Repost: original post 1/16/14
Happy New Year folks!
I’ve been holding off on posting new entries, since T10 stated they were going revise (update) the Forums, and the effort put into these threads was destined to disappear, but decided that the community could still benefit from this info.
A few of you have asked when the FAPSD series will return? Well, the FAPSD series will be back. At this time, the Fastest Street Car Association (FSCA) has agreed to administer this series while I am away from Xbox, when time and scheduling permits. As you well know, the FSCA is run by very knowledgeable and committed drag racers, who field exciting, competitive, and fun drag racing in the Forza platform. Get your “drag race fix!” by the folk at FSCA!
This is basic stuff regarding the key performance producing systems in your cars. I wont try to give advice on every system, just the stuff that makes a difference in the FAPSD rule book, as my ultimate dream/goal is take this series to the Real World, and apply the same concepts.
WEIGHT REDUCTION: The FAPSD rules allow street weight reduction.
While the performance industry has often used the gauge of power-to-weight ratio, we decided to look at weight-to-power (W/P) ratio instead, since it’s the pounds we’re improving as power remains the constant. We find the W/P ratio by simply dividing total vehicle weight by horsepower. Consider this: a 3,000-pound car packing 450 hp requires each horsepower to carry 6.66 pounds–the exact same ratio as a 4,000-pound car with 600 hp or a 2,000-pound car with a mere 300 hp. Work the numbers backward and it becomes clear that shedding pounds is just like adding horsepower.
To explore the effect, we took a cost-is-no-object stance to shed a total of 588 pounds from our 408hp '70 Plymouth Duster. Sharp readers will note the lack of an aluminum radiator, light battery, and aluminum master cylinder. We had planned for these goodies but magazine deadline realities prevented their inclusion. Despite this, we managed to drop total vehicle weight (less driver) from 3,012 pounds to a shocking 2,424 pounds. Best of all, eighth-mile dragstrip performance improved from 7.627 seconds and 89.38 mph to 7.235/93.95. For approximate quarter-mile numbers, take those e.t.'s and multiply by 1.57. This shows a drop from 11.93 seconds to 11.35 seconds (5.8 tenths) and proves, almost to perfection, the drag racer’s assumption that 100 pounds lost equals a tenth gained in the quarter. Also, we used our Longacre scales to reveal not only the total weight loss, but also how it affected the car’s weight distribution.
infor from:Hot Rod
Read more: http://www.hotrod.com/howto/113_0310_weight_reduction/#ixzz2ppXbvz8q
REAR GEAR RATIOS. The rules require SPORT transmissions, and allow changes in final drive ratios (actually encouraged) in the FAPSD series.
What’s in a Ratio?
An automobile uses gear ratios in both the transmission and the drive axle to multiply power. The two ratios multiplied together equal the final drive ratio. Spend a few minutes in any bench-racing session and soon you’ll hear rear axle gear ratios discussed. For many performance cars, 3.73s and 4.10s are common gear choices. The rearend gear ratio refers to the relationship between the ring gear and the pinion gear. By simply dividing the ring gear tooth count by the pinion gear tooth count, the ratio is determined. For example, if we divide a ring gear with 41 teeth by a pinion gear with 10 teeth we find that the gear ratio is 4.10:1 (41/10 = 4.10).
Tire diameter will also have an effect on a vehicle’s final drive ratio. As tire diameter changes, so will engine rpm at a given speed. We can demonstrate this with the simplified formula: rpm = (mph x final gear ratio x 336*) / tire diameter (*see “Formulas for Success” sidebar). For example, given 65 mph, a tire diameter of 30 inches, and a final gear ratio of 4.10, the engine speed will be approximately 2,984 rpm–(65 mph x 4.10 final gear ratio x 336) / 30-inch diameter tire. If we reduce the tire diameter to 25 inches, the engine speed increases to 3,581 rpm. By installing shorter tires, the vehicle will accelerate as though it has a 4.73 (higher numerically) gear without the expense of gear swapping.
