HP, do we really need so much?

[samandw]

I've been thinking a lot about this lately. I recently purchased a 1963 Dodge D100 for trips to the dump and lumberyard. The truck has a 198 cubic inch
Slant-6 rated at 127 Gross hp. It weighs just a tad under 4000 lbs with me in it. Since modern cars are rated in net vs. gross hp, which is generally about 80% of the gross number. That would put my truck at right around 100 hp. Last time I took it to the dump I dropped off 1/2 ton of garbage. While I wouldn't be winning any drag races, I had no problem keeping up with traffic or mantaining the speed limit. That's at 50 lbs/hp (albiet only around 35lbs/ft-lb). Compare that to a Honda Fit economy car, which weighs probably around 2650 with a driver and tank of gas, and has 109 hp and 105 ft-lbs. That's 24 lbs/hp and 25 lbs/ft-lb. To match the numbers for my loaded truck it would only need 53 hp and/or 75 ft-lbs. To match my unloaded truck it would only need 66 hp and/or 94 ft-lbs Still, you could easily make that with a properly tuned 1.2L engine, maybe even a 1.0L.

I think Americans have been fooled into thinking they "need" hp, when in reality, a slow-turning, torquey engine would be far more efficient while still producing acceptable acceleration. A 1.5L Atkinson cycle engine in that Honda would likely net a massive increase in mpg albeit at the expense of unneeded acceleration potential. Sounds like a fair trade to me as gas approaches $4/gallon.

[fumesucker]

High horsepower from a small engine does indeed come at the expense of overall efficiency.. To make horsepower numbers with a small naturally aspirated engine you must spin it up pretty hard.. Engine friction increases rapidly with rpm's, probably at about the square of the engine speed..

I understand that engines generally are at their highest efficiency near their torque peak, lower the peak torque rpm and it seems logical that overall efficiency would increase since engine friction would be lower at peak torque rpm.

[monroe74]

Originally Posted by fumesucker

I understand that engines generally are at their highest efficiency near their torque peak

Efficiency tends to be high near the torque peak, but efficiency is also high at larger throttle openings. See here:

http://www.autospeed.com.au/cms/gall...0&a=110216&i=6

So samandw is exactly right. Our engines are excessively powerful, and this is a problem because it encourages us to use low throttle settings, which are inherently inefficient. P&G works because it gives us a way to use large throttle settings without accumulating excessive speed.

A small motor running at full throttle (which doesn't necessarily mean hi rpm) is going to be more efficient than a big motor operating at partial throttle, producing the same amount of power.

[bobc455]

"Horsepower sells cars, torque wins races". HP is sexy and can bring in money, but the fact is that torque is what most people are after. And yes, they have more than they need.

-BC

[dkjones96]

Horsepower is a numbers game. An engine can make 200+ hp and only 50ft lbs if it revs high enough. My old nitro truck made 2.7HP at 35,000 rpm(yes, 35k) that's only .375Ft-Lbs.

GM has one of the lowest torque peak V6 engines in production from what I've been able to tell. The G8 3.6L makes 256hp at 6300 rpm and 248Ft/Lbs of torque at 2100 rpm. Nice, low torque in a HUGE power band.

The engine in your old truck is a 3.2L inline 6 but if you were to compare that with a newer inline 6 the power differences for the same displacement are pretty gross. My old 1988 Cressida with a 2.8L L6 made 156HP @ 5200 and 161Ft-Lbs @ 4400(figures that engine kept since its intro in 1984) and I averaged about 27mpg when I sold the car. What kind of mileage do you get? As the engines get more efficient it doesn't mean the displacement drops to make the HP numbers match.

An 88 corolla with the 1.6L got 23/31 making 90hp @ 6000 rpm and 95ft-lbs @ 3600 rpm and a new one has the 1.8 and gets 30/38 making 132 hp @ 6000 rpm and 128 lb.-ft. @ 4400 rpm both with a 4-speed auto.

