Drag racing is a contest of acceleration, not of speed. The first to get from a standing start to the finish line is the winner. Nothing else matters.

Every drag racer that sets out to make their machine accelerate faster has to contend with Newton's second law: "The acceleration of an object is directly proportional to the magnitude of the net force, and inversely proportional to the mass of the object."

In equation form it looks like this:

"Directly proportional " means that as force is increased, acceleration increases. "Inversely proportional" means that as mass decreases, acceleration increases.

It boils down to this?. According to Sir Issac Newton, there are only two ways to increase the rate of acceleration of your machine (clutching issues aside) (1.) - An increase in "force" and (2.) - A decrease in mass.

Some definitions are in order here so that I don't get a flood of email from people that want to correct me:

Acceleration: is the rate of change in the velocity (feet per second) of an object per unit of time (seconds) or feet per second per second (feet/second ^2).

Force: is a push, or a pull, exerted on an object by another. This push or pull, if it is strong enough, will accelerate the object. In the case of our snowmobiles the torque generated by the engine is the force.

Mass: is the amount of matter that makes up an object, while weight is the gravitational force of the Earth acting upon the object.

If you know the weight of the object, you can calculate out the mass of the object then by using the equation

Drag racing is nothing more than a high-speed science fair. Whoa, sorry, I was having a Bill-Nye-the-Science-Guy moment there. I just had a flashback to my college physics professors' VW bus that had a "Physics is Phun" bumper sticker on it. And you would have thought none of this stuff would be useful in real life ?

Like any scientific problem, the whole concept of acceleration can be addressed at several levels of complexity. We will not address a force increase in this article. That's pretty straightforward, take your checkbook to your favorite speed shop and have them build you a more powerful engine.

This article is about reducing mass. Take for example the "rotating mass" question. Everyone knows that rotating mass has a different effect on the acceleration of a vehicle than static (non rotating) mass does. Read any of the discussion boards and you will find many personal interpretations of the effect of rotating mass. This article is not about rotating mass so we will not go very deep into the topic. What we will say is that rotating mass has an increased effect on acceleration as compared to an equal reduction in static weight. In other words, the benefit to acceleration by a reduction in rotating mass rather compared to an equal reduction in static mass is that the effect of the rotating mass is multiplied. Various studies published in automotive chassis tuning guides have shown that a given amount of mass reduction that rotates at crankshaft speed is typically equal to 15 times that amount of static weight reduction. This effect is proportional to crankshaft speed. If you reduce the rotating mass of something that turns at 50% of crankshaft speed then the equivalent static weight reduction is 15 x .5 = 7.5 times that of a static weight reduction of the same amount.

Even the rotating mass question is not so simple. The rotational inertia of different size parts having the same mass effect the amount of force it takes to accelerate them. It depends on how close the "center" of the mass is to the center of rotation. The further from the center of rotation, the more force there is required to accelerate it. There is a separate article that dives deeper into this topic located at: Rotational Weight

In short, given a choice between reducing an equal amount of rotational mass or non-rotational mass, the most benefit is almost always in reduction of the rotating mass.

Now that we've determined that a reduction in mass is like free engine work, what are the options for trimming the fat from you machine?

Depending on what kind of racing you are doing and what class you are racing in, you may be restricted as to what you can change. If you're in an open or "outlaw" class then there are no restrictions. Maybe you've already put on all the lightweight parts you can find? maybe not.

We did an off season makeover on the Snowmobile Online asphalt project sled (and driver) trying to find some more elapsed time (acceleration). The sled is a 1997 Mach 1 and because of its stock weight (540lbs) it has earned the nickname "Mach Ton". Last season the sled chassis was stock plus some additional wheels and axles in the skid. The engine is the original Rotax 700 modified by Iantomasi Track and Trail of Bowmanville, Ontario Canada.

The vital statistics on the sled before we put it on the Slim Fast plan:

• Sled 540 lbs
• Driver 265 lbs
• Engine 175 hp
• Et 10.6x seconds pretty consistently

A decision was made to keep the engine as-is because it has proven to be extremely reliable. We choose to address the "mass" part of the equation. Transforming a stock machine into a lightweight machine has the advantage of being a piecemeal job. That is, it can be done in steps. If you decide to work on the "force" part of the equation, there is no half way. You get the engine, carbs, pipes and new clutching to make it work. That is usually a significant investment of both time and money. There is no way go into it a step at a time. On the other hand, shaving weight on you and your sled is something that can be done in steps as time and money allow.

