The great torque/HP debate

[Motor Daddy]

if the only goal is acceleration and there is no limit of gears Tq can simply be ignored....

Not true.

sounds like you jumped the fence to me. Prove your stance.

Jumped the fence?

I explained to you why.

[randy331]

I don't need torque to calculate HP. HP is 550 lb-ft of WORK per second. I can calculate torque from work. It's easy:
No torque required to measure HP, and no dyno required to measure torque!

So if I have an engine sitting on the engine stand, and I want to know how much HP it makes. What devise do I hook my engine to, so I can measure the WORK it puts out?

Randy

[Motor Daddy]

I don't need torque to calculate HP. HP is 550 lb-ft of WORK per second. I can calculate torque from work. It's easy:
No torque required to measure HP, and no dyno required to measure torque!

So if I have an engine sitting on the engine stand, and I want to know how much HP it makes. What devise do I hook my engine to, so I can measure the WORK it puts out?

Randy

Hook the crank to a load and measure the maximum load you can place on the engine at each RPM at WOT without the engine increasing or decreasing RPM, just like the old days.

Or you could couple the engine to a shaft with a drum and find the maximum weight and height the engine can do at each specific RPM. You can then calculate the torque from the work per minute (HP).

If you want to do it the modern way, just use a modern dyno.

The point is, just because we do it this way in modern times does not mean it wasn't done the old fashioned way back in the day!

You can calculate torque from power:

Torque=HP (work per minute/33,000) * 5252 / RPM

[F1Fever]

if the only goal is acceleration and there is no limit of gears Tq can simply be ignored....

Not true.

Torque can never be ignored because it is the "load rating" of the RPM. The higher the "load rating" of the RPM, the higher the "NET FORCE" between the "load rating" and the load, at that RPM. A higher "NET FORCE" means a greater acceleration.

a rose by any other name is the same....horsepower.

[Motor Daddy]

if the only goal is acceleration and there is no limit of gears Tq can simply be ignored....

Not true.

Torque can never be ignored because it is the "load rating" of the RPM. The higher the "load rating" of the RPM, the higher the "NET FORCE" between the "load rating" and the load, at that RPM. A higher "NET FORCE" means a greater acceleration.

a rose by any other name is the same....horsepower.

My only point was, you can not ignore torque. That's like a weight lifter ignoring the weight on the bar. Big mistake.

[F1Fever]

if you know the Hp the only reason to know the Tq would be to gear appropriately ie, you don't know the rpm.

[Motor Daddy]

if you know the Hp the only reason to know the Tq would be to gear appropriately ie, you don't know the rpm.

HP is a measure of the ACTUAL amount of work per minute/33,000.

Back in the day, they decided to measure work by the amount of work a horse could do per minute. They set the standard to 33,000 lb-ft of work per minute as being equal to 1 HP. It equals out to lifting a 200 lb weight 165 feet in one minute (200*165=33,000).

The problem with RPM is that a 4 cylinder Pinto can be turning a steady 4,000 RPM at part throttle, or a top fuel car engine could be turning a steady 4,000 RPM at part throttle.

In order to determine how much power each has at 4,000 RPM at WOT we need to measure how much load can be applied to each and still maintain that steady 4,000 RPM. Once you find the load, you know the torque. Of course, the one that can carry the greatest load at 4,000 RPM will accelerate a lower load at a greater rate, proportional to the torque and load.

Sorry if this seems over simplified, but it's a easily understood explanation.

[kurt454]

I concede the point that the higher horepower engine can always be geared steeper to increase it's output at the rear wheels.

I still believe that the bigger engine makes for a better towing engine due to the more practical gearing in a daily driver, but I do see that higher HP is king.

Here is a link to an article which covers our discussion.
http://www.mustangsandmore.com/ubb/DanJ ... eVsHP.html

[af2]

I'm not sure what is being proved here. If you wouldn't limit the smaller engine with the same gear, why would you limit the larger one with a less than adequate head and cam? Everyone here knows what goes fast. And they know a poor combination of parts isn't as fast, even if it has more torque in a RPM range you really didn't want to use for the purpose.

Again, the point is not which engines they are, or which can be made to run faster. The point is "how torque and HP work", and why a peak power is so important to acceleration.

Look at a diesel motor and it should give you the answer you are looking for.

[Motor Daddy]

I concede the point that the higher horepower engine can always be geared steeper to increase it's output at the rear wheels.

I still believe that the bigger engine makes for a better towing engine due to the more practical gearing in a daily driver, but I do see that higher HP is king.

Here is a link to an article which covers our discussion.
http://www.mustangsandmore.com/ubb/DanJ ... eVsHP.html

Thanks for the acknowledgment, Kurt.

The "practicality" is otherwise known as "streetability", and yes, the 455 may very well be more streetable, but that is a horse of another color.

