Horsepower isn't the only thing that will make your car faster. The weight of your car is of near equal importance. To elaborate, generally every 100 pounds lost will net you .10-second faster in the quarter-mile. There are hundreds of pounds to be spared from our cars to help us meet our performance goals.
Weight borrowed from some places on the car has a better outcome than other places, and if you're going for the best bang for your buck, you should know where to focus. Knowing the difference between rotating weight, sprung weight, and unsprung weight will help you to determine where you want to concentrate your efforts.
All the components between the crankshaft and the tires are part of the rotating-weight family. Any weight you can trim from those spinning parts helps them rev more freely, making them accelerate-or decelerate-faster. The diameter and mass of the part determines its effect on the engine. For example, lowering the weight of a 20-inch wheel will help way more than a 3-inch driveshaft. If you can picture twirling a short lead pipe compared to a long one, the short one will spin and change direction easier if input is applied.
Sprung vs. Unsprung Weight
Let's start with a definition: Sprung weight is any part of the car that is supported by the suspension, and only moves when the suspension is active. That means that unsprung weight is any part that is directly connected to the road without cushioning from the spring.
The reason it's important to differentiate between the two is because removing unsprung mass is a more effective move than shaving sprung mass. There is no rule of thumb, like "for any 1 pound lost for sprung weight, it's like 10 pounds unsprung weight," or any conversion like that. With the exception of rotating mass, less unsprung weight will not make you go any faster in the quarter-mile than if it were sprung weight, but it does have handling benefits. The lighter the wheel and other unsprung components, the easier it is for the tire to follow bumps in the road. On a vehicle with extremely high unsprung weight, the inertia of the wheel and associated assembly can't move fast enough to follow the road, resulting in a jarring, crashing ride. What's more, a heavy wheel/tire combo requires a heavier spring and shock package to control it, upping the ante with even more weight, bigger brakes (still more unsprung weight), in a situation that spirals out of control.
Lowering the unsprung weight and rotating weight yields multiple dividends, with better acceleration, better braking, better ride, better fuel economy, and better handling. Money spent to reduce unsprung weight may be great, but it's a much better payoff than with sprung weight.
Fiberglass Body Panels
They don't make cars like they used to. You see an older car tangle with a little Honda, and the import comes out looking like a crumpled-up garbage can and your old-school musclecar comes away with just a scrape. This is because the sheetmetal on the older cars is so much thicker than newer cars. Though it's a plus for an accident, it's also an easy way to drop a ton of weight.
Year One offers a wide range of fiberglass body parts to replace the stockers. Hoods are the most common to replace, and come with many different mounting and styling options. If you're a traditionalist, you can order a flat hood that uses the factory hinges and latch. On the other hand, you can also get a 9-inch cowl and use hood pins to retain it.
The hood isn't the only place you can replace panels. Fiberglass replacements are available for near any bolt-on panel, including fenders, decklids, bumpers, and doors.
Shown is Year One's fiberglass hood for '67-69 Camaros (PN S800), weighing in at 44 pounds versus the 56-pound stock steel hood. It comes with a sticker price of $449, which turns out to be a pretty good deal.
Price per pound lost: $15.80
Relocation Of Weight
It is not always possible to remove all the heavy items from the car. In these cases, you can move them to a more desirable location. If you must carry the weight in a car that you drag race, you might as well shift it as far back as possible to help weight transfer. The battery is about one percent of your car's total weight, so changing your front-to-rear static weight distribution that much from one modification is quite good.
Relocating the battery is a simple and inexpensive way to shift the weight. You can get kits that come with the box, mounting hardware, and cables to complete your installation. Check out Taylor Products' battery relocation kit, PN 48101. It's made from aluminum, and comes with everything you need to complete the project.