2007 Silverado vs 1988 Silverado. 315hp @ 5200 and 338Ft-Lbs at 4400 in the new 5.3L while getting 16/21 while a 1988 Silverado with the 5.7L made 210hp at 4000 and 300 ft lbs at 2100 while only getting 14/18.

Take a 2007 Chevrolet Silverado for example again. The official EPA numbers for the 4.3L V6 automatic is 16/21 and for the 5.3L V8 automatic is 16/21 both with a 4-speed. Which one would you rather have? They get the same fuel economy but that V8 will have more power and probably last longer than the V6.

More HP doesn't always mean worse fuel economy. The Silverado here has 105 more HP(50% more) than it used to have 20 years ago but gets better economy with .4L less displacement.

[northwoods]

I see this as one of the simplest ways to increase efficiency - increase the stroke length and reduce the piston diameter, extracting more work per F/A charge. A discussion along these lines could be very informative. This is 1940's technology! Many moons ago I recall riding in a 1965ish Ford van that could seat around 10+. It had a long stroke 6 in it. Owner reported getting around 20+mpg with it as long as he kept the speed within reason. Does it make sense to sleeve a current engine block and hassle with new pistons/rods/camshaft to get this effect?

[monroe74]

Originally Posted by dkjones96

My old 1988 Cressida

Cool, another Cressida fan.

I had a '78 wagon, an '83, and an '85 wagon. And a family member had an '89. My favorite of the bunch was the '78.

I drove the '83 for over 10 years. It came to an untimely end when a kid ran a light and totaled it. A fairly severe accident, and I almost got hurt. The car had almost 300k at the time.

Sorry for the commercial interruption.

[RoadWarrior]

Originally Posted by northwoods

I see this as one of the simplest ways to increase efficiency - increase the stroke length and reduce the piston diameter, extracting more work per F/A charge. A discussion along these lines could be very informative. This is 1940's technology! Many moons ago I recall riding in a 1965ish Ford van that could seat around 10+. It had a long stroke 6 in it. Owner reported getting around 20+mpg with it as long as he kept the speed within reason. Does it make sense to sleeve a current engine block and hassle with new pistons/rods/camshaft to get this effect?

Might be easier to get a lower displacement motor that will fit what you want to drive then get a stroker kit for it.

However... this can lead to poor top end (if you ever need it) due to increased piston speed. And done to excess can put you in that area at midrange.

But! Mods to increase burn speed will win some of this back and will increase thermal efficiency... to a point...

Myself, I'm looking at a shorter rod and getting a 2mm offset crank grind on Marvin's "new" motor for 4mm more stroke... it's not much really, but will keep torque nice and strong where I need it. Anything making peak torque much over 3500 is a useless POS IMO. Well I guess I should quantify that, there's some motors with decent low end, that have the peak shoved over by variable length induction systems and other tricks. Let's say anything that isn't making 80% of it's peak torque by 2K or so is a worthless POS.

[samandw]

Originally Posted by dkjones96

The engine in your old truck is a 3.2L inline 6 but if you were to compare that with a newer inline 6 the power differences for the same displacement are pretty gross. My old 1988 Cressida with a 2.8L L6 made 156HP @ 5200 and 161Ft-Lbs @ 4400(figures that engine kept since its intro in 1984) and I averaged about 27mpg when I sold the car. What kind of mileage do you get? As the engines get more efficient it doesn't mean the displacement drops to make the HP numbers match.

I completely agree, my point was that we don't need nearly as much hp to be "functional" as people think. Obviously my ancient Slant 6 isn't a good example of an efficient engine. But if all I really NEED is 100 hp, that Cressida engine would only need to be 1.8L, which if it made good torque, should see significantly better mpg.

Originally Posted by dkjones96

More HP doesn't always mean worse fuel economy. The Silverado here has 105 more HP(50% more) than it used to have 20 years ago but gets better economy with .4L less displacement.

