Hey all,

I made a few passes out at State Capitol Raceway in Port Allen, LA this weekend, and I was kind of disappointed in my ET and speeds. I averaged about 12.6xx at 113. Best was like 12.50 at 115 I think (don't have the timeslips in front of me).

Now, I've previously run at the same strip and made several 12.1xx runs at 119-120. These runs were made last December, so there's a pretty significant temp difference. Less than a week after those I ran an 11.97x at No Problem Raceway.

The car is a '13 A6 base. All the runs were on Pilot Super Sport tires.
I have a set of Pfadt headers, a Halltech MF107 intake, B&B PRT mufflers, and a good tune in the car. Also a 160* ECT thermostat, and a B&M transmission cooler with temperature controlled fan run in series with the factory tranny cooler.

I didn't have any wheelspin whatsoever. I want to say that my 60' times were pretty consistent between the different times, maybe a maximum of a tenth variation.

Keep in mind that this was only my third trip to a drag strip, but I made 10 runs on Saturday and they were all pretty consistent. Ran in comp mode with a little bit of driveline preload (like 1500RPM most runs).

Temps (consistent):
EOT: 220-225
ECT: 190-200
TFT: 178-190

Shifts were perfect and crisp so I'm pretty certain I'm not seeing any losses there.

Here's one of my runs (1080P, so watch fullscreen and crank the quality if you want lol):





So here's my question: can I chalk this difference up to higher IAT's, or is there something deeper going on here?

 

I found on my car it seemed that for every 1000DA it was .08 difference roughly. I never checked against the IAT.

 

Since you didn't specify the times you ran on each of the two days, I picked noon on July 11th and then noon on December 11th to get a rough frame of reference.

A good tool for comparing timeslips is by using something called density altitude, which is a calculated number using track elevation, humidity, barometric pressure and temperature.

As a general rule of thumb your car will slow down by around a tenth for each 700ft increase in the DA. Back in December the DA was -1099ft and this past weekend it was 2203ft which equates to a little under 5 tenths and more than explains the ET difference.

Post the two timeslips and I can get you more accurate numbers.

 

Thanks for the info! I'll try to remember to grab some scans when I get home.

 

A couple other factors to consider is that different tracks can report different ETs and trap speeds depending on how their timing equipment is set up. I always seem to run a full tenth quicker at Sacramento compared to Sonoma and my trap can be as much as 2MPH there too. Oddly enough though my 60ft times will be almost a half tenth slower at Sacramento.

Also, unless you're scanning each pass you'd be surprised at how much wheelspin there can be even when you're certain you hooked properly, especially with street tires.

 

Car numbers 102 and 217 are me:

Best at State Capitol last December:


Best 2 at No Problem last December:



Best from this past weekend at State Capitol:


Not the best scans but scanning receipts is decidedly annoying if they've been folded for over 6 months..

I used the DA calculator on dragtimes and here's what I got:



column F is estimated ET difference in 10ths, assuming a 1 tenth difference per 700 feet difference in DA as you mentioned..which leads me to believe I'm either missing something in my calculations, as I'm not seeing any substantial differences there, or that there's something more at play here.

thoughts?

 

The key to understanding timeslips and subsequent tweaking of tunes, is knowing the conditions that existed at the time of each pass. Ideally, it'd be a recording weather station attached to your car for the atmospheric conditions and temperature sensors for the track surface and tire tread after a burnout. A scan of the pass will ID any wheelspin and other on-board data.

Since most of us run for fun vs big $, we either use a handheld weather station or rely on local stations nearby for the DA numbers. As a last choice, you can use data from the Dragtimes.com site. Consistency is important for whatever your source for data. Dragtimes has several elevation errors and only uses hourly weather from the closest major airport. You can get better data for elevation from Google Earth and weather from private stations at wunderground.com.

Plugging the numbers into the Dragtimes calculator will give you the DA adjusted times. While none of this will be NASA accurate, at least it'll be consistent. Keep a logbook for future reference and note any changes you make to the car.

 

There's a problem with your math, in that the DA at NPR at 8:56PM was -847ft, not the 821 you have listed below.

I have another online calculator I use and corrected all four of your runs to 0ft DA:

12.243 at 1177ft = 12.092 at 0ft
12.02 at -754ft = 12.115 at 0ft
11.979 at -847ft = 12.086 at 0ft
12.576 at 1651ft = 12.344 at 0ft

The first three passes are all within .029 seconds of each other (12.115 - 12.086) which is fairly typical. The last pass is the anomaly in that it's .258 slower than the quickest corrected ET of 12.086.

I'd bet money that the issue lies with your 330ft time, in that it's 5.503 which is almost 3 full tenths slower (.291 to be exact) than your best of 5.212. Although you appear to have launched pretty well (given that all your 60ft times are fairly close), that big jump in your 330 was likely due to wheel spin coming from the 1-2 shift as I've seen it be quite a bit with street tires.

That much wheel spin is also what caused your 1/8th and 1/4 mile MPH to be off so much as it was.

 

Hmm...I'll definitely have to remember to scan next time. Forgot the laptop last weekend and didn't have time to drive back home by the time I realized.

I will say that I am fairly confident that I'm not spinning on that shift. I say this only because I don't even chirp the tires on that shift on the street.

