Facts, Figures & Formulas
How to determine horsepower from ¼ mile times.
HP = weight x (mph
divided by 234)2
(This works for vehicles less than 4000 pounds and running ¼ mile times between
9 and 16 seconds)
How to determine the volume of air needed to make power at a given
engine rpm.
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CFM =
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engine displacement (in cubic inches) x desired rpm
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3456
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How to degree a harmonic balancer
Sometime
it would be useful to have accurate degree marks on your harmonic
balancer. Whether it be marks at 5 or 10 degree intervals or just one
mark where you want the total advance to show. Here is a simple
and accurate method of marking the balancer.
New mark = balancer diameter x π (3.1416) divided by 360 X how many degrees you want to mark.
If
you have a 6" diameter balancer and you want to have a mark at 20
degrees, the formula is 6.00 x 3.1416 (18.85) divided by 360 (degrees
in a circle ) x 20 (# of degrees you want to measure) = 1.20".
So you measure, against engine rotation, 1.20" from TDC mark on
balancer and make a new mark on balancer. You can now mark
balancer for whatever your needs.
How to determine compression ratio
(V1 = volume of cylinder
in engine block; V2 = volume of space above piston at TDC –
V2 includes volume of the combustion chamber plus the volume of head gasket)
(www.csgnetwork.com/compcalc.html ,- this site allows you to play with
“what-if variations to see how they effect compression ratio)
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Cylinder volume
(displacement) =
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3.14 x bore x bore x stroke
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4
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Piston Speed (ft. per
minute) = 2 x RPM x stroke (in feet)
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MPH =
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RPM x wheel diameter (in inches)
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(wheel diameter is overall including tire)
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Gear ratio x 336
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1 mph = 1.467 feet per
second
Differential Gear Ratio
Solution(s)
When making performance
changes to a vehicle, it is imperative to know what RPM is best for the
application. Examples would be at what RPM does the cam give optimimum
performance. Same for intake air volume (see formula elsewhere in this
section). This can be done by changing differentail ratio..
RPM = MPH x
Trans. ratio x Rear end ratio x 336
Tire Height (inches
Rear end ratio = RPM
x Tire Height (inches)
MPH x Trans. ratio x 336
Quick overview of
spring rate & ride height. Be sure to check the "Swaybar Rate & Handling section of
our website for more useful data.
Ride
height is a function of wheel rate, which in turn is a function of spring
stiffness, damping, and suspension geometry. Static (car sitting still,
subject only to force of gravity) is a different situation than dynamic (car in
motion, subject to forces from gravity AND cornering and braking).
Damping does not factor into static ride height at all--it only affects dynamic
situations. Any number of combinations of spring stiffness (rate) and
free dimensions of the springs (e.g., coil spring free length) can yield the
same static ride height. Performance enhancing springs are typically
stiffer (higher rate) AND shorter in free length and typically result in a
lower static ride height. This is to improve DYNAMIC response, i.e.,
handling of the car while it's in motion. Higher spring rates and lower
vehicle height typically yield higher wheel rates and lower moments (torques)
and better tire-to-road geometry and contact and thus better adhesion and
higher speed through turns and faster braking and acceleration.
Lowering static ride height without stiffening
is bad because the RATE of suspension travel has not changed at the same time
the amount of suspension bump travel has been reduced, thus greatly increasing
the likelihood of bottoming-out the suspension. Therefore, using shorter free length
springs that are the same rate as stock is not recommended. Running out of
suspension travel and hitting the bump stops is harsh, leads to sudden
understeer (hitting the front stops) or oversteer (hitting the rear stops) and
can cause loss of control and is potentially damaging. Replacement springs need
to be stiff enough to be compatible with and consistent with the reduction in
bump travel but not so stiff as to make handling worse, so the right approach
is to replace the stock springs with shorter and stiffer ones that have the
right combination of stiffness and free length to achieve the desired static
ride height and improve dynamic performance.
Coil Spring Rate (This formula
is for straight coil spring, not for a spring that has "pig
tail" style end. "Pig tail" design spring will have a slightly
different final result but this formula will be close enough to give
realisic results)
k = Gd 4/8nD 3
G = modulus of rigidity - torsion. For spring steel
use 11.5 million psi
d = wire diameter in inches
n = number of active coils (an active coil is a coil that
does not touch another coil)
D = diameter of coil in inches (you can use center to
center of wire or outside diameter + inside diamter/2)
NOTE:
using inch measurements will give you rate (k) in lbs/in). Since spring rate is
proportional to wire diamter to the 4thpower, it is important
to not include thickness of paint of powder coat in this calculation.
