Power Mods, Part 1: Introduction

[Under Construction]

Adding power is often the first place people look when planning out their modifications. It's especially important for the early V8 Vantage with the 4.3L engine, which is often derided as being underpowered and slow. These pages will go over the basic modifications you can do to improve the performance of your Aston Martin where engine power is concerned. There are two main themes to understand before we begin: power output and power delivery, which are covered on this page. The following pages are vehicle specific, but the topics covered in each are common for all cars, so it's worth reading each page regardless of which care you have.

These articles will cover subjects at a high level. Meaning, I won't be getting into the science, physics, or engineering of a given topic. The goal of these articles is to give an overview of the basic concepts of modifying an Aston Martin, what options are available, and how those options will affect your car.

DISCLAIMER: As always, follow all safety protocols. Don't undertake this task if you aren't comfortable with it and fully understand it. You are ultimately responsible for anything you do. Neither Redpants, LLC or myself is responsible or liable for anything that may occur.

WARNING: Laws vary depending on where you are. It is impossible for Redpants to keep tabs on all laws for all places. You are responsible for ensuring your compliance with any laws that apply to you.

Basic terminology

This first section is to cover terminology as well as some basic information regarding those terms. These terms may conflict with what you've heard somewhere else, which is why I want to take the time to go over them. These are the terms I use when talking about cars, and they're the terms I'm using throughout the articles. I'm not saying other terms are wrong, I'm just getting us all on the same page for the sake of clarity.

Power Output VS Power Delivery

There aren't a huge number of places to gain power in an Aston. Rather, it's just the basics: Intake, exhaust, and tune. There are ways to improve power delivery, and these are going to be just important (if not more so) than the peak HP numbers most people focus on. The distinction between power output and power delivery is very important because both have a related but different effect on how the car behaves when you get on the throttle.

(A quick note: I'll often say throttle instead of gas pedal, though they're the same thing. The term "gas pedal" kinda bothers me because it isn't a gas pedal, it's an air pedal. You press down on it and it opens the throttle body, allowing more air into the engine. The additional gas is provided to maintain a given air-fuel ratio due to the increased air flow, so it's a reaction to the primary function of the throttle pedal: air. Okay, pointless tangent over, let's continue.)

Power Output

Power output is how much power your engine is making, and the terms used to describe power output are distinct and important to understand.

Horsepower (HP) comes in two flavors: brake horsepower (BHP) and wheel horsepower (WHP). Brake horsepower is named after the source of its measurement: an engine braking dynamometer (dyno). It's a type of dyno that connects directly to an engine to measure the engine's power output. Brake horsepower has nothing to do with the brakes of the car.

The general term "horsepower" is the same as brake horsepower, but wheel horsepower is different. Wheel horsepower measures the amount of power at the wheels of the car. WHP will always be less than BHP because power is lost between the engine and wheels. The amount of loss depends on a large number of factors, but typical loss for a rear-wheel drive (RWD) car is 15-18%. So a car making 400 BHP will have around 330-340 WHP. All-wheel drive (AWD) cars have an even greater loss of power in the drivetrain, as much as 25%. When you see a car driving in place on a platform, that's a chassis dyno (or "rolling road") which measures WHP. You may also see small individual dynos attached to each of the car's hubs where the car's wheels should be. It's another way to measure WHP.

Another figure you may see is pferdestärke (PS), which is very close to BHP. A car with 400 BHP would have approximately 405 PS. It's a small difference, so don't worry about it too much. The main issue with this measurement compared to horsepower is marketing - you'll see conflicting reports of a vehicle's horsepower, when someone may have mistaken PS for HP while writing an article.

The other main measurement is torque (TQ), which is expressed in pound-feet (lb-ft) or Newton meters (Nm). Horsepower and torque are related and are in fact two ways of expressing one thing: engine output. An easy rule of thumb to help you differentiate between the two is that torque is the power that matters in the lower part of the RPM band - say, when you're starting from a stop or cruising at a steady speed on the highway. The more torque you have, the quicker your car will launch from that stop, and the quicker your power (and speed) will build when you want to pass a car without downshifting. Horsepower is the snappy, quick power burst you get in the upper RPM band. If you've ever driven a diesel that feels "gutless" above a few-thousand RPM, you've felt firsthand the difference between torque and horsepower.

A massive amount of information is available online about horsepower and torque, and how engine output can be increased (or decreased, or changed in other ways) with modifications like an exhaust system, so I won't rehash that. Instead I'll go over these things as they are specific to an Aston Martin.

The main takeaway from the information above is the difference between BHP and WHP, and the difference between horsepower and torque, as I'll be describing characteristics of various cars and their modifications in these terms. While the differences may be subtle in print, the differences in the real world can be substantial.

