-2009, 05:55 PM   #11
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I think their point was to prove that tuning from the tailpipe post cat can be just as effective as tuning from the dp pre cat.
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Old 07-16-2009, 06:28 PM   #12
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"just as effective"?

Isnt tuning from the tailpipe the most widely used method on the dyno?

It has been at every facility I've ever been to.

Most customers dont have AFR bungs and even when i did the tuner still used the tailpipe also.

I think a more useful test for a dyno operator would be catless at the tailpipe and catted at the tailpipe.
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Old 07-16-2009, 07:43 PM   #13
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This test is also using two different O2 sensors. Readings can vary a bit from sensor to sensor, so it makes it even more difficult to put any real weight on this test.

At the end of the day, a/f measurement is not an exact science considering the many variables that can come into play. Its the tuner's job to determine the most appropriate a/f level by looking at power gains/losses and gauges. This is also why an EGT gauge is extremely important when tuning. Many people believe there is a single optimal a/f ratio for a given fuel type or car, but this is completely false considering that our measuring equipment is not as consistent and precise as we'd like to believe. I've tuned cars with measured a/f around 10.3:1 and others around 11:1 on the same fuel. The important part is how the engine responds and how the temps look.

-- Ed
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Old 07-16-2009, 09:26 PM   #14
Dom Terreto
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Quote:
Originally Posted by Phatron View Post
"just as effective"?

Isnt tuning from the tailpipe the most widely used method on the dyno?

It has been at every facility I've ever been to.

Most customers dont have AFR bungs and even when i did the tuner still used the tailpipe also.

I think a more useful test for a dyno operator would be catless at the tailpipe and catted at the tailpipe.
How would you possibly ever conduct that test lol!!?!? The change from a catted downpipe to a non-catted, a completely different run, different fueling to compensate for the airflow change..... etc etc..

Basically we eliminated as many factors as possible while conducting this test. BOTH sensors are brand new, so the readings SHOULD be as close as possible. The reading is from the SAME run. This was not back to back runs with an overlaying graph.

Keep in mind what the test is done for. . . It is not to show that people have done anything incorrectly. It is not to put an exact number on what to tune your afr's to. It is not saying that cats will perform the same every time. However, there ARE many out there that have a certain mindframe about this debate, myself included. And this is an interesting piece of data to share with everyone.

I do however agree that a non-catted test is needed for further study. Stay tuned as it is in the works as we speak.

Evan @ Akuma
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Old 07-16-2009, 09:29 PM   #15
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Quote:
Originally Posted by Vaus View Post
This test is also using two different O2 sensors. Readings can vary a bit from sensor to sensor, so it makes it even more difficult to put any real weight on this test.

At the end of the day, a/f measurement is not an exact science considering the many variables that can come into play. Its the tuner's job to determine the most appropriate a/f level by looking at power gains/losses and gauges. This is also why an EGT gauge is extremely important when tuning. Many people believe there is a single optimal a/f ratio for a given fuel type or car, but this is completely false considering that our measuring equipment is not as consistent and precise as we'd like to believe. I've tuned cars with measured a/f around 10.3:1 and others around 11:1 on the same fuel. The important part is how the engine responds and how the temps look.

-- Ed
All true! But again, read the my above post. We're not trying to concrete a definative answer to anything... just trying to share our findings. However, it is a nice piece of info to see and hopefully will help our community out.

Evan @ Akuma
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Old 07-16-2009, 09:39 PM   #16
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Didnt realize it was the same run. To go with vaus' point about it being two sensors you could just do 1 more run with them swapped locations.
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Old 07-16-2009, 09:46 PM   #17
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Quote:
Originally Posted by Phatron View Post
Didnt realize it was the same run. To go with vaus' point about it being two sensors you could just do 1 more run with them swapped locations.
This is the same run, the same AFR module. I have two sensors on a single wideband. they were calibrated and tested together before any testing. Remember, I have been testing like this for some time. It is my fault I did not explain that this is one module, two sensors, same run. I clarify next time.

For reference. I have 2 widbands(same module) and 2 5BAR (identicle) map sensors that we can test with.

John
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Old 07-17-2009, 12:08 AM   #18
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Quote:
Originally Posted by Vaus View Post
At the end of the day, a/f measurement is not an exact science considering the many variables that can come into play. Its the tuner's job to determine the most appropriate a/f level by looking at power gains/losses and gauges. This is also why an EGT gauge is extremely important when tuning. Many people believe there is a single optimal a/f ratio for a given fuel type or car, but this is completely false considering that our measuring equipment is not as consistent and precise as we'd like to believe. I've tuned cars with measured a/f around 10.3:1 and others around 11:1 on the same fuel. The important part is how the engine responds and how the temps look.

-- Ed
Quoted for 100% truth. I tune on 91 octane, like Cali, and there is no magic AFR. Each car responds differently.

Tuning via the tailpipe with a cat in place is no problem.
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Old 07-17-2009, 02:45 AM   #19
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Also, cats with different cel counts may skew the AFR results differently so you can't really expect the same delta at all times.
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Old 07-17-2009, 08:24 AM   #20
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good test
i also noticed this many times when logging through my wideband on the downpipe and the tailpipe

i think it the result makes sense to be a bit different from right at the downpipe to the tailpipe...
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Old 07-17-2009, 09:19 PM   #21
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Hey do us a favor and roll a stock WRX/STI on the dyno and test per cylinder EGT/AFR's - Stock intake/exhaust manifolds as well..

Please!!!
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Old 07-18-2009, 12:52 AM   #22
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Quote:
Originally Posted by Phatron View Post
Didnt realize it was the same run. To go with vaus' point about it being two sensors you could just do 1 more run with them swapped locations.
+1! This is a pre-requisite to drawing any conclusions from the first chart.

It would also be helpful to do 3-4 pulls each time, to filter out any noise. From the looks of the first pull, there isn't much noise, but you don't really know until you try.
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Old 07-18-2009, 12:55 AM   #23
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Quote:
Originally Posted by JSarv View Post
Hey do us a favor and roll a stock WRX/STI on the dyno and test per cylinder EGT/AFR's - Stock intake/exhaust manifolds as well..

Please!!!
+1 again. That would be very informative. Especially if you do something to verify that the sensors in question read comparably.

You wouldn't need 4 sensors, just compare cylinder 1 with 2, 3, then 4, and do enough pulls to filter out the measurement noise.
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Old 07-18-2009, 09:18 AM   #24
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That test is a possibility... I have the afr readings and dyno plot of a stock sti already though if you wanna see that..

Evan @ Akuma
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Old 07-18-2009, 10:19 AM   #25
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Quote:
Originally Posted by Airboy View Post
I did the same test a while back with Cobb catted downpipe and didn't see any significant difference in the AFR readings.

I am glad you posted this - as I have noticed that the closer the wb02 is to the turbo the bumpier the afr reading is - which is shown in your pic when compared to the reading from the tail pipe.

I'm actually considering moving my wb02 further down the dump to right before the flange in an effort to smoothen the reading and make tuning OL AFR more consistant and accurate.

Leslie.
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