Because transmissions are comprised of several gear choices, the transmission allows the vehicle to accelerate quickly with lower gears and to maintain a cruising rpm using higher gears. In the '60s and '70s, most transmissions offered three or four gears with a 1:1 high gear. Using a TH400 as an example, First gear is 2.48:1, Second gear is 1.48:1, and Third gear is 1:1. Multiplying the 2.48 First gear by the 4.10 rear axle results in a final drive ratio of 10.16:1 (2.48 x 4.10 = 10.16). For most street performance applications, a 10:1 final First gear ratio is usually considered optimal. The disadvantage of operating a 4.10:1 axle ratio on the street with a 1:1 high gear is excessive freeway engine speed.
Fortunately, today’s transmissions frequently utilize Overdrive high gears in the neighborhood of 0.70:1, which allow reduced engine speeds. Combine these overdrive transmissions with a 4.10 axle ratio and you have a fuel-friendly final drive ratio of 2.87:1 (4.10 x 0.70 = 2.87) in high gear. A TH200-4R overdrive automatic utilizes a First gear of 2.74, a Second of 1.57, a Third of 1.00, and a 0.67 Overdrive. With this transmission’s First gear ratio of 2.74 combined with a 3.73 axle ratio, the final drive ratio >> yields a 10.22 (2.74 x 3.73 = 10.22). In overdrive, the final drive ratio equates to a Bonneville-ready 2.49:1.
Making Torque Multiply
Acceleration is all about torque. One way to accelerate more quickly is to multiply the torque at low speeds to help move the vehicle forward. That’s what a torque converter does. The torque converter features a component called a stator. The stator changes the direction of oil flow to the pump impeller’s rotating direction and also incorporates a one-way clutch assembly. This redirection of fluid increases torque by applying the energy remaining in the oil.
By applying the basics of gear ratios and power leverage, you can easily improve your vehicle overall performance.
Read more: http://www.chevyhiperformance.com/techarticles/148_0208_gear_ratio_calculating/#ixzz2pcHGiblvsource for info below: marsh racing wheels
source below: Marsh Racing Wheels
An example of a automobile transmission gear ratio
A final drive ratio of approximately 2.8 to 1 is a commonly used gear ratio, in cars with an automatic transmission. This means that the drive pinion (small gear) must rotate 2.8 times to make the ring gear (large gear) rotate one time. On cars with manual transmissions more torque power ratio is needed, generally a ratio of approximately 3.5 to 1 is used. Small engine cars and trucks use a final drive ratio of up to 4.5 to 1 and higher to provide even more torque to enable them to pull or move heavy loads. Also shifting to lower gears in the transmission requires more turns of the engine to provide a single turn of the drive wheels, producing more torque at the drive wheels.
“EXAMPLE” A transmission and a 3 to 1 final drive
First gear 3 to 1 + 3 to 1 = 9 to 1 = max. torque
Second gear 2.5 to 1 + 3 to 1 = 7.5 to 1
Third gear 1.5 to 1 + 3 to 1 = 4.5 to 1
Fourth gear 1 to 1 + 3 to 1 = 3 to 1
Overdrive 0.75 to1 + 3 to 1 = 2.25 to 1
= max. speed
Advice to help choose the gear ratio for your race car. One would be wise to talk to one who has raced the track preferably a winner. There are many variables that determine the gear ratio best for your car - Weight of the car, size of tires, length of track, condition of track, weather, track rules, max h.p. to rpm curve, and many other factors you will need to consider. Even with all variables considered, you will still have to run the track many laps and change several times to get it right. Good Luck
Advice for choosing the gear ratio for Off road Rockcrawling, mud, bog, woods, sand, tundra, etc, One would be wise to talk to one who has run the coarse preferably a winner also. Good Luck
source: Chevy HiPerformance. http://www.chevyhiperformance.com/techarticles/148_0208_gear_ratio_calculating/
SUSPENSIONS
Twists And Turns
It’s important to understand how the rear axle moves in relation to the car before we can get into how each different rear suspension operates. Let’s look at what happens when you drop the hammer on your 500hp street car at the dragstrip. Not every twist is as it appears. As torque is applied from the driveshaft to the rear axle, multiple forces begin to leverage the car. Engine torque multiplied by the transmission’s First gear ratio and the rear axle ratio is equal to several thousand lb-ft of twisting motion. The first thing the pinion gear tries to do is climb the ring gear. This forces the nose of the rear axle upward. As the car begins to accelerate, the torque leverages the front of the car upward, causing weight transfer to the rear. As viewed from the rear of the car, engine torque twists the body clockwise, lifting the left front and compressing the right rear (passenger-side) spring. As the pinion continues to apply this massive torque through the ring gear, the rear axlehousing is also being leveraged in a counterclockwise direction as viewed from the rear–lifting the right (passenger) side of the axlehousing while planting the left. As the car accelerates, it appears to be planting the right rear tire when in fact axle torque motion is unloading the tire, reducing traction. That is why a car equipped with an open differential will spin the right rear tire even under light acceleration. Limited slips are used to improve traction, but as you can see, they are merely a Band-Aid on the real problem. By using proven chassis modifications and tuning techniques, it is possible to equalize the load onto both rear tires.
