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John,
HP is the measure of work and that is what accerates a car. Partly a matter of semantics, but it is important to understand that just because an engine has more torque does not mean that it will out acclerate another. Comparing the acceleration of a Volvo B20 with 120 ft lbs. of torque and only 80 HP with a Volvo engine with 120 ft. lbs. of torque and 120 HP will quickly convince you of the correct anwswer to this.
Okay, looking back to my Physics days, that must be right. It takes work to raise the kinetic energy of the car to a higher level, and HP is indeed the measure of that work.
But I've read time and again in magazines that the area under the torque curve is a better predictor of acceleration that peak HP. So, just to keep it intuitive, can we say that it's torque that moves the car, and HP is a measure of the rate at which torque is applied?
Have just forwarded to you a dyno chart of a test of a B20 with IPD street torque cam and downdraft weber that should illustrate this - 75 Hp 120 lb. torque - dissapointed owner. Will also send test of 120 ft lb. torque stock B20 E.
Ummm, the stock E test shows just over 100 lb/ft at the wheels, not 120. Stock spec is for 130 at the flywheel, so it would take a super-efficient driveline to deliver 120 to the wheels.
The IPD motor shows over 120 lb/ft at the wheels, a big increase, until it falls on its face -- a high peak value, but not much area under the shorter curve. Sounds a lot like my old "How Not To" motor that had a very strong midrange and wouldn't rev above 4200 rpm. My stock B18B was clearly much faster at 6000 rpm.
[dynos measure torque]
On dyno measurement, again, not strictly true. The most popular chassis dynos measure the time it takes to accelerate a given mass, their rollers, to a given speed and that is not stricly a torque measurement.
True only of inertia type dynos, not "brake" dynos (eddy-current, water brake, whatever). Inertia dynos cannot provide varying loads and are useful mainly for full-power testing -- not what I need. Also, the A/F measurement lags the power curve, so they are only partly useful for diagnosing tuning problems. This info is right from either the SuperFlow and/or DynoJet website(s).
On Steves car being able to out accelerate any stock E, I have just sent him a dyno test of an essentially stock E, that showed much more torque - your measure of acceleration.
See above about wheel vs. engine measurements. Nore also that Steve's motor -- mistuned as it is -- has a wider torque curve than either the stock or IPD motors, essentially flat from 2500 - 4600 rpm, where the tuning falls apart. It never really gets to the expected crossover of torque and HP curves at 5200 rpm.
But going back to your Vclassics articles of several years ago on "doing it right", we don't have data yet to show that using Unitek parts is doing it right, any more than there was on using some of the old combinations which data are now showing was "doing it wrong".
Yet to come. I'm not done yet, and Steve's only one step further along. Let's see how his dynos after the new injection is properly mapped.
Dyno readings aside, I can state without any trace of doubt that mine accelerates *much* harder than a stock motor from 3000-7000 rpm.
BTW, I will still pay the cost for you to put your car on the dyno. If you can get a deal like steve's I'll pay for you to put it on twice - once now and once after further modifications.
I've asked for recommendations for a competent dyno place on the Classic Motorsports board. So far, they're all a few hours away. I'll make the trip, but I need alternate tuning parts in hand to make it worthwhile. We've discussed this numerous times, I do believe.
Another related point. Most people would get better results by just raising the compression ratio and installing a knock sensing ignition to take care of any detonation/pinging and leaving everything else stock.
That could well be, but I don't believe we have that data yet ;-)
--Phil
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