I did a little G-tech testing on my 94 Vette (6spd). I wanted to record the horsepower two different ways: one by recording the G's and the other by the horsepower mode on the G-tech.

I gathered two G force points in 2nd and 3rd gear at 5000 RPM

2nd gear @ 5000 RPM: .44 G's Raw Data
3rd gear @ 5000 RPM: .33 G's Raw Data

I always look at the baseline before getting on the gas and it was around .01 for both runs so that is subtracted. Also when you accelerate your car body tilts back which makes the values read higher (picking up Mother Natures G forces) I've estimated this to be around +.02 G's. So to adjust the values I subtract .03 G's from each point.

2nd gear @ 5000 RPM: .41 G's Corrected Data
3rd gear @ 5000 RPM: .30 G's Corrected Data

Using the figures above that comes out to "247" applied horsepower. The HP mode of the g-tech agreed at (2 passes 252 & 247). This is not the rear wheel or flywheel horsepower. This is my net power. For example, If I were topped out at 170 MPH my applied horsepower would be zero, even though my motor would be making 300+ horses. There just happens to be 300HP worth of air resistance making a net applied power of zero.

I have a program that I made that will backout flywheel and rear wheel "dyno" horsepower using the applied figures from the G-tech.

***Results***
Flywheel Horsepower: 368 @ 5000 RPM
Rear Wheel Dyno Horsepower: 272 HP @ 5000 RPM
************

So what if you take the RWHP figure and divide it by the .83 multiplier (like most dynos do to find flywheel HP)? You get 328 HP. So why did I calculate 368 at the flywheel? Because my program backs out engine inertia. You can see about 40 horsepower is used to accelerate the engine/trans/tire components (the weight of the components) at a fast rate (like on the road in 2nd or on a chassis dyno in 4th).

When you go and dyno your car on a chassis dyno you are getting the rear wheel horsepower. This is your flywheel horsepower minus the drivetrain losses minus the power it takes to turn over your engine internals/trans/driveshaft/rear end etc (INERTIA).

So by my calculations my true engine HP (net) is around 368HP.

:yesnod:

(I backed this up with a data master log using the dyno plot)

 

BTW,

I ran a G-tech 1/4 mile pass.

13.67 @ 109.1

I've run the G-tech at Houston Raceway Park to compare to the track. I noticed the MPH is around +2 higher than the track. Also, you get a roll-out delay at the track (about 2 tenths) but the g-tech starts timing instantly. So to get a good track estimate take off 2 tenths and subtract 2 MPH

**** Corrected ****
13.47s at 107.1MPH

:cool:

 

Good numbers.

My G-tech manual has a printing error and the page for measuring HP is missing. Could you scan that page and email it to me? Thanks.

 

I don't mean to be so negative, but that G-tech isn't worth crap. I tested it at the track and it was nowhere near the numbers I actually ran.

The G-tech will show a higher MPH, usually by 4 mph because the track averages the speed for 66 feet.

The HP calculator is way off also.

If you are making 368 hp, you should be going faster than 109 mph.

I went 109 with my stock LT1.

The G-Tech is good for making comparisons on mods, but to use it to obtain 1/4 numbers and such, I wouldn't trust it.

 

Realistically your not making 368HP with the mods listed on your identity page.
But the rest of those #s look good. That's about what mine should do :cheers:

 

i want a gtech

 

An engine dyno measures the flywheel horsepower. A chassis dyno measures rear wheel horsepower. These are useful numbers. There is no reliable correction factor to compare one with the other. Only, general rules, which can vary, considerably. The real proof is in the vehicle performance. What purpose is served by backing out engine inertia? Maybe you should just measure the amount of fuel consummed, and figure the potential energy used. Think of all the inefficiencies you could eliminate, besides engine inertia.

We race cars...not dynos. Or in this case, calculators.

 

I don't know why you are doing all the math to calculate the HP. The G-Tech Pro has a specific mode for that.

The G-Tech Pro is accurate. See the results I have got. This is another repost of mine.

"it is a piece of crap", right! :rolleyes: You decide. Here is my drag strip runs while I had the "G-Tech Pro" connected. The G-Tech Pro mph is always high due to the drag strip averaging the mph at the end. The G-Tech Pro shows your true mph.

Timeslip - 13.699 @ 104.94
G-Tech Pro - 13.63 @ 110.3

Timeslip - 13.746 @ 105.22
G-Tech Pro - 13.79 @ 110.5

Timeslip - 13.678 @ 104.89
G-Tech Pro - 13.68 @ 110.0

I had a friend at the strip that was bad mouthing the G-Tech Pro for a long time. It was priceless to see his face when I showed him the timeslip and the G-Tech Pro on each pass!

As for statements like "it is a piece of crap", all I can figure is the previous model "G-Tech" may not have been too accurate.

I am not saying the G-Tech Pro is a replacement for the strip. Getting a G-Tech run somewhere other than a drag strip simply adds all sorts of variables into the equation. If you are not a the strip then the G-Tech numbers are not going to be very close.

Like others have said, it is a good measuring device for baselining the car. Then as you do mods you can see the difference without going to the strip.


[Modified by ericcer, 7:30 AM 5/20/2002]

 

Have you seen the new competition model that's comming out in the fall?
http://www.gtechpro.com/competition.html


It's in the latest MidAmerica Catalog
Trying to find out if it will give you a track map?

 

YOu guys might look at Race Technology AP-22 and AC-22. I have found it to be more accurate than the G-tec by far. It is a nice tool to see if your mods are giving you anything but is not a replacement for a dyno or the 1320. I live in BFE so it is hard for me to get to a track or a dyno.

http://www.cb-racing.com/rt-index.htm


[Modified by Rob90, 10:35 AM 5/20/2002]