Poor Man's Dyno

Here I am putting my 2 years of engineering schooling to work! I made an excel spreadsheet that calculated Horsepower based on a video that I took of my car accelerating. Here's what I did:

1) Got the Gross Weight of my Tbird with myself and camera man in lbs
2) Converted weight into mass in slugs, weight/32.2
3) Video taped a 2nd gear pull from 0-70~(whatever redline was lol)
4) Every 1 second interval I recorded my speed. To be more accurate one should do 1/2 second intervals or smaller
5) Converted MPH to ft/s, which is mph*1.4666
6) Found Kinetic Energy of the car, which is (mass/2)*velocity^2
7) Found the change in kinetic energy over the change in time (Ke1-Ke2)/(T1-T2)
8) Converted the power units given there into HP which is That Number/550

To find RPM, since I only recorded the Speedometer, I used the rear end ratio, 2nd gear ratio, and the tire size to find RPMs. Attached are my results (btw the weight is an estimate. Any ideas what an 89 SC manual with 2 170lb adults and a 10"sub and amp would weigh? 1/4 tank of gas) I spun the wheels a little bit around 40mph on one of the pulls, think I hit a tiny bit of gravel. Here's what I've done to the TBird:

Cold Air Intake
76mm MAF
75mm TB
94 Blower with 89 pulley
42lb injectors
Cut out resonator

Haven't gotten a tune yet But this seems to be right on the money

PS When I figure out how to calculate Torque I'll let you guys know.

or you can use a gtech pro.... same thing thats doing.

Yes but mine is still cheaper :-D In case anyone is curious, I also found the formula for Torque. Torque = (HP*5252)/RPM

In my case I'm hitting 288 torque in what I did. However I never had a reading at what I think my optimum torque range is, so I believe its a tad bit higher.

so would you be able to come up with anything in a 0 to 120 run i did(using first thru third)? i have mph and rpm in the view.

Results will more than likely be higher if you did your calculations correctly as we arent accelerating a vacuum

XxSlowpokexX said:

Results will more than likely be higher if you did your calculations correctly as we arent accelerating a vacuum

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I tried to factor in drag but I need to do more tests to calculate drag. I'm going to drive up to 60 then just coast in neutral and do calculations to see what its costing me. I've heard that cruising at 60 costs approx 15-20 hp, but thats just a rumor. Plus I think I might have under weighed my car. Its just a guess. 4200 lbs sound right? Quarter tank of gas, 2 adults, and subwoofer with a big box and amp. Maybe a little more?

pbdevastator said:

so would you be able to come up with anything in a 0 to 120 run i did(using first thru third)? i have mph and rpm in the view.

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I imagine you could, but I found it a lot simpler to just do one gear.

Cd of our cars is .28 so just plug it def equ.

bowez said:

Cd of our cars is .28 so just plug it def equ.

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Well I was using Wikipedia, and it said .31... either way, thats not a giant difference and I ended up not calculating power draw due to air anyway. I'll just pretend its significant to make my car sound faster haha

sts70004 said:

I imagine you could, but I found it a lot simpler to just do one gear.

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Its the only recent in dash video i have, and its before i took 500lbs out of car, so it is still a little older. but from 70 to 120 is all 3rd gear, thats the best i can do.

link is http://www.youtube.com/watch?v=K6U7B00UzMQ

Let me know if its worth trying or if its not in 1 gear long enough.

Well here's what I come up with, not sure if its accurate or not lol But does that sound right? What have you done to that car? 369hp?

sts70004 said:

Well here's what I come up with, not sure if its accurate or not lol But does that sound right? What have you done to that car? 369hp?

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I forgot to ask if your numbers is rear wheel HP or flywheel HP. This link http://www.sccoa.com/forums/garage_vehicle.php?do=view_vehicle&id=215 has most of my mods listed, few still not listed. Again video was taken befofe weight reduction. As for my dyno, aod was shifting into OD at 4400rpm on the dyno, so couldn't get a good pull to get a number. Other cars with simular mods are around 320wrhp i hear. It did however get torque, so im interested to see what you come up with that too.

Thanks in advance btw.

Well I think I ran your calculations assuming the car weighed 4200 lbs... so if you have a more accurate weight I could get you a little closer. And its at the wheels I'm measuring.

curb on it was 3701, it has moonroof, power everything, and duel power seats up front. I weigh 155. I figure at the time with all that and me in the car prolly around 4000lbs. btw torque on the dyno was 357 at the wheels if that helps you out. Let me know if there is anymore more info i can provide that could get you better readings. Thanks again.

I think I screwed up the torque calculations... but the HP ones are reading about right...

Attached is calculated for 3900 and also for 4000 lbs

What it gave me for torque was over 400, but at like 4000 rpms. Do you think thats right?

numbers seem high for rear wheel for my setup prolly, and too low for flywheel. The only sure thing i have from dyno is the torque.

Well maybe I forgot to change one of the constants. I'll start over from scratch here in a bit and see if it does better

Oh I just had a thought. I've run into youtube videos that are sped up by youtube, so that 1 second on the video is really like 1.1 seconds in reality. If that happened, it would skew your numbers... I had to make a calibration run on my video. I played a 400hz tone through the radio and then recorded that with my camera to see if the tone was the same when replayed. Perhaps youtube has accelerated your car.

Ill compare my video i have to the youtube one tomorrow and let you know if its different.

I checked and timed my original video 70 to 110 and compared it to youtube version, its the same amount of time.