Eventually, after making some modifications, you are going to want to know where your car stands in terms of performance. There are several different types of measurements available to give you some feedback.

First, and probably the least reliable test, is the track. While it is generally true that the 1/4 mile times get lower as the car gets faster, much of it is also in the driver's skill. The only fairly dependable way to measure performance gains at the track is to go often and drive the same way each time, like me. All things being equal, any gains from mods will yield themselves in terms of faster ETs, higher trap speeds, or both. In all fairness, the nightly stats should be averaged together over a period of time to reflect trends.

Once you have some averages, go back to any source that you can find and compare your figures to that of a stock model that's been tested. Find as many sources as possible as each will likely have slightly different results.

To see how my PGT-S performed at the track and how mods effected its times/mph, see my time slips page.

Thanks to John Lee!

Another way of testing your car's performance is by utilizing a device called an accelerometer. The most popular, and probably the cheapest ($140) of these, is the GTech Pro. It mounts just like (and is about the size of) a radar detector. Plug it in your cigarette lighter, attach it to your windshield, and GO! The GTech is equipped with high-tech computer chips that can calculate 0-60, 60-0, 1/4 mile ET, 1/4 mile mph, horsepower, continuous G's, and instantaneous G's. It does this by making calculations using acceleration (based of G-Force that the unit receives), time, distance, and vehicle weight.

The next logical question is going to be, "How accurate is it?" Well, the chart to the right is what TESLA Electronics says it should be. I, on the other hand, came up with some very different numbers. I originally borrowed it because I wanted to measure my 0-60 time. While I had it, I thought that a few measurements at the track would make a nice test of how close the accelerometer was to the track's computers. For the first run, the track's computers said that I ran a 14.28 @ 97.77 mph.....the GTech said that I ran a 14.43 @ 102 mph. The next run I ran a 14.53 (spun tires) @ 97.50 mph and the GTech said 14.74 @ 97 mph. My first run without NOS since I got it yielded a 15.71 @ 88.83 mph and the GTech said 17.13 @ 72 mph? A miss is a mile!

The GTech's main drawback is that it doesn't activate unitl after you start accelerating. This is why the GTech's times are consistently slower than the track's, but certainly by more than what TESLA claims it should be.

Dialing in a weight of 3100 lbs. (using the scale at the track plus my weight), I tested the HP with similarly far-off results. Without NOS, the figure was about 10HP off what the dyno said and with NOS, it was > 30HP off. I believe that at best, the GTech Pro gives a good neighborhood of what your car can do.

The 0-60 times are a little more accurate, I think. Based on the fact that there isn't as long of a time to calculate as with the 1/4 mile (i.e. less of a variation based on the time measurement). Again, they are are a little slower than I was expecting, but that may be due to the fact that it begins measuring after acceleration starts.

If anyone has some GTech figures of their own, send them to me and I will post them here. Please include what model/year and any mods that you may have.

Probably most reliable and accurate measuring device for the end-user is a chassis-dynamometer. Basically, your car is loaded on the dyno (hence chassis-dyno) and the wheels are placed on rollers that weigh approximately 2200lbs. each. After the car is strapped down, the dyno is then connected to two ignition leads to keep track of RPMs. While driving on the rollers, the computer that the dyno is connected to determines the the HP and torque curves AT THE WHEELS.

Being "at the wheels" is the key figure. Once we have the peak numbers, we need to back out of them to get the HP and torque figures of the engine (flywheel HP). Sometimes, a driveline loss chart may be obtained from the dyno in which you can get an almost exact flywheel HP number (see Tammy's at the BaPOC site). Usually, simple math is used. Generally, we assume a 15% driveline loss for manuals and 20% for automatics.

The MAX horsepower and torque are really the least useful information obtained from dyno tests (other than to see how mods increase them). The curve itself is what needs to be looked at. That will give you a lot of information about how your car runs. It is especially useful if you can make adjustments in between runs and see how they effect the curve. It is also helpful if you can compare to other cars similar to yours to see how they stack up. With that said, see the Bay Area Probe Owner's Club site for Tammy's, Rich's, and Dan's dyno charts.

Mine are here and I am also putting up William's (Ntruder) since no one has his up yet. For those of you who don't know Ntruder, he is the person who has been made famous in Probe circles by taking this photo while making these very dynos! (see Dyno Chart #7).