[nitro2]

The race engine would have a harder time getting the load moving in the first place.

I don't agree with this statement.

The load is reduced on the crank proportional to the total gear ratio.

A higher numerical gear means a lighter load on the crank.

If the rear wheel torque were the same on both, and the 400 had a higher numerical gear, and a higher launch RPM, they would both accelerrate the load at the same rate.

If the 400 has a HIGHER rear wheel torque at that proportionally higher launch RPM, the 400 will accelerate the load at a greater rate.

Unfortunately I didn't state the conditions I was referring to with the statement (essentially those inferred from the paragraph preceding the original statement). The statement has moved well away from the 400 vs. 455 controversy as I have already agreed with you that for the 400 vs. 455 power plots the higher HP will win and I have backed this up with engineering formulas in this thread.

More specifically what I was referring to was as follows: If you have a 500 HP race engine and a 500 HP towing engine and both are geared to pull a load up a hill at 20 mph at peak HP rpm, the towing engine will have a much easier time getting the load moving than the race engine because of its torque curve. I don't think there is anything astounding or controversial about this, I'm just clarifying what was meant.

Since both engines must pull the load at 20 mph which requires 500 HP and as such peak HP rpm at 20 mph, the gearing is thereby defined. The towing engine will have much more low rpm torque and low rpm power than the race engine and will pull the load away from a stop much easier than the race engine. If the load is present right from the get go (i.e. parked on a hill) the race engine would have a harder time as you would have to rev it up quite high to get on the torque and slip the clutch or run a high converter stall. The towing engine will also be less likely to allow the load to come to a stop should the hill get a little steeper as the race engine will fall off the torque curve and the towing engine will come onto the torque curve as the speed comes down.

I'm not sure how things diverted into towing from racing.

Clint Gray
TFX Engine Technology Inc.
(Combustion Pressure Analyzers)
www.tfxengine.com

[Motor Daddy]

Clint, I'm not exactly sure what you are saying, but I think I still disagree.

If both the 400 and 455 line up at the light (same weight), no matter what the launch RPM is on the 455, the 400 can adjust its launch point accordingly and have more rear wheel torque at launch. The car that has the greatest rear wheel torque will accelerate at the greatest rate from a dead stop, regardless of the "streetability" or classification of the engine, or what the torque is at the flywheel. Rear wheel torque is KING when comparing acceleration rates at MPH!

[Motor Daddy]

You can think of the rear wheel torque as a weight lifter's maximum potential, and the load as the weight he is lifting. The closer the weight lifter gets to his maximum potential, the slower he will accelerate that weight. The further away from his potential the faster he can accelerate the load.

Same in a car. The rear wheel torque is the strength of the axle's speed. The greatest strength will accelerate the load at the greatest rate, regardless of how the body builder looks.

[randy331]

Hook the crank to a load and measure the maximum load you can place on the engine at each RPM at WOT without the engine increasing or decreasing RPM, just like the old days.

I think they call that a water brake/absorber.

Or you could couple the engine to a shaft with a drum and find the maximum weight and height the engine can do at each specific RPM. You can then calculate the torque from the work per minute (HP).

Everytime I try that, the drum goes flying the instant I start the engine!

If you want to do it the modern way, just use a modern dyno.

That makes more sense!

You can calculate torque from power:
Torque=HP (work per minute/33,000) * 5252 / RPM

I think most are familiar with the math required to figure HP.

Randy

[nitro2]

Clint, I'm not exactly sure what you are saying, but I think I still disagree.

If both the 400 and 455 line up at the light (same weight), no matter what the launch RPM is on the 455, the 400 can adjust its launch point accordingly and have more rear wheel torque at launch. The car that has the greatest rear wheel torque will accelerate at the greatest rate from a dead stop, regardless of the "streetability" or classification of the engine, or what the torque is at the flywheel. Rear wheel torque is KING when comparing acceleration rates at MPH!

Actually the statement was totally removed from the 400 vs. 455 issue.

In a nutshell what I am saying is if you have two 500 HP engines which are making 500 HP at 20 mph (towing), then the one with the towing torque curve (i.e big diesel) will make for example 150 HP at 4 mph and the one with the race engine torque curve (8000 rpm 302 or whatever) will make 80 HP at 4 mph. Both engines must make the same peak HP as they must pull to 20 mph. The one with the most bottom end power will make the most RWTQ from a stop and will pull away from the stop the easiest, etc. Of course you could always rev up the race engine and drop the clutch, spin the tires etc. but this was meant to be a practical towing example. The statement has nothing to do with the 400 vs. 455, but is related to someone's twist which got into towing.

Now if the example was about 2 engines with different HP, or towing speeds that were not fixed, that would be a different story altogether.

Clint Gray
TFX Engine Technology Inc.
(Combustion Pressure Analyzers)
www.tfxengine.com