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the power to weight ratio conundrum

The power-to-weight ratio conundrum

It’s a pretty self-explanatory ratio; divide the engine’s power by the vehicle’s mass for a metric independent of the vehicle’s size. Manipulating that ratio is the essence of improving performance and this Mercedes-Benz A45 AMG takes the route less travelled

Dinesh Appavu Photo

Dinesh Appavu

18 Sep 2018

A ratio is defined as the quantitative relation between two amounts showing the number of times one value contains or is contained within the other. As a petrolhead, the most common variant of this ratio you’ll come across is the power-to-weight ratio.

As the name suggests, you divide the engine’s power by the vehicle’s mass for a comparative metric against other vehicles. Though noble in intention and an overly simplified comparative for the layman to understand, the harsh truth is that the ratio often quoted by manufacturers is at the engine’s peak value and the actual value may vary widely depending on the powerband of the engine.

However, today’s not to open that can of worms. Instead, the spotlight brightly illuminates the manipulation of that ratio. Increasing the power of the engine will result in a ratio more favourable for performance and that’s precisely what has been the lynchpin of the aftermarket industry.

Hotter cams, more boost, larger injectors and so forth all undoubtedly crank up the horsepower count but the thing most of us have forgotten about a ratio is that manipulating the other side of it will lead to the same outcome… something more favourable in making greater haste.

Reducing the poundage of said vehicle will alter the ratio into something more advantageous not just on the straights but also when roads do that thing to change direction… they turn.

Furthermore, cars these days are more powerful that any of their predecessors. Hot hatches in factory form boasting more power than supercars from 20 years ago is old hat. Safety requirements also dictate that these cars need to absorb harder impacts.
One way around putting down the power down effectively is with all-wheel drive systems. This also means more weight. The use of more steel in the structure leads to more of the same; weight.

Renowned carmaker Gordon Murray; designer of the McLaren F1 and Formula One machines, acknowledged that the paradigm shift in the industry is stressing the loss of weight over more power.

You can’t even begin to quantify the benefits of this method. Cutting weight helps it handle better and in improving the power-to-weight ratio, keeps it just as quick. Extracting more power from an engine does hinder its ability to meet increasingly stringent emission regulations and cutting weight helps circumvent that.

Take for example the Mercedes-Benz A45 AMG, the current king of the hot hatch crop. It’s modest sounding 2.0-litre turbo inline-four makes an astonishing 360hp in stock form. The issue then is grip. Naturally, all-wheel drive is necessary. This brings it from overweight to obese.

Next up is the transmission. Manuals are tragically going out of favour and dual-clutch transmissions helped themselves to an extra slice of pizza from the fridge.

Nonetheless, the A45 AMG is for all purposes, a hot hatch, and one that’ll dance around even modern supercars till they catch fire.

So, what’s someone to do in the pursuit of more performance from an A45 AMG? Listening to the gospel of Murray and Lotus founder Colin Chapman, you put the hatch on a diet… a high fibre one.

There’s more carbon fibre here than Lindsey Lohan movies that flopped and most of them are from the fine hands of local outfit Carbonetics Arts. It’s a name that’s going to be on repeat as we dissect the flashy exterior.

Yes, almost every carbon fibre piece on this build is locally made. Carbonetics Arts from Johor provided the front canards, rear canards, rear hatch, spoiler, fuel flap, battery and air filter cover in the engine bay and the most impressive part of the weight loss programme, the rear doors, all in carbon fibre.

You know the build has gone onto the next plane when the rear doors are made from the magical weaved material.

Although sporting an aggressive façade, the A45 was further injected with cosmetic steroids in the form of front lips, rear diffuser, Advanced Liquid Concept carbon fiber fenders, Utmost Performance carbon fiber side mirror, Boca Design dry carbon bonnet and CT Motorsport dry carbon engine cover. Yes, even more carbon fibre.

Rumour has it, Formula One called the owner and pleaded that he leave some for them.

It’s all wrapped up like Christmas came early in Raptor R Techwrap vinyl that’s a shade of we-forgot-to-ask.

One aspect of modern performance engines that we can all revel in is the large safety margin in tuning. Software becomes as cardinal as hardware under the hood with remaps letting our more ponies from the pen.

The engine though wasn’t left in a virgin state. Inhaling and exhaling was smoothened out via an AMS Performance Alpha Performance air filter together with a 3.5-inch Remus downpipe and mid-pipe combo.

Heat is an unwelcomed guest in any engine bay and to improve cooling efficiency, the stock cooling element was swapped for an AMS Performance Alpha heat exchanger and AMS Performance Alpha intercooler. This was further fortified with a Snow Performance boost cooler / methanol kit to the tune of 300psi to function as a charge cooler. Lastly, a Lithiumax 3.8kg lithium battery keep the weight loss theme going.

