Modded L67 TB for L36--NOW with Gutted Airbox! - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 05-08-2007, 12:04 AM   #1
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Default Modded L67 TB for L36--NOW with Gutted Airbox!

Well, after talking about it here:
http://www.bonnevilleclub.com/forum/...ic.php?t=76660

Here'* some shots of an L67 TB modded to fit my 98 Buick LeSabre L36:






I got this thing in the state you see it off ClubGP for $40 shipped. Can't wait to make sure all the sensors work
(They're supposed to all be completely functional)

In the last pic you can see that, like with 95naSTA'* L67 TB mod:
http://www.bonnevilleclub.com/forum/...ic.php?t=50403

I need to do some filling around the MAF. This thing could probably also be polished a bit more inside. Also, the bottom of the TB bore sits a bit lower than the UIM inlet...but I'm not sure drilling the mount holes actually fixes this, because then (according to my measurements) the top of the TB bore will sit higher than the top of the UIM inlet by the exact same amount.

Finally, I don't think I'm gonna "hog out" the back in that butterfly shape, for two reasons:
1) I don't see the need.
2) NOT doing so provides just the shroud for UIM runner 6 I may need when I finally get around to testing this mod:
http://www.bonnevilleclub.com/forum/...ic.php?t=73706
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Old 05-08-2007, 12:16 AM   #2
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how much bigger is that TB compare to a L36 .it looks almost the same but the L36 is oval at the exit
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Old 05-08-2007, 02:03 AM   #3
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The throttle plate on this L67 TB is 70mm, while the L36 is 65mm. This equates to 16% greater area. Also, this modded L67 TB has no MAF "pillar" like my L36 TB (and is ported inside, to boot). Add the idea I mentioned earlier about the air being not so directly aimed at that cut-down cylinder 6 runner (in the UIM mod I haven't installed yet ) and I'm thinking this TB (plus a gutted front half of the airbox) will do me some good at future mod levels.

I thought better of the fitment issue. After some more measurements...

I drilled out the mounting holes with a 7/16" bit:


Pushing the TB up all the way raises it about 1/16":


Here you can see that better matches up the bottom of the TB bore and the bottom edge of the LIM bore, while causing only a very slight instrusion of the LIM bore at the top (and no gasket shows anywhere):


The TB bracket has some vertical "play" where it bolts to the LIM, so it should fit even with the TB raised a touch.

A couple notches in the edges of each hole (on both sides):


To hold the epoxy "plugs" in place:


After that cures, I'll sand it down and re-drill new mounting holes with a 3/8" bit.
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Old 05-08-2007, 08:26 AM   #4
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Good to see someone else, besides myself, can confirm that miss-alignment. A lot of people on CGP kept saying there wasn't any untill I got pictures.
Ya know by not hogging out the outlet to match, you may be sending more air torward that # 6 runner more than you think. Since there is a step down, there is going to be a low pressure area right behind that point on the TB. That may pull the air torward the runner.
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Old 05-08-2007, 09:05 AM   #5
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Quote:
Originally Posted by firebuick
how much bigger is that TB compare to a L36 .it looks almost the same but the L36 is oval at the exit
http://www.bonnevilleclub.com/forum/...ighlight=story
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Old 05-08-2007, 12:22 PM   #6
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Props to willwren'* original thread for putting this TB idea in my head in the first place, and 95naSTA'* thread for serving as a model.

Quote:
Originally Posted by 95naSTA
Good to see someone else, besides myself, can confirm that miss-alignment. A lot of people on CGP kept saying there wasn't any untill I got pictures.
Yeah, the guy I got this TB from also said it fits, no problems...there'* no misalignment.

Quote:
Originally Posted by 95naSTA
Ya know by not hogging out the outlet to match, you may be sending more air torward that # 6 runner more than you think. Since there is a step down, there is going to be a low pressure area right behind that point on the TB. That may pull the air torward the runner.
I can see where the big step from the round hole on the back of the TB to the oval/butterfly-shaped hole in the UIM inlet could create a pressure differential or turbulence issue. Perhaps I'll figure out a way to fill the sides of the neck of the UIM inlet with epoxy to make it more cylindrical or perhaps a more gradual transition from cylinder-to-oval.

What would really be neat would be a 70-75 mm I.D. cylinder reaching from the UIM inlet all the way to the other end of the inside of the UIM, with holes or slots drilled to put air right in front of each UIM intake runner inlet. This would both distribute air more evenly AND reduce plenum volume (which may benefit low-end). Unfortunately, I don't think there'* enough of a "straight shot" inside the UIM to do that reasonably easily.

IMO, second best to that idea is to fill the entire bottom of the UIM about 1" to 1.25" deep with pourable epoxy (with runners in place, of course, and making some accomodation for the brake booster vacuum port) to both eliminate LIM surface turbulence and reduce overall plenum volume from ~4.6L (or ~5.4L, with cut-down runners) to ~2.6 to 3.0L (or ~3.4 to 3.8L with cut-down runners). This is my "other idea" (also sorta ripped off from the HV insert) on UIM modification

I've now got enough UIMs sitting around to test all three permutations:
1) Cut-down UIM runners
2) Filled UIM
3) Both 1) and 2) together

I've just got to find the right epoxy
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Old 05-08-2007, 12:53 PM   #7
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I'm almost positive that the entrance to the L26 manifold maintains a circular path from the TB (know that for sure) to the plenum.
So, if you were to reduce the UIM inlet to be circular, it may not hurt anything.
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Old 05-08-2007, 10:49 PM   #8
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Here'* the finished new mounting hole, drilled with 1/4" bit (I think I said 3/8 before...that was wrong):



And mounted on a UIM:


Here again, this placement matches the bottom of the TB bore and the LIM inlet, with very little LIM showing up top:


Now to put the TB w/MAF screen (and gutted front half of airbox) on the car and tune it...
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Old 05-08-2007, 10:52 PM   #9
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very nice when are you going to install and test it on the car .what did you use to polish the TB
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Old 05-08-2007, 10:58 PM   #10
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Quote:
Originally Posted by firebuick
very nice when are you going to install and test it on the car .what did you use to polish the TB
It was already mostly polished when I bought it. I finished it up with a 240-grit flapwheel on the dremel.
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