Racer, please try not to quote me using your words such that it is difficult to distinguish who said what.
MPH is (respectfully) BULLSHIT. You can stick a 4.88 gear in a 3600# car and have it run mid 12s at under 100 MPH. How much HP is that? Math says 260-ish RWHP. Somehow I'm thinking that a big block 427 is making more than 260-something RWHP.
I've seen funny cars go up in smoke down the track and run only 140 MPH. How much HP is that? What is being measured, how much traction is lost going down the track? A friend of mine runs 7.20s in a 3200# car on 10.5W tires smoking them the entire length of the track. How much power is he making?
A dynamometer is by definition a device for measuring mechanical power. From the available torque, horsepower is calculated using engine RPM and simple math.
Try not to tell me what I should know or not. I stand by what I said. A dyno is the best way to tell power. A POS dyno is just as good as a POS anything else.
I think that the point some may try to make is that the actual numeric output from a dyno is not to be compared to other dyno figures, as was stated previously "take dyno figures lightly." I read this to mean that dyno output figures vary between different dynos. From the perspective of one guy makes XYZ power at ABC dyno and EFG power from OPQ dyno, the numbers are meaningless. One the same dyno, assuming that it is fairly consistent, the measurements can be used to properly tune the vehicle for best power given the dynamics of the environment.
Maybe some hardware out there sucks, and yes, we largely use DynoJets for chassis dynoing in Arizona. However, my comments are related to all dyno types whether engine or chassis.
They are the only way to accurately measure engine power, when properly calibrated and used by an astute professional. Any bloke can misuse even the simplest measuring device. I don't suppose that anyone here ever cut a board too short in their lives, regardless of what they "should" know or not.
Your argument that driver ability and chassis setup doesn't adversely affect MPH is BULLSHIT. Try this. Launch your car at the lowest possible RPM to get it moving. Stay in first gear the entire length of the track with your foot mashed to the floor and the engine bouncing off of the rev limiter. What happened to your MPH and how much power did your engine make? I'm guessing that your MPH will be WAY OFF. Are you saying that your engine makes more power in 2nd gear than 1st just because it allows the rear wheels to turn more rapidly?
As a racer, I know what you mean by using MPH to see if your power is off, but it is still very dependent on known good data and consistent driving ability AND making a good run down the track. If you don't think that driving affects MPH, get out of the groove and see if your MPH slows. It will, as will your ET. It doesn't mean that you're making any more or less power. MPH just tells you how much power you effectively used, not how much power you've got available.
One day on one of my blown big block cars, I jumped the boost up to 22% over driven, ran both sides of the track repeatedly as a result of traction loss. Had this whole "S" thing going down the track. I don't think it got over 100 MPH without me having to brake to get it to return somewhere near to the middle of my lane. It was probably making about 1150-1200 HP on that day, certainly more than enough to overpower the chassis. Still ran like an 11.25. For a 3500-3600# car, how much power does my 100 MPH pass say that I make? How much will MPH be affected if you stutter and miss a shift? Driving has a lot to do with ET and MPH and bad driving will make both worse.
Quote:
|
Originally Posted by Racer
Being a drag racer, and engineer, i would have thought you would have known that!
|
The more I learn about what is happening during each pass (from data capture/analysis), the more I realize that I know nothing. I've designed dozens of pieces of hardware and written software to support my data collection and analysis of what happens everytime I strap in and light it up. I even built a small, high speed CMOS imager running at 110 frames per second to take pictures of my tires throughout passes. I used a scaled background behind the tire so that I could see how much growth they underwent, how much deflection and distortion due to high speed and wind drag...can you even imagine all of the "tire" data I collected? Several gigabytes of video data alone. I wrote an image processor to calculate the variation in tire size from frame to frame so that it plotted a graph of tire changes for the course of the entire pass. I had such meaningful information as average tire size, peak tire growth and maximum launch distortion values at the end of it all. I tried several different brands and types/compounds of tires. I had a whole slew of information about which grew more/less, distorted more/less and when I was done, I was still left wondering how to actually use all of that data to actually do anything meaningful at all. I even thought about trying to sell it to a tire manufacturer to use in some marketing effort. You can almost imagine a series of still frames of OUR TIRE versus COMPETITOR'S where our's is somehow supposedly better and this picture supposedly proves it.
The truth in knowledge is realizing that you know nothing. What an excellent oxymoron.
:davis:
Linear Mode