Battery relocation kit:
Taylor Products (PN 48101)
$149.95 from Summit Racing
A lightweight flywheel isn't for everyone, as it does change the way the car drives, but there are big gains to be had, strictly outside of its reduction in mass. In the September 2008 issue of PHR, we got into more detail about steel versus aluminum flywheels. The gist is a steel flywheel stores more energy and keeps things running smoother than an aluminum one because of the high rotational inertia. This is why a lot of companies make lightened steel flywheels to create a middle ground. The corollary argument is that a light flywheel also accelerates quicker in its rotation while providing an overall reduction in vehicle mass.
|Flywheel: ||Part Number: ||Summit Price: |
|Aluminum 15-lb ||560130 ||$466.99 |
|Steel 22-lb ||460122 ||$301.69 |
|Steel 30-lb ||460130 ||$323.39 |
|Steel 40-lb ||460140 ||$338.99 |
Price per pound lost: $5.00
Shown here is a driveshaft from Inland Empire, which we used on our project '68 Chevelle. It was almost 11 pounds under the stock weight of the old steel shaft. Though not as effective as an aluminum flywheel in lowering the rotational mass, the driveshaft is still an easy way to shed some pounds.
Unlike wheels, driveshafts don't have the diameter to have much effect on reducing rotational inertia-that is, reducing the motor's effort to spin up the shaft-so the weight savings is mostly to bring down the overall weight of the car. Looking at the price difference of having a factory replacement driveshaft made compared to a custom aluminum or chrome-moly version, it's really just a matter of how much lighter you want to go.
|Driveshaft: ||Weight: ||Price: |
|Stock, 50-inch ||17 lbs ||$245 |
|Aluminum 50-inch ||10 lbs ||$285 |
|Chrome-moly steel 50-inch ||12.5 lbs ||$275 |
Price per pound lost: $5.71
inland empire driveline
In this issue, we feature three aluminum-block crate engines that offer a dramatic decrease in weight. If you plan on doing a little more experimenting than what a crate engine allows, there are options for you to purchase a bare aluminum block to build up as you choose. Dart offers blocks for Ford and Chevy in both iron and aluminum, which we've listed below for your perusal.
|Engine: ||Material: ||Weight: ||Retail price: |
|SBC ||iron ||205 lbs ||$2,711 |
|SBC ||aluminum ||95 lbs (110 lbs lighter) ||$5,517.81 |
|BBC ||iron ||260 lbs ||$2,886.17 |
|BBC ||aluminum ||136 lbs (124 lbs lighter) ||$6,266.75 |
|Ford ||iron ||167 lbs ||$2,817.21 |
|Ford ||aluminum ||85 lbs (82 lbs lighter) ||$5,578.90 |
Price per pound lost (average): $28.80
The weight of an aluminum fuel cell is less than the stamped steel of the stock fuel tank, but a lot of the benefit comes from limiting the amount of fuel you put in your car.
If the car is primarily used for short trips and racing, using a 10-gallon fuel cell is easy, but might be a bear on the street. A 20-minute session on a road course should not consume more than 5 gallons. At the dragstrip, it's even less. With fuel weighing in at 6.2 pounds per gallon, carrying less can decrease your weight substantially.
|Tank: ||Part number: ||Price: |
|Year One factory tank Chevelle, 20-gal ||FA46 ||$199 |
|Summit, plastic 16-gal ||290108 ||$169.95 |
|Summit, aluminum 15-gal ||293215 ||$175.95 |
|Summit, aluminum 10-gal ||293210 ||$165.95 |
|Summit, plastic 8-gal ||290103 ||$99.95 |
|Summit, plastic 5-gal ||290101 ||$94.95 |
|Summit, aluminum 5-gal ||293205 ||$139.95 |
Price per pound lost: $7
Weight savings can look cool, too. As long as you aren't solely into the sleeper look, you'll love the look of a clean set of race seats. Not only is this a place to spare some pounds, but it's the best thing you can do to control your car. Twisting the wheel of a 35-year-old car is hard enough without the deficit of using a 35-year-old seat. Sagging springs, no bolstering, and that poke in the thigh from where something came loose sure won't help your driving abilities.
