Off the Shelf Performance Parts







Many, many aftermarket parts to choose from
Many are poorly designed and tested
Make an educated decision
If it’s cheap, it’s probably because it’s cheap
Avoid products that use ‘buzzwords’ or slang in place of technical terms.
It is a ‘you get what you pay for’ world, but it can also sometimes be a ‘you paid too much for what you got’ world.
Remember to build your torque curve for your application and choose parts that develop torque in the right area of the rev band.

Off the Shelf Performance Parts

Intakes


Stock air box is there to muffle noise.


Inside airbox is a labyrinth used to cancel out noise

Stock intake is ‘the other muffler’
Air does not like to turn corners, this makes the airbox restrictive especially at higher rpm.
Cold air intakes

Air intake tube pulls air from outside the engine compartment





Outside air is colder, and therefore more dense.
Is usually a straight shot to the throttle body or carburetor, no labrinth.
Flow better, provides additional horsepower at higher rpm.
At lower rpm, volume of airflow is less so power increase is less.
Cold air intakes can make engine sound much better.

Off the Shelf Performance Parts

Intakes

Short Ram intakes ( or just an air filter on carburetors )





Basically just a performance filter shoved onto the throttle body.
Sucks in all its air from under the hood.
Air under the hood is hot, not conducive to good power.
Airflow into engine compartment when vehicle is moving is not enough to offset heat of engine.
On FI engines, as vehicle sits at stoplight ECU picks up heat from
IAT sensor.

Mixture gets richer



Timing is retarded
When vehicle starts moving again, it takes a while for mixture and timing to improve
Falsely show power on the dyno, because hood is open.

Off the Shelf Performance Parts

Performance air filters


Efficiency: How efficiently the filter can trap small particles
Capacity: How much dirt the filter can hold before it becomes restrictive




These definitions apply to all filters.
A standard paper filter element is most efficient at filtering dirt




Flows well when new
Gets restrictive faster
Surface area is key to capacity
The best choice for the street
‘K and N’ type filters flow very well



Not as efficient at removing dirt, K&N does not claim it does, advertiser do.
Flow well when new
Flow well when partially dirty


This is the key advantage of this type
Have high capacity.
All filters are most efficient when dirty




A clean air filter will not ‘protect your engine better’
As particles get trapped on top of each other they create smaller and smaller pores
A dirty air filter will not reduce mileage on a modern fuel injected vehicle
A dirty air filter can cause mixture to be rich on a carbureted engine

Off the Shelf Performance Parts

(draw on board)





MAF’s are tuned for emissions from the factory
Real gains can be made at high RPM
Bore is small to keep velocity high at low rpm

This makes readings accurate at low rpm
MAF ‘ element ’ (the actual measuring part) are usually replaceable

Allows you to replace with a larger housing without replacing element
Mass air flow meters are tapered

Increase velocity of air past the sensor


Straight sensors can cause erratic readings
Straight housing causes surging or stalling at idle

Off the Shelf Performance Parts

Mass air flow meters


Takes reading ‘sample’ from center of bore

Relocating sensor into a curve is a bad idea

You may do this if installing a turbo kit, for example


Air will get thrown to the outside of the pipe and not get measured
This causes inaccurate readings as the center of airflow changes at different loads and rpms.
Larger MAF requires recalibration




For same amount of voltage, MAF output voltage will be lower
Computer can not compensate
Computer must be retuned to work with MAF
(Draw voltage curve on board)

Off the Shelf Performance Parts

Throttle bodies

Bore of throttle body can be made larger






Increases total flow
Power gains will show up at higher RPM
If increasing redline of engine will be needed
May show improvements on stock engine because stock throttle body is tuned for idle/low speed
Will need to make new throttle plates

Plate is not round, requires some math to determine proper size.
Electronic ‘fly-by-wire’ throttles may need to be remapped for drivability (draw on board)

Can make power more ‘linear’ (draw map on board)

Off the Shelf Performance Parts

Intake manifolds (draw on board, label parts)

Larger (more volume in the runner, plenum) manifolds make more power


Short, fat runners for optimum high rpm
Long, narrow runner for optimum low rpm




Raise torque peak higher in the rpm band
Velocity drops at lower rpm with large runners, this can be detrimental to low end torque
Aluminum manifolds can be ‘ Extrude Honed ’

Abrasive paste is forced through manifold to remove material and polish walls of manifold

Follows existing contour.
Fuel injection manifolds only have to flow air


Fuel and air does not stay homogenous (well mixed) when it has to turn corners
This is one of the main advantages of fuel injection

