Power Mods, Part 2: 05-08 V8 Vantage

Of all of Aston's recent cars, the early V8 Vantage is the one most in need of increased power. In fact, the only major complaint anyone had about the car when it was first released is that it needed an extra 50-100 hp. From what I've experienced, it wasn't that the car was under-powered. Its 380 hp, while not a breathtaking, was on par with other cars in its performance category at that time.

  • 2005 Jaguar XKR, 4.2L V8, 390 hp
  • 2005 Porsche 911 Carrera GT3, 3.6L engine, 380 hp
  • 2005 Aston Martin V8 Vantage, 4.3L V8, 380 hp
  • 2005 Porsche 911 Carrera S, 3.8L engine, 355 hp
  • 2005 BMW E46 M3, 3.2L engine, 333 hp
  • 2005 Porsche 911 Carrera, 3.6L engine, 325 hp

Note: The V8 Vantage did first release in 2005. It was released late in that model year (MY), so most markets didn't get the Vantage until MY06.

The V8 Vantage had as much or more horsepower than its competition. Despite that, many reviewers, owners, and potential buyers have said (and still say), that the car is too slow.

There were two distinct issues that, when combined, made the car feel rather slow. The first is that the Vantage looked and sounded much faster than it was. This affected a driver subconsciously as they expected the car to be faster than it was, therefore making it feel slower than it was. Second, there's a considerable amount of lag between throttle input and engine response. That lag is a much bigger issue than many people realize, so let's address that first.

Let's use a couple of basic diagrams to illustrate what I'm talking about. Here is a diagram showing the power output of two identical engines:

Engine Power vs Response 1.png

The engines produce the same power at the same RPMs. That means, all things being equal, the cars with those two engines will have the same acceleration. But if we change one engine so it can respond more quickly, it will reach higher RPMs before the other.

Engine Power vs Response 2.png

The engines still produce the same power at the same RPMs, but one engine climbs through RPMs more quickly. In the above example, the slower engine would have only around 300 HP when the quicker engine has 400 HP. So although the two engines produce identical power, one engine will outperform the other because of how quickly it gets to higher RPMs.

FIXING THROTTLE LAG

The 4.3L engine throttle lag can be largely remedied with two changes to the car. One reduces the electronic lag that causes the throttle body to open more slowly than the relative input you're giving the gas pedal. The other reduces the mechanical lag caused by an incredibly heavy flywheel. Either one will benefit the car, and both can be done to further improve engine response.

Reducing throttle lag matters because it means you get to the higher power output of the engine more quickly. It also allows you to better control the engine as quicker response means the engine won't take as long to get to the RPM level you want.

ENGINE TUNING

Aston Martin uses drive-by-wire throttle bodies. That is, an electrical signal is sent from the pedal to a solenoid on the throttle body to tell the throttle body what to do. It's pretty much the standard setup for all modern cars, having replaced drive-by-cable throttle bodies which had a physical cable running between the pedal and throttle body to pull it open.

The nice thing about drive-by-wire systems is that they can be reprogrammed to give more-or-less response at the throttle body based on pedal input. From the factory, the 4.3L V8 Vantage had a very leisurely throttle response. Engine tuning has the dual benefit of giving increased power as well as a quicker throttle response.

Lightweight Flywheels

A big issue affecting the 4.3L V8's engine response is its very heavy flywheel. A heavy flywheel does make a car easier to drive smoothly. It's hard to understand how much a flywheel affects a car's performance, so let's break it down a bit.

A Flywheel Spins
The flywheel is attached to the back of the engine, and it spins at the same rate as the engine. The weight of the flywheel has a direct impact on how much energy the engine needs to use to spin itself up, as it has to spin up the flywheel as well.

Weight Equals Momentum
The heavier a flywheel is, the more momentum it has. Momentum is resistance to change - for a flywheel, that means resistance to changing its rate of spinning. Having a lot of weight, and therefore a lot of momentum, means the flywheel will not easily change the rate it's spinning. Reducing the weight of a flywheel will allow it to change its rate of spinning more easily.

