Guys, I don't know whether this is the correct place to ask or not, but I don't have someone else to ask.
I've been reading a lot about all that torque vs HP, and gearing and such stuff, and the result was that I got a brain fart. :cry:
So, here are my questions, please be kind enough and give me good explanation.

1- How does different cars (or same car on different runs) gets the same ET with different trap speeds?

2- How do spinning tires or not spinning affect the 60ft, the 0-60 mph and the 1/4 mile (ET and trap)?
I remember that Z06 guy (probably he was called J-Rod) who got the best ET for a stock Z06 (11.96?) saying that turning off the TC and spinning a little enhanced the 60ft., how?

3- What's the best way to do powershifting, and what gain does it give?

Hope you bear my questions, but pleeeeease, I need answers badly.
I'm sure people here are with enough experience and will answer me good enough. :yesnod:

 

There must be a 1000 posts just here in CF Archives that speak on this subject. If you do a search, you'd be busy for a long time reading what people have to say on this subject. But since i dont mind talking about it any time, i will chime in:
1. ET's are a true measure of gearing, traction, weight, driving skill, etc., more than a true measure of a car's power. you can take a car and simply change the gears in the rear end and improve ET drastically with everything else being the same.
2. Trap speeds are more a true measure of engine power. It takes x amount of hp/tq to achieve certain traps speeds with less regard to traction, gearing, driver skill, etc.

so, in theory you can pit two cars against eachother, one that trap's 110mph regularly and one that traps 120mph regularly and it would be possible that the 110mph car can beat the quicker car ET-wise if it has superior gearing, traction, weight ratio, driver skill. Case in point: I regularly see a TT Supra that dyno's 600+ rwhp only manage mid 11's every time he runs even though he traps over 130mph. This is because his power band is abrupt and narrow, gearing is terrible and driver skill leaving something to be admired. I have seen some old iron trailer queens ET in high 10's with only 114mph traps. See the picture yet?? a great drag car will be able to apply a broad power band with a flat torque curve to the ground quickly through gearing and tires matched to motor & vehicle weight, along with consistent driving.

On the powershifting- i wouldnt go there. Powershifting really hams up these cheesy transmissions in our C5's.



[Modified by rwj383, 2:44 AM 1/7/2003]

 

Well put rwj383. :yesnod:

 

By accelerating differently at different parts of the track.

You really need calculus to start looking at it in detail, but for simplicity's sake, let's just look at four blocks of the track.

1st, 2nd, 3rd and 4th gears.

You can accelerate differently in each of the gears, and end up with a different trap speed, even though you take the same amount of overall time to get there. Kind of like a trip with four legs. If you average a faster speed on the second leg, but a slower speed on the 4th leg, you may arrive in the same time as another trip with different speeds on each leg.

This is not immediately intuitive, but if you do any drag racing, you will eventually see that it is true. As a general rule, spinning gives you higher mphs. Why? Because even though you are accelerating the same DISTANCE on each run, you are spending more TIME accelerating on the run where you spun the tires on start up.

During this extra TIME, you store energy in your wheels and tires that is eventually (when you get traction) added to the run, and shows up in the higher mph at the top of the track.

HP determines TRAP SPEED, and HP is a measure of TORQUE over TIME. So more time gives you more power.

I'd settle for speedshifting myself. If you want to powershift, wait until you have mastered speedshifting first.

Some of the fast guys here swear by powershifting (WOT during the shift) but I don't know HOW they don't hit the limiter. I used to power shift my Mustang Cobra, but the rev limiter was somewhere around 6,100 and the car shifted around 5,500 so there was plenty of headroom for me to powershift without banging the limiter all the time.

Shifting VERY fast will probably be plenty for you for a while. Speed shifting just takes PRACTICE.


[Modified by Tom Steele, 12:43 PM 1/7/2003]

 

Remember the ET game is fractions of a second. Any deviation in what driver does from one run to another can make a difference in ET. My understanding is that power shifting can be worth .10 or a little more.

Spinning at the line will usually slow you ET. Comparing it to traction control on is not fair as TC is designed to slow you down so you don't spin. TC off and no spin usually is a better et than TC off with spin. The definition of spinning is relative also. 1/2 revelution I would not consider spinnig.

