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Old Today, 03:05 AM
 
Location: the Permian Basin
4,130 posts, read 2,924,939 times
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Quote:
Originally Posted by EckyX View Post
As others have said, acceleration "feel" is a function of torque and gearing. Horsepower is torque x RPM.

Let's set up a hypothetical scenario:

Motor A has 200 ft-lbs of torque and 200HP, with a redline of 4000rpm
Motor B has 100 ft-lbs of torque and 200HP, with a redline of 8000rpm

*If both are attached to the same transmission, motor A will feel twice as powerful, but you can only stay in first gear half as long before needing to shift to 2nd, at which point acceleration would slow down a lot.

*If motor B is attached to a transmission whose gears are half as tall, it will feel identical to motor A, since both produce the same total (horse)power.

Tractors often have relatively small engines, it's gearing that let's them pull trees out of the ground or drag huge pieces of farm equipment behind them through dirt.

Be aware that the mass of the vehicle to be moved is also a factor here. A vehicle that weighs half as much will accelerate twice as quickly with the some motive force.

If I may add to these points, the reason gearing allows tractors to move heavy implements is because gearing multiplies torque. But "HP flows straight through."
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Old Today, 07:34 AM
 
2,019 posts, read 3,465,591 times
Reputation: 1943
The tuned diesel BMW 335D is a monster with over 550 lbft of awesome instant torque which means huge instant acceleration.
It only has 500 HP but it drives and feels more than that since we feel torques (acceleration) not HP.
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Old Today, 08:24 AM
 
Location: Maryland
1,175 posts, read 351,016 times
Reputation: 2665
This is the single best, most concise, explanation of this thread’s topic I’ve ever read. Enjoy.

1 Heading 1

IIRC, he’s an engineer who like racing. His time slip for his Panoz roadster is still available at dragtimes.com.
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Old Today, 10:34 AM
 
4,595 posts, read 1,705,872 times
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Quote:
Originally Posted by Slowpoke_TX View Post
Assuming that the driver can cut a light, and that the tires hook.

Not being familiar with the HP curves of electric motors, I'd be interested to see those - and timeslips.

Here's an example: Tesla Model S vs Corvette Z06. Tesla in red, timeslip at the end.
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Old Today, 11:27 AM
 
9,224 posts, read 7,661,213 times
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In more urban driving wouldnít you want better 0-45 mph acceleration out of lower powered economy vehicles than the torque to accelerate and pass on the highway quickly? Itís the acceleration to jump out and merge into traffic quickly and get up to speed. Majority of my travel is rural or urban, rarely open highway. This is why I mainly own compact sedans. Iíve driven larger sedans with V8 engines (late70s to mid 80s models) that would crawl away from a dead stop but were great on the open highway but small compact sedans with less than a hundred HP and torque could easily take off and get up to the city or country road speeds. I know some vehicles are great at both off the line and top end acceleration but most of those are performance machines. Iím wondering if this quick take off and bogged down around 45 mph is also a symptom of the goal of increased fuel efficiency requirements?
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Old Today, 11:46 AM
 
Location: Podunk, IA
3,055 posts, read 1,401,256 times
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Quote:
Originally Posted by ohio_peasant View Post
This whole torque/Hp/gearing discussion is fantastic, but we're missing a crucial point, as regards specifically the Chevy Cruze: drive-by-wire. It's the software operating the throttle-body that's killing off-the-line acceleration when the gas pedal is mashed. No amount of gearing, no change in camshafts, no addition of a turbo, will ultimately change that.

What the Cruze needs is a reflash of the ECU, to fix the throttle-lag problem. Fix that, and acceleration (for commuter-car purposes) will be fine.

To reiterate: it's not a problem of horsepower or torque. It's not a problem with the engine itself. It is 100% a problem with the engine-management software.
The last gen Cruze 2.0TD doesn't have this problem.
The diesel has so much ballz that it's quick 0-30, but still runs at low rpms on the highway.

