If I remember correctly there have been a few ported throttle bodies installed over the last few months. I think many of the TBs ported by Bill W. have had some of the MAF post removed from the middle of the TB, and I would like to know what kind of scan data has been retrieved from cars using this setup. Are MAF readings affected in any way? Have the MAF frequencies at different throttle percentages changed when comparing before and after? How are the fuel trims for the test vehicles? I hope some of this stuff has been recorded during test runs!

I did some testing and came up with like 3% increase in flow, But with alot more throttle response. There'* a thread where I did the MAF mod tb.

Yeah, I remember that stuff. Doug and I are wondering how it affects the MAF readings, and whether this affects the way the PCM "sees" the incoming air. Doug is concerned that removing part of the MAF post will throw the MAF frequencies out of calibration, so to speak. Perhaps he can describe it better in the morning. I just want to know if there is any hard data from before and after a swap to compare MAF frequencies at any given throttle position.

No, the MAF will still read correctly. You don't remove the MAF sheild. I think I know what he means by out of calibration, But it'* still going through the 58mm (in my case) TB inlet which I assume the MAF to be calibrated to. You get more laminar flow and I'm not sure of the the flow characteristics there but it can't be much with the way my engine ran.

http://www.bonnevilleclub.com/forum/...hlight=maf+mod

That'* the original thread, I later found the problem to be a cracked plug and a retardedly cracked EGR mount causing a dead cylinder and a huge vacuum leak. The car ran Awesomely Good with the MAFMod TB, but I didn't do much scanning. I'm piecing the engine together in the Bonneville to make it a beater while I mod my new toys' suspension. I have a stock TB around here somewhere and can probably get goo scantool data within a month.



I would definatly do the MAF mod in your position.

Okay, found the stock TB, good thing you reminded me about this mod, I think I owe BonneMeMN a TB. don't tell him right away, eh?

Ben and NoLastNameDoug,

Wren isn't removing the maf support when he'* working over the throttle bodies. The single biggest change he'* making is milling the throttle plate shaft and using countersunk screws.

I think with those small changes the throttle body flows quite well. Also, I did try to remove the screen (since Bill is still using mine as a coaster for his beer.). The SES light was my friend the moment it didn't have a MAF screen.

Think of it this way. The MAF senses the amount of air and is calibrated for the way the TB is designed. If you port the TB too much the maf tables in the PCM will no longer be calibrated and the values the PCM is using will be skewed. Meanwhile the O2 is monitoring the exhaust and richening the mixture to ensure you don't run lean.

As I get closer to tuning and pay more attention to it...I start to realize some of our possible errors in methodology toward going faster. I "THINK" that with the increase in bore/airflow we should be altering our MAF tables slightly to see the increase that the sensor can not.

Our sensor is mounted the same before and after porting. MAF screen left in..that sensor sees the same amount of air, the actual amount has increased. Now...the PCM will learn some of this, but how much?

Enough rambling from me..I think I went in a cirlce...Lookey..there'* my tail.

This is my main concern. But as Dame said, it'* not that the MAF tables changed. That doesn't change unless you alter them in the PCM. What changes is ratio of air entering the engine vs. air being metered. Basically the MAF, and ultimately the PCM is seeing less air going into the engine than what really is. I also believe that the alterations to the tail end of the sample tube could also effect this outcome by allowed either too much free flow through the tube, or not directing enough into it.

Maybe I'm completely flawed in this, but that'* my concerned before I get too gung ho in destroying another TB....

I went nuts on a 99+ L67 TB.
I port matched the rear, grinded down the maf hump, smoothed out the transition from the inlet to the plate, half shafted the TB shaft, epoxied from the tip of the inlet to the base of the maf, and smoothed everything out.
Even though I was told I would have I terrible time tuning it, I didn't.
I WAS able to get great st/ltfts.
All I'm really trying to say is, if you have a way to tune it, it won't be that bad on a L36.
Many have cut out the maf post on L36s and L67s. But, they also drill out the hole for the maf and install a 99+ maf.

So ultimately, to have the best results, cut the post out, bore it open, smooth it up, and install a 99+ MAF and program the PCM with the new MAF tables?

Yeah, cut out the post, open it up for a 99+ maf, smooth the transitions all out, port match the rear (theres a little left to be desired on a stock L36 TB), polish, shave down the shaft like willwrens with counter sunk screws or half shaft it, and adjust maf tables accordingly to get good ltfts and wot exhaust o2s.