A Guide to Basic Bolt-Ons

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In the world of aftermarket performance, the first step for most owners begins with the bolt-on upgrade.

What They Are: Bolt-on parts get their name from (you guessed it) their ability to be bolted-on. The best part about bolt-on parts is that they normally require no tuning, timing changes or anything complicated after their installation. Simply remove the factory or stock component, bolt-on the new part and drive! Let’s begin with the air induction system.

Air Filter/Air Induction/”Cold Air” Intake/ Cone Filter -

What It Does: In a matter of minutes (sometimes seconds), the factory air box, paper filter and induction system can be replaced with an aftermarket set-up. Since the tubing of the new kit has mandrel bent piping of a larger diameter attached behind a cotton filter, the engine can breathe better immediately. Even brand new cars will net gains from an aftermarket air filter set-up.

Expectations: A rough estimate for a WHP increase should be around 1-3% of the baseline dyno.
Example: A car dynos at 400HP. After swapping the air filter and induction system, you should see a minimal gain of 4HP, and not expect a gain larger than 12HP. Your individual results may vary. At the dyno, expect the lowest number so you’re pleasantly surprised.

What It Does: A larger aftermarket throttle body allows for more air to enter the intake manifold. In addition to being larger, some factory throttle plates don’t open to a full 90 degrees (common on LS1 F-Bodies). A good aftermarket unit will net an even bigger increase in gains when complimented with an air induction kit.

Expectations: Alone, a throttle body might be worth a few HP and some increase in throttle response. Combined with an Air Induction Kit, the gain increases. Add an aftermarket intake manifold, camshaft and heads, and the gains continue. Figure an extra 1-2% by itself, 3-4% with an induction system and anywhere from 5-7% gains in HP combined with top-end parts.

What It Does: An aftermarket intake manifold has a larger diameter inlet (behind the throttle body) and increased diameter runners feeding the engine head(s). The increase in the air volume nets massive gains in HP, especially when paired with other parts.

Expectations: Intake Manifolds are not common as the “only” bolt-on part. Simply upgrading your stock one is sure to gain a few ponies. Since it never quits and is always increasing the air volume, expect gains throughout the entire RPM band and bigger gains in the mid to upper range. An intake is worth about 3-4% of power throughout the entire band. Coupled with an air induction and throttle body, you might see gains in excess of 5%. They really become worth their weight in gold when increasing displacement, swapping head(s) and cam(s).

I can’t discuss the induction side of things without the exhaust side of things.

The entire exhaust system is normally a very quiet set-up from the factory. Not everyone frequents RacingJunk.com, nor does everyone see RPMs above 4000 daily. As such, auto manufacturers decided “quieter is better” and most cars, even hyped up for performance, have quiet exhaust systems.

When it comes to exhaust, quiet equals restriction!

The easiest part of the exhaust to change is the rear end. The muffler, tailpipe, and sometimes a few resonators are only a few bolts away from being swapped out.

What It Does: The muffler, cat-back and axle-back all comprise the rearmost portion of the exhaust system. They are mainly there to quiet the engine sounds before they enter the atmosphere. This is accomplished by using a lot of bends, mufflers, resonators and smaller diameter piping. A good aftermarket muffler, cat-back or axle-back will change the sound of your car entirely. Comprised of smooth mandrel bends, straight-through designs and limited restriction, these systems will free up plenty of HP. They go great with any intake side parts as well. Remember, what goes in (intake) must come out (exhaust), so there’s no use having a great induction side and a weak exhaust side or vice versa.

Expectations: Regardless of the brand or system you choose, you will gain HP and noise. How much depends on the brand. Consider the material (mild or stainless), design (straight-through, mandrel bent), piping size (2”, 2.5”, 3” or bigger) and how many other modifications you’ve done. Expect a 1-2% minimal; when coupled with other mods, the gains increase.

What It Does: Even after replacing the restrictive factory muffler, there are still more restrictions in the exhaust. Replacing the headers, cats and downpipes (H,X,Y-pipes) with higher flow aftermarket ones will increase HP even more. They are best paired with your muffler or cat-back system. Diameters vary, but a rule of thumb is an increase over stock size - but nothing too dramatic. Consider your engine size before bolting on the biggest headers and pipes you can find. Try to find piping diameters that flow with your current engine set-up. Remember, exhaust pipes shouldn’t be restrictive, nor too big. A true-dual 4” system on a stock 5.0L Mustang is overkill. What is currently on the market is usually a good indication of what works on your car.

Expectations: HP gains from exhaust systems alone, especially long tube headers and high flow cats, can be upwards of 7%. I personally picked up 30RWHP with a set of long tube headers, high flow cats on a mandrel bent Y-pipe and a Magnaflow cat-back. Your results will vary, but swapping the full exhaust system as opposed to only changing the muffler, downpipe or other component will always yield higher gains.

What It Does: Weight is an enemy of every racer. Rotating weight (or mass) is the biggest enemy of racers. Lowering rotating mass on an engine will free up HP, and lots of it. Aftermarket pulleys are made of aluminum or other lightweight metals and replace factory steel pulleys. Although the weight savings might seem minimal, being only 5lbs or so, this is directly rotated by the engine. In turn, the weight savings frees HP throughout the entire RPM band. Regardless of any other mod on the engine, a lighter pulley or set of pulleys will immediately reduce restriction and recover lost power.

Expectations: Expect gains of 1-2% and increases throughout the entire RPM band. This mod needs no other supporting mods and will only increase the efficiency of the engine. If displacement, head(s) or cam(s) change, power will increase as well.

All images courtesy of knfilters.com, bbkperformance.com, services.magnaflow.com, fuelairspark,com, randomtechnology.com, pacesetterexhaust.co or dynomax.com.