Useful Hopups

Air Filters Heads Tuned Pipes
Aluminum/Titanium Parts


Universal Shafts
Ball Bearings Super Chassis Tuned Springs
Belt Tensioners Sway Bars
Fiber Brake Disks Tire Inserts


Air Filters
This hopup is often overlooked as it's perhaps one of the least glamorous in nature, however it is an important one that does deserve a second look.  An air filter's job is simple enough in theory; it simply filters the air coming into the carburetor with the least resistance.  However the practicality of this is that air filters have one main shortcoming that engineers have tried for years to overcome.   That is, that in order for a filter to be effective, it must finely sieve the airflow that comes in but at the same time, not clog itself in the process.  Just a slight intake resistance from a partially clogged filter can greatly effect performance.
MotorSaver dominates the very short list of superior filter design by using a dual filtration method.  By using a dry, fine woven plastic fabric on the outside of a basket frame and then using a conventional wet-type sponge filter in the center, the filter is far less likely to get clogged.  This is because large debris (normal dust, dirt, sand, whatever) get deflected off the dry outer filter before they have a chance to cling to the inner wet filter.  Only the fine dust particles that make it through the basket's filter get to pass through the wet filter... a very small percentage of the total contaminant.  The MotorSaver filter also has far more surface area exposed for filtration.  Most wet-type filters just have a single-end surface that is exposed and take on the brunt of all the contaminants that come its way.  It doesn't take long in dusty conditions for these type of filters to get clogged.  The paper canister type filters don't attract as much dirt as to the wet type, and are often covered in a dry sponge outer-shell, but because this outer shell fails to deflect any of the contaminates, and because the paper canister cannot be washed, this is hardly any better than the conventional wet types.

Highly recommended, especially under dusty conditions.

Hop Up Meter:  8.0

Aluminum/Titanium Parts
It's hard to find a kit or RTR these days that doesn't contain at least some aluminum parts.  This is because aluminum is extremely heat conductive, rigid and extremely light-weight.  It makes for a far better parts material than traditional plastic that most kits start out with.  Titanium takes things even farther with an unprecedented ability to take any abuse you can throw at it.  One of the hardest, lightest metals in existence, it was first made popular in NASA's space program where an extreme tolerance, light-weight, virtually indestructible material was needed to construct the space capsules of the time.  Today, titanium is seen nearly everywhere where extreme high-demands are in order, from high-quality watches, to tools, to precision instruments.  Because of the manufacturing process of titanium as well as the demand, it does tend to be rather expensive, but often, well worth the investment.

Popular R/C applications include tie-rods, ball ends, pulley shafts, transmission gears, etc.

Always a good idea as it will add a tremendous amount of durability to your car/truck/buggy.  Can add up in cost very quickly, so choose parts wisely.  Titanium a must for serious racers for ball ends and tie rods.

Hop-Up Meter: 7.0-9.0 (depending on application)

Ball Bearings
Perhaps the single greatest improvement that can be made to any car or truck that uses bushings.  Because bushings are far cheaper to manufacture, they are usually found on most entry-level kits and RTR's.  They provide somewhat adequate support for a very limited time.  Usually made of either nylon or bronze, they are subject to a great deal of friction.  This causes both a serious performance drag on the car or truck as a whole and tend to wear out rather quickly, especially in high-speed/powered vehicles.  Ball bearings are designed so that the inner hub and outer hub roll past each other by use of small steel balls that roll on track that is machined on the inner surfaces.  This completely eliminates any "rubbing" that is inherent in bushings.

Definite must-have!  Will give the greatest performance boost.

Hop Up Meter:  9.0

Belt Tensioners
These are perhaps more of an esthetic enhancement as well as a belt-saver than a real performance hopup.  Belt tensioners simply take up the slack that tends to develop as belts stretch from normal use.  By helping to prevent the belt from slapping around you can actually enhance overall efficiently in some cases and increase the life of the belt by allowing it to properly seat on the pulleys.

Belts are typically only used on either 4-wheel drive on-road sedans and some rally type cars.  Often the belt that drives the front wheels is the longest and gets the most benefit from a belt tensioner.

Not usually a must have, but does clean up the esthetic quality of the overall machine.

Hop Up Meter:  4.0

Heads    dynhead2.gif (3152 bytes)
This one is fairly simple.  The performance difference between one head and another is it's ability to dissipate heat.  The more air surface that is exposed, the better it will cool.  Most (or all) are made of aluminum which conducts and dissipates heat very rapidly.  Since these engines are not liquid cooled, the majority of engine cooling is performed by the head, so this is an extremely important item on your engine.  These are considered hopups because a cooler running engine runs more efficiently and therefore can put out more horsepower.  Not to mention that a cooler engine equates to longer engine life!   The O'Donnell head is your best bet for .12 to .15 engines as they are easy to install, tough as nails, dissipate heat extremely well and come in a rainbow of different colors to match your body or chassis.

Well worth the investment.  Increases horsepower while keeping your engine cooler; adds to lifespan of your engine.

