Early Ported TB (ZM) impressions v L27 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 04-01-2007, 01:05 PM   #1
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Default Early Ported TB (ZM) impressions v L27

Spent a few hours in the rain yesterday with Gordy (SSEi95) doing some datalogging, and TB swapping. Anyone who'* ever worked on an L27 TB knows about "that bracket" with "that bolt" behind the exhaust manifold crossover, that thing didn't go back on at this point. Also had an issue that any L27 owner removing their TB will need to be aware of. I'll post more on this later, and a possible fix/workaround. When removing the TB mounting stud, one of the plastic anchors in the UIM was spinning freely, we were able to finally get a wrench on the anchor, and remove the TB.

No pictures as of now, I was not going to pull out the camera with the weather. But the ZillaMotorsports work was a slimmed down throttle body shaft and countersunk throttle plate screws. Bill also started smoothing work inside, which i finished up with sandpaper, wirewheel, and rubbing/polishing compounds. I also smoothed out the raised lip behind the MAF screen area (mine is removed).

Scary part at the end was when the cruise control cable was holding the throttle open after re-assembly. First couple starts the RPMS ran up quickly, and I had to kill it instantly. The cable is disconnected right now, and i'll have to look into why it'* not the correct length.

Initial driving impressions
My idle hasn't calmed down yet, I haven't adjusted the idle set-screw yet, but will if the PCM doesn't lower it. The laptop is saying that the desired idle is 850, but it'* idling around 1200.

I wasn't able to really get on it much below 20-25 yesterday due to the rain, but response was improved, and midrange power seemed better. My butt dyno is off due to the weather being different every day the last two weeks. I've gone from 20'* to 81 (perfect) on monday, back to 40'* + Rainy this weekend.

And Bill, why'd you send me an L67 gasket?
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Old 04-01-2007, 01:10 PM   #2
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Teaser. (gasket)

That screw shouldn't need to be adjusted if the throttle plate is fully closed. Unless you removed material around where the plate closes?

The screw is only for that purpose. To adjust fully closed. It has no effect on idle. That is solely the job of the IAC. Check for vacuum leaks.

And on the cruise cable, make sure it'* not swapped or mixed up with the throttle cable location.
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Old 04-01-2007, 01:26 PM   #3
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I only cleaned off some of the gunk around the the plate, nothing with the bore.

Throttle'* on top, cruise was on the bottom, as per my recollection/and your techinfo http://www.bonnevilleclub.com/forum/...e=article&k=64

We did pull the vacuum line off of the cruise module, so maybe i'll need to adjust the cable? Cruise has always worked and never had an issue.

Maybe someday i'll put that gasket to use
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Old 04-03-2007, 01:06 AM   #4
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Found the cause of my high idle...

The black throttle bracket that surrounds the TB was mounted on the head before the stud was put in, like a conventional bolt. In the race to re-assemble after 3 hrs in the rain, i just wanted it back together. Idle is perfect now.

The Cruise cable wasn't working well though. The only place it didn't pull on the throttle linkage was in the longest setting, but then I had issues with a guide holding up the cable, and causing problems trying to press the throttle. So i took off the cruise cable for now to not leave it hanging in the engine bay.

Driving 70 Miles back to Mankato wasn't fun without cruise.
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Old 04-03-2007, 04:04 AM   #5
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Quote:
Originally Posted by BonneMeMN
Found the cause of my high idle...

The black throttle bracket that surrounds the TB was mounted on the head before the stud was put in, like a conventional bolt. In the race to re-assemble after 3 hrs in the rain, i just wanted it back together. Idle is perfect now.

The Cruise cable wasn't working well though. The only place it didn't pull on the throttle linkage was in the longest setting, but then I had issues with a guide holding up the cable, and causing problems trying to press the throttle. So i took off the cruise cable for now to not leave it hanging in the engine bay.

Driving 70 Miles back to Mankato wasn't fun without cruise.
Hehehehe. Once you get a car with cruise, it really spoils ya, eh?
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Old 04-11-2007, 02:45 AM   #6
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Still looking at data on my side, and compiling a few spreadsheets, but it looks like i've gained atleast 6 grams/sec airflow @ WOT. Went from around 129/130-134/135.

Now that the car has settled in, i've really noticed the power band expand, especially around small % of throttle applications. It can be somewhat jumpy on the throttle, the biggest increase has been passing power when the torque converter is locked in OD.

Going up the steep hills in town @ 1500 RPM, 40 MPH is easier than before.

One issue i'm having with the data sets i've logged, is when I've done the tests of holding the car @ 1500, 2000, and 2500 RPM. Two flat roads have produced extremely varying data sets, the car was continuously running at the same temp, etc as well.
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Old 04-11-2007, 09:07 AM   #7
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Considering the smaller size of your throttle plate, that'* a pretty good gain for such little material removed.

Now you see what 'throttle response improvement' really means. I recall my guess was 3-5% gain, and it looks like it came in pretty close to that.
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