Removing the safety shackled and allowing the engine to unleash its full potential is a Unichip Q Stage 3 remapped ECU that includes more boost into the mix. The final result is 413whp and 565.4Nm of torque after some fettling by John Tang of Jtuned and GT Auto in the horsepower haven of Sunway.

Remember that dual-clutch transmission that’s replacing the manuals? The one here has seven ratios and while they allow for some rifling through the gears, dealing with an extra 130+hp from the factory can take a toll. To counter that, a Wortec transmission cooler was fitted and positioned at the bottom left of the front bumper for optimal flow.

Now we all know the A45 will corner like its riding on rails but who said you can’t make the train ride better? Some simple enhancements in the handling department take the form of sports springs and anti-roll bars at both ends from H&R as well as an Alutec strut bar to tie up the front struts.

Supercar-beating performance usually mandates supercar-stopping brakes. Only the best will do here and AP Racing Pro 5000 R six-pot calipers up front bite on 380mm grooved rotors held in place by titanium nuts because weight is bad. Goodridge stainless steel braided hoses make it a proper party.

Seeing that the hatch gets used on the daily, rubber choice is crucial here… much like in the bedroom. Michelins and their fantastic Pilot Sport 4 S are some of the best all-rounder tyres money can buy. Since money appears to be no object here, they wrap around Rays ZE40 wheels in a 19x8.5 square setup.

Finally, we come to the interior. If you guessed that carbon fibre is the theme here, we’re sorry but Captain Obvious already beat you to it. Carbonetics Arts delivered the centre console, metre console, B-pillar cover and door lock console. Utmost Downforce Performance added the most distinguished touch to the cabin with its carbon fiber seatback cover and carbon fiber paddle shift extension.

The floating infotainment screen has been replaced with a larger 10-inch unit and an AMG 3.0-bar boost gauge now occupies the centre air-conditioning vent.

So to sum it up, improving your vehicle’s performance isn’t all about squeezing more power from the engine. You can also look at putting it on a slight diet. Heck, while we’re on the topic you could probably shave a little off the muffin top as well. Either way, remember the ratio.

Behind the Build

Car – Mercedes-Benz A45 AMG

Engine – M133, Remus downpipe + mid-pipe 3.5-inches, AMS Performance Alpha Performance air filter, AMS Performance Alpha heat exchanger, AMS Performance Alpha intercooler, Snow Performance boost cooler / methanol kit 300psi, Lithiumax 3.8kg lithium battery

Electronics – Remapped ECU Stage 3 with Unichip Q

Transmission – Wortec transmission cooler

Chassis & Handling – H&R sport springs, H&R anti-roll bar (front & rear), Alutec strut bar

Brakes – AP Racing Pro 5000 R six-pot caliper, 380mm rotors, titanium nuts, Goodridge stainless steel braided hose

Wheels & Tyres – Rays ZE40 19x8.5 +44 (front) +38 (rear), Michelin PS4S 235/45R19

Interior – Carbonetics Arts carbon fiber centre console, Carbonetics Arts carbon fiber meter console, Carbonetics Arts carbon fiber middle pillar, Carbonetics Arts carbon fiber door lock console, Utmost Downforce Performance carbon fiber seatback cover, Utmost Downforce Performance carbon fiber paddle shift extension, 10-inch touch screen monitor, AMG 3.0-bar boost gauge

Exterior – Carbonetics Arts carbon fiber front canards, front lips, Carbonetics Arts carbon fiber rear canards, diffuser, Carbonetics Arts carbon fiber rear hatch, Carbonetics Arts carbon fiber rear doors, Carbonetics Arts carbon fiber spoiler, Carbonetics Arts carbon fiber fuel cover, Carbonetics Arts carbon fiber battery and air filter cover, Advanced Liquid Concept carbon fiber fenders, Utmost Performance carbon fiber side mirror, Raptor R Techwrap vinyl wrap, Boca Design dry carbon bonnet, CT Motorsport dry carbon engine cover

Garage – Carbonetics Arts, Pasir Gudang, Johor, Advanced Liquid Concept, Masai, Johor, Patrick Teo, Masai Johor, Raptor Auto, Mount Austin, Johor, Speed Demon Motorville, Johor bahru Johor, Raptor R, Mount Austin, Johor, Utmost Downforce, Puchong, Selangor, CT Motorsport, Sunway, Selangor

Tuner – John Tang, Jtuned, Singapore/Macao, GT Auto, Sunway, Selangor

Power – 413whp + 565.4Nm