Hop Up Meter:  6.0

The purpose of shocks are two-fold.  To absorb the shock of bumps and dips in whatever track you run on and to stabilize the chassis bounce that normally accompanies handling such bumps.  Keeping the tires in contact with the ground at all times (with the exception of jumps) is a necessary demand for any car, truck or buggy.  Without proper tire contact, the vehicle would be impossible to control.  By allowing the relatively low mass of the wheels and a-arm assembly to travel up and down to compensate for the dips and bumps, the chassis can remain fairly stable through it's handling phase.  This all sounds more complicated than it really is.  The important thing to remember is that allowing controlled vertical travel of the wheel assembly is the key to keeping the tire contact at it's maximum and shocks are the main ingredient in this system.  The better your shocks, the better your handling.

Most shocks today are fluid dampened with various grades of silicon oil that are forced through a piston/cylinder assembly that acts to absorb the kinetic energy of suspension flex.  To main factors effect the handling characteristics of shocks, the plunger's by-pass holes (through which the silicon fluid passes) and the viscosity (liquid thickness) of the silicon fluid.

R/C shocks are generally single action, that is to say that the upward and downward dampening are the same (unlike today's advanced cars which have one dampening factor for up-thrust and another one for down-thrust which allow more tuning flexibility).  This limitation requires experimentation to find the correct compromise between the two.  This is one of the biggest reasons you will see guys at the track tinkering so heavily with their shock/spring setup... trying to find that sweet spot where handling is at it's best for a particular track.

Most kits come with silicon shocks nowadays, but for those who don't have them yet, a definite must.

Hop Up Meter:  10

Sway Bars
This is one of the most controversial hopups out there.  Sway bars (or actually anti-sway bars by their proper name) are bars that run width-wise, pivoting on a common axis and joined at both ends by the suspension control arms.  The tensile strength of the bars determine the effectiveness they have on dissuading the natural chassis leaning factor that independent suspension produces when a vehicle takes on a corner.  

The problem with vehicles leaning when going around a turn is it tends to compound the problems of traction roll and reduction inside tire traction.  Under severe conditions this can lead to the vehicle flipping over when cornering.  Sway is more problematic with vehicles that have a high center of gravity.. that is that there is more mass sitting up high on the vehicle rather than in the preferable base.  Because of the heavy machinery of nitro cars, they tend to have a higher center of gravity than their electric counterparts and sometimes require a countermeasure to compensate for the excessive body roll.  This is where anti-sway bars come in.  By minimalizing the independent suspension characteristics of the chassis, body roll can be reduced.   When the vehicle goes around a corner and the outer side of the vehicle tends to lean in, the a-arms on that side will tend to compress more than the others.  The sway bars help to artificially compress the inner a-arms while at the same time add tensile strength to the outer arms by dissipating the compression energy to the inner arms.  

Very useful for nitro sedans that tend to flip excessively around turns or have severe oversteer..

Hop Up Meter:  5

Tuned Pipes   pipe_sm.gif (1259 bytes)
Those of you out there that have started with anything other than a tuned pipe will know that this is one of the single most important hopup you can buy.  One of the only cons that I mentioned about the HPI RS4 was that it came with a muffler (the old airplane canister types), and many of you out there may have gotten similar exhaust devices in their kit or RTR. 

The idea of a tuned pipe is to create sufficient back-pressure in low RPM's to allow the engine to idle properly, but to "open up" when the RPM's are cranked up.  All the reasons for this are beyond the scope of this article, but let's just say that the physics of 2-cycle combustion engines require this.  Tuned pipes achieve this proper back pressure by utilizing gas turbulence.   Based on the design of these pipes, slower moving gases such as with low RPM exhaust have more resistance to vacating the pipe than gases that move at a faster pace as with higher RPMs.  The exact method varies from manufacturer to manufacturer, but the concept is the same.  Paris' ring pipe is a prime example of this technology at work.   In theory the "rings" running width wise through the pipe create turbulence which creates a natural resistance, or backpressure.

Any of the tuned pipes out there will give you a significant advantage over mufflers because they allow the gases to escape at a high velocity at high RPM's where the engine power-curve is at it's maximum.  Mufflers tend to do just what their name muffle.   This suffocation tends to lead to higher engine temperatures and poor engine performance.  The only advantage to mufflers is that they tend to keep the noise down quite a bit.  If you live in a neighborhood that enforces noise ordinances you might have to consider keeping your muffler (or get better neighbors).

CVEC and Paris seem to be the two preferred pipe manufacturers out there.  As to which is the better one... this all depends on the application.  Check with your local KNOWLEDGEABLE hobby store clerk or better yet, ask the guys down at the track which they prefer.  Mounting size, ease of installation, back pressure requirements, and normal operating temperature all effect the experts opinions on what pipe to use. 

Highly recommended, especially if you do any racing.  Dramatically increases engine power, especially in higher RPMs. Increases decibel level which may be a problem in some neighborhoods.

Hop Up Meter:  9.0, 1998, 2011
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This page last modified: 07/26/11