Why isn't the 35d quicker?
 

Why isn't the 35d quicker?

Okay, let me start by saying I love our 35d, but has anyone ever thought about this, or just me? Its acceleration is adequate, but with 425 ft-lbs of torque, I'd honestly expect better. The 35i is roughly a second quicker to 60, despite its 125 ft-lbs deficit..

How about this comparison for you. 2017 Ford Expedition. 3.5 Liter Ecoboost. It weights roughly 1000 lbs more, has essentially the same torque rating, but its a few tenths QUICKER to 60, despite carrying an extra 1000 lbs, and having essentially the same max torque output. How quick would it be if you dropped a 1,000 pounds out of it?

Both have 6 spd autos..

Obvious difference is the Gas vs Diesel, but Torque generally equates to acceleration, so what's going on? Is it all about the gearing?

Surprisingly 1st and second gears in the 35d and the Expedition are the same rations..

The Expedition does have a slightly lower axle ratio (3.73 vs 3.64), which equates to a 2% lower gearing through 2nd gear..

Just doesn't make sense to me.. What am I missing (besides a tune)?
2013 X5d (6 speed auto)

Torque: 425 (@ 1,750 rpm)
Weight: 5,192
0-60: 6.8
1/4 mile: 15.0

Final Drive: 3.64
1st Gear: 4.170
2nd Gear: 2.34

2016 Expedition EL (6 spd auto)

Torque:420 (@2,500 rpm)
Weight: 6091 lbs
0-60: 6.5
1/4 mile: 15.1

Final Drive: 3.73
1st Gear: 4.170
2nd Gear: 2.34

No, torque doesn't accelerate you.
Torque is instantaneous force. You can weigh 200 lbs, use a 2 ft long bar on a wheel and be putting 400ft lbs at 0 rpm on the wheel and barely move the car.
Horsepower is force that can be done in a time period.
Horsepower does because of gearing which can keep the engine at an rpm where it's at max hp.
Hp=torque x (rpm/5252)

That's why you use the hp curve to determine acceleration, not torque.

The 35d has been evolving, while looking for a replacement for my '09 35d, I drove a bunch of 2015s and 16s as well as Cayenne diesels and the newer (more modern) diesels are significantly quicker. (Decided to get a Cayenne S in the end)

Last December I rented a Benz E400d in Munich (a four banger!) and it was a rocket-ship despite not being very light. I just had a C200d for 2 weeks from Sixt in Lisbon and these things are smooth and quick. The later models are just way better.

However, the old ones are nice to drive and run well well at 60 to 80 MPH, hence the' 09 is coming with me to Europe. I put a lot of time into fixing it and am very happy with it but it is no comp to my Cayenne....

Hmmm, I'd always heard it as, "Torque gets you up to speed, horespower keeps you there." And although I know that the Internet is full of misinformation, I didn't have any trouble finding similar statements with the help of Google, so color me confused..

Interesting, I thought I remembered Car and Driver saying the 2014 X5 35d was a tad 'slower' than the Model it replaced..

My family owns both. The 35i power ratings are under reported by BMW. The 35d power delivery is inconsistent most days. If it is 50 degrees out I feel fast, If it is hot out, I feel slow. The 35d likes slow consistent changes in the accelerator pedal, the 35i does not care and just goes like a modern engine shoule.

Also, in the 3 series with the N55, switching to the 8 speed got them at least a half second increase for 0-60. Compare 2011 E90 N55 to 2012 F30 N55

2014 has the N57 with a single turbo. It makes less power than our M57 with two turbos. But it also got the 8 speed which makes up for most of the power loss.

What diesels offer is more hp down low. Compare dynos between a gas 35i and 35d.



Use the red lines in the dynos below that start lower for stock HP.

2k, 35i 95hp, 35d 150hp
2400rpm 35i 140hp, 35d 190hp
3k 35i 180hp, 35d 220hp
3400 200vs 240hp
Then the diesel tops out around 260
While the 35i hits that around 4600 and keeps climbing above that to around 290hp.

So low end, the diesel feels stronger because it makes more hp down low.
Around town in low to mid rpm, diesel is faster/more responsive.
But in a race, you drive the engine at peak hp at higher revs, where the gas engines shine.


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https://chiptuning.ca/public_content...92976de916.jpg

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I think it has to do with software. Another reason why I think something like 'Sprint Booster' works or helps to eliminate that off the line sluggish feeling in some cars.

My 35d has a stage one tune and I love it, but off the line in D mode isn't anything spectacular. Then again, its my DD and its 95% stop and go commute =/

Why would HP matter and torque needs rpm as a relation?

HP takes into account speed/rpm. (aka rate or energy per time)

If you wanted to use wheel torque as an example,
you can have 2000 ft lbs at 2 mph wheel speed during launch
and yet it's less work (hp) than:
200 ft lbs at 100 mph. That's why HP translates directly to actual work done.

Another benefit of diesels as you see in the dynos I have linked above is the very flat hp curve across most of the graph, because the torque drops but rpm climbs- you get a flat hp curve.
Meanwhile on gas engines, like the 35i, you get a flat torque curve, but the hp is a line that increases with rpm.
Some engines have a narrower peak- (lets say 500 rpm of peak hp on an n/a M3 V8) and that means to keep those accelerating at their best hp - they need narrower gear ratios (and more gears)- which gives up acceleration due to gear changes.

That's why the Audi diesel lemans car first had only 5 gears, with such a wide power curve, they didn't need as many gears to keep it in "peak range".


Edit: Another analogy if you are knowledgeable in electricity.
Amps is like torque- it can burn wires up- like torque breaks shafts.
Volts is like rpm- it's the momentum of the electrons or the mass being spun.

A bulb or motor does heat or work based on WATTS, not amps or volts.
A 120 watt bulb does 120 watts of heat+light whether its rated for 10 amps and 12 v or 1 amp and 120v.
A 1 hp motor (746w ) does 1 hp of work whether it's 7.46 amps at 100v or 74.6 amps at 10v...
The volts X amps (simplified) is what does the work.
The rpm X hp (simplified) is what accelerates a car.

I guess I'm getting older. I feel that the 35d is quite quick. People who ride in it appear very surprised and invariably comment how quick it is. They don't qualify that with "for a diesel" or anything. I have a stage 1 tune.