The great torque/HP debate

[Motor Daddy]

You using two different gear ratios in your two engines. Equalize the gearing between the two engines and the 455 dominates.

Towing is not a contest of acceleration over a broad rpm range. It is brute force(aka Torque) being applied at a fixed speed.

The 455 in your OP has a 511 ft-lbs of peak torque. Your 400 is showing a peak of 465. With EQUALIZED GEARING the 455 can pull a heavier load. Big engines are not just for durability.

Kurt, I'm not trying to be disrespectful so please don't take it that way, but you are wrong. The 400 will be able to tow a greater load at EVERY MPH because it has more HP which can ultimately be reconfigured into a greater torque at the wheels than the 455 at every MPH due to the torque multiplication of using a higher numerical gear. This is the whole point of this exercise.

Why would I equalize the gearing for a 3.75" stroke compared to a 4.21" stroke?

[kurt454]

"Why would I equalize the gearing for a 3.75" stroke compared to a 4.21" stroke?"

Unless you are drag racing there is no reason not to.

400cid peak torque is 465 x 1.98 x3.73 equals 3434.21 RWT

455cid peak torque is 511 x 1.98 x 3.73 equals 3773.94 RWT

I agree with you in a drag racing situation that high rpm, high horsepower engines can run a steeper gear ratio, and has an advantage over the lower rpm, lower HP engine.

Towing is not a contest of speed. Rerun the numbers on your two engines, and give them identical gearing. Look at your rear wheel torque numbers then.

[Motor Daddy]

"Why would I equalize the gearing for a 3.75" stroke compared to a 4.21" stroke?"

Unless you are drag racing there is no reason not to.

400cid peak torque is 465 x 1.98 x3.73 equals 3434.21 RWT

455cid peak torque is 511 x 1.98 x 3.73 equals 3773.94 RWT

I agree with you in a drag racing situation that high rpm, high horsepower engines can run a steeper gear ratio, and has an advantage over the lower rpm, lower HP engine.

Towing is not a contest of speed. Rerun the numbers on your two engines, and give them identical gearing. Look at your rear wheel torque numbers then.

That's your mistake, Kurt. You don't understand what is being said about the ability of that peak HP to be effectively used at all MPH through the use of gearing. The peak torque at the flywheel is irrelevant because the flywheel does not touch the ground. The engine operates at a RPM proportional to the total gear ratio, with respect to stroke and tire circumference. In other words, the ratio of the distance the piston travels to the distance the car travels. The greater the ratio, the greater the torque.

[Motor Daddy]

Also, when comparing those examples, what are the MPH of each? You are mistaken "streetability" for "performance".

[nitro2]

With equalized gearing, and equal rotating inertia in the engine/drivetrain, the engine with the highest torque will pull the heaviest load (for towing) and generate the greatest acceleration (for racing). Load comes in many forms and acceleration is a load.

However, if the goal is to pull the heaviest load at a specific speed, say 20 mph, and gearing is not restricted (again assuming equal rotating inertia in the engine/drivetrain), the engine generating the highest HP at 20 mph will pull the heaviest load (for towing) and generate the highest acceleration (for racing).

The laws of physics are fixed.

However, because of the difference in the shape of the torque curves a towing engine is more suited to pulling a load from a dead stop and keeping the load from coming to a dead stop. The race engine would have a harder time getting the load moving in the first place.

Conversely a racing engine has a lot less rotating inertia in the engine, flywheel, drivetrain than a towing engine and can get more of its HP/torque to the ground when accelerating.



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

[Motor Daddy]

The laws of physics are fixed.

I refer to that as "mass, distance, and time".

It's a "Unified Field Theory".

[Motor Daddy]

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.

[Bubstr]

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.

[Motor Daddy]

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.

[F1Fever]

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

[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]

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.

[kurt454]

If I average the rear wheel torque in yout hypothetical 455 running 3.23 gears, I get ~2981.5.

The average of the 400 with 3.73 gears is ~3133.9

If I up the gearing in the 455 to 3.73 I get an average of ~3443.

High peak horsepower is beneficial in a drag engine because the rpm operating range of the engine can be narrowed greatly though loose converter, gearing, and or transmission gears. If you have a high peak in a narrow band, the average HP/Torque goes way up. Look at Pro Stock running 5 speed transmissions.

[F1Fever]

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.

[Motor Daddy]

If I average the rear wheel torque in yout hypothetical 455 running 3.23 gears, I get ~2981.5.

The average of the 400 with 3.73 gears is ~3133.9

If I up the gearing in the 455 to 3.73 I get an average of ~3443.

High peak horsepower is beneficial in a drag engine because the rpm operating range of the engine can be narrowed greatly though loose converter, gearing, and or transmission gears. If you have a high peak in a narrow band, the average HP/Torque goes way up. Look at Pro Stock running 5 speed transmissions.

When you up the gear on the 455 you are reducing the MPH per RPM (increased ratio of distance piston travels to distance vehicle travels).

I can do the same thing to the 400 and still beat you, because the 400 has more HP.

Kurt, You can't dispute the example. No matter which gear you pick for the 455, I can pick a higher numerical gear and beat you, and I can tow more weight per MPH because the 400 will have a higher rear wheel torque per MPH. There is no two ways around it.