Of course, one could argue that with 105 less hp, a modern technology Silverado could get better mpg than one using 20 year old technology.

[fumesucker]

Originally Posted by monroe74

Efficiency tends to be high near the torque peak, but efficiency is also high at larger throttle openings. See here:

I'm aware of that, what I'm saying is that, all else being equal, an engine tends to be most efficient near its torque peak..

Make the the torque peak lower in rpm and you will most likely raise overall engine efficiency.

Which is one reason that diesels are more efficient than otto engines, the torque peak is almost always at a lower rpm on a diesel.

[R.I.D.E.]

The power levels of the old 198 Slant Six would be achievable with a 2 liter 4 cylinder turbo diesel engine. Give it to gayle Banks and he would make it a monster, you could probably go as low as 1.5 liter.

Add a 5 speed and some aero and you have a truck that could get what a Corolla gets now.

A Dodge Sprinter engine and tranny (Mercedes engine and 5 speed auto) would get you close. I hear the small ones get close to 30 with an atuomatic.
A manual would be better for P&G.

I worked in a Chrysler dealer body shop when that truck was 5 years old.

Old memory but I thought they offered 170 and 225 engines in 63, thought the 198 was a later motor, but those are ancient memories.

regards
gary

[fumesucker]

Originally Posted by northwoods

I see this as one of the simplest ways to increase efficiency - increase the stroke length and reduce the piston diameter, extracting more work per F/A charge. A discussion along these lines could be very informative. This is 1940's technology! Many moons ago I recall riding in a 1965ish Ford van that could seat around 10+. It had a long stroke 6 in it. Owner reported getting around 20+mpg with it as long as he kept the speed within reason. Does it make sense to sleeve a current engine block and hassle with new pistons/rods/camshaft to get this effect?

I had a '65 Econoline with a 200 CI six cylinder and a three speed manual.. It would do well over 20 mpg at 65 mph average and was roughly as aerodynamic as a brick.

What was amazing was that the distributor had no centrifugal advance at all, it was all vacuum.

Beyond a certain point, increasing stroke and reducing bore becomes ineffective and indeed even counterproductive. For a certain amount of power you need to be able to flow a certain amount of air, and if the bore is too small the valves become shrouded by the cylinder wall and airflow drops off.

Not to mention that longer stroke engines tend to have high internal friction.

A lot of motorcycle engines have roller bearing bottom ends and do not need anywhere near the oil flow rate and pressure of a plain bearing bottom end.. Perhaps a really efficient engine should have roller bearings, that would keep the need for an oil pump at a minimum.. Pumping oil around the engine is a source of parasitic horsepower loss..

[RoadWarrior]

If you look at the BSFC map though, the pretty colored one, you can see that you can have too little power also. For example, if you take a vehicle that is notorious for "not being able to get out of it's own way" like a 2.3HSC Tempo with the 3 speed ATX, that highway cruises at nearly 3500 RPM, where we should knwo that in frictional and pumping terms round about 3000 rpm is equivalent to around 55-60mph aerodynamically, because like aerodynamic resistance the frictional losses also square with speed. Anyway, this thing chugs along with a motor rated at 90 horsepower, and on good days, they all even manage to run in the same direction. So you're figuring, hey, I'm only using about 30 horses to roll along the highway and thrash transmission fluid, why do I need all 4 cylinders to do that? and decide that this would be the ideal vehicle to prove the superiority of DoD once and for all, so you cut the injectors to 2 of them....

Well what has happened is that you were sitting at about the equivalent of 3500, 50 in the light blue on that graph and have now shot up to about 3500, 100 with your foot flat to the floor.... and you still need that 30hp to keep you moving, and it's still sucking around .5lb/hp.... no change in FE.... so then obviously you've proved that that motor is not a good candidate for DoD or cylinder cut.

Geared different, you might jump it into the red spot.... putting a 40hp motor in that needs you to gear it to 4-5000 RPM to keep it at highway speeds might put you in the dark blue or magenta.

