OK, so here's the deal: I had made the following modifications to my 1999 C5:

• Max. Modified Mass Air Flow Sensor
• Timing Tricker (makes the temperature always read 57 degrees)
• B&B Tri-FLow Exhaust
• Donaldson LS6 Air Filter
• Nology Wires
• Beru Plugs
• 178 Degree Thermostat
• Throttle Body Coolant Bypass

And saw the following results at Dyno Day #1:	Now at Dyno Day #3 we get:	Dyno Day #4 Since an engine is mostly an air pump, I figured that more air in = more HP.  That's what the modifications above mostly do anyway;  The Breathless Vortex Power Duct claims to increase airflow by 30% over the stock air intake tube.  They allege that it is good for 6-8 HP.   So I get one and install it.  Next dyno day:
306.9 RWHP,  313.2 Lb-Ft Torque  (assuming 15% drive train loss, that's 361 HP at the flywheel) as shown in Chart 1.	331.8 RWHP,  336.4 Lb-Ft Torque  (390 HP) as shown in Chart 2.	Torque drops by 1.9 Lb-Ft and HP is down by 8.2 RWHP to 323.6 RWHP, 311.3 Lb-Ft Torque (381 HP)  See Chart 3.
Chart 1. Pretty disappointing so I added: Ported Throttle Body Custom Tuned PCM (Power Control Module) by Pro Auto Tech	Chart 2. More like it, but still not 400 HP.	Chart 3.  Hmmmm.  Methinks this is not good.

What is wrong here?  Tom the dyno guy said that he could hear the car pinging during the pulls.  And he thought it might be the gas - Oregon uses oxygenated gas in the winter.  But - everyone else was running the same gas and their HP was still up.  So, it's probably not the gas (drat).

Being an analytical type, I got out my trusty AutoTap cable adapter and my PC and went for a ride.  Click *HERE* to see ten minutes of data I collected (why anyone would ever want to do that is beyond me but it's here for completeness).  You can download my AutoTap configuration file if you want. For Netscape, right click on this:   and select "Save Link As..." (for Internet Explorer, just click and save it).  It is the AutoTap (Windows version) configuration file I use.  It is a binary file so you can't read it without the AutoTap software but you could use it as a starting point for analysis).  Using a way cool
spreadsheet tool I snagged off of the web, I got the following information:
 
 

Figure 1.  Run 1 Initial Analysis	Figure 2.  Prior to mods.

Figure 1 shows us two things, both of which indicate that the engine is running lean.  A positive value for Long Term Fuel
Trim (LTFT) indicates that the PCM (Powertrain Control Module) is having to adjust for a lean condition (negative value = rich).  WOT (Wide Open Throttle) is indicated in the AutoTap log files by a Throttle Position Sensor (TPS)  reading of greater than 99.5%.  When we examine the O₂  sensor readings during WOT runs, we see in FIgure 1 that the average for the 13 AutoTap scans is 0.864038.  These scans were done during a WOT run through about 103 MPH.  It is generally accepted that a naturally aspirated engine should indicate WOT  O₂  readings of between 0.875 and 0.910.  A higher reading indicates a rich condition and a lower reading indicates lean.  Here we have two pieces of data that indicate a lean condition on my car.  Looking at Figure 2 which was captured prior to the modifications, we can see that there was a slightly rich condition under WOT and that the LTFT was much closer to 0.0 which indicates a better air/fuel mix, however the WOT O₂ information was higher than the desired range. This means that I was running slightly rich before.

Another bit of interesting information is shown in Figures 3 and 4:

Figure 3. WOT Information From Run 1

Figure 4.  WOT Information (pre-modification)

In Figure 3 we see that of the four Knock Retard (KR) occurrences (over 3 degrees), three of them came during the WOT run and the fourth came as I lifted off of the throttle.  It is possible that this is causing the pinging that Tom heard during my last dyno run.

The goal here is to have LTFT readings of as close to 0.0 as possible and an O₂  reading in the 0.875 - 0.910 range.  Figure 4 shows that prior to the air flow modification, things were much closer to the recommended range.

My thinking is that the addition of the new intake duct increased the airflow through the MAF and leaned out the mixture because the MAF is designed to work with the stock MAF ends and air filter.  It is possible that I am flowing more air than the MAF can tell the PCM about.

OK, so what to do?  Since I love gadgets and gizmos, the natural thing to do was to order a MAF Translator (about $180 at partsforyourcar.com).

Figure 5. MAF Translator Box

The MAF Translator allows the user to adjust the Air/Fuel ratio across different parts of the RPM band. It is easy to make
adjustments by simply  turning two 16 position switches inside the unit.  The switches allow you to make whatever part of the fuel curve you wish richer or leaner.   The switches adjust as follows:

• The MAF BASE adjustment is for selecting the basic airflow characteristics of the MAF sensor in relation to the vehicle/engine configuration.  It can be set to compensate for non-stock size injectors, modified or transplanted MAF sensors, or other basic fuel delivery offsets.  The adjustment has effect over the entire airflow range.
• The MAF WOT adjustment is for adjusting the fuel delivery under wide open throttle conditions.  The fuel delivery correction is only applied during WOT conditions in order to prevent the ECM/PCM from compensating for the change.

View from front side showing MAF Translator mounted at the top right of the radiator shroud.	View from inside looking toward the MAF and Donaldson filter.  MAF Translator can be seen on the left.  Note wire covering.	View from front of car through hood opening.	Detail of the wiring harness I used.

I used duct (Duck) tape to affix the unit to the top of the radiator cover during testing.  Once I got things figured out, I bolted it to the radiator shroud and covered the unsightly wires with some flex covering.