One classic moment during this project was the time I was kneeling next to the sled in the workshop, gazing under it with a droplight. My son (11) walked in the workshop and said, "what did you loose?" "Nothing" I said. There was a long pause and he said "then what are you looking for?" laughing, I said "a half a second" It reminded me of a classic three stooges episode where they were working on car and Curly was under the hood yanking parts out and throwing them away. After a while he stops and says "Hey Moe, what's a squeak look like anyway?".

While the snowmobile was stripped to the tunnel, every part that came off of it got a weigh-in. The intent of the project at this time was not to build a complete super lightweight pro-stock sled but to identify what each component weighs.

The bare sled stripped to her tunnel with everything except the engine removed. Click picture for larger image

Then make some decisions about what components to change now and then some more over the course of the next off-season as time and budget permit.

After all the parts were weighed, one particular box of parts totaled up at a surprising 23 pounds. This was a box that contained all the nuts, bolts and washers from the entire sled (no including the engine bolts). When you are trying to lighten up a machine that is already mostly plastic and aluminum, 23 pounds of steel makes an excellent target for weight reduction. The skid frame and the cowl/windshield/dashboard, steering components are the usual weight hogs and those will be addressed, but here was 23 pounds of weight that is often overlooked.

What are the alternatives to steel hardware?

A quick visit to www.mettec.com was in order to get their phone number. Mettec is located in Placerville California. I discovered them a while back when I was searching for some titanium axle bolts for one of my motorcycles. Mettec "specializes in custom components and standard hardware made from complex metallurgical alloys". In fact their mission statement is right to the point: "Mettec's mission in life is to produce light weight components and parts from metallurgical complex alloys. We bring sophisticated processes and treatments into ordinary use. Our primary focus has been TITANIUM ALLOYS however we also manufacture parts from ALUMINUM, CHROMOLY and more exotic steels like 300M."

Why Titanium ?

Titanium is approximately half the density of steel while being slightly stronger. Aluminum is one-third the density of steel but only one-third to one-quarter of the strength of steel. Aluminum is not a suitable substitute for steel fasteners.

Why Mettec ?

Their mission statement sums up their commitment to motor sports: "Complex metallurgy and sophisticated processes are the primary focus for Mettec. Combining modern materials and technical advancements in machining, joining, coating, forming and heat treatments offers major improvements in competitive motor sports. We strive to bring futuristic concepts into commercial reality."

"Mettec's engineering background and interest in motor sports has led to the development of engine, drive train, and suspension components which are light weight and durable. Mettec provides innovative engineering design to our customers. Mettec's engineering and manufacturing services are performed under proprietary agreements. Quality parts begin with design and carries through final inspection and field-testing. In order to be current in modern technologies, Mettec engineers are active in professional societies including American Society of Mechanical Engineers (ASME), American Society for Metals (ASM), American Welding Society (AWS) and Society of Automotive Engineers (SAE)."

Mettec uses ASTM B348Ti-6AI-4V grade 5 titanium. All of their bolts have forged heads and rolled threads, which provides for greater fatigue strength and reduced galling on the threads when compared to threads formed by cutting processes.

The Mettec bolts exceed minimum Ultimate Tensile Strength (UTS yield strength) of 120,000 psi. They conform to both DIN and ASTM specifications. Titanium bolts can replace both steel grade 5 (UTS 120,000 psi) and steel grade 8 (UTS 150,000 psi) bolts. They can also replace steel metric grade 8.8 bolts. However, steel grade 10.9 can "sometimes" be replaced with titanium, depending on intended use. Any bolts with a higher grade than 10.9 cannot be replaced with titanium.