[monroe74]

Originally Posted by fumesucker

all else being equal, an engine tends to be most efficient near its torque peak

Good point. Thanks for explaining.

was roughly as aerodynamic as a brick

No, I think the brick was more aerodynamic.

Originally Posted by RoadWarrior

Geared different, you might jump it into the red spot

I think that's a key point. Gearing is so important. Too many cars tend to have short gearing, even in top gear, because it makes the car feel more powerful. The car creates the impression of being more powerful if it doesn't require a large throttle opening. There's a natural tendency for buyers to avoid a car that calls for a large throttle opening. But the larger throttle opening is more efficient.

Once I owned a '68 GTO and a '72 Skylark at the same time. I had too much time on my hands, so I decided to swap differentials (I also swapped the front brakes, because the GTO shipped with drums). The GTO had something like a 4.x ratio, and the Buick was something like 2.7.

The results were predictable and entertaining. The speedo error was huge.

[samandw]

Originally Posted by R.I.D.E.

Old memory but I thought they offered 170 and 225 engines in 63, thought the 198 was a later motor, but those are ancient memories.

regards
gary

That might be right, I'm still learning about the Slant 6. All I know is that it's got the short thermostat hose indicating it's a 170/198, but the VIN tag says it's rated at 127 hp. Being as it's 45 years old though, who knows. Still haven't found the displacement stamp on the block.

[jcp123]

Originally Posted by samandw

I've been thinking a lot about this lately. I recently purchased a 1963 Dodge D100 for trips to the dump and lumberyard. The truck has a 198 cubic inch
Slant-6 rated at 127 Gross hp. It weighs just a tad under 4000 lbs with me in it. Since modern cars are rated in net vs. gross hp, which is generally about 80% of the gross number. That would put my truck at right around 100 hp. Last time I took it to the dump I dropped off 1/2 ton of garbage. While I wouldn't be winning any drag races, I had no problem keeping up with traffic or mantaining the speed limit. That's at 50 lbs/hp (albiet only around 35lbs/ft-lb). Compare that to a Honda Fit economy car, which weighs probably around 2650 with a driver and tank of gas, and has 109 hp and 105 ft-lbs. That's 24 lbs/hp and 25 lbs/ft-lb. To match the numbers for my loaded truck it would only need 53 hp and/or 75 ft-lbs. To match my unloaded truck it would only need 66 hp and/or 94 ft-lbs Still, you could easily make that with a properly tuned 1.2L engine, maybe even a 1.0L.

I think Americans have been fooled into thinking they "need" hp, when in reality, a slow-turning, torquey engine would be far more efficient while still producing acceptable acceleration. A 1.5L Atkinson cycle engine in that Honda would likely net a massive increase in mpg albeit at the expense of unneeded acceleration potential. Sounds like a fair trade to me as gas approaches $4/gallon.

I think you hit on something there. I'd take a low-revving torque pumper over a high revver any day. I never really cared for revving my SVT Focus, so I really wouldn't even miss the ability to do that. My Mustang now shifts @ ~1100-1200rpm when I take it easy - it's so understressed it's not even funny.

[monroe74]

Originally Posted by jcp123

My Mustang now shifts @ ~1100-1200rpm when I take it easy - it's so understressed it's not even funny.

It's good that you're at low revs. But the problem with a motor that's understressed is that this probably implies small throttle settings most of the time, and that's inherently inefficient.

[jcp123]

Well, even keeping up with the rushed pace of traffic from the light without getting a holeshot puts me around a 1600rpm shift point. If I'm seeking a holeshot from the light, it rarely revs much past 2k rpm, just because of the cam and head tuning as well as tall factory gearing. At WOT, the trans shifts at 4400rpm, about 150rpm above peak HP. 2-bbl carbs end up using so much throttle almost anybody who drives a carb'd car will tell you that 2-bbl's don't yield any extra fuel economy (more so in pickups than small cars like Mustangs), but sure sacrifice a lot of top end flow and power. I'm no engineer, to be sure, but I'm not sure that's an escapable conundrum in this car.

