InfernalVortex

iTrader: (4)

It's just simple physics.

Force multiplied by distance divided by time = power

( Force x Distance )/ Time = Power

Or...

(lbs x feet)/minute = power

Starting to look familiar? See that lb-feet component there? Force times distance = work, or torque (in certain situations).

(33000 lbs x 1 foot)/ 1 minute = 1 horsepower

What complicates this is we are measuring rotational torque, not just distance, so there's a component measuring RPMs, because there's another complication in the way of the power making its way to the ground (the rotation of the wheel).

Anyway, most of that is irrelevant, but I wanted to point out that one of the factors in creating a "horsepower" number is, in fact, torque. Torque is the direct measurement, horsepower is the sum of how much that torque is applied within a time period.

This should start to explain why diesels dont work so well for racing. They provide LOTS of torque, but they aren't suited to doing it quickly. Consider a smallblock chevy 350 makes more torque than a 2.4L 800hp Formula 1 V8. That 2.4L V8 is torque limited to around 300 peak ft lbs. In order to make that kind of power, it has to spin those ft lbs to 1800+ RPMs.

Consider the amount of air being drawn into an engine as an indicator of peak theoretical torque. In a 350 with 100 percent volumetric efficiency, that's 350 cubic inches of air. That will determine your peak theoretical torque number.

Remember, the main drawback of gasoline engines was their limited operating range. Certain technological advancements over the years were invented to extend that, but the multi-speed transmission was the big workaround solution that made gasoline engines practical. But even with multi-gear transmissions around these days, you still have to deal with the consequences of a limited operating range in a gasoline engine. For the Chevy v8, it's usually around 3000-4000 RPMs. For a stock v8, it's about 600 RPMs to 4500 RPMs. For a high performance one, it's 4000-7500 RPMs.

Remember torque is determined by how much air your engine can bring in. That amount of air is a fixed amount in a given engine. If you want a commuter car or towing vehicle, you want that torque to be applied at low RPMs, and so you build your engine to be efficient from 500-4500 RPMs. If you want that torque applied at high RPMs in your road race car, you put a big camshaft in there and make it efficient at 4000-8000 RPMs.

The problem is that we have to choose. Air velocity, port size, valve size, camshaft duration, intake plenum size, exhaust diameter, header primary size, primary length, ALL of these things play their own parts in improving airflow either at low or high RPMs, sometimes they improve airflow at low AND high RPMs, but in a lot of cases, we have to choose. The biggest example of that is head port size and camshaft duration. The more overlap in your cam the worse the car will run at low RPMs due to all the inefficiencies there. A lot of the fuel goes straight out the still open exhaust valve. Larger head ports ruin velocity at low RPMs too and cause further issues there. But at high RPMs, these things are a HUGE advantage, because the engine is rotating so quickly that the larger parts and huge overlap are the only way enough fuel/air mixture can even get into the cylinders in time for combustion to happen efficiently.

Small high velocity head ports like on stock heads keep air moving at low RPMs, but they cant feed the engine enough air and fuel at 6500 RPMs for it to continue to make more horsepower. They just choke the engine due to lack of volume. Remember, RPM's create horsepower, but if you cant get enough air into the cylinder to make any torque, the torque side of the horsepower equation will start to fall and your horsepower numbers eventually start to go downhill on that dyno graph.

Air into the cylinders makes torque. How fast that air can be pumped in and out makes power. Every single performance mod you make is to tweak the amount of torque you make, and where in the RPM range you make that torque. The larger the displacement, the more air you can pump into the engine, and the more torque you make. The more torque you make, the more potential power you can make if you shift that torque production to high RPMs by making low RPM sacrifices.

But again, horsepower is how fast you can make torque. The more horsepower, the faster you are. Horsepower wins races. Torque just allows you to make that horsepower, but in colloquial usage, people dont understand that horsepower is just high RPM torque. You could even say that torque is low RPM horsepower. But in reality they're both interrelated, it's just a matter of where you want the engine to be the most efficient, and you choose that depending on your usage for the vehicle.

So remember how I said diesels are bad for racing? It's because they tend to have a very, very limited operating range, even worse than gasoline engines.Which means you are constantly wasting time shifting gears or waiting for the engine to hit its powerband. Not only that, but they are low RPM ranges. Hard to make a lot of horsepower when you cant spin that engine very quickly. So even though a 5 liter diesel can take in the same amount of air as a 5 liter (305 cubic inch) gasoline engine, it wont make as much horsepower because the 302 (lets use a 302 because it's still 4.9 liters) may be able to spin up to 7000 RPMs, very possibly twice as many RPMs.

So then how do you see these crazy 4500 lb diesel trucks doing 11's on the drag strip? Well theyre running big turbos on BIG boost. They cheat by forcing more air into the motor, because when you cant turn the engine any faster, you just have to cram more air into it to make more torque, and that extra torque makes the horsepower.

300 ft lbs at 4000 RPMs vs 600 ft lbs at 4000 RPMs.... the 600 ft lbs will make twice as much horsepower...

But you can turbo the 302 too, and accomplish about the same thing. The advantage with diesels is that they have much higher cylinder pressures and usually can better withstand the turbo pressures.

Another twist on this... We all know cam/heads/intake make power. Well, assuming a few special things stay equal and within reasonable ranges, if you put the same camshaft, cylinder heads, and intake on a 302 as you do a 383, your horsepower numbers will be about the same on both. Believe it or not, the 383 will make more torque, but it will do it at lower RPMs and therefore there wont be any increase in horsepower. This is why people say not to use a TPI on a 383, because it restricts airflow when so much air is required to flow through it. It will make the same power it would make on a 305 if the cam and heads were the same.

There are a lot of small caveats to this, but in a lot of cases if you build a strong 302, and then you build a 383 bottom end and bolt your heads/cam/intake onto it, you wont gain much if any real horsepower. The only real reason to build a larger engine, is because with the greater torque production, you can move the power band farther and farther up the RPM range and still leave enough low RPM torque to keep the car rolling around. So ideally if you had a fast 350, you could bolt everything onto a 383, and then you can use a larger camshaft to push the power band higher, but you'd make the same amount of low end torque as you made with the 350. You can make it faster, and keep it streetable. That's the reason cubic inches (and therefore torque) wins races, it's because you can shift that torque up and make even more horsepower.

ZONES89RS

iTrader: (2)

Ah, now that makes sense, thank you for some good information. There is nothing there I can remember stumbling across. It makes a usable figure, never thought of it like that nor have I ever looked into how a dyno meter works either.

jhainer

build this then race the stangs tq is what gets a car moving and this motor has more than enough. http://purplesagetradingpost.com/sum...%20engine.html

ZONES89RS

iTrader: (2)

Yep, nice heads and roller equipment with a small cam is nearly always a tq monster.

jhainer

one part of it that is funny there ford inline 6 rods

kmcn47

and i lost track of the argument after the first few posts what was initially resloved from all the mathematics? and what about 5.0s mustangs or camaros?

InfernalVortex

iTrader: (4)

Real displacement (How much air is drawn into the engine every complete cycle) determines torque. How quickly that torque is applied determines horsepower. So the less displacement you have, the faster you have to turn the engine to make the same horsepower.

Less displacement + more RPMs = more displacement + less RPMs.

Engine mods are all about making engines efficient within certain RPM ranges, hence the need for the "combo" to be done right.

kmcn47

now i get it, thanks