Corbeau offers a basic, nonreclining seat as well as more cozy, adjustable seat backs. Both are significantly lighter than the stockers. At a hefty 32 pounds each, the '68 Camaro factory seats don't offer much for support, and can be easily traded in for a race seat without losing comfort. These seats come in black, yellow, blue, red, or black micro-suede. The A4, a reclining model, can be covered in a black/grey combination micro-suede, or even black leather for an additional cost.
|Seat: ||Weight: ||Price: |
|New stock seat ||32 lbs each ||$400 |
|Forza ||20 lbs each ||$229 |
|Forza (wide) ||22 lbs each ||$259 |
|A4 (reclining) ||25 lbs each ||$320 |
Price per pound lost: -$14.25 (negative number-the seat pays you to buy it!)
Wheels are a large contributor to unsprung weight and rotational mass. Reducing the wheel weight is like killing two birds with one stone. Unfortunately, it takes superior design (read: expensive) to be able to remove mass from the wheels without sacrificing their strength.
The loss of rotational weight will directly affect the performance of your vehicle more than general weight loss. Removing weight from anything that accelerates rotationally-as well as linearly-pays a double dividend, because there are two inertia types here that impact performance. Many people have attributed higher mph trap speeds and quicker road course lap times solely to changing the mass of their wheels.
Forgeline is a leader in low-mass racing wheels, and their wheel production begins with a computer simulation that can test for weak spots before it's even machined. Once it proves to be an excellent design, a basic shape is forged from 6061-T6 aluminum with a 6,000-ton hydraulic press. After that, the wheel is machined and heat-treated to be 40 percent stronger than cast aluminum.
The wheels may be expensive, but to get the combination of weight savings and strength, there is a hefty price to pay. But like we said, light wheels pay a double performance dividend, so the price per pound won't actually reflect the true benefit.
|Wheel type: ||Weight: ||Price:(each): |
|15x8-inch Wheel Vintiques steel ralley ||30 lbs ||$92 |
|17x8-inch Wheel Vintiques aluminum ralley ||32 lbs ||$515 |
|18x8-inch Forgeline S03P aluminum ||18 lbs || $1,000 |
Price per pound lost (steel to S03P): $34.64
We hate to say it, but there is a lot of weight sitting in the driver seat. For some vehicles, between 20 and 200 pounds can be lost from the car by adjusting the nutritional intake and exercise output of the driver!
|Engine: ||Material: ||Weight (pair): ||Retail price (pair): |
|SBC ||iron ||104 lbs ||$784.08 |
|SBC ||aluminum ||46 lbs (58 lbs lighter) ||$1,136.96 |
|BBC ||iron ||140 lbs ||$1,338.12 |
|BBC ||aluminum ||58 lbs (82 lbs lighter) ||$1,970.62 |
|Ford ||iron ||98 lbs ||$830 |
|Ford ||aluminum ||46 lbs (52 lbs lighter) ||$1,136.96 |
If swapping blocks is a little too expensive or involved, changing out cylinder heads is a great alternative. Not only does this shed front-end weight, aluminum heads typically have a higher octane tolerance than iron. The huge number of choices compared to iron also means (with the right choice) you can bag some extra horsepower in the deal through improved combustion efficiency. Aluminum heads aren't just for full-race applications either; they come in a wide range of sizes and performance goals. For half the weight, without half the cost, this is the best weight saving investment.
Price per pound lost (average): $6.56
You have all seen bigs and littles on drag race cars, and there's a reason why. The smaller wheels and tires reduce weight in the front of the car, while reducing the rolling and aerodynamic resistance. Between buying 8-inch-wide wheels and 4-inch-wide wheels, the 4-inch will be cheaper, and the same goes for the tires you wrap them with.
For the street, you have to be careful because with the smaller contact patch, you will be losing some braking and turning ability. The little front tires should only be on a car you do mild driving on the street with, and then blast at the dragstrip.