Changing Momentum Takes Energy
From a stand-still, it takes energy to get a flywheel to start spinning. It takes energy to increase the flywheel rate of spinning. Without energy being given to the flywheel, the flywheel will gradually lose momentum on its own and its rate of spinning will slow naturally. While spinning, it takes energy (in the form of resistance) to get the flywheel to stop spinning more quickly that it would on its own.

Putting It Together

To help this all make sense, let's look at various scenarios.

Scenario: Starting from a stop

  • A heavy flywheel will take more energy to get moving, but will maintain its momentum so it will not stop as easily.
  • A light flywheel will take less energy to get moving, but will slow down more easily because it has less momentum.

Although it takes more energy to get started, the heavier flywheel is easier to use from a stand-still because it won't lose momentum as easily. In this scenario, losing momentum will result in the engine stalling. In the real world, this is a serious concern when considering a lightweight flywheel for your car. If you get a flywheel that's too light, it'll stall pretty easily. If you drive your car in normal roads, and especially in heavy stop-and-go traffic, this can be a real pain.

Scenario: Accelerating

  • A heavy flywheel will resist increasing its rate of spinning. It will take more energy and more time to increase the spinning rate of the flywheel.
  • A light flywheel will be easier to increase its rate of spinning. It will take less energy and less time to increase the spinning rate of the flywheel.

Since it's easier to change the momentum of a light flywheel, that flywheel will accelerate more quickly than a heavy flywheel. The engine will accelerate its rate of spinning along with it - meaning it gets into the higher-RPM range more quickly. The higher the RPMs, the more horsepower the engine is putting out. So, a lightweight flywheel is best for accelerating since it allows the engine to get into its higher output range more quickly. And, since it takes less energy to spin up the flywheel, more energy can get from the engine to the wheels.

Scenario: Coasting and steady driving

  • A heavy flywheel will have more momentum when the engine is no longer giving it energy, which will result in a slower deceleration of its spinning.
  • A light flywheel will have less momentum when the engine is no longer giving it energy, so its spinning will slow down more quickly.

When you let off the throttle, the engine will naturally slow down on its own. The flywheel has an effect on this - a heavy flywheel will use its momentum to reduce the rate at which the engine slows down. That means the engine is going to maintain its power output at a more steady rate even after you stop giving it gas. In the real world, this translates to a smoother driving experience as the engine doesn't abruptly drop in power any time you lift off the throttle. If a flywheel is too light, the engine would feel 'twitchy' as you get on and off the throttle.

The Benefits of a Lightweight Flywheel

What all this means is that using a lightweight flywheel comes with a variety of benefits with a few concerns.

The main benefit is that you'll have a more responsive engine. It'll behave how you want it to rather than having that sluggish delay that plagues the 4.3L V8 Vantage. And since it's a more efficient component, more power will get from the engine to the wheels - an increase in WHP.

Primary concerns about a lightweight flywheel are drivability and cost. If a flywheel is too light, it makes the car difficult to drive - specifically getting started from a full stop, and maintaining smoothness as you get on and off the throttle. Picking a properly-weighted flywheel is key to ensuring you're getting the benefits of a lightweight flywheel without ruining your driving experience. Cost is difficult to avoid, but given the benefits it's still a very worthwhile thing to do.

The Clutch is part of this whole equation. It acts much the same as a flywheel but its primary goal is functioning as a coupler between the engine and transmission. Going to a dual-plate clutch will have its own benefits, but will add weight compared to the original single-plate clutch. The upside to this is that the weight is more centrally-located along its axis, so it isn't much of a detriment. Here's a picture of the VelocityAP clutch and flywheel installed in my grey V8 Vantage.

VelocityAP Clutch.jpg

Primary weight loss from the flywheel was managed by removing material from its outer ring. Weight positioned furthest from a spinning object's axis has the greatest effect on its momentum.

The Exhaust System

The factory exhaust system of the 4.3L V8 Vantage isn't that bad of a design. It has tubular exhaust manifolds, two catalysts (one per bank - that is, each side of the engine has its own), smooth mid-pipes, and a muffler that flows well.

Let's start at the front and work our way back.

Exhaust Manifolds

One benefit the 4.3L V8 has against later cars is that it doesn't have any catalysts in the headers. Here's a picture showing an OEM manifold (top) and an aftermarket manifold from VelocityAP (bottom).