Not gonna vouch for the current Cruze TD.
I drove an Equinox with the 1.6TD and it was clear that they neutered it in the quest to market the highest possible fuel economy.
Very disappointing... the old diesel was much better from a drivability standpoint. The 2015 Cruze TD was rated 46 hwy, plenty good enough for me.
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Old Today, 12:37 PM
 
2,167 posts, read 508,751 times
Reputation: 2403
Quote:
Originally Posted by victimofGM View Post
In more urban driving wouldnít you want better 0-45 mph acceleration out of lower powered economy vehicles than the torque to accelerate and pass on the highway quickly? Itís the acceleration to jump out and merge into traffic quickly and get up to speed. Majority of my travel is rural or urban, rarely open highway. This is why I mainly own compact sedans. Iíve driven larger sedans with V8 engines (late70s to mid 80s models) that would crawl away from a dead stop but were great on the open highway but small compact sedans with less than a hundred HP and torque could easily take off and get up to the city or country road speeds. I know some vehicles are great at both off the line and top end acceleration but most of those are performance machines. Iím wondering if this quick take off and bogged down around 45 mph is also a symptom of the goal of increased fuel efficiency requirements?
Depends if you intend to pass the person while lugging the engine, or you intend to perform a 6-3 downshift and smoke them. Remember, when measuring the power of a vehicle, torque and HP curves always intersect at 5252 RPM.

Torque vs HP
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Old Today, 12:42 PM
 
2,586 posts, read 3,146,697 times
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Quote:
Originally Posted by ddm2k View Post
You can gear a car with a weak engine down to the point where it feels quick off the line but you'll be sorely disappointed by the time you reach the top of 2nd gear.

Only a truly powerful engine coupled with the correct gearing can throw you back in the seat from a 70 mph roll.

FWIW the sweet spot seems to be *somewhere* near 3.73 because I keep on seeing record setting drag runs cite a 3.73 rear end in the specs list of their car. On these vehicles, tires appear stock diameter (I'm sure there are aftermarket wheels to accommodate a wider profile), but just are not over-sized 31" drag radials.
Yes, 3.73 to 4.10 has pretty much always been the sweet spot for quarter mile type runs. The trick is to either eliminate a shift in the 1/4 mile or quicken up the shifts enough you get a long enough pull in your final gear rather than shifting in the last few seconds of the run if you can't eliminate that final shift without slowing your elapsed time down. Sometimes a particular gear ratio can change where you are in the torque curve when you hit the next gear. If you are in the low end of the torque range when you shift to the next gear it can result in slower acceleration. It seems like a 3.73 hits it about as well as you can in most cars.
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Old Today, 12:57 PM
 
2,167 posts, read 508,751 times
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Quote:
Originally Posted by dijkstra View Post
Yes, 3.73 to 4.10 has pretty much always been the sweet spot for quarter mile type runs. The trick is to either eliminate a shift in the 1/4 mile or quicken up the shifts enough you get a long enough pull in your final gear rather than shifting in the last few seconds of the run if you can't eliminate that final shift without slowing your elapsed time down. Sometimes a particular gear ratio can change where you are in the torque curve when you hit the next gear. If you are in the low end of the torque range when you shift to the next gear it can result in slower acceleration. It seems like a 3.73 hits it about as well as you can in most cars.
I agree.

With the exception of towing rigs, or an off-road vehicle with enormous tires, I see no problem with axles coming with only a few different gear sets. Let the transmission do the rest. You have more control with ratios because engineers can also control spacing, which is just as important if your goal is to prevent too much RPM drop in the first 3, get your traditional 1.00:1 for 4th, and fuel efficiency in 5th and 6th.

Probably the WORST 6 speed (auto) ratios I've ever driven with is a 2012 Chrysler 200 (not 300). The 3-4 upshift would drop 1500-2000 RPM and it was definitely not your friend when merging into interstate traffic.

I have a 2004 Dodge Durango (Hemi) with the 3.73 and it will still snap your neck on a 2-1 downshift. 5 speed auto, not too much difference between gears, but with lockup I can roll 77 mph at 2000 RPM.

Some owners of Ford Superduty trucks got all excited when they found out Ford offered a 4.88 rear end. But on the interstate, I believe the trucks were topping out at 81 MPH pedal to the metal.
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Old Today, 01:09 PM
 
Location: East of Seattle since 1992, originally from SF Bay Area
28,850 posts, read 52,066,378 times
Reputation: 29611
My 2017 F150 5.0 V8 is 385 Horsepower, with the 3.55 rear end for a compromise between economy and towing power. It will burn rubber from a stop, but doesn't have the initial torque of even a 3.6 V6 as found in a Challenger SXT. Where you have the real fun of that "throw me back in the seat" power is when passing on a highway, when you are up to about 4,000-5,000 rpms. It should do about 110 mph but I wouldn't expect to go more than about 80 so that doesn't matter.
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