Rick's G35 6MT

Download the G-Tech Pro data files (GTP files).
Download GTech PASS (GTP file viewer).

New Data Tools: 10/09/2004

This weekend I made some more acceleration runs to test out my new car testing toys (more on those later) as well as to see if I could better my previous runs after my y-pipe installation. I made four runs in back-to-back pairs for better consistency. I was aided a bit due the temperature (45-50 degrees) so I'm sure the G35 was making a bit more power, although I'd expect slightly worse traction due to the cold temperatures as well.

The two new toys I got are: (1) an electronic barometer/thermometer, and (2) an OBD2 data logger. The barometer/thermometer is actually a Bushnell DNS (Digital Navigation System) Pro. It is designed for rock and mountain climbers since it records temperature, altitude, barometric pressure, and time so they can measure their ascent/descent rate. I'm primarily interested in barometric pressure and temperature so that I can perform atmospheric corrections on the data. The OBD2 data logger is a Davis CarChip E/X. I bought it since it's very small and doesn't require a laptop or anything else to record the data. I did find a shortcoming because of that, however...


As I mentioned before, I performed four acceleration runs with in back-to-back pairs going opposite directions. My launches were from 2000rpm varying from a clutch drop (resulting in waaay too much wheelspin) to a slight feathering of the clutch. The results of the acceleration runs ranged from 14.3seconds @ 101mph down to 13.8seconds @ 103mph! Sweet! (... and by sweet, I mean totally cool. Nevermind.) My average was a 14.0seconds @ 102mph.

My best 0-60mph time was a smoking 5.6seconds, and my average was 5.9seconds over the three runs where I didn't have too much wheelspin. The first two runs both had times 6.0seconds or greater, so on the last two runs I delayed the 1-2 shift by another couple hundred RPM to get better numbers. Unfortunately, that means the RPMs at each shift point get damned high. With the power peak at 6400rpm, the redline at 6600rpm, and the 2-3 shift occurring right on top of 60mph, I've got a pretty bad Catch-22.


The highest power output was 212bhp @ 6400rpm. As part of the atmospheric corrections, I'm also using a better method of estimating aerodynamic drag. After all the proper calculations (more info on that later, too) the adjusted output is between 258-263bhp @ 6400rpm.

Those figures seem a bit low, since my expected output with my modifications should be about 275-280bhp. When comparing the trap speeds (102-103mph) against the calculated and published figures (~99 mph), my G35 is definitely putting out more power than stock. Most of the readings of the other cars have been pretty accurate, although I've noticed more possible error on the more powerful cars (mine, Brian's Mustang, and Chad's Monte, etc.) The new G-Tech firmware has a "pitch factor" that is supposed to account for this, but at present it has bugs in its RPM detection routines so I'm waiting for an update to fix that first.


I've already covered the shift points and my difficulties in staying between the power peak and redline. The other thing I've noticed is that I'm getting a bit too much wheelspin in the 1-2 shift, which delays things by a tenth or two. I'm not sure that slowing down the shift will help... less wheelspin, but a slower shift.

The other bit that I need to examine and practice more is the launch. In the past I've launched between 2000 and 2500rpm with medium-to-heavy throttle and medium-to-fast clutch engagement. This normally gives me a 0-60mph time of 5.8-5.9 seconds if I delay the 2-3 shift, or 6.0-6.1 seconds if I don't. For all of my launches today I started at 2000rpm, but the first run I used immediate full throttle and dropped the clutch. Whoops. The second and third run I put the pedal down slower with a faster clutch engagement which avoided nearly all wheelspin. The last run I let the clutch out more slowly, and used more throttle (and only released the gas lightly to control the wheelspin.) When you compare the best two runs you can see where the addtional RPMs and power were worth a bit more wheelspin. The last run was 0.25 seconds faster to 60mph, and 0.125 faster to the quarter mile!

Corrections and Other Factors:

I have been planning for some time to better measure and compensate for environmental conditions. Changes in the temperature, humidity, and atmospheric pressure all make a significant difference in a car's performance. Although I've corrected for fuel and passenger weight in the past, I never performed any atmospheric corrections since I didn't have the proper tools to measure conditions.

Now, however, I can both measure ambient and vehicle conditions. The ambient temperature, humidity, and barometric pressure are all recorded by the DNS Pro, and my CarChip E/X records data like vehicle speed, RPMs, throttle position, coolant temperature, and intake air temperature. The intake temperature is critical by itself, since it varied by 10-15 degrees from ambient. Unfortunately the CarChip will only log data every five seconds -- boo! -- so I'm going to contact Davis and see if we can improve that.

I put a few hours into creating a total, end-to-end spreadsheet that will handle all necessary data corrections and standardizations. It corrects for atmospheric changes, aerodynamic drag, driveline losses, and standardizes to 1/4 tank of gas and just the driver's weight. All of these are handled dynamically after the run data is entered. Going forward I will provide the spreadsheets' figures to show how everything is handled.

Here is the data from the averaged runs versus the best run in original and fully corrected form:

Recorded Data Corrected Data
Averaged Runs 0-1/4 mile in 14.0 secs @ 102mph 0-1/4 mile in 14.0 secs @ 102mph
Best Run 0-1/4 mile in 13.8 secs @ 103mph 0-1/4 mile in 13.9 secs @ 103mph