mythical numbers to avoid
 

I only came up with a few things to avoid, of course epa fuel mileage is one..as most of us under our own hoods knows.

Horspeower in general is another bad think to rely on..
I recently saw mention of "horsepower to weight" as a reminder how silly that number is: "horsepower"

I also wanted to share how I decipher a car...
ecomodder:
horsepower is often less than the torque.
mid range >4cyl:
horsepower is often squared up with torque.
race car:
horsepower exceeds the torque.

To give an idea how silly the hp number is...
my 90hp subaru at 2800 pounds can do a quarter in 15seconds as a 4x4...33.1 pounds of weight per horsepower..
the brand new 412hp mustang with just 8.8 pounds of weight per horsepwer is getting there just 2 seconds earlier...
something is way offset here...:rolleyes:

and lastly, a figure from my dads rig..
500hp for 79,000 pounds is..158 pounds of weight per horsepower..and it will do 85mph+ loaded. I don't think a 500hp mustang could do that..

if you cannot decipher numbers for power on any given car, find out the engine and figure bore and stroke...
an inline needs a deep one in the same car weight as a boxer, in the four cyl category, the 6 and 8 can be little strokes and big bores, and vice versa, it does'nt matter..this is where weight of car comes into play...all while ignoring the hp, go by liters and weight, derive your own conclusion, with engine design, like diesel or gas etc...

that hp number is like a fantasy derived from drug addiction. :confused:

Um, 15 second quarter miles with a 90 hp 4X4 at 33 lb./hp? I don't think so. The only quarter mile time I could find for your '87 wagon was 3 seconds slower at 18.7. That's a lot more realistic for a 33 lb./hp vehicle. You need a 15 lb./hp weight to hp ratio to turn mid 15s. It's simple physics, and the numbers do not lie.

And the 2011 Mustang GT will be in the high 12s, or very low 13s.

1/4 time improvements are not linear.

i.e. 8000hp = 4 second quarter, whereas it requires much less than 2000hp to run a 16 second time.

*not the best explanation, but the best I could do with my current brain power.

Actually that is a very good explanation. I ran high 16's in my stock ford taurus... I think that was 130hp or so.

And your Dad's rig has what, 1400 ft-lbs of torque?

I think he means an eigth of a mile in 15 seconds...

I actually got to watch a jet-engined dragster make a run. 5.6 seconds for the quarter at 300 MPH. Loud as heck.

Horsepower allows you to sustain high speeds, torque gets you moving. That's why I love my V8. 245 hp in a brick doesn't make it fly (15.2 1/4 mile), but the 345 ft lb of torque kicks it off the line pretty hard.

I can get almost the same mpg as a the same vehicle with the much smaller 4.0 I6 (22-23 @ 60mph vs 20-21 @ 60mph, both around 12 - 14 city), but I can haul it from 0-60 in 6.8 seconds if I need to. Plus, the V8 never downshifts on the highway (will happily turn 1800 in OD with the TC locked doing 60 up some BIG hills), and can get into the high gears faster around town. In areas with lots of big hills, the V8s sometimes get better mileage than the 6.

Having good power AND FE is all about a good, usable, low powerband and matching the engine to the vehicle.

YEE HAAWWW!!!! I don't even bother looking at HP. If someone starts telling me how much HP something has I like to ask them how much torque it has and then they admit they don't know and it doesn't matter. I like having torque on tap. My truck does not care if it is empty or has 6,000 lbs in it...it still goes....it just takes a little more pedal to stop.

HP does not allow you to maintain high speeds.

HP, technically, is an imaginary number, created by an algebraic equation which factors torque over time.

While it does give you an easier to understand indication of the correlation between torque and engine speed, it does not "allow" for anything.

Torque at 2,000 is the same as torque at 5,000, plain and simple as it gets. But if you only had Torque figures to rely on, you'd think that engine was puny at 5,000, because it makes so much less torque (in some cases, like my 300 I6 Ford) than it does at 2,000 RPM.

The figures are simple, when you actually know what they're for.

Torque = work performed (able to be performed)

HP = Work able to be performed in a certain span of time.

They mean nothing more than that.

And NO, a 90HP Subie WILL NOT make a 1/4 pass in 15 seconds. My 92 HP Civic could barely keep 16-17second runs, and it was nearly 1,000lbs lighter.

Yeah, around 260ft lbs just off-idle will do that for ya. ;)

I've been running around on 5 cylinders with a really bad misfire for quite awhile, and I can still hold 60-65 MPH with no problems, and tow a trailer doing it.