V8V Headers.jpg

The dents in the OEM manifold are not actually impeding exhaust gas flow. The OEM manifolds are made with double-wall construction. There's an outer wall that you see, and an inner pipe that actually contains the exhaust gas. The outer wall acts as both a heat shield and sound-dampener. The dents in the outer wall are there to give easier access to the studs used to hold the manifolds to the engine.

You can see in the picture above that the VelocityAP manifold has more piping. This is done to ensure that the runners (the individual pipes that originate at the engine block) are all equal length. Making them equal length allows the exhaust pulses to travel through the manifold without colliding at the collector (the middle section where the runners join together). The cylinders fire one at a time, each firing producing an exhaust pulse. If all the exhaust pulses have an equal length to travel through the manifold, they will never collide. If they have a different difference to travel, they will begin to collide in the collector. That collision creates turbulence, which slows down the exhaust gases traveling through the manifold. By ensuring the pulses don't collide, the exhaust is able to flow more freely, giving you more power and engine efficiency.

The smoothing out of exhaust pulses does affect the exhaust note. Specifically, you'll get a slightly higher pitch. Since a secondary wall isn't used on them, you'll get a little more resonant noise as well. It's not quite a drone, but I did notice it a little when I installed them on my grey V8 Vantage.

Another benefit of the VelocityAP manifolds is that they weigh less than the OEM manifolds. I measured a 9-lb weight difference between them and the OEM units.

High-Flow Cats

The 4.3L V8 Vantage has two 600-cell catalytic converters. There is one cat per bank, and they're positioned immediately after the headers. The cats are attached to the headers with three studs per cat. A slip-joint is used at the rear of the cats. You can see this in the picture below (the pipe on the right-hand side of the picture is the OEM header).

OEM cat.png

As you can see in the picture, less than half of the catalyst material is actually monitored. The first O2 sensor located at the front of the cat takes readings of the exhaust gas exiting the header. The gas then passes through the first portion of the catalyst material and then is read by the second O2 sensor. The exhaust gas continues through the rest of the catalyst material and then exits the cat. The difference in readings between the first and second O2 sensors gives the car's central computer an idea of how much the exhaust gases have been affected by the catalysts.

Since only a portion of the catalyst is actually monitored, the unmonitored portion can be removed with no effect on the car's tuning. This is one of the reasons why you can use high-flow cats without needing a tune (though I do highly recommend getting a tune as well).

Cat Delete Pipes

If you want to go for maximum performance, a set of cat delete pipes will remove the catalyst material entirely. These will flow better and have less weight than the high-flow cats, but there are some important caveats if you use them.

First is that by removing the entirety of the catalysts, you're going to get emissions warnings and fault lights. You'll need to get an engine tune so the car's computer can be told how to handle this change. Second is that you'll have a lot louder exhaust. Here's the difference between the original 600-cell cats and 200-cell cats (jump ahead to the 18-minute mark).

The cat delete pipes will make it even louder. If you plan to go this route, you'll want to be extra careful choosing a muffler.

Mufflers

Aston Martin's mufflers flow pretty well. You'll gain a little bit of power by switching out for an aftermarket one, but the main benefit is going to come from reducing weight and getting the sound you want from your car. There are two primary factors to consider when choosing a muffler: valving and loudness.

The OEM mufflers have bypass valves built in. These are closed by default, which forces the exhaust gasses through a longer path within the muffler. The longer path reduces the loudness of the exhaust note. Under load, the valves will open at a certain RPM to give the exhaust a shorter path - this makes the exhaust note louder.

Muffler Valving.png

Because of the added complexity of exhaust valving, valved mufflers tend to be a bit more expensive than non-valved mufflers.

Non-valved mufflers come in a variety of flavors. The primary difference you'll notice most quickly is that there are a few levels of loudness. Typically, these will be described as Touring (quietest), Sport, and Super Sport (loudest). If you want to go completely wild, you can eliminate the muffler entirely. Make sure you've got some ear plugs!

Regardless of which muffler you choose, you won't need to worry about tuning - swapping out the muffler has no effect on the car's tuning.