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Originally posted by jimberg:
I can only assume that this is directed at someone other than myself since I didn't disagree with you on this particular point other than the fact that it is possible that if the simulation could be flawed to the point that too much load is put on the car causing you to tune out performance that didn't need to be tuned out.
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Perhaps, but this is where the experience of the person doing the tuning comes into play again. Given the choice, most of my customers would prefer a tune that gives up 10-20hp vs. one that has them changing gaskets all summer instead of driving.
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My other problem is with a prior statement of yours where you said "I will gladly put a car that makes 400rwhp on my MD1750 up against any car that makes 400rwhp Dynojet in a race." If you're implying that your car will win, tell us how it could with less actual horsepower. I'd say it can't unless it was inaccurately reporting power.
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How do we know that the Dynojet is not artificially high is some applications? Just because a larger number of them are in service (probably because they are literally half the price of a load bearing unit) does not mean they are more accurate. Turbo cars in particular are incredibly sensitive to loading for their tune. I have seen turbo 5.0L cars spin the hell out of a Dynojet, but for some reason run mediocre at best at the track. There is a reason for this.
Granted, for the garden variety N/A motor car, a Dynojet isn't half bad at all.
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A dynamometer is a measuring device much like a torque wrench or a thermometer. No matter what torque wrench or thermometer you use, the readings they return should be the same when measuring the same thing. I suppose this doesn't really matter, though, if your only purpose is to make changes to the point that you know if you make more power than you did on a previous run.
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...and much like a good torque wrench, one should be able to calibrate the dyne AND verify torque readings vs. a known force. Since Mustang dynos measure torque directly with a load cell (strain gauges) that can be calibrated and certified, I have a higher confidence in them than a dynamometer that gets torque by extrapolating HP from roller acceleration and again extrapolating with respect to engine speed. Dynojet claim to "measure HP directly", but I have yet to ever see a "horsepower meter" in any instrumentation catalog. Every other accurate engineering power measurement I have ever seen deals with measuring force directly at a fixed distance (torque) and multiplying by speed to find power. Look into how power outputs of turbines, generators, and engine dynamometers are measured...
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It becomes a problem, though, if you are trying to make a statement about how much power you are able to gain by your tuning when comparing it to results of other tuners.
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In all honesty, I'm not too worried about this. We keep a database of all previous runs on our dyno and when a customer returns here, we have no problem showing them gains vs. earlier runs or during a given tuning session. I can assure you that it is very real HP we find when tuning cars on our dyno too.
Once again (and I think I'm repeating myself here), we use the chassis dyno as a tuning tool. Our results do the talking for us at the track and on the street where it matters.
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Greg Banish
President,
Detroit Speedworks, Inc.
'93 LX Turbocharged Road Racer
'00 Bad-Ass F150