...the basic constant-power approximation (CPA) equations for ET and MPH from vehicle WT and HP are:

ET = 5.82 * (WT / HP )^(1/3)

MPH = 232 * ( HP / WT )^(1/3)

...or, approximately: ET = 1350 / MPH

...let me know if you want to know *where* the constants 5.82 and 232 came from.

1 horsepower is about equal to 746 watts.

HowStuffWorks "How Horsepower Works"

According to Watt, one HP is 33,000 foot pounds of work per minute

HP and torque curves cross at 5252 rpm, not open for debate.

http://vettenet.org/torquehp.html

Horsepower is a measure of work done over time. Torque is a measure of turning force. An engine will maintain max vehicle speed at its horsepower peak, where it's doing the most work per unit of time. It will accelerate the hardest at its torque peak, where it's turning the driveshafts the hardest.

My transmission has more than one gear too, makes a huge difference. Coupled to a smaller engine and body makes for more smiles (or less frowns) at the pump.

Are you sure? Since horsepower is a measure of work done per unit time, I think it's analogous to acceleration. You want the most work done per unit time to accelerate the vehicle as quickly as possible. If you had 500 ft-lbs of torque, but only 1 rpm at your disposal, the vehicle wouldn't accelerate very fast. 500 ft-lbs with 5000 rpm will get you moving. You need the combination of torque and speed (rpm), which equals horsepower, to get the acceleration. So the vehicle should accelerate the hardest at its horsepower peak (assuming you can keep the engine there while the vehicle accelerates). A CVT would be great. Or am I missing something?

you must be correct, that peak POWER (assuming you get the gearing right) is where best acceleration happens. Though I'm happier with most efficient, not fastest, acceleration.

As much as I love my Jeeps own I-6 for it's torque, but I definately pay at the pump for it as everytime I take off from a stop, it eats a ton of gas whether I'm super easy or not on the throttle, but at least it gets good mpg cruising.

Yeah, that'll happen when gearing doesn't match the torque curve... I keep telling people that my truck only really ever needed 3 gears... get going, keep going, and really go.

None of those gears would ever need to see any higher than 2400-2500 RPM.. Hell, I can run my I6 down to 700ish before it even feels like it's having any sort of difficulty moving the truck. I'd imagine that ~1,000 RPM would be the perfect cruise location for Gerald, which is why I still want to find a gear splitter for the rear axle. As it sits, I cruise at 2k ish @ 60 MPH... consequently, that's my torque peak... With a splitter, I could be in 5th(2) at 60-65 running ~1,000 RPM, and if I'm towing or need the extra torque, I could simply switch back to 5th(1) and be right back at my peak torque number, and it wouldn't affect my 4wd parts, either. I could run 4x4 with the splitter on (1), which is a simple 1:1 gear interface.

I think the rule of thumb is that gearing changes are marginalized without a corresponding aerodynamic change, it moves you left (rpm) on the bsfc chart, but since the power requirements are basically the same it moves you up the load axis. So if you happened to be southeast of the bsfc sweet spot then you might get lucky, but generally it doesn't work like that.

I'm just far south of it right now... there's no way it takes even close to 265 lbft to move that truck at 60 MPH. Not even close, considering that it takes less than 20% throttle on a flat to maintain my speed. I can pull a 4-6% (According to the last land map I saw) grade at 20-25MPH in 5th gear without downshifting, as long as I don't let the RPM's drop much below ~800. I usually pull that hill in 4th, though, just over 1,000 RPM.

For some reason, I feel most comfortable with the truck at ~1,000 RPM.

I think I could get a pretty nice gain by halving my cruise RPM, though, especially if I use the splitter to accelerate and skip gears. I can keep the engine loaded better if I skip gears, and having the splitter will keep the engine loaded better under acceleration (not that I do that much of it).

My peak BSFC (theoretically) is probably going to occur somewhere around 80% load at or slightly above 2,000RPM, provided everything is working correctly. I can guarantee that at less than 20% throttle, I'm so deep into the area under the curve that I'm pretty close to running rich, despite the OBD-II system installed, and the EEC-V ignition control system.

Under the average circumstances, I think you're pretty well correct, though.

I mostly agree, although I think I have had some marginal improvement with having slightly larger tires than OEM (1.7 inches larger diameter) which lets me cruise a bit faster and be at the engines peak range for FE. So far everything is good to 68, but as soon as I cross over to 70 MPH, FE starts diving dramatically... guess it's just time to move to the aeromod side.

