If you've g-teched your s2000 for horsepower, what weight did you use and what horsepower did you get out of it?

I did mine tonight (also posted under the hood) and got an average of 190hp and max of 200hp, but I had no clue about the weight so I used the GRVW on the door. These results were based on 5 runs to redline in 3rd gear. I just want to see if anyone's come up with anything similar.

 

I think you should subtract 400 lbs from the GVWR. The 2002 and 2003 brochure list the curb weight as 2810.

 

You need to add your weight to the GVWR man...

 

GVWR is the gross vehicle weight rating. The MAX weight with all liquids full and a full load of 400 lbs. of passengers and luggage. If the tank is full and you weigh 400 lbs. it is the number to use.

 

Ok so let me get this straight:

Curb Weight - 2809
Gross Weight - 3385
Total Weight (full fluids / no extra load) is 3385 - 400 = 2985

That means we're cruising around with 176lbs of fluids in our cars? I guess that works.

I just recalculated my Gtech horsepower for the new weight value and came up with a peak HP of 184.3. Now this doesn't take into account loss of HP due to drag (running the car in 3rd gear to redline). Does anyone know how much to add for drag, or if it's already calculated into the Gtech?

 

Fluids don't weigh that much. Full tank of gas is approx 80 ilbs, radiator holds another 15 or so. Add a few (but not many) for W/s washer, diff and tranny and you have about 100 max. For G-tech use, I'd use curb weight plus your own weight plus 50 for 1/2 tank of gas, 100 for full tank. That's close enough.

 

You could start with your gTECH horsepower figure and multiplying that by 107% for 197.2 hp
My guesstimations for my own S2000 seem to show a drag factor of around 7% which is higher than other cars I've owned but hey...the S2000 isn't very streamlined in the front with regards to its .cd rating...look at the windshield rake (or lack of).
My Camaro SS' GTECH drag "rating" was around 3%.
Best way to do it is simply do a dyno run and then a series of GTECH runs and compare the difference. You'll have established a baseline drag factor.
For instance, I dyno'd my SVT Contour bone stock and got 170. My first series of GTECH runs were in the 162.5hp range so I figured at the top of 3rd gear at speed, the gTECH hp rating was
being affected by drag somewhere around 5%.
For subsequent testing, I always took the gTECH figure and multiplied it by 105% to "simulate" a dyno run. Several months later after doing some mods, my gTECH rating prior to having the car dyno'd was averaging around 179.5hp. Took it to the dyno and got 188.7 hp. The difference between the gTECH and dyno? You guessed it...just about 5%. The car's .cd rating didn't change (no air dams or front spoilers installed) so why would I have expected the drag factor to change (as long as I was using the same gear during the gTECH runs). Then again, I'm sure there are atmospheric conditions which may have affected the testing parameters but I never saw any significant changes in hp readings when I tested within 10 degrees of each other. Obviously you can't compare a winter run with a summer run. For each 10 degrees of temp difference, I've noticed a 1hp change in the car's performance. My car now, as long as the roads are clean and free of snow/ice, runs as if it has some hidden modification somewhere. Today, it's nine degrees outside. The S2000, once warmed up, will run like it has 10 more horsepower than it did four months ago. Even my girl has commented on the difference and she hardly pays attention to these things...it's THAT
noticeable. I'm going in for the car's first legit dyno pull soon but unfortunately, it will be far from stock. At best, I can cull some dyno #'s, go out and run some hp gTECH pulls and figure out how much drag is affecting me. I'm guessing it will be close to my guess of 7%.
BTW, any truck weighing station will gladly weigh your car...it's not a big deal for 'em. Accuracy for weight is important for these hp runs. You should have one or two in your area, especially if you live near the interstate.

 

Great writeup Russ, thanks for the info! I'm going to take my car to get weighed this afternoon and repeate the runs.

 

no need to "guesstimate":

Find a flat road and get your car to more than 60mph. Select neutral. Measure the time it takes to slow down from 60mph to 55mph and record it as time1.

Repeat the process but now measure the time it takes to slow down from 15mph to 10mph and record it as time2.

You can now compute the Cda, that is, the coefficient of drag times the frontal area (in square meters) by inputting the car weight in kgs and the previous measured times:

Cda= (Weight*(time2-time1))/(169*time2*time1)

Now, lost horsepower is a function of the Cda and speed and is given by the following formula (with Cda in square meters, speed in MPH, and power in HP):

Lost Power = Cda*Speed*Speed*Speed/13596

An example:

Assume it takes 5 seconds to drop from 60 to 55mph, and that it takes 13 seconds to drop from 15 to 10mph. Assume the S2000 weighs 1260kgs.

Your Cda is = 1260*(13-5)/169*13*5 = 0.93

Now if you want to calculate your lost HP at say, 60mph, you get:

Lost power = 0.93 *60*60*60/13596 = 14hp. For any other speeds just substitute 60 accordingly.

Now, this is accurate but pretty useless in your case. Why? I don't believe the g-tech does not try to compensate for aerodrag in some fashion. To see my point, just try to calculate how much HP is lost at 120mph using the above formula...

My advice would be to throw away the Gtech and get an AP-22 . You can input the Cda, the rolling resistance and a few other correcting factors and get much more meaningful results