Power Delivery

When driving, power output is how much power you feel when you get on the throttle. Power delivery is how you feel it. Power delivery is affected by things like engine response and drivetrain efficiency. Engine response is incredibly important as it heavily affects the car's drivability. I get into this more in-depth in the next section as it's a key issue with the 4.3L V8 Vantage.

Drivetrain efficiency is a little harder to explain. Everything in the drivetrain, going from the engine and its ancillaries, through the transmission, to the tires themselves, and everything in between, has an effect on efficiency. For the most part, Aston Martins have an efficient drivetrain because components are linked fairly directly. Direct connections create a solid link that doesn't allow for any twist between the components. When there's twist, it's wasted energy. Think of when you're looking at an engine and someone revs it up - you can see it moving in the engine bay. That twist is wasted energy because the energy is being sent into the engine mount bushings rather than being sent to the wheels.

An example specific to Aston Martins is the Vantage's use of a carbon fiber prop shaft inside of a torque tube. The torque tube directly connects the engine and transmission. The carbon fiber prop shaft is one piece, which is another direct connection. A traditional layout wouldn't have a torque tube so the engine and transmissions move independently, and the driveshaft often has a U-joint in the middle, which is a point of inefficiency.

A single inefficient component in a drivetrain may have very little effect on overall efficiency, but it does add up. Improving efficiency results in more energy being sent from the engine to the pavement. That means although you're not producing more BHP, you are producing more WHP. If you can reduce drivetrain loss from 18% to 15% in a 400 BHP car, you've gained 12 WHP.

Improving efficiency isn't always simple, as there are pros and cons for everything involved. It's impractical to redesign a drivetrain (like adding a torque tube to a car that doesn't originally have one), but there are two major ways to make improvements. First is by reducing weight. Second is by using stiffer materials.

Reducing weight results in less energy being needed to move components (like the flywheel, which is discussed further in the next section). Stiffer materials ensure energy is sent to the road rather than being lost elsewhere (like the engine and transmission mounts). Each of these must be done with a certain balance in mind. Reducing weight too much can result in twitchy engine response, weak components, or prohibitively high costs. Making every material as stiff as possible will make the vehicle incredibly uncomfortable to drive.

Exhaust Components

Terminology for exhaust components get thrown around interchangeably quite a bit, so let's clear those up.

  • Exhaust manifolds AKA headers: The first part of the exhaust system. These collect exhaust from the individual cylinders of the engine and combine them into a single pipe.
  • Catalytic converters AKA cats: These contain pollutant-reducing material to help a car meet emissions requirements.
  • Mid-pipes and rear-pipes: The pipes that connect the cats to the muffler.
  • Muffler AKA rear exhaust: The large noise-reducing section of exhaust at the rear of the car.
  • Tail pipes AKA exhaust tips: The end pieces of the exhaust, visible at the rear of the vehicle.

Changing any of these can have an impact on the performance of the vehicle as well as the sound of the exhaust. There are a few different exhaust system setups used in Aston Martins so please check each section for details for a given car's exhaust components.

Exhaust Noises

Let's set a few terms in place for this topic as well. Again, much of this is related but distinct.

  • Exhaust note: How the exhaust sounds as a whole, mostly regarding pitch and pulses, and also volume to a smaller extent.
  • Exhaust pitch: How high- or low-pitched an exhaust note sounds. A pickup truck has a low-pitched exhaust note. A Ferrari has a high-pitched exhaust note.
  • Exhaust pulses: The individual exhaust noises that you hear. When you make exhaust noises with your mouth, think of each syllable is a pulse.
  • Exhaust volume: How loud the exhaust sounds.
  • Droning: The constant resonating noise you hear in the cabin of a car from some exhaust systems. Not to be confused with loud volume.

Like everything else, balance must be struck to get the right qualities for a person's specific taste. Exhaust note and volume are very subjective. Some don't want to hear any noises come from their cars, some want to make sure everyone hears the noise of their cars. Most of us fall somewhere in between. Some people like how Ferraris sound, some people aren't fans of the high-pitched scream. This too can be tailored for your preferences.

There are many variables to consider when looking at exhaust components, but there are a few consistent things to keep in mind:

  • Catalytic converters act as mufflers. If you reduce the size of a catalyst (like switching to a high-flow cat) or remove the catalyst entirely (cat delete pipes), the exhaust volume will get louder, but the exhaust note will stay the same.
  • Mufflers can look the same but sound different. This is based on their internal construction. Aston Martin mufflers have exhaust valves that open up to make the exhaust volume louder. Some aftermarket mufflers retain this functionality, some do not.
  • Smoothing out exhaust pulses (equal-length headers or an X-pipe) can increase the exhaust pitch and make the car sound more exotic and less like a muscle car. Some mufflers have X-pipes built into them.

The car with the biggest room for improvement is the early 4.3L V8 Vantage, so let's start there.