I've got to do some improvements to my truck, both in aero terms, but only light modifications there, and also in terms of things that load the engine.

I may have a manual steering box sourced for it, which will eliminate the PS pump, I may have an electric fan w/ a thermo control sourced as well, which eliminates the fan from engine drag, and allows a faster warm up time. I'm going to be leaving the AC installed, though, on this one. It works perfectly, and there have been days where I could use it, especially if I have to head any distance south or into a city for any length of time during the hotter days.

Those things should help out a bit, especially when I have to accelerate.

I just happened across something by COMP (of course, I can't find the URL again) that claims that their "RV" grinds increase low-end torque and improve MPG over the OE ratings, as well... Would be great to get the best of both worlds, and since my HP/TQ peaks are so close together, I should see an improvement in HP as well.

How many times can you say you got more power, torque, and MPG?

What in the world are "RV grinds"?

The key for those of us with big engines is to make the engine itself more efficient. By doing this, it can develop more power when needed, and also get better mpg.

An RV grind is meant to give more low-end torque, for moving a heavy vehicle off the line.

Also, after thinking about it, with a properly geared transmission (not CVT), you would get maximum acceleration by shifting at, or just past, the horsepower peak, and having the RPMs fall back to the torque peak after the shift.

Maximum acceleration occurs when the area under the curve between the shift point and the pickup point (new gear engagement) are nearly equal on both sides of the peak.

Dropping back to your torque peak won't get you maximum acceleration, unless your HP and torque peaks are within 1,000 or so RPM of each other. Gears designed for quickest acceleration seldom are desirable for high maintained speeds, and the same goes for the other way around... high maintained speed will require gearing that isn't conducive to the quickest acceleration. That has nothing to do with torque and HP peaks, though... it's only got to do with redline and RPM shift between gears.

yes, that is basically how you accelerate quickly, but not how you accelerate efficiently.

To accelerate efficiently (in a general sense), you have to know your engines bsfc map, and keep the engine load right (about 80% very roughly) and center your shifts on bsfc peak rpm, say 2500 rpm but do your own homework (and post a pic and some details if you find a map for your vehicle) Brake Specific Fuel Consumption (BSFC) Maps - EcoModder

Cruise is the same philosophy, you want to be at the bsfc peak, but most vehicles have engines that are waay to big for optimal cruise, so various detuning strategies might help (i.e. advance the intake cam)

Technically, that's correct. However, in stock form, most of these larger engines have pretty close peaks. My torque peak is at 3200, HP at 4000, with plenty of guts down low as well.

Regarding the gear thing, I'll agree that while low gearing helps acceleration, it's brutal on the top end. My Jeep rips 0-60 in 6.8 seconds, but runs a 1/4 mile in 15.2 at about 90. Once you break 70 or so, and it's out of 2nd at WOT, it's done as far as moving fast. Fortunately, gas mileage prevents me from going that fast anyway.

Yeah, I'm able to get Gerald up to speed pretty quickly, if not for the crappy, notchy gear changes from the M5R2 tranny. They eat up at least 2 seconds from 0-60 where I'm not really accelerating at all.

Someday, I may install a smoother, quicker shifting transmission. This one's even a PITA to shift w/o the clutch, it's so finicky... wants exactly the correct RPM for the gear, or you get a "nick nick nick" noise on the way into engagement. Never tried it after revving over 3k, but I assume it'd be the same, only worse.

My shifting method is about as quick as it gets with a manual transmission, too. Out of gear when you let off, clutch as soon as you're off the accelerator completely, and by the time the clutch has released, you're already in gear and letting the pedal back out.

Drag racing a barn has got nothin to do with efficiency, see pinky wave:
http://www.youtube.com/watch?v=SgV9Oa6z5wY

;)

I am not worried about going fast. I am perfectly happy with climbing a hill with 6000 lbs in the back. The only problem with the massive torque at idle is the tires sometimes spin in 1st and reverse if I am not real smooth.

I don't have that problem, really, unless I get up to Farmer's Valley inlet, which is a like a 40*incline off the main road, around a nearly 90* curve. If I get too low in the R's hitting that incline, I get some bad wheel spin on the inside wheel, usually, and end up having to downshift and feather the clutch for a second to "tame the beast".

I hope to take care of this with an LSD 3.55 gearset, but that probably won't happen for awhile. Instead, I normally just take the turn (which is a right hand turn) from the left lane, so I can make it wider and line up before I hit the incline.

you wouldn't happen to have a bsfc map would you?

