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.


engine displacement (in cubic inches) x desired rpm



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

CR =

V1 + V2



(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)

Cylinder volume (displacement) =

3.14 x bore x bore x stroke



Piston Speed (ft. per minute) = 2 x RPM x stroke (in feet)


RPM x wheel diameter (in inches)

(wheel diameter is overall including tire)


Gear ratio x 336


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/s
2 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/s
2 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
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.

Exhauspipe sizes for street performance.
rrect 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
2.25"            2"                                                             150                                                            200 - 250 cid
2.5"              2.25"                                                        200
2.5"              2"                                                             250
2.5"              2"                                                              200                                                            250 - 300  cid
2.5"              2.25"                                                         250
3"                 2.5"                                                           300                     
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 


75 mph

120 km/h

Off-Road & Light Truck Tires


81 mph

130 km/h

Temporary Spare Tires


87 mph



93 mph

150 km/h


99 mph

160 km/h

Studless & Studdable Winter Tires


106 mph

170 km/h

H.D. Light Truck Tires


112 mph

180 km/h

Family Sedans & Vans


118 mph

190 km/h

Family Sedans & Vans


124 mph

200 km/h


130 mph

210 km/h

Sport Sedans & Coupes


149 mph

240 km/h

Sport Sedans, Coupes & Sports Cars


TS Imported Automotive, 108 South Jefferson St., Pandora, Ohio, 45877, USA
Tel 800.543.6648 (USA & Canada only) 419.384.3022 (Tech / General Information)
Fax 419.384.3272 (24 hours) tedtsimx@bright.net
Hours 8:30 - 5 p.m. Monday - Friday, 9 - 1 p.m. Saturday (unless attending an event)

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