I'm using Craig's software to datalog for tuning. Do any of you use the 0-60 and 1/4 mile functions? I've been using the 0-60 as a performance meter for tuning changes. I assume it triggers when the wheels start rolling and triggers again at 60. Am I correct in assuming that I could be producing worse than "real life" times because of wheel spin, but could not produce faster than real life times? I'm down to 4.8 and even saw a 4.7. The car definately feels that strong, but that would put it in pretty good company according to the current magazine tests of different sports cars.

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'87 Formula WS6 - ZZ4 Crate TPI, SDPC ported heads, LT4 hot cam, 1.6RR, Accel runners, Accel lower, ported plenum, Edelbrock 58mm TB, pulleys, SLP cold air, SLP headers, !cat, Summit exhaust cutout, Walbro 255, Koni yellows, aftermarket panhard & LCA's.

[This message has been edited by Steve10 (edited August 30, 2001).]

 

Any computations based on the VSS are suject to a multitude of small errors, and when they all stack up right can be miss leading.

On the optical VSSs they only pulse 3 times per tire rotation so there is a varialbe of 2' before before the tire turns, tire spin can fubar the reading.

Now with that said, they can be used very successfully for noting general trends, and then that gives you a head start when you get to the track and can be more accurate.

I've been using a VSS timer for tuning (roughing things out like I mentioned above) for oh about 8 years now.

 

Yeah, pretty much. I forget what I ended up doing, thought I had a trigger speed (like 3mph) to start the calculation so it would ignore the initial launch. Then I thought I put in a linear extrapolation back to zero time/MPH based on the acceleration curve subsequent. Know what I had in mind, but unsure what ended up in the code. Guess I could look?

That being said, a linear extrapolation back to zero time-distance is pretty reasonable and doesn't introduce significant error beyond what is already present.

Interpolation is also used in determining threshold events through time elsewhere. For instance, if at 5.56 seconds you are traveling at a speed of 57mph and at 6.56 seconds you are clipping along at 63mph then the program calculates that your 60mph time is right at 6.06 seconds. Since data is only logged as it is refreshed at the ECM, and assuming that the ECM data is timely with respect to the actual performance, the interpolation techniques will avoid to some extent gross introduction of error. These same techniques are utilized for distance (time-integrated speed), time (PC clock), and speed (VSS). You have essentially a speed term (U) and a time term (t). Distance is the integral of U with respect to time, since U=dx/dt, separating you get dx=Udt. The definite integral bounded in t with corresponding values of U will give you the change in distance. Since time intervals are typically quite small (0.1s), U can be assumed as constant at the average of its values at the beginning and end of the intervals.

Then you've got acceleration, or dU/dt. Comes right from the measurements, but you don't need it for the time/distance relations. When we get into power and torque calcs though, it's there for ya. What is it, F=ma=(3400#)*(dU/dt), W=F*dist=3400#*(dU/dt)*(Uavg*(t-t0)). Don't know, I'm no mechanical engineer.

When coupled with the zero-time intercept determination, the interpretation comes pretty clean, as clean as it can with what you get. Wheelspin will introduce error no doubt. If the threshold time or speed is specified appropriately and the back-extrapolation carried out properly, the error introduction can be minimized.

Caveats include the difficulty in identifying wheelspin and excluding it, and the fact that acceleration through wheelspin does not have the same speed-time curvature as that of hooking up. So the extrapolations back to zero could be in error. One solution? Get some meatier tires! Another? Wire in some kind of phantom VSS at the front wheel and feed the signal in to the ECM instead of the regular VSS. Cross-check the program results against a GTech. I did and found my VSS was off by like 10%. So my 1/4 times on the way to work (open road, no traffic of course...) were closer to 97 rather than the 88 reported by the program.

Hope this helps some in understanding, didn't mean to get too off track in the ramblings.

-Craig

 

Nice work Craig......

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1987 GTA L98 MD8 GH3
355 '97 Vortec 4-bolt block, TRW(suck) forged pistons 10:1 CR, TFS 23*, LT4 Hot Cam, Ported plenum and intake, SLP Siam Runners, BBK 52mm TB, Edelbrock TES, gutted Cat, Flowmaster, CAI w/K+N cone, AFPR, TB bypass, !AIR, !A/C, !EVAP, ARAP, 2300 stall, Alum. Driveshaft, Hotchkis STB, '99 Camaro seats.

Coming Soon!!: Fourth gen 3.42:1 rear, Spohn LCAs and Panhard.

 

In my tinkering, traction was the key to things. I had to kill alot of the low end performance (under the stall speed of the conveter), to get the car to move rather then light the tires.
I was ignoring the first 3 tire revolutions, and even then at times I'd get a bogus time. If you want accuracy, I'd go for like 10-60. Interpolating backwards means assuming the converter's operation is linear, traction is linear (even just as a matter of tread heat, it's not).
If you want accuracy then, an ABS sensor ring (on a front tire)would be the trick.
ALso with a 0-60 your *hoping* the tranny shifts exactly the same.

Not saying what your doing is bad, just, that it's a tuning tool, not a statement of fact of what the actual 0-60 is.

 

Thanks for the comments guys. I'm not looking for exact accuracy, and it is working for tuning purposes. I'm going to save the money on the Gtech and apply it toward some drag radials, then prom burning stuff, then the 24lb inj., then the Superam, then...

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'87 Formula WS6 - ZZ4 Crate TPI, ported heads, LT4 hot cam, 1.6RR, Accel runners, Accel lower, ported plenum, Edelbrock 58mm TB, pulleys, SLP cold air, SLP headers, !cat, Summit exhaust cutout, Walbro 255, Koni yellows, aftermarket panhard & LCA's.