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Best performance mods

Best performance mods to increase engine power

Every day I see owners on car forums ask which are the best performance mods as if you can simply bolt on a few accessories and dramatically increase your car’s performance. If you really believe that, I have some swamp land in Florida I’m looking to sell.

The truth about increasing your car’s performance

First, give up the idea that automotive engineers are stupid. They’re not. Designing an engine/transmission combination involves a lot of tradeoffs. They have to design the perfect combination of acceleration from a dead stop, acceleration for passing, torque, MPG, and emissions. Change any one of those factors from factory and you upset the entire design.

What performance mods are available

On the intake side:

• Cold air intake
• Turbo

• Supercharger

• Larger throttle body

• Ram air

• Throttle body spacers

• New air filter in existing filter box to increase airflow

On the exhaust side

• Headers

• Performance exhaust

• Cat-back exhaust

On the computer side

• Performance tuning

On the engine side

• Performance cam

• Performance injectors

Now let’s talk about how each of these impacts the tradeoffs the engineers built in

Cold air intake: I’ve written a complete article on cold air intakes. Click on the link below to read the entire piece. The bottom line is that they don’t improve performance until the throttle body is wide open and the engine is running at or near red line. Below that point they don’t do squat for your performance. In fact, they actually reduce performance. I’ll remind you again, auto engineers aren’t stupid. If your fuel injected car was made after the mid ‘90’s, you already have a factory tuned cold air intake. Removing it and adding an aftermarket intake will not get you colder air, will not improve HP or performance, and will most likely reduce performance especially if your engine is equipped with a MAF sensor.

Worse yet, if you install a new cone filter style intake and locate the cone filter inside the engine compartment, you’re effectively removing the cold air intake and turning your engine into a hot air intake. It’s self defeating.

Finally, this isn’t just my opinion. Read the story below and you’ll find independent testing links that prove they’re worthless.

Here’s the cold air intake story

Air filter inserts: These are direct-fit panel air filters that fit right into the factory air box and claim to allow more air through so your engine can breathe better. At first glance, it sounds like a good thing—making it easier for your engine to suck in air. But keep in mind that the total square inch area of the filter box, the diameter of the air duct from the box to the throttle body and the throttle body itself hasn’t changed at all. You’re simply installing a less restrictive air filter that’s the exact same size as the factory air filter. How do they make that work?

Well, the theory is this: add more surface area with more holes and the filter media won’t be as restrictive. Think of this like a spaghetti colander with twice as many holes. You can add more holes in the same space by increasing the total surface area. The only way to do that in the same physical space is by increasing the number of pleats.

So now you have more holes and less restriction. Is that necessarily better? Think about this: The amount of air that goes into each cylinder is determined by the displacement of the cylinder, the area of the intake valve(S), valve timing, and the difference between engine suction and barometric pressure. Remember, while the piston is sucking in air, the atmosphere is pushing it in as well.

You can’t suck in more air than the cylinder’s total displacement at a given atmospheric pressure unless you force it in with ram air, a turbo, or a supercharger. If the engine designers build the factory air box and filter to provide enough airflow to fill the cylinder with air, how does having more holes get you more air? It doesn’t.

Worse yet, many of these panel filters are made out of oil-saturation cotton. GM has discovered that oil soaked cotton fibers break away from these filters and deposit on the hot wire in the mass airflow sensor. During the self cleaning cycle, the fibers and oil bake onto the wire and skew the MAF sensor readings. Since the PCM uses MAF readings to determine transmission line pressure, incorrect MAF sensor readings can result in too low a line pressure, resulting in slipping clutches and transmission damage. GM voids your powertrain warranty if your transmission was damaged due to the use of an oil soaked air filter.

Performance throttle body

The diameter of the throttle body and the throttle plate are two limiting factors in how much air can enter the engine at each throttle position. So it seems to make sense that a performance throttle body will allow more air in. That part is true as far as it goes. But it doesn’t take into account valve size and valve timing—those are also limiting factors. If you’re install a performance throttle body but don’t change the valves or cam timing, you haven’t increased engine performance.

Performance exhaust: Once again the theory is that if you make it easier for the engine to breathe, you’ll get better performance. I’ve written an in-depth article on the fallacy of decreasing exhaust backpressure as a way to increase performance on an otherwise stock vehicle. It comes down to this: If you’re install a performance exhaust but don’t change the valves or cam timing, you haven’t increased engine performance.

Read the exhaust backpressure story here.

Performance engine tune

This one is actually pretty simple. Profession tuning works—well, kinda. Keep in mind that engineers build an engine with all kinds of trade-offs. They can easily increase acceleration from a stop by ignoring MPG and emissions issues. Or, they can get you better acceleration and power at highway speeds too. But there’s no free lunch. You can’t get better acceleration from a stop AND better acceleration and power at the high end while still getting maximum MPG and staying within emissions standards. A professional tune usually gets you faster acceleration and more torque from a stop so you feel really macho. But you pay for that with worse MPG. And, since the automatic transmission wasn’t designed for that kind of torque from startup, you’ll literally burn up the clutches. So start saving for a performance automatic transmission rebuild.

Add a Turbo or Supercharger

Look, they work. They really do. But if you want to retrofit your engine, you can’t just bolt these babies on. Boosting cylinder pressure requires stronger pistons and a stronger crankshaft, along with different bearings and sometimes even stronger crank journals. They also require new high flow fuel injectors, and a complete PCM performance tune. At that point you’re better off buying a vehicle with a factory turbo or supercharger.

The bottom line:

The throttle body, valve opening, and valve timing are the most limiting factors in how an engine breathes. If you don’t change those, then save your money–no performance mod with help.

©, 2015 Rick Muscoplat

Posted on by Rick Muscoplat

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