Off the Shelf Performance Parts

Intake manifolds

Carbureted manifolds for V8’s


Dual plane manifolds


Create peak torque in the lower RPM range
Best for street vehicles and trucks



One side of carb feeds 4 cylinders, other side feeds other 4
Creates smaller runners and plenum, more velocity
Image: Dual plane manifold
Single plane manifolds

Create torque in higher RPM range




Best for racing vehicles and lightweight vehicles
All 4 barrels of carburetor feeds all cylinders
Larger plenum and larger effective runners
Image: Single plane manifold

Off the Shelf Performance Parts

Intake manifolds

Tunnel Ram

Not for street use

Uses large diameter, long runners to build velocity at high
RPM.

Have poor drivability and torque at low RPM

Usually have two carburetors

Good for raising impression ratio, your friends will be impressed

Image: Tunnel ram intake

Off the Shelf Performance Parts

Intake manifolds

Other available parts

Intake trumpets

Velocity stacks

Off the Shelf Performance Parts

Cylinder heads


Variety of aftermarket heads available for both domestic and import engines
Can get aluminum heads for engine originally equipped with iron heads, can use higher effective compression ratio = more power.








Good heads are CNC ported . Hand ported heads can be inconsistent from cylinder to cylinder. Some heads are ‘as cast’ and can be hand polished = lower cost.
Choose your heads before choosing cam
Have upgraded valves, retainers, keepers, springs, etc.
Using displacement ratio math, determine what volume (cubic centimeters or inches) combustion chamber you need to achieve your desired compression ratio.
Get manufacturer supplied flow chart from flow bench to help determine which cam you need.
Manufacturer should be able to help you determine what port volume you need to achieve your power goals.
In general, smaller ports will develop torque in the lower rpm range and larger ports will develop torque higher in the rpm band.
Have upgraded valves, retainers, keepers, springs, etc.

Off the Shelf Performance Parts

Camshafts


There are way too many aftermarket camshafts on the market.
Terms such as ‘stage 1’, ‘stage 2’, ‘tuner series’, ‘pro series’, ‘fast ramp’, ‘Xtreme’,
‘fireball’, ‘thumpr’, etc are all marketing buzzwords and are COMPLETELY
USELESS.









Many companies sell camshafts that were manufactured by someone else, and put it a box with the companies name on it.
A cylinder head flow chart is needed to properly choose the lift of a camshaft.
In general, the higher the engine revs, the more duration the camshaft will need to have.
Camshaft selection is extremely complicated.
It is best to let the experts give you advice, no one persons knows everything there is to know about engines.
Don’t be afraid to get advice from more than one source.
Camshafts have a bigger influence on power than anything else.
Once a cam is broken in, it must not be separated from its paired lifters.
Always use new lifters on American V8’s

Off the Shelf Performance Parts

Exhaust manifolds/headers


Stock exhaust manifolds are made for emissions/cost
Designed to keep heat in so they heat up the catalytic converter as fast as possible.







Often are very restrictive and a good way to ‘free up’ power.
Newer vehicles have ‘pre-cats’ close to exhaust ports to ‘light off ’ quicker.
‘Headers’ are made of steel tubing and flow better than cast iron manifolds.
Length and diameter of primary pipes, as well as header configuration determine rpm range.



Tri-Y header – best for producing torque at a lower rpm
4 into 1 header – best for producing torque at higher rpm
Has to do with timing of exhaust pulses. ‘Rarefraction’ timed to help draw in air and fuel during valve overlap.
Balance pipe – Used on V8 engines that do not have a flat plane crank.
Dinan headers
Get A. Graham Bell’s book Performance Tuning in Theory and Practice for good information on exhaust system design.


Mufflers







High performance mufflers have less restriction.
Will make more power higher in the rpm band.
Low rpm will see little gains unless there was a problem with the original design.
‘Tunes’ the sound of the engine – like a musical instrument.
Universal performance mufflers may or may not work well on your car.
Application specific mufflers are designed by trial and error – tuned to what is most pleasing to the ear.
Helmholtz principal used on good mufflers (draw on board).


Electronics




Power chips

Make power by altering fuel and spark

Optimize for premium fuel
‘Software’


Can be programmed through OBDII port
Alters fuel, spark, cam phasing, fly-by-wire throttle, idle, rev limit, top speed, etc.
Plug and Play ECU’s

Plug into existing wiring and allow tuneability
Stand alone ECU’s

Eliminate any emissions controls but allow ultimate in flexibility.