[Blk16SS]

I have the red ones also. I meant to ohm them out against the stockers. MSD claims far less resistance... Could simply adding low resistance wires create a lean condition?

[EFI Tuning]

I was able to get some clearance on the stock wire that was arcing. If it's arcing it will misfire on the cylinder and run rough. If there is no arcing changing wires isn't going to make any difference unless the wires are in really bad shape.

[EFI Tuning]

Originally Posted by Blk16SS

I have the red ones also. I meant to ohm them out against the stockers. MSD claims far less resistance... Could simply adding low resistance wires create a lean condition?

No. That should have no impact.

[Bobfly]

This is a good thread. My SS seems to have a miss at idle. I need to check for arcing...

[stars_fan]

Why did you go with 2"?

[EFI Tuning]

Slight gain at the top end vs the 1 7/8". My personal preference is to maximize the upper end. I know many want max mid range torque but on a street car you can only utilize so much mid range torque. As you run through the gears you see that area only briefly and only once on the A8. Others will have different preferences.

Tim

[EFI Tuning]

For anyone interested I just completed a full VVE tune for 93 octane with the headers. I will be transitioning back to E85 and tweaking for that as well over the weekend. You will not get this level of tune from simple hand held units. It is a very time consuming process but the results are well worth the effort. The car drives great.

Some updates on what we are up to next...

1. nGauge... I am testing the E92 compatible beta firmware right now. The nGuage is a really nice alternative to HP Tuners for those that want to leave the actual tuning process to someone else. It can act as gauge mounted scan tool. You can select which PIDs are shown. It will log data to a SD card for import into HP Tuners for review/analysis. The other very significant benefit is that we can supply new HP Tuners calibration files and the nGauge can flash them to the ECM. The end user does not need to buy additional credits or have HP Tuners.

I will be putting up a technical blog post in the next week or two with all of the details. It is very slick.

2. Bundle packages... we will be expanding out package offerings in the near future. I will also be offering AEM products so expect to see some one stop shop options for tuning solutions (ie. AEM 30-0333 WB)

3. FI/E85... I'm in the middle of a full Z06 tune with E85. I will share the results when that effort is complete.

Tim

[oldman]

I got a bad alcohol problem, and it is EFI Tuning's fault...

[Atomic Ed]

Originally Posted by EFI Tuning

For anyone interested I just completed a full VVE tune for 93 octane with the headers.

Tim

OK, I'll show my ignorance. What is a VVE tune? And how does it differ from a regular tune?

[EFI Tuning]

Atomic Ed great question! My response is not a crituque of other tuners. I am just going to try and educate here.

There are different levels of tuning that one can do. I will start with the easiest and go from there...

1. Dyno tune... more often than not this will consist of dialing in the WOT AFR and timing to maximize full throttle power. Some will brute force the calibration, some will take the time to correct the calibration for other issues such as an inaccurate MAF transfer function before dialing in the WOT fuel. If this is not done on a load dyno the post dyno tune should really be verified on the street. You will likely see some small variances that need correction.

There is nothing particularly wrong with this level of tune but depending on your modifications it may leave other areas completely unaddressed. This will be your least expensive type of tune in most cases. If the shop has a load dyno they may do some additional work in #2.

2. So WOT tuning is pretty straight forward. The area neglected many times is the part throttle calibration. Part throttle tuning is very time consuming. The ECM can adapt quite well but when you start looking at the details in the data logs you will see areas that are not ideal. VVE = Virtual Volumetric Efficiency. The ECM has two ways to estimate actual airflow... the MAF and MAP vs RPM. If the ECM were to use only MAF you would have very poor transient response. If you are cruising and stab the throttle the ECM will initially rely on the VVE calculations rather than the MAF readings. If it didn't it could provide 3-4x more fuel than necessary during the transition. Once the airflow stabilizes it will deviate back towards the MAF readings.

The VVE table is not actually a table in the ECM. It is a tuning tool view of the VVE calculations that allow us to properly derive new coefficients. Modifying this portion of the tune is very time consuming but is really critical when you have made significant changes from stock. I can tune a MAF transfer function in less than an hour max. A VVE tune could take an entire day or multiple days depending on the combo. If you don't have a load dyno you need to do this on the street. A wideband sensor is a necessity.

If someone wants to push a MAF only tune I would really question as to why. On this platform it is a deficient approach.

Tim

[PRAY]

Originally Posted by Atomic Ed

OK, I'll show my ignorance. What is a VVE tune? And how does it differ from a regular tune?

VVE is the Virtual Volumetric Efficiency table. Virtual is just how the tuning software displays it now. There is technically just the VE table. It is the base fueling table. The MAF references is to make corrections up to 4,000 rpm in most stock tunes. It is directly correlated to the MAP sensor which moves instantaneously once you hit the throttle. The MAF lags behind since it has to sense an air flow change before it can start it's math to determine the fuel needs.

Once you start to modify the car the base VVE table can't keep up with the fuel demands on throttle transitions. The PE table also lags. There really isn't much you can do to accelerate the PE tables at a certain point. So when you hit the gas you get a lean spot. This happens even more above 4,000rpm since GM didn't put much of any effort into the VVE table above that point.

There are many points where the MAF will hit the same portion during different fueling requirements based off of the MAP sensor. So if you keep adjusting the MAF you will never get the correct fuel. This is especially true with an A8 and the stock converter. When you hit the throttle from a stand still your MAF frq/hz will start around 4,500hz. The car needs more fuel there but if you do that it will be rich during normal driving conditions.

Usually once you do a cam things get really messed up. There is way to much fuel in the idle areas where your new cam's usable MAP area will be. A dyno tune with just adjusting the MAF is good enough and is not unsafe but it is absolutely not ideal. It is just difficult and very time consuming. 99% of your professional tuners are not going to start at OLSD and do your VVE table and then turn the MAF back on and line everything up. It would take to long and cost way to much money for the normal car guy to pay for it. And unless you have a load bearing dyno you can't mimic all of your street driving conditions. However, if you are doing a known combo to the tuner then it is a simple cut and paste for a 90% solution as a starting point.

For a car to be completely tuned you must address the VVE, MAF and the PE tables. Your best bet is to go with a known combination that has all three portions tuned as a collective.

Just my 2 cents.

[PRAY]

LOL. I didn't know you responded Tim. Phone is in the garage.

[solobaric]

Both great explanations guys, thanks.

[Atomic Ed]

Thanks guys! I learned something today.