Acceleration or
Deceleration (g rate)
a= F/m
1 g = 32.2 /ft2 So, if you know your acceleration or deceleration (same
thing - just change the sign; a is a vector),
You can divide by 32
ft/s2 to get the number of g's. Especially useful in figuring
force needed to accelerate or brake something weighing a certain amount to
reach a given speed or stop in a certain amount of time.
G force in a turn - a = v 2/r.
Example - you want to know how many g's in centriptal accelration (a turn
or cicle) a turn rate of
1o m/s (about 48 mph) on a turn of 10m radius
(about 39 feet) you are pulling 10m/s2 or just over 1 g.
Minimum Brake Fluid Boiling Points
Sea-Level Boiling Point
Dry
Wet (3.7%
water by volume)
Dot 3 205 C (401 F) 140 C (284 F)
Dot 4 230 C (446 F)
155 C (311 F)
Dot 5 260 C (500 F) 180 C
(356 F)
Dot 5.1 270 C (518 F) 190 C (324 F)
Engine bearing and crankshaft failure causes
1. Dirt &
debris in oil.
2. Lack of lubricaton from oil starvation or
"dry" starts.
3. Impact to
rod journal bearing surface rod stretching at top of each exhaust
stroke and compression load at top of each
compression stroke.
4.
Bending fatigue of crank
as opposed to torsional twisting. The heat generated by a bearing
failure will often cause a
crank to bend.
Exhaust pipe sizes for
street performance.
Correct exhaust pipe size is
a function of both engine output and displacment. The higher the engine's
power output, the larger the
pipe(s) should be. This same theory holds true for larger
displacement
engines. But, this can be overdone.
Reducing exhaust restriction
increases both power
and fuel mileage. Too large a pipe can "over-scavenge" an engine and actually decrease power and fuel
efficiency. Muffler and catalytic convertor inlet and
outlet size should correspond to exhaust pipe
size to avoid
creating a flow restriction.
"H" pipes or "X"
pipes equalize back pressure with a
resulting midrange power increase.
Pipe sizes - both single and dual
exhaust configurations - street,not race use!
Note: table only applies to engines larger than 2.5L (150 cid). We do not have
corresponding specs for smaller engines.
Pipe OD
Engine HP
Engine displacement
Single Dual
2"
2"
100
150 - 200 cid
2.25" 2"
150
2.5" "2
200
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2.25"
2"
150
200 - 250 cid
2.5"
2.25"
200
2.5"
2"
250
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2.5"
2"
200
250 - 300 cid
2.5"
2.25"
250
3"
2.5"
300
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3"
2.5"
250
300 - 350 cid
3"
2.5"
300
3.5"
2.5"
350
Block & Head requirements for a good head gasket seal
In order to achieve a
good head gasket seal, stock or high performance engine, there are
certain prep basics for head and block. No, not the clean degrease prep, but the
flatness of the head and block surfaces. Flatness is critical on
any engine, rebuild. Flatness should not exceed .001" within
3" in anydirection. Even less than this spec on a performance engine. For
4 and 6 cylinder inline engines, .006" lengthwise and .002" sideways
out of flat is the mnimum. .003" lengthwise and .001" should
have you with a well sealed headgasket. V8 engines spec is .004"
lengthwise and .002" sideways. .002" either direction is target
for a performance rebuild.
For MLS gaskets, surface finish should be 30 Ra
(roughness average). Waviness of surface should be no more than
.0004".
Valve Event Codes
TDC = Top Dead Center
BDC = Bottom Dead Center
BTDC = Before Top Dead Center
ATDC = After Top Dead Center
BBDC = Before Bottom Dead Center
ABDC = After Bottom Dead Center
Common tire speed rating
symbols, maximum speeds and typical applications
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L
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75 mph
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120 km/h
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Off-Road & Light Truck Tires
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M
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81 mph
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130 km/h
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Temporary Spare Tires
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N
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87 mph
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140km/h
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P
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93 mph
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150 km/h
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Q
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99 mph
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160 km/h
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Studless & Studdable Winter
Tires
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R
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106 mph
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170 km/h
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H.D. Light Truck Tires
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S
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112 mph
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180 km/h
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Family Sedans & Vans
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T
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118 mph
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190 km/h
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Family Sedans & Vans
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U
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124 mph
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200 km/h
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H
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130 mph
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210 km/h
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Sport Sedans & Coupes
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V
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149 mph
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240 km/h
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Sport Sedans, Coupes & Sports
Cars
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