If you want more technical information on this stuff, take a look at this article I downloaded from the C5Forum.

Gather some data:  This is the fun part because driving is involved.  Here's the plan:

Install the MAF Translator
Connect the AutoTap system
Make a run with a 0/0 setting on the MAF Translator
Analyze the run
Make a run with a 5/0 setting
Analyze the run -if still lean, make another run at 10/0, if rich, we're done - back off one click.
Analyze the 10/0 run - if still lean, make another run at 15/0, etc.
After getting the LTFT numbers in line, then make a run at <working MAF setting>/2
Analyze that run and adjust as appropriate.

After capturing the baseline run, I set the MAF Base switch to +5% and made another run.  It was still lean so I went to 10% and made another run.  That one was too rich so I backed off to 5%.  Next I set the MAF WOT switch to +2% and made my fifth run.  It looked pretty good.  Here's the details:

LTFT/O₂ Analysis
April 5, 2001

Figure 6. Test Data Summary

We can see from Figure 6 that run 4 gave me good results for the WOT numbers, the LTFT was too rich (negative numbers).  I then backed off the MAF Base setting to +5% (no need to test since run 3 was good).  I then set the MAF WOT to +2% for run 5.  Looking at the run 5 results we can see that the LTFT numbers are much closer to the desired 0.0 and the WOT O₂ numbers are in the preferred range.
 

Figure 7. Ongoing Data Collection - April 11(1) (note no WOT this run)	Figure 8. Ongoing Data Collection - April 11(2)

After letting the car sit and think about things for a few days, I logged about 40 minutes of "normal" driving to see how things are.  From Figures 7 and 8 above, we can see that both the LTFT averages and the WOT numbers (Figure 8 only) are in the target range.

OK, so what?  Remember, we started all this because of a drop in RWHP and Torque.  The question is - did any of this do any good as far as making horsepower and torque is concerned?  Well, we'll know after the next Dyno Day ("Dyno Day Number 5 - This time it's personal").

-----some time passes-------

So, after dyno day number 5, my HP and T are the **SAME** .  PLUS, my car stalls all the time.  The MAF Translator is a PIECE OF SHIT!  I think that anyone who buys one is (like me) *STUPID*.

-----even more time passes as I slowly get pissed -----

Next Steps - Phase 1:
My next step was to take my car to McGee's Auto Service and let Steve have a crack at it.  First step was a baseline dyno run:  The results were 326.22 RWHP and 337.72 Max. Torque as shown on this GRAPH(1) from the Dyno Jet.  About the same at on Dyno Day 5.  We did a bunch of additional runs while changing the configuration of my engine slightly.  The results were that I was consistently LEAN (just like we determined above).  Here's proof - take a look at the Air:Fuel Ratio GRAPH(2) - it is clear that 14:1 is too high (i.e. too much air for the fuel).  I should be at about 12:1.  After a morning of various tests and tweaks, we were able to get the HP and T up to 333.19 and 344.37, respectively as indicated in this GRAPH(3) from the Dyno Jet.  I have also enclosed the Air:Fuel GRAPH(4) from that same run.  Still at 14.  The Plan is now to use LS1 Edit and hack the code in the PCM to compensate for the lean condition under WOT.

Stay "Tuned" - no pun intended

Next Steps - Phase 2:
Figuring that the lean condition may be mitigated by some custom PCM tuning, I get a license for LS1 Edit (from www.carputing.com) from Robert Judd - LS1 wizard and tuning guru.  This program lets you modify the PCM settings, tables and parameters and re-flash the PCM.  With Robert's guidance (and analysis of many pages of AutoTap data), we did a few changes to the PE (Power Enrichment) tables with dyno runs after each.  We were able to get the air:fuel ratio down quite a bit but the engine was continuing to ping.  Another AutoTap run revealed that through most of the low part of the power band we only had around 3-5 degrees of advance.  The thinking now is that this LS1 engine may be contaminated with a carbon build up on the valves and cylinder heads.  This has been seen on other Corvettes and seems to come by way of oil being introduced into the intake manifold by the PCV system.  Now, we are finally beginning to develop a plan.

Finally, Some Resolution:
So, I get my act together and return to Steve's shop for (1) an engine flushing with the trusty Motor-Vac (this will remove the carbon deposits from the valves head and cylinder walls); and (2) treatment with a can of 3M Intake System Cleaner (this cleans the intake manifold and fuel system).  Here's a few pictures.  With that done, we climbed back on the dyno and made a run.  The Air-Fuel ratio - GRAPH(5) - dropped significantly, especially above 3000 RPM  - the car was not running so lean as before (see GRAPHS (3) and (4)).  HP and T were a bit lower as shown in GRAPH(6).  Next we tweaked the PCM a bit more to flatten out the A/F curve by cutting back the PE/RPM table from tune # 4 by 5%.  While I was at it, I bumped the RPM at idle to 825 across the temperature range to smooth out the idle which was a bit rough at times.  Returning to the dyno, we see by the RED line in GRAPH(7)  that the A/F ratio is now in the mid 12's except for a slight bump in the lower RPM range.  This is getting better.  Finally, we added 1% more fuel across the RPM range and 2% at the 3600 RPM cell.  The curve presented in GRAPH(8) is much flatter across the range and the horsepower/torque curves are where we would expect - as seen in GRAPH(9).  So, now we are at 333.75 RWHP and 348.36 RWtorque which is well up from our 306.9 (up 8.75%) and 313.2 (up 11.23%) starting points.  Additionally, the engine is running much better, not pinging.  I'll make some extended AutoTap runs for further analysis - my scientific advisor and LS1 table guru (Robert) feels that we should tweak the high and low octane tables a bit.  Wait, there's more...