My last post was on the performance issues you might run into when your car is creating too much torque. The issues don’t end on the racetrack though, they continue in the shop. Increasing torque heightens the likelihood of mechanical problems throughout the car.
Torque increases wear and can eventually break both the engine and the drivetrain. Torque is calculated by multiplying cylinder pressure and displacement. Increasing cylinder pressure puts more load on all the engine components and is usually responsible for engine failures on modified turbo engines.
Torque is a twisting force, think of a torque wrench measuring the twisting force on a bolt. A dramatic increase in torque without supporting modifications will damage the clutch, gearbox, driveshaft, differential and axles.
For example, I have recently been building a lot of S63 M5 BMW engines after connecting rod failures. While I can increase the strength of the engine components, it will always be possible to add enough cylinder pressure to break it again. Engines are limited by their weakest component, so the pursuit of torque is really a game of chasing the next weakest part of the engine. Increase torque, break a component, repair and repeat.
If we were to increase torque less and increase HP more when we modify the car, the car would go faster and be much more durable. This creates a better overall driving experience, costs less in repairs and increases the lifespan of the car.
I was recently looking at the specs on the new Porsche GT2 RS. Really cool car. 700hp and 500 lb/ft torque. It reminded me of a tech tip Tuesday video I made when I owned Dinan about why more torque is not always better. (link to video)
You see, more torque does not always make a car faster. Once you exceed the traction capabilities of the tires they go up in smoke and the car doesn’t go anywhere. This is why dragsters have slipper clutches, the slipper clutch reduces torque to the maximum amount the tire can handle. As the dragster goes faster, and down force increases traction, the clutch reduces slipping and adds power in just the correct amount to get maximum acceleration without breaking the tires loose.
On a street car we have a transmission that increases torque at the rear wheels dramatically for acceleration from a stop. With modern, high-performance turbo cars it is very easy to break the tires loose from a stop and on gear changes. This loss in traction slows acceleration. Most 2WD road cars – even with large grippy tires – can’t handle more than 400-500 lb/ft of torque. AWD cars can handle as much as 600 lb/ft without losing traction.
The smart folks at Porsche reduced torque and increased HP so the 2WD GT2 RS can accelerate as fast as possible. In addition, the car is much easier to drive and more docile at its limit. This is an important lesson in building a well-balanced car, as performance relies on much more than just power and torque.
Having been in the car repair business for 39 years it still surprises me how many customers defer important repairs that will cost them many times more down the road.
For example, water hoses dry out and fatigue over time and have a usable life of around 8 years or 80,000 miles. Changing a set of hoses on a new German car is expensive, usually around $1,000. Most of my customers change the hoses one at a time as they break. This a very costly and potentially dangerous approach.
Your average new German car has around 9 cooling hoses. By changing the hoses one at a time you pay more for labor. Every time the car is brought into a shop part of the labor costs come from inspection, disassembly and a test drive. It’s a cost built into every service that will be charged each time you come in to repair another of the hoses. In addition, you pay for labor to drain and refill the cooling system and for the antifreeze every time it is drained and refilled. In the end, changing the hoses one at a time cost between 150%-200% of doing them all at once. You also run the risk of overheating and ruining the engine every time a hose breaks. If the engine is damaged, you could be paying anywhere between $10,000 and $30,000.
As you can see it is penny wise pound foolish not do all the hoses all at once. It is important with any recommended repair to ask the shop what the ramifications are for not doing recommended repairs. In some cases it is ok to defer maintenance, but in most, immediate repair is the safe bet.
When customers bring out-of-warranty cars in and get a large estimate for repair, they often talk about selling instead of paying to fix the problem. That first out of pocket bill can be a shock. But while repair costs are not always as predictable as a car payment, they are usually 66% to 75% less costly than purchasing a new car.
For example, if you purchase a new German car for $70,000, financed for 5 years at 2.9% interest, you will make payment of $1,255 per month or $15,060 per year! Once the car is beyond its 4-year, 50,000-mile warranty and paid off, the only cost will be maintenance. Annual repairs will cost between $3,000 and $5,000 per year or equal to 3-4 car payments. While it’s always nice to have a new car, fixing a used car will save you between $10,000 – $12,000 per year, money you could potentially put into modifications.
Don’t let the sticker shock of a big repair bill scare you into purchasing a new car. It’s usually cheaper and more rewarding to hold onto the car in the long run.