Leaf Springs
The classic leaf spring suspension has been around since the early 1800s with horse-drawn carriages. The advantage of leaf springs is that they are simple to design, and the springs also serve as the locating points for the rear axle. Disadvantages begin to appear when massive torque is applied to leaf springs. It’s difficult to control spring wrapup, which creates the dreaded wheelhop that most factory leaf spring-equipped cars experience. Let’s get into what happens when we plant gobs of power through a pair of leaf springs.
Applying big power through a pair of multileaf springs generally creates what is called spring wrapup. First of all, leaf springs are designed to bend, but lots of torque tends to deflect the forward portion of the spring into an S shape. When this bend becomes severe enough, the spring binds and then bounces the tire off the road, which relieves the tension in the spring. The tire then returns to the pavement, and the process repeats itself with a nasty shudder. This violent wheelhop can quickly damage axles, housing mounts, and shock absorbers and even yank the driveshaft out of the transmission. The earliest solution for this problem was a traction bar that placed a rubber, cone-shaped snubber just below the leading end of the leaf spring. When the spring begins to wrap up, the snubber contacts the spring and prevents wrapup. While this works, there are other, more elegant solutions.
Factory Mopars are noted for not needing traction bars, and if you study how a Chrysler leaf spring is designed, you understand why. All GM and Ford leaf springs are symmetrical, centering the rear axle between the front and rear spring eyes. Chrysler engineers cheated this deal by moving the axle mount toward the front of the spring. This shortens the length of the front segment of the spring, which increases stiffness and minimizes the effect of spring wrapup. Chrysler also placed a small rubber bumper (called a pinion snubber) just above the flat portion of the rear axle pinion area, which limits the amount of vertical pinion travel.
While the leaf spring is still around because of its simplicity, there are drawbacks. The springs themselves are heavy, which contributes to the car’s unsprung weight. This is defined as the weight not supported by the car’s suspension. From a dynamic standpoint, less unsprung weight is an advantage. Because of their weight and size, leaf springs are also more expensive compared with coil springs. There are composite material leaf springs available that do a great job of reducing weight, but they’re also more expensive.
Another important step to help control unwanted rear axle movement is to invest in high-quality suspension bushings for the front and rear. Polyurethane is a popular and inexpensive upgrade, but you should consider the virtually bulletproof aluminum insert Del-a-lum bushings first created by Global West almost 30 years ago. The aluminum bushings use a Delrin insert that prevents metal-to-metal contact, enhancing wear while also offering near-zero deflection. Global offers these bushings for all popular performance body styles. If you’re going to go fast, these bushings are an excellent investment. This part obviously cant be changed in the game, but its important to know.