My tune is slightly different from when I made the runs in December.
The only things that were changed were (this is all in EFILive):
1. moved the rev limiter down from 7200 to 7000, so that if someone was driving with the paddles they wouldn't go crazy over-revving it (not relevant as the car shifts right at 6600 when not using paddles [runs were all made in sport mode, no paddles]).
2. Rev limiter by gear to 6800 for moving gears and 5500 for p/n (from 7100/4500 respectively (still not relevant)
3. Changes to torque model table to improve shift feel (had great benefit and made shifts faster and smoother)
4. Restored Max spark retard, power reduction min timing, and max torque reduction to stock values (were previously all zeroed), to enable improved torque management on shifts. This is the only thing I see that may have caused a real issue.
5. Changed upshift torque limiting in the TCM tune to via spark/fuel from none.

All the runs were made with all other torque management values enabled

These changes were primarily made to mimic the shift feel of the C7, and I've gotten pretty darn close to it. The shifts have gotten faster and very positive, but without jerking or jarring like they did before I re-enabled any of the TM stuff. The only way I can really describe them is "instantaneous". There isn't any feeling of ever being between gears

I suppose I'll need to scan and see whether the ECM is putting the car in torque reduction modes outside of any shift events. Wheelspin is still a possibility, but I just feel like I'd definitely notice it on the street. I'll find some time to do some scans and get back to you re: spinning off the line and on shift. I'll also keep an eye on my timing and see when and how much the ECM is taking away from me. Anything else I should take a look at?

Now, I'll be quite frank, and say that, to me, the improved shifts are worth losing .3 in the quarter (this is a DD that's on the street 99.99% of the time). I also believe that, if properly executed, one could make a car shift/drive faster with TM on than one could with it off. This has unfortunately become one of my personal goals for this year, which means soon I'll have to bite the bullet and move to a flashscan from an autocal.

If I would've thought about it (and had my laptop), I could've done a few runs with the old tunes to see if that was the issue. I believe NPR has a TNT tomorrow afternoon, so depending on how I feel after my exam in the morning I may head out there and do a little research.

Also, for future reference, which site do you use for your DA calculations?

Thanks for all your input. Learning more about this car and high performance vehicles in general has become one of my genuine passions thanks to this forum.

 

Apart from wheelspin and additional timing being pulled somewhere for some reason, that's all I can think of.

I use www.smokemup .com. It's a subscription based website but they have a handy tool (among others) that will let you correct an ET from one DA to another.

 

Had a chance to get out to No Problem Raceway last Thursday for a TNT, and tried my current set of tunes as well as combinations of my current and last engine and tranny tunes.

Don't have the timeslips with me, but I did put the ET and MPH into a spreadsheet for all the runs I did.

I made 8 runs, the fastest of which was 12.515 at 115.68 (2323 DA corr.: 12.175, 118.991), and average was 12.648 at 114.96. Using an app that gives supposedly accurate DA values for your GPS location at that exact moment, and using the internal baro on the phone, I got an avg. of 2317ft. Correcting with Dragtimes. com's calculator, that yields a 12.305 at 118.242, so about 2 tenths slower than my best corrected runs from December.

Anyway, I noticed no significant difference in ET/MPH between the various tune combinations. I made 2-3 runs on each tune combo, and logged each. Ambient temps were over 95* at the track all day. All runs made from 1-3PM.

A few things that I noted from my logs:
1. for some reason only my last 2 logs got valid speed sensor data
2. On every run, initial intake temperature is over 145*, and drops to about 118* by the end of the pass.
3. Final timing is 15-16* for 1st gear, and 18-20* for 2&3, because of high IAT's.
4. I'm consistently seeing 0.5-2* of knock retard above 5500RPM.
5. Although I didn't log them, I know EOT, ECT, and TFT were at 210-225, 190-205, and 175-190 consistently.

All the runs look about the same, and I didn't get any big wheelspin on the logs that did get the speed data. A little jitter on the 1-2, but nothing that causes me to think that they're spinning enough to slow me down from runs in colder weather with the same prep and older tires.

Now, I'd have to see logs from the winter runs to know for sure, but in my non-professional, non-expert opinion, this explains the difference pretty well. I think I'm taking a pretty significant timing hit across the board, especially in 1st gear, due to intake temperatures. Obviously toward the end of 3rd it's trying to get a little more aggressive and that's even giving me a little knock.

For reference, looking at some year-old logs, with 90* IAT's I'm looking at 20-24* of timing across the board. I'm thinking with 70-80* IAT's (which I probably had on a 50* track), I'd see even higher timing, and just overall greater fuel/air flow/density/all that good stuff.

Thoughts? Opinions? Does this adequately explain the 2-3 tenths I'm losing in corrected ET?

 

If you are tuning your car, lower your timing in the appropriate areas to get rid of that knock. You don't want to be relying on knock sensors to always pull it.

A Vararam or other cold air intake would help you a lot. Even the toggle bolt mod to prop the shroud would help a lot.

Yes the terrible DA is causing the decrease in ET. You are just not going to run quickly in that soup. I don't put much stock in the correction factors, you want your car to run very close to the same number each run on a particular day. The Vararam will help in this regard. When the timing corrections kick in it makes the car inconsistent.

 

I am not yet doing my own tuning on the car, though I plan to be by the end of the summer. Not a cost issue, more just a time investment to really learn how to do everything the right way and not cut any corners.

I currently have a Halltech MF107R intake with the Beehive isolator, but the factory NACA duct/shroud is still in place. I'm sure removing that restriction would help a bit; not sure how/if it would affect water ingestion risk on a daily though (we sometimes have nasty unavoidable standing water here). It would be a cool project to build a variable shroud that could be opened/closed based on different factors...

I've toyed with the idea of switching to a VR intake but considering I've already spent the time and money on this one and the MAF corrections it needed, I decided that any gains wouldn't be worth it. From what I've read, the Halltech definitely has headroom to grow for a H/C upgrade in the future.