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Old 06-28-2005, 11:45 PM   #11
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So the question remains, do you need to reprogram the pcm if you port your throttle body?
In just about all cases yes. Either you can use an AFC or you'll need to reprogram.

Cheers,
Ok then you would want to program it the same ratio as air flow? ie if you gained 10% then you would add 10% to your Maf table?
Sort of...there are BIN or CSV files available for each different MAF which can then be imported or manully entered into the complete PCM BIN file.

MAFs flow a given amount of air (grams/second) at a given frequency.

Cheers,
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Old 06-29-2005, 01:10 AM   #12
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I smell a new mod in progress by PDad. :P
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Old 06-29-2005, 01:31 AM   #13
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I smell a new mod in progress by PDad. :P
Haha you ol' hound dog :P

I got a wbody stage 2 ported throttle body, only 50 miles on it, all sensors included, coolant passages blocked, powder coated red for $125 shipped. Nice job of porting, powder coating is a bit thin in the corners if you look for it though.

Not installing it untill I have the facts straight which might take awhile, would like to have it on by wcbf2
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Old 06-29-2005, 08:20 AM   #14
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The only reason you would need to reprogram the PCM with a ported L67 TB is if you started to flow more air than the MAF sensor could read (called being off the MAF table). Until that point the MAF sensor should meter the air properly. I think stock MAF tables for the L67 TB stop at around 49-50lb/min or 11,500 Mhertz.
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Old 06-29-2005, 01:16 PM   #15
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In theory the stock MAF should read the airflow for a ported TB. All GM MAFs are the heated wire variety, that means that the MAF measures how much voltage it takes to maintain a constant wire temperature and reports that back to the PCM as a frequency.

On that basis, the L67 should be able to read the flow correctly. The only problem is that in practice the ones I've seen run 3 to 5% lean on ported throttle bodies, because of this most use an AFC to correct for it.

You might be just fine without making any changes, but you should of course scan thoroughly to be sure. As a precaution, you might want to consider lining up an AFC 2.0 for purchase in event you need one.

The only time you will definately need to reprogram the PCM is if you use a different MAF. The LQ4 MAF is commonly used as a stand alone unit, this is the one ZZP offers. While you could use an LS1 or other MAF, they don't actually flow a great deal more than the L67 one, but the LT1 and SLP MAFs do. On the otherhand, the LQ4 MAF is fairly easy to tune.

As Todd mentioned, the stock L67 MAF can read airflow to support 350 WHP so you will not likely outflow it'* capabilies just yet. It'* only a question of calibration and that can certainly be done.

The short answer to your question? There isn't one. In theory the stock MAF will do but any ported TBs I've seen needed adjustment either by way of an AFC or PCM tuning.

Cheers,
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Old 06-29-2005, 01:48 PM   #16
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Originally Posted by Foghorn
In theory the stock MAF should read the airflow for a ported TB. All GM MAFs are the heated wire variety, that means that the MAF measures how much voltage it takes to maintain a constant wire temperature and reports that back to the PCM as a frequency.

On that basis, the L67 should be able to read the flow correctly. The only problem is that in practice the ones I've seen run 3 to 5% lean on ported throttle bodies, because of this most use an AFC to correct for it.
One of the reasons ported throttle bodies run lean is the difference in cross-sectional area at the location of the sensor. The stock sensor is claibrated for that particular cross-sectional area and when that area is increased the sensor needs to be adjusted like you were saying.
Another thing that would throw off the calibration is altering how the air moves past the MAF. The 99+ have a hump that directs the flow torward the hot wire element and the pre 99 have the maf post which also seems to direct the flow. Grinding down the hump or removing the maf post has to alter the flow past the element.
I had this one fluids lab where we calibrated a hot wire sensor that was placed after different shapes. The flow direction mattered a lot. It'* a shame the wind tunnel is too big for my TB. :(
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Old 06-29-2005, 10:24 PM   #17
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Things are becoming clearer, the more the car goes lean the better the flow through the throttle body because the maf sensor (which is a calibrated hot wire) may not be have the air directed to it and the pcm has a table that says how much air must be there because the maf reads this value.
A program upgrade would write new values in the table while an afc would read the maf and add a little to it and send it to the pcm.

The best route to go is to reprogram the pcm as this provides a cleaner signal and a more accurate reading of air volume. But you have to send away your pcm and tell them to set it to something, how do you know what to send it to? Can you get the info directly from the O2 sensor reading and from it determine your perfect setting or is it more trial and error?
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Old 06-30-2005, 09:24 AM   #18
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Things are becoming clearer, the more the car goes lean the better the flow through the throttle body because the maf sensor (which is a calibrated hot wire) may not be have the air directed to it and the pcm has a table that says how much air must be there because the maf reads this value.
A program upgrade would write new values in the table while an afc would read the maf and add a little to it and send it to the pcm.

The best route to go is to reprogram the pcm as this provides a cleaner signal and a more accurate reading of air volume. But you have to send away your pcm and tell them to set it to something, how do you know what to send it to? Can you get the info directly from the O2 sensor reading and from it determine your perfect setting or is it more trial and error?
The only way to accurately account for this is to either get an inline MAF sensor that is not affected by the porting of the TB and have its tables put in the PCM or richen/lean the af mix in the pcm via programming or AFC while on a wideband 02 reader (such as available by most dyno shops). There is no way you will ever get an accurate or safe setup if you tune based on the narrowband 02 sensor in the car.
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Old 06-30-2005, 09:55 PM   #19
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PDad, I would recommend waiting until after the Meet to screw with this mod.

I don't want to hear any excuses why Bill whoops your ***.
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Old 07-04-2005, 04:01 PM   #20
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PDad, I would recommend waiting until after the Meet to screw with this mod.

I don't want to hear any excuses why Bill whoops your A$$.
Too late mod in progress......

Draind and flushed the coolant, removed old tb and cleaned up the sc inlet.

I have the afc set to 105% to start with, I'll watch my Ltft while at idle then make a few wot pulls once the Ltft have settled to 0%.

I plan to tune with the afc then have the pcm flashed with the new values.

Damn rain has me in here rather than finnishing up
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