Price comparison between 15x8-inch Weld Star wheel and 15x3.5-inch: -$25 each
Price comparison between 245/60R15 BFG radial T/As and 155/80R15: -$19 each
Chrome-moly vs. Mild Steel Tubing
If you're going fast, you're going to need a rollbar or rollcage. Not only is it required by most sanctioning bodies at a certain e.t., but it's a safety issue. There are two materials you can use to build your cage: mild steel, or chrome-moly. The advantage of chrome-moly is that it's stronger, so a thinner wall thickness can be used, thus saving weight. Chris Alston's Chassisworks offers cage kits from four to 14 points to fit many popular cars and trucks. For comparison, let's look at the price and weight of its best-selling kit for early Camaros.
|Design: ||Material: ||Weight: ||Cost: |
|10-point ||mild steel ||157 lbs ||$295 |
|10-point ||chrome-moly ||118 lbs ||$604 |
Price per pound lost: $7.92
Chris Alston's Chassisworks
Plexiglass / Lexan Windows
Windows weigh a lot. Replacing them with Lexan is a fairly inexpensive alternative, and can be a do-it-at-home project. Lexan, sometimes mistaken for plexiglass, is a much stronger material, and is used in storefronts for security. It is stronger and more shatter resistant than glass, yet some states don't allow it on street cars. The materials are all available at Home Depot, including the tools to cut and mount it. To attach fixed windows, a simple rivet gun will do the trick, and stock glass retainers should work for the roll-up windows. For extra scratch protection, you may invest in some higher-quality material available at a plastic supply store that has a tint film. Clear One Racing Products has a selection of precut pieces for many early cars to make the job easier for you. For more custom applications, it supplies uncut sheets in various thicknesses.
Price per pound lost: est. $20
Clear One Racing Products
Strip It Down
Here is a truly free way to lower your car's weight. There are many unnecessary things put into cars for race day, or everyday, that can be removed.
If you don't live in a place that gets extremely hot, A/C really isn't needed. There are a lot of parts in this system that can drop 20 pounds off the front of your car and clean up the engine bay in the process.
The heater might be a harder thing to let go, but the heater core and blower motor cost pounds! Removing the heater tubes and blower motor box on the engine side of the firewall cleans things up, too. Heater core failure on a 40-year-old car is a pain to deal with, so nipping it in the bud isn't a bad idea. Along with the parts themselves, the extra 5 pounds of coolant can be discarded from the car for a total of around 10 pounds.
If you have ever sat in the back of an early ponycar, you'll agree they aren't that comfortable. You may have to cut down on the total number of people cruising with you, but giving the back seat the boot is another 20 easy pounds out. For race day, don't forget you can remove the passenger seat for another 32 pounds.
Carpet and Undercoating
Now we are getting down to the nitty and gritty. Many automotive manufacturers installed undercoating and carpet padding to reduce interior noise and keep some of the heat from under the floorboard away. Carpet was just installed to make the car look good, so if you scrap it all, you are looking at up to 10 pounds total weight loss. We recommend spray painting over the floor after the carpet is up for a clean look. If you prefer to keep your carpet, we'll point out that modern carpets and underpadding weigh much less than their older counterparts-as little as half the original's weight.
Price per pound lost: $0
Brakes are a big part of the vehicle's unsprung weight, so trimming the pounds from this system without losing their performance is optimal. Different cars need different brakes depending on how the car is used. An autocross or track car will need much more braking power than a drag or street car because the brakes are being used much more often and require a larger diameter and thickness rotor to dissipate heat. For the basic street car, Wilwood offers an 11-inch rotor, four-piston caliper setup to fit behind 15-inch wheels, and these brakes are significantly lighter than stock. This kit is great for street driving, drag racing, and mild autocross use. On a GM A-body, this kit lowers front-end weight between 20 and 25 pounds, while massively outperforming stock drum or disc brakes. At the extreme end of the brake kits, the drag-racing-only setup using a solid 10x3/8-inch rotor and single-piston caliper is 10 pounds lighter than the street kit.Since the brakes would need to be bled after this swap, you might as well pick up one of Wilwood's aluminum tandem master cylinders for another easy 7 to 10 pounds of weight reduction.
Price per pound lost: $13.73
|Brake Kit: (A-body/first-gen F-body) |
| ||Weight: ||Retail price: |
|CPP stock single-piston kit ||62 lbs ||$449 |
|Wilwood 11-inch street kit ||39 lbs ||$765 |
|Wilwood drag-only kit ||29 lbs ||$670 |