Correction: the 200ci I6's these cars were available with had a 1-bbl carb and were usually able to average around 20mpg in normal driving and some could even touch 30mpg on the highway. I've heard similar stories about GM's 235 I6 in the biggies. Combination of smaller motor size and less pumping losses past the butterfly valve?

[monroe74]

Originally Posted by jcp123

I'm not sure that's an escapable conundrum in this car.

I think the basic issue is common to pretty much all automatics. The problem is that it's almost impossible to combine heavy throttle and low revs. But that's generally what's needed for high efficiency.

[tjts1]

There is no direct correlation between peak HP and fuel economy. This is a non issue.

[RoadWarrior]

Here's a good example, large vehicle, different motors, virtually the same FE....
http://www.fueleconomy.gov/feg/compx...Field=Findacar

The autos were virtually identical A413 type in different cases, same ratios.
2.2L 4-cyl & 3-spd auto 96hp @ 5200 RPM 119ftlbs @ 3200 RPM
2.6L 4-cyl & 3-spd auto 104hp @ 4800 RPM 142ftlbs @ 2800 RPM
2.5L 4-cyl & 3-spd auto 100hp @ 4800 RPM 135ftlbs @ 2800 RPM
3.0L V6 & 3-spd auto 136hp @ 5000 RPM 168ftlbs @ 2800 RPM

Then in later vans 96-00 there was little difference between the 2.4, 3.0 and 3.3, and in the '08s the 4.0 looks like being the dark horse with a flat torque curve like the legendary buick V6

[R.I.D.E.]

One way to determine the CU of a slant 6 is to measure the stroke with the plugs out. Use a welding rod or equilavent.

All memory here but I think the 225 was 4.5 inches, whicle the 170 was 3.5 (stroke).

I think the 170 was rated at 101 HP while the 225 was rated at 145. Your rating souds right for the 198. I think the 198 came out at the same time they abandoned the 170. My 63 Valiant got 28.5 MPG but was fairly gutless.

regards
gary

[lunarhighway]

my light kadett (1863)had a 1.3L witch 75Hp
my curent "fat" (2337)vectra has a 1.6 with only 70HP

wich one would you buy based on those figures?

well the kadett has 101Nm of torque at 4200rpm
while the vectra has 125Nm of torque at 2600rpm

they're both very well drivable. but you really had to rev the kadett like hell to get something from it (wich was fun, but noisy). you can feel the vectra has more weight but if you take of from the stoplight it just launches like a rocket.

for the moment it even seems to get slightly better economy than the kadett

[monroe74]

Originally Posted by tjts1

There is no direct correlation between peak HP and fuel economy. This is a non issue.

If the power is achieved by a small motor that can reach high revs, I tend to agree with you. A driver can choose FE, at any moment, just by avoiding high revs. But if the power is achieved by displacement, then the situation is more complicated, because it's hard to avoid excessive pumping losses. Especially with an automatic, because heavy throttle will trigger a downshift. Unfortunately, big displacement combined with an automatic is the typical Detroit design.

[kamesama980]

wow I'm late...
-sweet, another Cressida fan. DK and I know eachother from some other forums because of the Cressidas. I still owe him some used head bolts if I recal lol (long story)
-my 87 chevy s10 2.5 4 cyl makes an advertised 90 hp, 125 ftlb, and redlines about about 50 rpm (seems like... I think the actual redline is 4500-5k). it gets a combined mpg of about 25-26 and I've loaded it past capacity (camaro V8 engine, suspension, few other bits plus myself and entertainment for a 5 hour drive) and while it took a little longer to get there, had no problem maintaining 70 mph and managed 24 mpg with a 30 mph head/cross wind for the trip back going 60-65.

"I need a 5k lb 400 hp suv to haul my 2 kids to school" just pisses me off