The car thread 2.

[nakamura]

All that money to buy and 150 ft lbs. It's shameful to be honest.

[Brad]

That's what I don't understand. Presumably my car accelerates better than that Fabia but with lower torque. What does it all mean!?

Ok, I think I understand it now and it gets pretty complicated. Torque on its own doesn't matter... except that it's the starting point for getting torque to the wheels i.e. horsepower, and horsepower is a combination of torque from the engine, multiplied by revs and then the car's gearing comes into play and the weight of the car. So, BHP is what ultimately governs acceleration.

Acceleration = force / mass
Force = bhp I think and bhp = torque x rpm / 5252

[nakamura]

Very loosely torque is acceleration force. The more torque the more kick you get under load.

The 3SGTE (MR2, GT4) from 1990 kicks out 225 ps and 220 ft lbs. Only 25 ps more than your GT but a wallop more torque so it is faster. However a turbo normally runs out of blow around 5.5-6k stock so the NA makes up for it because it generally keeps going to the red line.

NA power is linear so pretty much climbs constantly and never spikes. Turbo is a massive hit that tails off.
Supercharging is the same as NA but allows more power but the progression is generally fairly linear again.

Diesels lose out because the red line is so low and overall max power is lower. Much more shifting needed to keep them in the zone and run out of puff even earlier.

[nakamura]

That's a very loose description. Torque hits early on a turbo, often around 3200 when the turbo itself is at full spool. Then it tails off and you lose the kick but the raw engine power keep the car going. Engine power then often tails off before the red line because the engine is lower compression than a NA engine and the turbo is not longer blowing full tilt.

An NA engine runs a lot higher compression which allows it to generate power in a high rev range which is why the often generate maximum power right at the red line.

These are generally stock characteristics of engines for road cars. A lot of these can be negated with quality tuning. The RX7 and Supra for example use sequential turbos that allow for a smoother power delivery. Or you can twin charge with a super charger and a turbo.
Of course turbo chargers come in tons of sizes for performance. So a good turbo will remove the tail off in power if well set up but you are prone to lag if you go too large.

Higher capacity NA engines such as a 3.0 V6 will give you much more torque, easily around 200-250 from factory engines.

That's all a very loose description as I said and generally covers the low end of performance cars.

[Brad]

Cheers. Ultimately torque figures aren't something to judge anything by though are they? The quoted torque of a number of regular diesel family cars is going to be higher than, say a BMW 320i, but the BMW is going to perform better. I think real-world figures are what you need to look at because so many things can affect the overall performance. Probably BHP is a decent single value indicator? Do quoted BHP figures take the car's weight into account? Are quoted torque figures torque from the engine or at the wheels? So confusing!

[nakamura]

All BHP and Torque figures are quoted at the flywheel with losses through transmission roughly 25-30%. Very rough mind.

A torque figure is a good measure for that kick back in the seat feel. A small car similar to a BMW 320 with a good diesel torque figure will give you a nice kick but will not last long due to the low RPM nature. The BMW will ultimately outperform it on a track due to raw power.
Torque isn't really a good outright measure because on diesel cars, it will always be much higher than NA engines because it is turbocharged.

The benefit of these engines is lower emissions yet the turbo will negate sluggish performance usually seen with a diesel. More MPG generally too. Although I don't believe for a second these really lower emissions at all, diesels just dump crap all in one go, hence they normally have exhausts that point to the road.

For example the Toyota 2AD FHV (2.2 Rav4/ Auris) engine weighs in at 177 bhp with a whopping 295 ft lbs. That's Supra level torque but a Supra engine will absolutely murder it because it has the raw power to go with it.

BHP figures are all from the engine and the weight has no bearing on this.

[Brad]

Ah, all starts to make a bit more sense, thanks. So a diesel gives you a good acceleration from the lights but then you have to change gear sooner to maintain your acceleration? Whereas I have to try and get to around 4700rpm before I get close to full power and then keep it between that and 7000 to keep my power going.

[nakamura]

Kind of. One thing about a car like yours compared to a diesel is you will likely always be in the high power zone when shifting. The diesel will only have a small power band and will not be in it for too long. So when you shift at 7k the RPM will drop to roughly 5k and the power will be maintained.

[chojin]

It means if you don't work your gears at the right rev range my wife will leave you for dust without dropping a gear [emoji38]

[Brad]

haha! yep.

[The Moleman]

The Fabia vRS is an effortless car, a really good drive at legal speeds with enough poke to worry some hot hatches. 70mph+ though they run out of steam real quick, whack one of these bad boys on it!

http://www.turbodynamics.co.uk/shop/md446-stage-2-hybrid-turbo-for-vag-19tdi-130bhp-engines-p-2743.html

[nakamura]

Just buy a better car.

[The Moleman]

Just buy a better car.

True dat....


The sleeper appeal is there though.

[speedlolita]

You're still driving a Skoda though.

[The Moleman]

That's the whole idea. Pull up to some toff in their Boxster and smirk as they can't pull away from your Skoda.