What happens when you floor the gas pedal – Part 1

[LS1GN]

There are a number of events that occur within a split second of you stomping the throttle in your car. Understanding these events can help you with building a quicker car, utilizing the power you already have, and avoid wasting money on things you don’t need.
These principles will be true for most v8 RWD cars, but let’s assume that the vehicle is a G body with a warmed-over small block v8 which is making (with bolt-ons) approximately 300 flywheel horsepower.
When you floor it, massive amounts of air and fuel enter the cylinders. The pistons, rods, and crankshaft begin to reciprocate with more speed and intensity. The engine block which is housing, or containing all these explosions is actually not static. It’s reaction is to rotate in the opposite direction of this motion. The rotation will tend to give lift the driver’s side motor mount, and will plant the passenger side. The heads are reacting against the compression in the cylinders.
This twisting motion carries through the housing of the transmission, and any flex or slack in the mounting of these two important items is lost power. Of course, the more rigidly the engine and transmission are mounted, the more NVH is transmitted to the occupants.
You’ve heard people refer to the power of a drag car twisting the chassis? Yes, this is conceptually accurate. The twisting motion of the driveshaft has the indirect effect of applying torque to the rear axle housing. Ever notice how the passenger side tire always seems to spin easiest in a one wheel drive application? With this action the housing will want to lift the passenger side and plant the driver’s side. The opposite of the twisting going on in the front of the car.
Next time I’ll mention movement from a different force on the rear axle, and we will need to address the concept of the weakest link.

 

[pontiacgp]

This twisting motion carries through the housing of the transmission, and any flex or slack in the mounting of these two important items is lost power. Of course, the more rigidly the engine and transmission are mounted, the more NVH is transmitted to the occupants.

power is not lost, there is a few millisecond delay cause by the engine torquing but then again in drag racing you don't start off with the engine at idle and in circle track there is a rolling start.

You’ve heard people refer to the power of a drag car twisting the chassis? Yes, this is conceptually accurate. The twisting motion of the driveshaft has the indirect effect of applying torque to the rear axle housing. Ever notice how the passenger side tire always seems to spin easiest in a one wheel drive application? With this action the housing will want to lift the passenger side and plant the driver’s side. The opposite of the twisting going on in the front of the car.

if it's a one wheel peel then the passenger tire is the only drive tire. The only way the weight on the right will be shifted to the left is with a sway bar.

 

[King_V]

if it's a one wheel peel then the passenger tire is the only drive tire. The only way the weight on the right will be shifted to the left is with a sway bar.

Unless the left rear tire's traction is WAY crappier than the right rear tire... ask me how I know!

 

[LS1GN]

What happens when you floor the gas pedal – Part 2

Let’s think about the rear axles and housing now. The action here will be similar to the physics of the engine block and crankshaft. Imagine looking at the rear axle from the vantage point of the passenger side of the car. The axles will be spinning in a clockwise motion. The axle housing will be experiencing an opposite force. The torque delivered will actually tend to rotate the “pumpkin” in a counterclockwise motion. Consequently, the upper control arms will be stressed under tension (as if they were being stretched). The lower control arms will be compressed (as if they were being shortened). GM’s control arms are fairly flimsy stamped steel pieces that usually have some rust on them by this point in their lives. It is not difficult to see that a strong motor with some sticky tires could potentially deform one or both of the lower control arms. Old, stock rubber bushings can also deflect slightly. The results are lost power, possible wheel hop, and non-linear traction to the road surface. Remember that the pinion rotates through an arc during acceleration too.
Now about the weakest link. Each item in the entire drivetrain will be moved and/or twisted out of position as much as feasible. Any movement is lost power. For example, if the engine mounts are old and sloppy, let’s assume the engine moves ½ inch up (vertically) on the driver’s side. This is unnecessary motion. The torque of the engine must “sustain” holding the engine in this abnormal position for the duration of the acceleration event. Insignificant? Maybe, but success in racing is about 100 little things, usually not the one silver bullet. The weakest link also applies to old parts, or asking a part to perform a function it is not capable of doing. Horsepower seems to “find” weak parts in your car.

Next installment: how all of this matters to your car.

 

[LS1GN]

This twisting motion carries through the housing of the transmission, and any flex or slack in the mounting of these two important items is lost power. Of course, the more rigidly the engine and transmission are mounted, the more NVH is transmitted to the occupants.

power is not lost, there is a few millisecond delay cause by the engine torquing but then again in drag racing you don't start off with the engine at idle and in circle track there is a rolling start.

Read part two and then tell me what you think. Moving (and maintaining) anything out of its natural position requires energy.

 

[LS1GN]

What happens when you floor the gas pedal – Part 3

How all of this matters to your car.
I might need some of the smart guys to chime in and help with this part. As far as making your car hook up better, there are many choices: relocating control arm mounting points, altering control arm lengths, spring rates, dampers (shocks), and tire choices are all things which need to be considered. Remember that the front of your car also reacts at launch and factors into weight transfer.

Let me share an illustration regarding acceleration: In a V8 engine there are eight pistons in cylinders which are each receiving a “push” from explosions of air and fuel. The battle or contest is this: the resistance of the vehicle rolling versus the cycles of these eight explosions. The resistance is the weight of the car, the rolling resistance in tires and bearings, the wind resistance (especially at high speed), moment of inertia (first getting the car to move), transmission, and a slew of other things I can’t think of. A weedeater engine can’t move a tractor trailer. All the forms of resistance in the truck beat the little 20cc displacement explosion every time. Speed is basically helping those eight explosions be as powerful as they can possibly be so they can push on those pistons as much as they possibly can AND having as little resistance as possible (weight, friction etc.) putting up a fight against those eight explosions. Time is another part of the scenario. I used to have a huge old 1974 Cadillac. The motor was tired, but it could eventually get to 100 mph. It took a long time though. The eight cylinders could win the battle with that huge car but it took time. A dragster with a huge, powerful blown big block in a very light chassis doesn’t need much time to win its battle.

 

[bill]

And so then we come to the difference between HP and FT/TQ in relation to hole shot and top end speed....please continue...

 

[ssn696]

Actually a weedeater could move a tractor trailer, with enough gear reduction. Of course, you could tape the throttle down, eat a sandwich, come back and it might have moved 80000 lbs about two inches.