Ross' Dyno Chart #1 Baseline run and NOS run directly after (98K .jpg)
Ross' Dyno Chart #2 Non-smoothed version. (2) NOS runs and (1) non-NOS run (98K .jpg)

Ntruder's charts are all screen captures from the PEP files. In order to make them comparable, they are all corrected and non-smoothed (note the s=1 under the charts on the left side. This refers to the lowest smoothing setting)

Ntruder's Dyno Chart #1 Baseline: Hennessey exhaust, ram air intake, and Pacesetter headers.
Ntruder's Dyno Chart #2 2nd run, same mods
Ntruder's Dyno Chart #3 3rd run, same mods
Ntruder's Dyno Chart #4 4th run, same mods with nitrous.
Ntruder's Dyno Chart #5 5th run, same mods with nitrous, engaging a little earlier!
Ntruder's Dyno Chart #6 Same mods, no NOS, and VRIS tie-strapped open.
Ntruder's Dyno Chart #7 Top speed run.
Ntruder's Dyno Chart #8 Another top speed run.
Ntruder's Dyno Chart #9 Dyno with same mods and a test pipe.
Cat .vs Test Pipe is a comparison of Chart #1 and Chart #2 in one handy .jpg

Yes, he was busy that day!

As of our Southeast Probe meet in Atlanta on 3/7/98, these are the charts of all who attended. We must thank Rob of Atlanta Chassis Dyno for coming in early on his day off and then staying late when we had more Probes show than originally expected! He was patient and helpful...thanks Rob!

The weather was horrible, but at least the dyno was inside a bay! Temperatures inside ranged from 52°-55° throughout the runs. Humidity was high due to the rain. As before, these are the corrected and non-smoothed versions of the charts.

Ross' Dyno Chart #1 Baseline run: GReddy, custom cold air, and Hotshot headers.
Ross' Dyno Chart #2 As above with NOS. 650 psi bottle pressure.
Ross' Dyno Chart #3 Same NOS jettings with 950psi bottle pressure.
Matt Braun's Chart 1993 PGT, 111K miles, Super Turbo muffler.
Bob Harden's Chart 1993 PGT, 85K miles, completely stock.
Michel Fortier's Chart 1995 PGT, 85K miles, GReddy cat back, Hotshot cold air pipe, Hotshot headers, Unorthodox Racing underdrive pulleys, ACT clutch, lightweight (13lb.) flywheel, NGK wires and plugs, and MSD 6A ignition box.
Dan Dunhem's Chart #1 Baseline runs: 1996 PGT, 54K miles, Borla, Hotshot cold air with K&N RE-910 filter, Hotshot headers, Unorthodox Racing underdrive pulleys, original plugs/wires.
Dan Dunhem's Chart #2 As above with NOS. 36/42 jetting.
Felipe Torrejon's Chart 1995 PGT, 28K miles, completely stock.
Rick Mitchell's Chart 1993 PGT, unknown miles, HKS intake, no muffler (straight pipe in its place), all other piping is stock.
Daniel DeFranc's Chart 1995 PGT, unknown miles, Canadian version, Borla cat-back, Unorthodox Racing underdrive Pulleys.
John Lee's Chart 1993 PGT, unknown miles, GReddy cat-back, HKS filter with his own cold air pipe, and Hotshot headers.

OK, I think that about covers everyone and their mods, now it's time for comparisons. If you would like to see 2 or 3 charts overlayed that you don't see here, e-mail me and let me know and I will put them up.

36 jet pressures overlaps both 36 N2O jet runs with the bottle pressure at 650psi and 950psi.
40 jet pressures is the next logical comparison...40 jets with the different bottle pressures.
36 .vs 40 jet compares the NOS runs with the different jettings.
Stock Probes comparison compares charts of stock PGTs with 85K and 28K miles.
Stock .vs Mods compares Michel's modded PGT to Bob's stock PGT.
Dan .vs Michel compares charts of the two highest all-motor power PGTs at the meet.
HKS .vs Hotshot compares the HKS intake as sold to the Hotshot intake as sold.

Ok, I whined like a baby about my whimpy baseline run in Atlanta. I complained about how the car was hot so I didn't get a good run. Well, I broke down under the pressure and had my car re-dyno'd with a cool engine. While I think that the engine temperature had more to do with it than anything, the elevation may have played a role in these charts as well. I would believe however, that the increase in air temperature (52° to 85°) would have negated any low-elevation gains. Humidity was similar to that in Atlanta (same rainy-type day here) so I don't think it's a major factor either.

Ross' Dyno Chart same as in Atlanta, but with a cool engine!
Ross .vs Dan shows this chart compared to Dan's chart.
Ross .vs Michel shows my chart overlapped with Michel's.
Ross .vs John shows...guess what? Right! My chart over John's!
Ross .vs Stock shows my chart over a stock PGT's.
Ross .vs Ross haha....my Atlanta dyno chart over my Florida dyno chart!

Guess we need a Florida dyno meet to see if my new chart is due to a cooler engine or the change in elevation!

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