What is the Best PRV engine combination ?

[content22207_2]

You all have me convinced -- while I've got my 18,000 lbs school bus at the house over the weekend I am going to snatch out its cast iron V8 with a mere 220 HP and replace it with a lightweight aluminum motorcycle engine pumping out more than 250 HP. Surely those additional 30 horses will make the bus faster than it's ever been before -- numbers don't lie....

(And just look at all the extra space I will get under the hood. I could even mount the bus' new engine between my feet in the passenger compartment. This is going to revolutionize commercial transportation).

Bill Robertson
#5939

[Drive Stainless]

For what it's worth, Torque is also a mathematical calculation: Force X Distance. You just don't notice because your torque wrench is already calibrated to determine the force at the distance between the head and the midpoint of the handle.

Also, there most certainly is a "horsepower gauge," it's called a dynamometer, and in the engineering world, power/horsepower/watts are regularly used independently. And sure, you can make the argument that some dynamometers measure torque and RPM and do a calculation, but if so, you can also make the argument that a torque wrench just measures force and distance and does a calculation. That said, there are a lot of different ways to determine and calculate power without the need for torque. A lot of dynomometers actually determine the amount and rate of work (work as in the measure of a force through over a distance) being performed, and later back calculate the torque in order to also have that measure. In the end, horsepower is a measure of how much energy a device can output over a period of time. Any device that measures power or energy over time is a "horsepower gauge".

Sure when you're talking about engines, horsepower is a bit more difficult to perceive than torque (which you can compare to a wrench on lug nuts), but its measure certainly has it's use, just as torque does.

Nick,
I know that Bill started off with "Horsepower doesn't exist," but his other point was that the figure seems useless in comparing engines (250HP school bus vs. 250HP motorcycle). As a ME, could you comment on where is the horsepower measurement is most relevant?

[content22207_2]

(250HP school bus vs. 250HP motorcycle)

220 HP school bus.

By the numbers, a motorcycle is 14% more powerful than Ford's V8.

Bill Robertson
#5939

[content22207_2]

Of course my bus' front wheels alone (just the tires and rims) weigh about the same as a motorcycle, so I'm a little befuddled how a numerically superior motorcycle engine is going to manage to drag the rest of the vehicle around, but numbers don't lie....

Bill Robertson
#5939

[Nicholas R]

Nick,
I know that Bill started off with "Horsepower doesn't exist," but his other point was that the figure seems useless in comparing engines (250HP school bus vs. 250HP motorcycle). As a ME, could you comment on where is the horsepower measurement is most relevant?

Horsepower is always a measure of the rate at which the engine/motor/power system is able to produce/convert energy. For me, horsepower is very important because it never changes, despite gearing. If I spec out a 10hp electric motor, no matter how many reducers, gearboxes, pulleys, etc. I add, the system will still always be delivering 10hp. Most gearboxes and such are therefore rated by HP. Torque on the other hand changes at every step. A 30:1 gearbox multiplies the torque by 30 times, where a 1:30 gearbox divides the torque 30 times.

We say "100hp/100ftlbs at the rear wheels" but obviously thats not actually true. The torque at the wheels is a factor of the ratio of the gear you're in, and the differential/final drive ratio. With the DeLorean's 3.44:1 differential, even in 4th gear where the ratio is almost 1:1, the actual wheel torque would be 344ftlbs.

Now by no means am I saying that one measurement is more important than the other; both have value and both are important when considering an engines capability. You cannot compare the capability of a motorcycle vs a schoolbus based on one number because both have their merits. A school bus can haul far more, but obviously a motorcycle can accelerate far faster. Which do you want?

There really comes a lot of difficulty in comparing engines as though they're all like for like. A steam engine may produce 10,000ftlbs, but only at 10hp, since it's turning so slowly. Sure it can deliver a ton of torque, but the actual rate that it does that is arduously slow (Maybe 10-30RPM). To compensate, it will likely add a gearbox to increase the RPM but decrease the torque. On the other hand, a Formula 1 engine may make 1000hp, but only 250ftlbs. Torque is low, but the rate of delivery is ridiculously high (up to 20,000RPM). Similarly, a gearbox will reduce the RPM and increase the torque.

Personally, I wouldn't want either of those in my DeLorean, just like I wouldn't want a motorcycle or a school bus engine. I need and engine that is designed to produce power at a rate and RPM range that is consistent with the gearing of the car, with a torque rating that is appropriate for the amount of mass I'm trying to move. Though in my case that's not a PRV, it's a modified LS1

[Farrar]

I think the problem (and BOY are we off topic now, oops!) is that marketing pushes horsepower. It has "power" in it so otherwise uninformed consumers will go "ooh, more power" and buy the car with the bigger number. Personally, I think a power-to-weight ratio would be more useful, but tell that to marketing.

Long story short: marketing ruins everything. LOL

[Delorean Industries]

Well said nick. Rate of delivery.

[content22207_2]

A dollar is a dollar. Doesn't matter whether it's 100 pennies or a single dollar bill -- both have the same purchasing power.

Ipso facto, horsepower is horsepower. Doesn't matter if its a big cast iron V8 or a little aluminum 4 cylinder: 250 HP *MUST* be more powerful than 220 HP -- 30 horses more powerful to be precise. Numbers don't lie....

Bus is in service this week, but perhaps over the weekend I can bolt up a little motorcycle engine.

Wonder if I should snatch out the 60 gallon gas tank and install a 4 gallon motorcycle gas tank while I'm at it?

World's first 1.5 liter school bus with 4 gallon gas tank -- I am going to be the envy of every school system in the country.

Bill Robertson
#5939

[content22207_2]

I am negotiating buying my church's bus as a backup. That thing has a diesel engine that is bigger than my gas burner but only puts out 170 HP -- what a dog.

Bill Robertson
#5939

[davidc89]

I am negotiating buying my church's bus as a backup. That thing has a diesel engine that is bigger than my gas burner but only puts out 170 HP -- what a dog.

Well the Diesel doesn't have a carburetor so....