Negative. Been searching, to no avail, thus far.

Unfortunately, many manufacturers are reluctant to release this info. I haven't even managed to find a stock torque curve for my Jeep. But, I know the engine has plenty of grunt off-idle, and starts to get happy around 1200, and is really pulling by 1500-1600.

Also, DCB - That was just to prove a point that design for extreme low-end grunt and top end power tend to be mutually exclusive.

Yah, that's a gimmie. you move the torque curve left (i.e. rv grind) and you make less peak power. But it can be a good move for efficiencies sake when you are focused on operating at efficient rpms.

Exactly. That was my point. Having an engine set up and a vehicle geared to pull hard at the low end will give better efficiency, and is able to haul more weight, while sacrificing top end speed. If I actually run my Jeep all the way through the RPMs, by about 4400, it's falling on its face FAST in stock form. Compare to a little Honda that has to rev to 3000 to do anything useful, and is still pulling at 6000+.

If people would take a lesson from the big I6 and V8 truck engines, and apply that logic to a little 4 cylinder, with appropriate gearing, we'd have a winner (kinda like what the Metro XFi was intended to be). It would have plenty of power around town, be very efficient, and still be plenty strong enough on the highway up to 65 or so. Unlike my old 2000 Hyundai Elantra 2.0, which didn't even start to wake up on the highway until 75+.

To the OP!!!

HP is not some BS rating like you think it is. Its very real and very needed to compare one vehicle to another. If you understood engine cycle time you would get this.

History:

This is where the constant 5252 comes from.


The word horsepower was introduced by James Watt, the inventor of the steam engine in about 1775. Watt learned that "a strong horse could lift 150 pounds a height of 220 feet in 1 minute." One horsepower is also commonly expressed as 550 pounds one foot in one second or 33,000 pounds one foot in one minute. These are just different ways of saying the same thing. Notice these definitions includes force (pounds), distance (feet), and time, (minute, second). A horse could hold weight in a static position but this would not be considered horsepower, it would be similar to what we call torque. Adding time and distance to a static force (or to torque) results in horsepower. RPM, revolutions (distance) per minute (time), is today's equivalent of time and distance.
Now if we are measuring torque and RPM how can we calculate horsepower? Where does the equation HP=TORQUE * RPM / 5252 come from? We will use Watts observation of one horsepower as 150 pounds, 220 feet in one minute. First we need express 150 pounds of force as foot pounds torque.

Pretend the force of 150 pounds is "applied" tangentially to a one foot radius circle. This would be 150 foot pounds torque.

Next we need to express 220 feet in one minute as RPM.

The circumference of a one foot radius circle is 6.283186 feet. ft. (Pi x diameter 3.141593 * 2 feet)

The distance of 220 feet, divided by 6.283185 feet, gives us a RPM of 35.014.
We are then talking about 150 pounds of force (150 foot pounds torque), 35 RPM, and one horsepower.
Constant (X) = 150 ft.lbs. * 35.014 RPM / 1hp
35.014 * 150 / 1 = 5252.1
5252 is the constant.
So then hp = torque * RPM / 5252

Vehicle Horsepower Rating

In the early 1970s, the Society of
Automotive Engineers (SAE) published the standard J1349 which defined a
standard method of rating an engine’s horsepower. In a few words, the
horsepower rated under J1349 (or SAE net HP) is for a completely installed
engine, including all accessories and standard intake and exhaust systems. In
other words, it measures horsepower at the flywheel and excludes all transmission and driveline losses.
The J1349 standard was not without loopholes. Taking advantage of these
loopholes, some car manufactures are able to inflate their engine horsepower
ratings and therefore rendering the SAE net HP rating less accurate. This led the
SAE to introduce in 2005, new test procedures (J2723) for engine horsepower
and torque (See Certified Power - SAE J1349 Certified Power SAE International).
This testing procedure is optional. Manufactures completing it can be advertised as "SAE-certified".Transmission and Driveline Friction
The power lost in the transmission and in the driveline due to friction and
resistance is where a large portion of power is lost (See PMECH FRIC in Figure 1).
Compared to a manual transmission, an automatic transmission suffers more
losses due to its mechanical complexity and weight (increased friction), the
resistance/slip in the viscous coupling of the torque converter, the transmission
oil pump and hydraulic system. Not surprisingly, a 4 wheel drive vehicle suffers
even more losses compared to a 2 wheel drive vehicle. Also included in the
driveline power loss are the friction from the braking assembly and the friction
from the wheel bearings.