HEY! What's the big idea turning my thread into Virus Info Central?!

(BTW: No virus detected here - Using AVG )

Back to cars! You boyz have some 'splainin' to do!

Check out these graphs. The first one is gforce, the second is RPM (cleverly named too).

http://gmthunder.com/tino/z28gforce.jpg
http://gmthunder.com/tino/z28rpm.jpg
(^best of nine samples - others did not have good traction)

This car is an automatic TH350 with a foot-brake stall of about 2200 RPM,
and rated to 2800 RPM by the MFG.

I couldn`t do a sample from idle to peak HP because the torque converter
would flash and my tires would light up. Even with a loaded foot-brake,
it was no use.

THe tests were done in first gear again, rolling start at 2500, 2800, and 3000 RPM.

At 3000 RPM, the tires broke loose very violently. This run was eased into
the throttle which yielded the smoothest curve, and best traction until about
1.2 seconds into the sample.

The dips in the g chart represent tire spin.

The dips in the RPM chart indicate when I let off the throttle to save the
car from fish tailing. The RPM graph also shows at what RPM I punched
the throttle with corresponding colours to the g graph lines.

You will notice that the black line is the strongest 'g' reading and I eased into
the pedal somewhat to keep traction (which didn't work well).

Two things I`m seeing:

1. The starting g`s are highest at 2800 which is above my torque peak.

2. The g`s get higher as my torque curve gets lower...and my tires begin to
lose grip as the HP increases.

What`s going on here?

I`d like to take some more samples earlier tomorrow night when the roads are somewhat
warmer to keep traction.

 

I've started to say something in this thread a few times, but i've yet to see the question stated clearly. so show me a clear question and i'll try and help as best i can.

 

It's the old "HP vs. Torque" debate again (sort of)...but this has more to do
with torque placement over RPM because we all know HP isn't a force!

Question is:

Do vehicles accelerate according to their torque curve, or do they accelerate
according to their horsepower curve?

 

well your real world testing is flawed imho. the rpms are directly tied to mph and as mph increases the external forces mount against your engine in an exponential way. so obviously your higher rpms are at a disadvantage from the start as far as applying g's or accelerating the car.

otherwise my feeling is that horsepower is the answer, since its a "block" of work done in a certain amount of time (dictated by tq). and it takes x units of work to move your car from point A to point B. in a vacuum i think your acceleration would follow your hp curve really closely the faster you do the work the faster you get from point A to point B.

 

Feelings are nice, but in any given gear the acceleration is proportional to torque, not hp.

Rich

 

If the tests are flawed, give me some ideas to change my testing.

The accelerometer graphs are showing an increase of g's as my torque is falling.

 

If your Gs are increasing, the torque at the rear wheels is increasing. Between your assumptions about the engine's curve, the torque converter, and traction, I think the test is just flawed (in terms of trying to learn something). A car will accelerate according to the torque at the rear wheels, which SHOULD track torque at the engine. Horsepower is so we can take advantage of gearing. It doesn't tell us JACK about the acceleration *within one gear.*

I.e.
300lb-ft @ 2000rpm (engine) with a 1:1 final drive is 300lb-ft at the wheels @ 2000rpm

300lb-ft @ 4000rpm (engine) with a 1:1 final drive is also 300lb-ft at the wheels @ 4000rpm (we're moving twice as fast now).

The two above examples will be accelerating at the same rate at their respective rpms, barring all kinds of real world losses.

This is the gearing part:
300lb-ft @ 4000rpm (engine) with a 2:1 final drive is 600lb-ft at the wheels @ 2000rpm.

This one will be accelerating twice as hard as the ones above.

Torque at the engine was 300lb-ft in each instance. But the 4000rpm one had twice the horsepower, and when we used gear reduction, we got twice the torque at the wheels.

Within the same gear, the car will accelerate the hardest at the torque peak (at the road).

If we get to choose the gearing (i.e. gear it down), the car will accelerate the hardest at the engine's horsepower peak, because it's doing more work per time, even if actual flywheel torque output is down.

Easiest I can explain it.

 

These are not assumptions.

I have a dyno graph. I know the MFG rating of the converter, I also know the
'brake stall' point.

The traction loss is obvious because the rear end of the car slides out.

The g meter is showing increases in g while the the dyno torque curve is
falling.