Factory Coil Spring
The most popular factory rear suspension design for solid rear axle cars is the coil spring system. Under the coil spring umbrella are a number of subtle design variations that make coil spring suspensions more attractive to suspension tuners, compared with leaf springs. Because the coil spring’s only job is to support the weight of the vehicle, designers still needed a way to locate the rear axle under the car. This necessitated control arms (also called trailing arms). The simplest OE coil spring rear suspension is the four-link. This design uses two parallel lower control arms located near the outboard ends of the rear axle. The two upper control arms are angled outward instead of parallel to the chassis. This creates a triangle that locates the rear axle laterally (side to side) under the car, eliminating the need for a Panhard bar or Watt’s link. Popular examples of this rear suspension can be found in cars such as the '64 to '72 GM A-bodies and the '79 to '93 Ford Fox Mustangs. While the coil spring four-link system is more complex than a leaf spring design, it enjoys numerous inherent advantages. First off, the system is usually lighter than leaf springs. More importantly, leaf spring wrapup is eliminated, although wheelhop can still occur if the rear ride height is raised excessively. With a true parallel four-link rear suspension, the links form a right-angle box that allows the rear axle to move from side to side underneath the car. This system is most often used in drag cars and requires the addition of a Panhard bar or Watt’s link (these will be described later in this story), which limits rear axle lateral movement. The main advantage of factory four-link rear suspensions is that the rear axlehousing is securely located.
As production cars became wider and lower in the '80s, the classic four-link suspension evolved into the torque arm rear suspension most widely used in the third-generation, '82 to '92 Camaros. It is still a coil spring rear suspension, but the upper control arms were replaced with a single long arm that bolts between the nose of the rear axle and the transmission tailshaft.
Because the triangular four-link upper arms are eliminated, a Panhard bar is required to locate the rear axle laterally under the car. Torque arms can be used successfully in drag race applications, but on cars running quicker than 10s, it’s rare to find a third-gen Camaro still sporting its factory torque arm.
A fourth variation on the coil spring suspension hit parade is the three-link. As you have probably surmised, this design relies on a single upper control arm mounted on the top of the rear axlehousing. Obviously, a Panhard bar or Watt’s link is also necessary to laterally locate the housing. Chevy used this configuration in its '58 to '64 fullsize cars and more recently in '05-and-later Mustangs. The advantage is the rear suspension is allowed to roll laterally with minimal bind, although a potential downside is that it places the entire upper bar tension into one single mount, which may have to be reinforced when applying serious power to the ground.
Shock Tuning
Just bolting on the best suspension isn’t the end of the story. There’s still the necessity of tuning the rear suspension. Adjustable shock absorbers are almost a necessity if you are chasing that optimal 60-foot time.
Let’s start with some basics. The term shock absorber is really a misnomer. It should be more accurately called a damper, because the device is designed to dampen or regulate spring motion. Shocks are rated by their resistance to motion in compression (bump) and extension (rebound). Most car crafters know that a typical 90/10 drag race front shock is easy to pull apart and very stiff to compress. This design allows the front end to extend easily and then stay up to assist weight transfer. But what you really want is for the front end to rise at the proper rate on the starting line and then quickly settle to keep the nose low at the top end to reduce aerodynamic drag. Equally important is the ability to adjust front and rear shocks to create the effect you desire. Most single-adjustable shocks create changes only in the rebound direction. The more expensive but better approach is to choose double-adjustable shocks that can tune compression and rebound separately.
Let’s use a leaf spring Mopar as our tuning example. When the driver hits the throttle, the rear suspension separates, planting the rear tires. But let’s say this hit is too harsh, crushing the sidewalls of the tires and causing them to spin. By slowing the rate at which the rear shocks allow the body to rise with a stiffer rebound, the chassis tuner can tweak the rate of torque application to the rear tires. This slows down the application of load, making it easier on the tires, which improves the 60-foot times. On the front end, let’s imagine that it actually tops out too quickly, slamming up against the upper bumpstops almost instantly. When this happens, the car will sometimes porpoise, which unloads the rear tires and creates a loss of traction. Stiffening the front shock rebound slows the rate of front end rise, eliminating the porpoise action and generating a quicker run.
These are just two simple examples of why it’s necessary to tune both ends of the car to optimize traction.
Source: carcraft magazine
Read more: http://www.carcraft.com/techarticles/ccrp_0907_rear_suspension_tech_guide/viewall.html#ixzz2pcSaJjSm
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