When the package from METTEC arrived, the ship weight of its precious cargo was 6 lbs! Click picture for larger image

A few phone calls and a week later a box of bolt on horsepower showed up at my doorstep. I didn't go too radical and try and replace every nut, bolt and washer on the sled. I started off with replacing the 6mm through 10mm OEM bolts with titanium (the largest bolts in the rear suspension are 12mm bolts). This accounted for about 11 pounds of the 23 pounds of steel hardware. Since this project was taking place during mid season, I had to be sure that whatever modifications I was going to make could be done in one or two evenings after work so as to not miss any races.

The box as it arrived from Mettec had a UPS shipping weight of 6 pounds for replacement of 11 pounds of hardware. Sweeeet !!! A 50% BOLT ON weight savings. This has got to be the EASIEST lightweight modification known to mankind. It is the only true bolt on "horsepower". Here are the installation and tuning instructions:

Step 1. - Remove OEM bolt
Step 2. - Replace with Mettec Titanium bolt.

Does it get any easier? I think not.

The contents out of the box, I was ready to start comparing the savings in weight from the OEM bolts and the Titanium ones. I was ready loose some weight! Click picture for larger image

I ripped right into the Mettec box and spread the bolts out on the workbench. Nice! If you think polished aluminum makes your heart beat faster, wait until you have a bench top covered with titanium bolts. This is the time when you stand back and let out a few Tim "the tool man" Taylor grunts !

Using my clutch scale I weighed every size of steel bolt and then the titanium replacement as I reassembled the snowmobile.

The photos of bolts on the scales show the largest of the bolts being replaced (1/2-20 x 3.5"). There are five of these bolts in the front suspension. Four of them connect the radius rods to the bulkhead and one is the bell crank pivot for the steering. The steel bolt weighed 98.7 grams while the Mettec titanium bolt weighed 56.6 grams.

Steel bolts: 98.7g x 5 = 493.5 grams = 1.1 pounds
Titanium: 56.6g x 5 = 283 grams = .6 pounds

For this size bolt, the Titanium replacements were 54 % of the weight of the steel bolts. Note If you are wondering what the inch size bolts are doing on a ski?doo, it is because as a separate project I replaced the OEM metric bolts with inch sizes to match the custom radius rods on my sled that use half-inch aluminum heim joints rather than the metric equivalent.

The steel 8 1/2"-20 x 3 1/2" weighs in at 98.7 grams Click picture for larger image	The titanium 8 1/2"-20 x 3 1/2" weighs in at a weight saving - power gaining 56.5 grams Click picture for larger image

Some things to consider when purchasing the bolts:

• Metric threads come in different pitch.
• Make sure you buy the right pitch.
  
• Size your bolts so that the length is just enough to provide one to one and a half threads beyond the nut after installation.
• You will notice that many of the OEM bolts have 4-6 threads beyond the nut. This length is excess weight that is not needed.

The weight of the OEM bolts that I replaced was eleven pounds. The replacement bolts weighed five and a half pounds pounds. At this time I only replaced the 6mm through 10mm bolts, plus some inch size bolts in the front suspension. The remaining 12 pounds of hardware (23 total - 11 replaced = 12) I choose not to replace at this time due to my time and budget constraints. Over the next off-season, all the hardware will be replaced with Titanium components.
Typical weight savings will be between 50-55% of the steel. Potentially this is 11 to 13 lbs of weight savings. In addition, there is ~2000 grams of bolts in the engine. That is about 4-1/2 pounds. Replace those with titanium and you can pick up another 2-1/4 pounds of savings. Total potential: 13-15 pounds.

You will notice that the Mettec bolts have a little extra machining done on them as compared to the OEM configurations. The hex heads are a little thinner and the socket head cap screws (SHCS) are "tapered socket head cap screws (TSHCS).

The socket head shape and size are pronounced. Click picture for larger image	The hex head shape is also different in thickness. Click picture for larger image

Summary:

Cost per pound: Average cost per pound of weight savings for this project was approximately $125 per pound saved.

Ease of installation: Direct remove and replace. It doesn't get any easier. This by far has been the easiest of all the weight reduction projects that we've done on this sled this season. There is no compromise in strength, no fabrication to "make it fit". No re-wiring to do, no brackets to make. Nothing.

Difficulties: Make sure you have the correct thread pitch. If you're not accustomed to working with metric fasteners, the difference between a course and fine thread may not be so obvious.