What I'm going to try this evening is a standing sprint from 0-60 MPH.

I expect to see the highest g force at the launch, and have it roll off as
the car begins to move forward.

This goes against what I'm seeing when I punch it from a roll (see g meter
graphs above).

Still open to suggestions for testing.

 

This sounds simple. The tires break loose at or around the torque peak, and as we all know, kinetic friction isn't as good as static friction, so it pushes the car less. Then, as the engine spins up, its torque output falls, which allows the tires to hook up and push the car harder.

 

Tino,

When I said, "If you can record data from the G-tech, do a number of pulls in each gear recording each separately. Plot the acceleration (longitudinal) g vs. mph, convert the mph to rpm for each gear and compare to your dyno torque curves." I thought you had an manual trans car. Unfortunately that's not the case.

Don't get lost here. The torque converter really complicates trying to calculate back to what the engine is doing from acceleration measurements. Remember that the TC is multiplying torque especially when there is a large difference between engine (TC input) and trans input shaft (TC output) rpm. The multiplication ratio changes dynamically (and dramatically) with load, rpm and input torque. There's no way you know exactly what that is, except maybe the TC mfgr. gives a Stall Torque Ratio, which only applies with zero output rpm, before the drive tires start turning. You are not going to be able to tell much about the engine with the g-tech and an automatic, IMO.

As I predicted, this is getting into a "hp vs. torque is what does the job" discussion. That's not all bad, but, like every time this occurs, different folks have different ideas on how the world works. That doesn't mean the "world" (aka Ma Nature) does what we think...we have to try to figure out how she actually works. To quote my favorite source (myself ), Mother Nature is a practicing physicist.

"And the beat goes on..." S. Bono

 

Does anybody disagree with what I have said and the examples I have given?

 

I'll take some more samples as you suggested Jon.

I don't feel the converter is slipping, or multiplying torque at this stage.

If so, it would have shown the same result on the dyno graph correct?


Even though the tires are breaking loose, there is still an incline for the force
before traction is lost which doesn't resemble any part of the torque curve.

I really appreciate the feedback, and I hope I'm not coming across as being
difficult...but you have to understand that my results aren't adding up and
it's frustrating.

One difference here is the dyno was taken in 3rd gear; I'm doing the tests
in 1st gear to stay within speed limits.

A second gear pull will certainly take out the traction issue. I'll have to find
a highway on-ramp and a section of highway that is fairly level and straight.

You boys can pay my speeding ticket if I get caught.

 

You had a good start with "A car will accelerate according to the torque at the rear wheels."and "If your Gs are increasing, the torque at the rear wheels is increasing." Unfortunately you deviated from that thought. No offense intended, kevm14.

Unless a lockup converter is fully locked up, your "feelings" are not correct.

Zero, I don't think you are using a lockup TC and if you are it's not locked. Please do some studying of how a torque converter operates.

Uncontrolled tests give very little useful data. Wheelspin and torque converter slippage/multiplication makes your tests uncontrolled, IMO.

(I was being nice, by not saying, "Uncontrolled tests give useless data.")

'Bout time to change the subject?

 

No, it's not a lock-up type. I was afraid someone was going to throw that
into the equation despite my attempts to keep the converter loaded throughout
the samples.

We can change the subject if you like, I'm not trying to change science
with the purchase of my g meter.

 

I hope I am not comiong across as too critical or doctrinaire. You deserve kudos for actually getting data on this and trying to make sense of it. The problems you are having shows that designing even a "simple" experiement is complicated and is illustrative of why the "basic" laws of physics took a genius (one I. Newton). I can remember back to undergrad college physics lab where we had to do simple experiments to illustrate basic principles of mechanics. From our data, it was quite hard to prove what we already "knew".

In science, sometimes going back and repeating older experiments with better equipment will reveal incongruities in the data and eventually to a different theory to explain the data, thus proving the orignal theory wrong. Alternatively, someone coming up with a new experiment to verify something already "proven" may find that what was proven is, in fact, false.

So, again, kudos to you. But as a physics experiement it simply has too many variables to shed any light on "what gets the car accelerating faster, power or torque". If you look back at the definitions of the two terms, you can see that if the variables were eliminated, the fastest acceleration would occur when maximum torque was being exerted at the rear wheels.

Rich