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Old 06-12-2007, 04:18 PM   #1
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Default More on Modded L67 TB on L36...finally got it tuned right!

SInce day one, my butt dyno has been screaming that I was getting more out of the modded L67 TB than this thread suggested:
http://www.bonnevilleclub.com/forum/...ic.php?t=78557

My problem at that time was that dialing in the MAF table on this ported (i.e., "non-standard geometry") L67 TB was much more involved than I originally thought. Anyway, after a few weeks of hands-on self-education in the art and science of tuning, here'* the final story on this mod:


(NOTE: All data prior to the L67 TB stands as accurate, as those mod levels used the stock L36 MAF and TB, and those were a snap to tune for)

The bigger-bore TB shows a significant increase in calculated VE across the entire range from 2800 rpm up. And, as previously shown, the MAP increases faster versus TP%, allowing me to put that power down faster on acceleration:
http://www.bonnevilleclub.com/forum/...ic.php?t=79041

One thing I have learned; if you mod the TB at any point between the MAF screen and the plate bore (and that would, I suppose, include MAF screen removal), you can throw any stock GM MAF calibration table out the window.
(sidebar: I would think that the plate shaft shaving willwren has done would not cause this problem, as it does not alter the "chamber" in which the MAF sensor sits.)

So here'* the new incremental calculated improvements vs mod levels:

Mod Level---Torque (@4200rpm)---HP (@5200 rpm)
Stock-----------+0 ft-lb--------------------+0 hp
PLIM------------+10 ft-lb-------------------+8 hp
PEM-------------+6 ft-lb--------------------+5 hp
L67TB----------+16 ft-lb--------------------+17 hp

For a total of about +32 ft-lb @4200 rpm and +30 hp @5200 rpm over stock.

The TB mod could be said to have "added 17 hp" (which is more than the "7-12 hp" advertised at zzperformance for their bored-out TB'*); however, as I've always asserted, there'* likely a synergistic effect going on between these mods that enhances them all. I will say that it is obvious the L36 TB bore is a big restriction.

Definitely worth the $150 or so I spent on hard parts to get to this point--though I've probably spent more than that on gas tuning all this crap

(As always, these are calculated estimates only, not yet backed up by actual dynos...maybe in July or August)

Next up on the mod list is the SRR rockers...though I must say that my expectations on those are low until I get around to opening up my spare heads:
http://www.bonnevilleclub.com/forum/...ic.php?t=77163
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Old 06-12-2007, 04:49 PM   #2
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Default Re: More on Modded L67 TB on L36...finally got it tuned righ

Sick man. That'* awesome. I have a few L67s TB'* here I may have to try to see how they match up.
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Old 06-12-2007, 05:20 PM   #3
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I must add, without the ability to tune (i.e., change the programming in your PCM)--or at least to adjust fueling with an AFC--replacing your L36 TB with a bigger bore TB may cause you to run dangerously lean, as:

1) The MAF table may be off...potentially by alot (meaning the PCM will badly underestimate the actual air mass, thus underfueling)
2) Even if your MAF table is correct, your PCM may not be able to adjust fuel trims enough to compensate for all the extra air mass (thus underfueling despite it'* best efforts)

I believe there are certain years where the L36 and L67 use the same MAF sensor part number (and thus, potentially the same MAF table), and that may be a safer bet sans Tuner or AFC...I can check on that if anyone wants me to.

EDIT: scratch the paragraph above...while it is true that same MAF sensor p/n is used between L36 and L67 in 96-98 and 99-03, I checked and the stock PCM MAF tables are different between L36 and L67; so putting an L67 TB on an L36 without Tuning or some sort of AFC device will give the PCM an erroneously low reading on air mass, leading to obscene leanness. Now if you are an EE, maybe you could get around that problem with a frequency divider or something...
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Old 06-12-2007, 05:42 PM   #4
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good work man is that L67 Tb stock .youre stock TB was the one whit the post for the MAF like mine i think so its does make a difference to get more flow there
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Old 06-12-2007, 06:44 PM   #5
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Quote:
Originally Posted by firebuick
good work man is that L67 Tb stock .youre stock TB was the one whit the post for the MAF like mine i think so its does make a difference to get more flow there
Yeah, that was a 1999+ L67 TB. It had no MAF post originally, the MAF "hump" was ground away, and the throat was sanded down. The 1999+ MAF sensor is also a different part number than the 1998 L36 MAF.
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Old 06-12-2007, 09:43 PM   #6
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Andrew,
Amazing work as always. Truly inspirational. Would love to see how it runs on the dyno AND the track.
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Old 06-13-2007, 02:14 PM   #7
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Already said, but I'll repeat.... awesome work!
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Old 06-13-2007, 03:41 PM   #8
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Adding to the data bank in my head... Great stuff, Andrew!
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Old 06-13-2007, 04:19 PM   #9
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ok, im *really* new here..

are you saying you got 17hp from using a ported L67 tb on your L36?

How much tuning the pcm did that require??
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Old 06-13-2007, 04:29 PM   #10
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Oh stop it...you're embarassing me

On a serious note...is there such a thing as either of the following that will "cheaply and easily" fit the L36:
1) a 25-26 lb/hr injector (at L36 stock fuel pressure); or
2) a FPR that will raise pressure to get stock injectors flowing at 25-26 lb/hr?

If so, it seems to me a 97+ L36 could go to a 99+ L67 TB / MAF (mind you, with no TB porting) without the need to reprogram the PCM or use an AFC...
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