Porting the TB

[jonny985]

I've read all the posts discussing this issue but i still need some more info. As I understand it, it is not a good idea to port the TB without any tuning device. I was reading the post concerning the GMHTP article and noticed that Magnus used a 99+ MAF to account for the added flow.

IS a tuning device such as MAFT or an MAFT+ required if you use a 99+ MAF.

I am trying to hold out on buying the MAFT+ until I have to and trying to do the time consuming "free" work now.

I plan on taking down my engine this winter and doing some internal work so I would like to know EVERYTHING that I need to know before I go head on into it.

I already have all the gaskets and material for a TB spacer, but when I have it off the car I would like to do everything at once to save some cost.

Any thoughts or info are appreciated.

[John_D.]

I fully removed the post in my '98, and definitely had to convert to the '99 maf sensor. The '99 sensor did steady the readings, instead of them swinging all over the place.

Even so, I ran rich at idle and part-throttle, and ran lean at wot, and never did find quite the right combination of settings on the maft to bring both in to center.

After I added 24lb fuel injectors a couple of weeks ok, I got better o2 readings from side to side (left bank, right bank). And I was able to set the maft to 5% lean base and it pulled everything in a lot tighter all around. I don't run rich at idle anymore, and my wot is no longer lean (it's actually a little rich, .94 on the o2 sensors). I still need to tweak it a little.

[jonny985]

John, did you get the 99+ MAF from GM or did you get it off a junker? I don't plan on removing the upper post but I would like decent readings.

Also, did leaning out the top end help with your 1/4 mile times or was it crazy lean (.85 and lower readings)?

How rich were you running at base and mid throttle?

I'm still trying to get a handle on Autotap

[John_D.]

<blockquote>quote:</font><hr>Originally posted by jonny985:
John, did you get the 99+ MAF from GM or did you get it off a junker? I don't plan on removing the upper post but I would like decent readings.

Also, did leaning out the top end help with your 1/4 mile times or was it crazy lean (.85 and lower readings)?

How rich were you running at base and mid throttle?<hr></blockquote>

I got it from gmpartsdirect.com, almost got one from a junker, but I was ordering something else at the same time and figured I would just get it new. Nobody local had one, I was going to have to wait for shipping anyway.

It won't fit if the upper part of the post remains. In fact, you have to drill out the top of the tb to even get the '99 to drop in there. Another 1/4" or so, out to about 1". The '99 maf sensor includes a plastic part around it that essentially duplicates much of the upper post.

I don't remember how lean I was for sure. Before the port, I leaned it 2% and it ran stronger, no e.t.'s to back it up, just full throttle pulls uphill on the interstate. After the port, I richened it up about 5%. (when spraying I had to go full bore 14% and it still wasn't enough...)

Mid-throttle was ok, because the pcm compensates. So it wasn't quite accurate for me to say it was rich at part-throttle in the previous post. The idle richness was evident from the exhaust smell while sitting, the pcm was not compensating for that.

Yep, there is a lot of stuff potentially to watch in autotap. Mostly I just look at rpms and o2's now, turning on logging right before a wot run, and turning it off when finished. I like to look at the log for these in the graph view, the o2 ranges are very apparent there.

[jonny985]

John,
Do you have a part # for the sensor? how much was it?

[John_D.]

<blockquote>quote:</font><hr>Originally posted by jonny985:
John,
Do you have a part # for the sensor? how much was it?<hr></blockquote>

12568877 SENSOR $105.76

Plus about $20 for shipping I believe...