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:Acceleration = Force /
Mass
"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 Mass = weight/acceleration due to
gravity
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.
Material | Weight (grams/cubic
centimeter) | |
AISI 1020 Cold Rolled Steel |
7.87 | |
Titanium |
4.43 ~56% of steel | |
Aluminum 6061-T6 |
2.7 ~34% of steel |
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. |