Spinnig tends to yeild a higher MPH trap, something to do with momemtum.

Spend some time the Drag Racing section here and on the tech sections and more will come up.

Other good resouces are http://www.staginglight.com and http://www.prestage.com

 

speed = distance / time
velocity = speed at a given moment
acceleration = rate of change in speed at a given moment

The mile per hour that is on your time slip is really your velocity at the moment you are passing the end of the 1/4 mile.

If you calculated speed for a car that covered the 1/4 mile in 10.00 seconds, you would get the same value of 90 MPH regardless of wheel spin or horsepower. But, one car may be accelerating more than the next one running the same ET.

 

Imagine you took a 60 mile trip that took you one hour. Your speed would have been 60 MPH. But, you could have stopped along the way for gas and changed a flat tire. Then you must have been going faster than 60 MPH at some point (velocity) to still cover the 60 mile trip with in one hour (speed). The 1/4 mile time slip is the same thing except it is a shorter distance and a lot less time. Each gear shift or whatever is similar to the stops you took along the way during your trip.

 

:iagree: Consistency is the key once you found what works best with your particular car. Wow, I'm glad you guys explained the rest!! :cheers: :chevy

 

Now, that is way helpful.
What I was looking for was the physics and not the facts on the track, and I'm aware now of the guide lines.
Actually that prestage site is very nice, I'm still viweing right now, and I'll search for more on that topic in the CF.

So to make sure I understood well, look at this example and tell if it's correct or not, so imagining we have to cars that end up with a similar trap of 130, and the 1st car yields a 10.5 ET while the second yields an 11.5 ET, that's because the 1st car kept accelerating hard through all 4 gears so it reached their faster with the 130 mph, while the other one didn't accelerate as hard in all gears, maybe slow on the 1st 2 gears and harder on the other gears so it yielded the same trap, while with a lower ET because of the delay in the first two gears.
Correct? Am I getting it right?

Well, now other two questions appear:
1- What's responsile for a fast rise of the RPM, i.e. if I'm for example in the 2nd gear and no traction problems then WOT, what makes the RPM rise (car accelerate?) faster in a car than the other?
2- That's the final question I pomise :D , I don't understand the saying that says: "It is better to make torque at high rpm than at low rpm, because you can take advantage of gearing."

Thanks folks, you were such a help.
Corvette owners rule. :cheers:

 

Man that was info. :D :thumbs:

 

Actually, I believe it is the average MPH over the last 60 feet to the finish line.

:cheers:

 

You are correct, the MPH shown on the slip is the average MPH taken at various points within the last segment of the track. Most tracks will show this area by white lines for the last 60 or 100 feet. Either way... the MPH is your average MPH for that segment.

 

1) Power. More torque is the only thing that will make more power and more power is the only thing that will accelerate your cars faster than it currently does.

2) As for torque and RPM's, it really depends on your constraints and goals. Since the topic here is drag racing and not driveability, it is generally better to make the torque at higher rpms - this is assuming, however, that you have the freedom to match the car's gearing to the torque curve. While it is true that torque is the force that accelerates your car, horsepower is a better number to pay attention to. For example, if two otherwise identical cars have different engines, each with the same amount of avilable torque over an equally wide operating range, but one motor's range starts and ends 1000rpm higher than the other motor's, the higher revving motor will have more horsepower. Although these motors have the same amount of torque, you have the option of running lower gearing with the higher revving motor, and suddenly the torque applied to the pavement is more with the higher revving motor. If, on the other hand, your goal is to make your C5 faster in the 1/4 without changing gearing, then more torque at lower rpms would be more beneficial since the C5's are a little overgeared for drag racing.

 

Absolutely correct... MPH in 1/4 is an average of the last 60 (or 100) feet.

I like my 114-115mph 1/4 mph.... not bad for a 2002 C5 Coupe with just an exhaust....

"It does not matter if you win by an inch... or by a mile! Winning is the only thing that matters!" Vin Deisel from Fast and the Furious.

 

Wow, that exhaust got you around 375 RWHP then!

 

Oh yes, that explains things well.
Thanks for the answers, I could claim I know everything about the topic now. :thumbs: