You might be surprised to discover how few horsepower it takes to keep your car – or even a big SUV, for that matter – going.
Well, once it’s already going.
Last week, Dodge sent me a Durango SRT392 to test drive (the review of this beast is here). It has an interesting feature, a display that lets you know how many horsepower the engine is producing at any given moment – the number of them increasing or decreasing according to speed and load.
Once under way, as few as 40 or so horses out of the 475 that the Dodge’s 6.4 liter V8 is capable of producing are all that’s needed to keep the show on the road.
That’s about the same number of horses made by a classic VW Beetle’s much smaller four cylinder engine.
Of course, the difference is the Dodge can get to 60 about five times more quickly than an old Beetle – in four seconds or so vs. 20 or so seconds in the Beetle. And the Dodge can go much, much faster – in the vicinity of 150 MPH vs. around 80, if the wind is at your back, for the old Beetle.
The Dodge has a surplus of horsepower. The Beetle has just enough.
But when both are just cruising along at say 45 or so MPH on a flat, level surface – the same 40 or so hp is all it takes.
In part this has to do with gearing – leverage, really – the rest with inertia.
People don’t often think of the gears inside a transmission (and drive axle) as levers – but functionally, that’s their role. To lessen the load on the engine – while maintaining a given road speed.
It’s pretty neat.
Open up manual transmission and have a look inside. Automatics work on the same principle, too. The gears act like levers affixed to a wheel, in order to make the leverage applied continuous. 
The longer “levers” (first gear, second gear, etc.) greatly multiply the engine’s mechanical power to get those thousand of pounds of metal and glass and plastic in motion from rest. As you get going faster, shorter “levers” (third, fourth and up) maintain and increase speed with less effort.
It’s the same principle that lets a man of average strength move an object that would otherwise be too heavy for him to lift or even budge on his own.
And once budged, you now have inertia going for you – the tendency of something in motion to remain in motion unless something interrupts its motion. Think how relatively easy it is to keep a very heavy log rolling once you’ve got it rolling.
Modern cars make the most of both leverage and inertia. They have transmissions with multiple overdrive gearing, low-friction bearings and favorable aerodynamics. Once in the very top overdrive gear, it hardly requires any effort on the engine’s part to keep one of these vehicles moving.
I’ve test-driven a few that – because of their deep overdrive gearing – are idling at highway speeds. The Ford F-150 I test drove a week ago, for example, has a ten speed transmission that cuts engine revs to just over 1,200 RPM at a steady 65 MPH. It didn’t have a “horsepower meter” like the Dodge, but if it did, you’d be able to see that it, too, only needed about 40 or so hp to maintain that speed on a level road.
Using less horsepower also uses less fuel – the main reason for all those overdrive gears in the latest cars (and trucks and SUVs). An additional benefit is reduced wear and tear on the driveline – as well as reduced drivetrain noise, even at high road speeds.
Of course, if the road transitions from flat to hilly – or you want to go faster – then you’ll need (and probably want) more power.
If the engine in the car you’re driving hasn’t got much in reserve – like an old Beetle – you may not be able to go much faster and (if the hill is steep) might even find yourself slowing down, no matter how hard you mash the gas.
. . .
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Eric I have a 2000 acura TL, honestly one of the best cars made in its class, the 1995 integra GSR is also.
Anyway I plugged in one of the obd readers once, I think I only use about 50 hp on a normal commute and that includes getting up to highway speed. Cruising was only in the 30’s range. This car is fast, way faster than I would ever need. How much could be saved by ditching the whole Vtec system and tuning the cams for maximum performance in the normal range, instead of tuning it for 0-60 times and peak hp which no one ever uses? Could save money and fuel.
The other thing I noticed is all my current cars have ABS but it never activates, is it because tires are so good now? Seems like there was a time ABS was important but technology has made it obsolete.
Lol, ABS wasn’t meant to compensate for lower tire technology, but rather the poor driving habits and non-existent driving skills of the motoring public in general. Your ABS likely never comes into play for the simple fact that you probably utilize better driving skills than most.
Well I didn’t want to claim that. It does seem as though tires are more grippy now, I remember in the 90’s my cheap tires didn’t have a whole lot of traction.
Oh, most certainly, I agree. Tire quality has definitely improved. The fact that you even have a feel for your tire traction already indicates you possess an awareness most “motorists” are completely oblivious to. That certainly has not changed for anything but the worse.
I’ve gained a huge appreciation for the engineers and manufacturers of tires. Those tires are under such high stress conditions (high speed, high heat, sudden and constant blunt trauma from the shitty roads), with deadly consequences if they fail, and yet they hold up and keep us all going.
It’s not the tires. Lots of [non-performance] tires still suck- like some Michelin models which are very hard/not the least bit grippy.
I think what has improved, are the brakes [not the ABS part]- most vehicles having 4-wheel discs now. The old drum rear/discs front combo often had proportioning problems- especially as the vehicles aged. How amny people ever replace a proportioning valve? And the all discs allow better modulation and better control of all wheels.
ABS is like airbags- another forced “safety feature” that is really a hazard- as it usually INCREAES stopping distance.
And let’s not forget suspension improvements, too. These more modern sport-like stiffer suspensions help with grippiness…
It seems to me that the mainstream Michelin tires have been optimized for long tread life – because that’s what the clovers have been asking for. So while they’re still better than many other tires so far as ride quality, they aren’t as grippy as I think they ought to be.
Exactly, Chiff!
I’ve never felt the need to buy Michelins…but they were already on the last (used) vehicle I bought. Damned things are hard as a rock. I’m sure they’ll last forever….but who cares? I swapped them to my old pick-up which I don’t drive much, and put my good Hancook Dynapro A/T’s on my Excursion.
These Michelins are the worst tires I have ever owned.
“This car is fast, way faster than I would ever need. How much could be saved by ditching the whole Vtec system and tuning the cams for maximum performance in the normal range, instead of tuning it for 0-60 times and peak hp which no one ever uses? ”
No one ever uses? I have an ’03 CL Type-S and I just love to hear the VTEC come on around 4,500 RPM. The exhaust note becomes lower and angrier and you get a sudden rush of power whisking you forward. It’s awesome. I use it a lot 🙂
Riding a bicycle really helps one to understand and experience the physics of vehicle propulsion. This is why the statement that it only takes 40HP to keep the SUV cruising on level ground did not surprise me at all.
I’m not the strongest rider, but give me some level ground and little or no wind, and I can sustain 25MPH quite easily.
Throw in a little wind, and you either have to work harder, or go slower, or adjust your position to be more aerodynamic. You can read all the numbers on paper, but being able to experience it, tells a fuller story and much quicker, and lets you experiment and see/experience the difference that little changes make.
Ditto gearing…..
A bicycle is like a real-life vehicle propulsion physics lab!
I get so mad when I think of all the ridiculous things they do to try and comply with the CAFE fartwars- like employing all kinds of very complex Rube Goldbergesque fuel/engine management schemes; making bodies out of aluminum to save a few hundred pounds, etc. which things all do almost nothing- fractions of a MPG- while increasing initial expense, and the cost of repairs, while decreasing long-term durability….. While if they’d merely gear vehicles more sensibly, and use LARGER engines which could spend most of their time working at a fraction of their potential power (Instead of tiny engines that are maxed-out all the time), they’d accomplish what Uncle wants them to, while making a cheaper and longer-lasting product.
Riding a bicycle helps me understand how ignorant, selfish, and oblivious the general driving public really is. It also makes me realize what a Gift-From-God the IC engine truly was, and that Musk, Tesla-Corp, et.al. are spawns of Satan meant to test our faith in God! And if you don’t believe me, just ask the little man that hangs on the Tesla-Cross, posing as the “second coming”, are we? Sorry, the Moral Majority has nothing on me!
I owe a whole lot of my ability to troubleshoot problems to having to wrench my own bicycles when I was a kid. Especially since I pushed Sears-level bikes way beyond what they were designed to do. Having access to dad’s toolbox helped too.
Aint THAT the truth, ReadyK?!
Fixing my bike,
Building treehouses,
And a book about electricity that my sister bought me, that showed simple circuits/experiments with batteries…errr…uh “dry cells”….
THOSE things have served me well my entire life. There’s no telling how much more advanced I’d have been, if I hadn’t have had to waste my time going to the stupid government skool, learning a bunch of irrelevant nonsense that was good for NOTHING (except indoctrination) and forgotten 5 minutes later.
I get so mad when I think about it! At that age, we are eager to explore the world around us and find out how things work; we can learn and train ourselves to do just about anything…..and at that very time, a unique and wonderful point in our lives, we are prevented from acquiring true natural real education, by what fraudulently passes for “education”.
And we were lucky- at least we still got a little of that free-range do-it-yourself figure-it-out experience. Most kids today don’t get ANY of that.
That was my primary edumacation. Secondary was when we moved from the ‘burbs to NYC and I was in my mid teens….I’d use my school subway/bus pass to go anywhere except school. Learned more exploring NYC till I was old enough to drop out, than ANY classroom could ever impart…and timing it so I’d get home every afternoon from that day’s journey made me much more punctual for the rest of my life than merely forcing me to get up at 6:30AM [DAMN THEM!] and go to school….
Just think of these kids today:
Day care.
Pre-school.
Pooblik Skool.
College.
Work in a cubicle.
Live in an apartment, townhome or HOA, condo or heavily zoned and regulated suburb….
They’ll never know, their entire life, what it is to explore and discover and deal with reality on their own. Their entire lives are just one long structured narrow path of following rules and protocols established by others. 🙁
(This damn thing is still logging me out every time!)
The best MPGs tend to come from ridiculously underpowered engines, since a tiny engine has less drag than a bigger engine when not being run flat out, and uses less gas when idling at a stop light.
The automotive engineers trying to lower the CAFE taxes by squeezing incremental gains out of tiny engines know what they are doing. It’s the politicians who set these fatwas in motion who don’t understand cars.
Shorter: the engine size to maximize MPGs is much smaller than what people would choose if Uncle wasn’t nudging reeeally hard.
Hi Jim,
New cars would be so much more fuel efficient (as well as much quicker) if they didn’t have to be so got-damned heavy!And they are heavy precisely because Uncle insist they be “safe” – according to his standards.
And that’s where Jim’s theory falls apart: Put a tiny engine in a heavy vehicle, and that engine has to work at top capacity and above to get the vehicle up to speed/up hills/in momentum from a stop, etc. and STILL has to work in the upper echelons even at cruising speed- which means it’s always working hard- hence the turbos and double turbos and 10-speed trannies, etc. to try and wring every last drop of power out of the poor thing….
A bigger engine- one that could spend most of it’s time only using a fraction of it’s capacity, would not only be more efficient and not require all of the bloated, expensive add-ons, but would also be much more durable.
This is why too, in the real world, most vehicles that offer the option of a 6cyl. and an 8 cyl., the 8 cyl. will almost always deliver the better MPGs in real-world driving.
In my own case, my 10 cyl. gets better mileage in a heavier vehicle with lower gearing, than does my 8 cyl. -and if the 10cyl. vehicle weren’t handicapped by the lower gearing and 500 extra pounds, it would get substantially better mileage.
Tiny engines in big vehicles are retarded. It is done to comply with the various government edicts- such as emissions. (If VW did it, -using a small over-burdened engine that puts out barely any emissions at idle) they’d call it “cheating” and arrest everyone…..
Now Chevy has started putting 4 cyl. engines in full-sized pick-ups! It’s insanity!
Taking away choices is pretty much what government does. And so the artificially heavy cars and forced higher mpgs and having to drive stealth models shoves cars away from the optimum for a given use. 840 hp and a much lighter and more aerodynamic design, and we might have sub 2 second 0-60 for under 50K.
Cars like this only hint at the possibilities if freed of the heavy hand of govt control freaks.
Hey Eric, perhaps a stupid question but shooting nonetheless – why are some gears called “overdrive” gears? Is this only a US thing as I dont hear it out here much – infact cant remember hearing the term anywhere outside the US. How is a 4 speed auto + overdrive different from a 5 speed auto? Is there any difference or is it just a way its marketed in the US ?
I can answer that, correctly, I hope, lol! For the longest time, here in the U.S., overdrive was a term used in its academic sense, that is, a gear ratio above 1:1, hence, “over” drive. In the 1980s, I believe, more economy cars and small trucks were appearing on the U.S. market with 5 gears, 5th being a 1:1 ratio. The influx of foreign economy automobiles was hindering domestic sales to such an extent, that insurance companies became involved in govt./corporate attempts to stem the tide of imports. This was to proclaim that 5 or more speeds in ANY passenger vehicle (excluded large commercial trucks and tractors) mad it a “sports” car and was given a higher “risk” rating, and slapped with higher import duties and higher insurance rates. Yes, another govt.-encouraged scam to “protect” our domestic production. So Imports began labeling shifter knobs as “overdrive” rather that 5th gear, and most actually were produced as an actual overdrive, do the end-run of the phony rate-hikes was actually legit in most cases. Anyone have anything to add to this, as I am likely only scratching the surface?
Don’t know what the earliest mass produced OD transmission might have been but I recall Ford made 3 speed, 3 on the tree,as early as 1957.
Once in 3rd there was a pull like a parking brake that shifted it into OD. Seems like you could go to second or first on that side of the gearbox.
Help me out old farts if I’m wrong.
Every cell in my body has been replaced 9 times since then.
I have a right to be hazy.
Ive seen 49 fords with a 3 and over. Factory install, it has a cable pull and an electric solenoid to (disengage for passing?). Brits/europeans were using them in the 30’s at least.
That reminds me of the Mitsubishi 4 speed in our ’79 Dodge Colt. It had an extra lever that you used to select “economy” or “power.” I wasn’t driving then, but thought it was pretty cool that there was a POWER light on the dash when you shifted into that mode.
Have no idea how useful it was in real life.
Thanks for the video Eric!
Side note: The number of teeth(levers) on the driven gear divided by the number of teeth on the driving gear equals a gear ratio.
Gear ratios are usually odd ball numbers so that each tooth on one gear eventually contacts every tooth on the other gear as it goes around – creating an even wear pattern (a hunting gearset). If a pair of gears had even numbers of teeth – certian teeth on the driving gear would always contact certian teeth on the driven gear and create a very pronounced wear pattern (a non-hunting gearset).
i.e. 40 teeth on the driving gear / 13 teeth on the tiny driven gear = a gear ratio of 3.08…..
The speed in times the ratio equals the speed out (30MPH x 3.08 = roughly 90MPH out)
And the Torque(rotational force) in divided by the ratio equals the torque output (50ft-lbs in / 3.08 = roughly 16 ft-lbs of force out)
A steep overdrive gear for maximum MPGees like a ratio of 0.54 for the transmission and a highway rear differential ratio like 3.08 (A corvette in 6th gear, for examples sake) would be the following:
Engine power or speed (1200RPM/40HP) X trans ratio X rear ratio = (1995RPM/66HP)
Engine torque output 40Torques / trans / rear = 24 torques.
That is certianly not enough for the highway. The biggest lever of them all, to move the planets and your fat asses down the road is often overlooked. The math gets complicated here, and is really aside from the point.
Practical application of this knowledge is to avoid buying vehicles with aftermarket, big-ass rims unless you know what you are doing. Bigger than stock wheels/tires (hood rims) have the effect of gearing up the vehicle up in all gears. First may feel like you are starting in second gear, and you may get great highway mileage, but you will probablly feel like you are lugging it when in overdrive if you are going (italics) ONLY the posted limit. Conversely smaller wheels/tires have a gearing down effect, where you may be doing a lot of revs on the highway and can do the posted limit but everyones passing you because you don’t wan’t to blow the motor. Other problems with aftermarket wheels / sizing are suspension geometry and speedometer readout not right/ abs / traction control problems. Again, if anyone is interested in practical knowledge, modified cars can be excelent machines, but buying them or modifiying them without knowing what your getting or getting into can be financially disasterous. That gem you want may cost you when the wrench-man has to fix or the unintended consequences.
One of these days i’ll get some money to donate to the site. Untill then remember knowledge is power!
Thanks, Steve!
Great stuff on the “rims,” too!
In re overdrive gearing: I put a 2004R OD automatic in my old muscle car. Fourth (OD) is something like .67 and even with 3.90 gears in the pumpkin, my old muscle car now ambles along at around 2,100 RPM at 70.
With a non-OD transmission, the engine would be screaming at 3,200 or so at the same road speed.
Did that F-150 ever even enter 10th gear? The videos I’ve seen they’ll upshift to 9th and stay there. I suppose it might enter 10th at the NMSL 55 mph on flat ground.
I just try and stay under 2000 rpm (~70 mph) to get the best fuel economy I can (19mpg on a recent highway trip).
Hi Chip,
Yes, around 60 at cruise (back off the throttle and it’ll upshift to 10th). If the road is flat you can gradually reduce speed and stay in 10th down to about 50 – with the engine turning around 1,000 RPM at that speed.
Eric really enjoyed the videos, the 1936 transmission example reminded me of being in high school. 36 would be about the newest thing we’d see with early 30s or 20s being the norm, all government productions
You’d never know color movies existed. My science teacher in the 6th grade showed the class a real color science movie. We were astounded, not by the content but simply because it was current.
I can deal with lots more of the VW chick pics.
BTW shifting heaven is an 18 speed in a big rig. 17% difference in the last 8 speeds is maximizing fuel /speed. A Spicer 4 x5 all the way to a 5×6 lets a shifty guy stay entertained.
This is one of the reasons why traffic planners should work towards making sure traffic is moving steadily. Fuel economy would be far better with fewer stops and slowdowns. Unfortunately most planners are doing quite the opposite in their quest to further their anti-personal vehicle agenda.
Just shows that fuel economy isn’t really the end goal.
A very good, very depressing point
Recently at a town nearby I approached the first of the 3…..and only downtown signal lights. Half a block away the first began changing from green to red even though no other cars were present from any direction.
So I stop till it’s green. About halfway to the next light it began cycling to red. Same for the last one. This entire time there were no other cars in sight.
Go back to 1980 and for a year I worked for an electrical contractor who kept the signal lights working properly and I had those lights synchronized for 30 mph.
Since it’s technically a US Highway, the lights fell under the auspices of the state 20 years ago. That explains why they’re so fucked up.