Some questions about cars

[360evolution]

Ok, i'll be honest, i dont know much about cars. Please answer these...

1) What IS torque? 240lb ft at 6700rpm? What the hell? Explain please

2) Bhp. Brake or break horsepower? I know it puts a different hp to the wheels but?? Explain

3) Turbos, superchargers and natural aspirators. What is "supercharged" or "naturally aspirated" in this case? explain

Okay i think thats it for now.. haha.. thanks in advance

[fpv_gtho]

this is all from the mind of a 15 year old before you start to question my logic, but here goes:
1) torque? the simplest i can put it is the twisting force of an engine. the lower the revs and engine can produce it, the less the engine has to rev before it can be put under maximum stress. when you take off in a car, torque is what throwns you back in your seat
2)BHP? brake horsepower. im australian so im used to the metric system, so i cant tell you what they mean by BRAKE horsepower, but all i can tell you is its measured at the flywheel and im pretty sure its with the engine as it is in the car, so full exhaust, alternator, air con etc
3)turbos, superchargers, naturally aspirated? well in these cases, theyre different types of air induction into the engine, turbos and superchargers being forced induction. naturally aspirated requires the vacumm from the cylinders to draw in air, whereas turbos and superchargers use things similar to compressors, but alot smaller. turbo's are something that attaches to a cars exhaust system. theyre main components are 2 turbines, one of which is spun by the exhaust gases. the other turbine is connected by a shaft to the other one, and has the intake tract connected to it, and sucks in additional air which can make the engine use more fuel, producing more power. there are 2 main types of supercharging, so ill start with the one i know best:centrifugal supercharging. its basically like a turbo setup, but where theres a second turbine being driven by exhaust gases, the main turbine is on a direct drive from the crankshaft driving it, sucking in more air. the other types of supercharging are screw type supercharging and roots type supercharging. i cant really explain how these two work, so i wont bother

[megotmea7]

gtho your mostly right, i dont feel like typing alot right now just look in the "n00b questions" thread for a my explantaion of a turbo, and for most of your questions look at www.howstuffworks.com a good place to start if you know little about cars and their systems, now about your turbo describtion, its not made up of 2 turbines its made up of a compressor and a turbine, the compressor is present on both turbo's and superchargers and is what compresses the air for the combustin chamber, the turbine on the turbo powers the compesor as a belt/chain poweres the compressor on a supercharger, naturally asperated means the engine uses the vacuum create by the air entering the combustion chamber and uses no super/turbo or n2o to introduce "forced induction"

[pato]

the idea behind turbos and superchargers is to make more power and torque, instead of just the pressure of the atmosphere inside the cylinders they could have double that (measured in boost) obviously two atmospheres means more air and fuel in the cylinder which means more power which is good!

[megotmea7]

it is possible to get "boost" without a supercharger/turbo or anyother f/i device, if a cars engine has a well designed intake and manifold it is posible to get a VE(volumatric efficiency) of over 100%. a VE of 100% means inside the cylinder pessure is the same as outside the the car, if a car can get say 105% VE it is said to be creating naturaly asperated boost, most of the time a cars VE is under 90% usualy around 80% and its peak is almost always at peak torque on a turbo or shupercharged car its VE is almost always over 100% exept when your driving off boost

[NoOne]

After having owned cars with a supercharger ('94 Mustang with a vortec), a turbo ('85 Daytona & '89 Shelby Daytona) and several cars with nitrous set-ups.

My choice is the centrifugal supercharger as it is so smooth and linear in its power delivery with no lag, just makes your engine feel much bigger as if you had 25%+ more displacement.

Admittedly, I haven't had experience with twin turbos .... sequential or parallel, but I can't see it being as smooth as a supercharger for the fact that there is an engine speed where you will be in vacuum and not producing boost.

Everything should be blown !!!

[NoOne]

I should add that although I have never driven a car with a "screw" type supercharger, I think they are totally not practical for the street .... at least not in a daily driver situation, not due to the incredible boost available, but for the initial draw on the crankshaft as they are terribly inefficient when at low RPM .....then again the way cool "whining" noise could offset that.

[pato]

Originally posted by megotmea7
it is possible to get "boost" without a supercharger/turbo or anyother f/i device, if a cars engine has a well designed intake and manifold it is posible to get a VE(volumatric efficiency) of over 100%. a VE of 100% means inside the cylinder pessure is the same as outside the the car, if a car can get say 105% VE it is said to be creating naturaly asperated boost, most of the time a cars VE is under 90% usualy around 80% and its peak is almost always at peak torque on a turbo or shupercharged car its VE is almost always over 100% exept when your driving off boost

if u have a really big bonnet scoop feeding the intake it can have small amounts of boost but obviously only if ur driving fast enouhg in the first place to cram it in

[NoOne]

I think what you are talking about is a Ram-Air type scoop which have been around since at least the late '60's, but I don't think you'd actually get boost from it so much as get a colder charge of air - cold air from outside the engine bay compared to warm/hot air from inside the bay, just like a CAI setup

[Cappy]

Forced Induction 101:

Ram air - Cooler, denser air from outside the car enters through a scoop usually on the hood. At high speeds it is crammed in at slightly higher than atmospheric pressure. Can be used on NA or forced induction engines.

Naturally aspirated - Air rushes in vacuum of cylinder (pushed only by atmopheric pressure)

Supercharger - Air is crammed into the cylinder at higher than atmopheric pressure by a compressor (fan) or other type of pump. This pump is driven by a belt that is driven by the cranshaft. The extra power possible from increased air more than makes up for the increased work necessary to drive the pump.

Turbocharger - Air is crammed into the cylinder with a compressor. The compressor is driven by a turbine (windmill) that is driven by exhaust gasses. Turbochargers are more efficient than superchargers. However, if not enough exhaust pressure is produced, the turbine take a long time to speed up. As more power is created more exhaust gasses are created, causing a sudden viscious cycle of boost creep that must be controlled by a wastegate.

Wastegate - In turbocharged cars, an alternate path for exhaust gasses around the turbine. This controls boost levels.

Blow off valve - In supercharged and turbocharged cars, an alternate path for intake air when the throttle plate closes and the air being crammed up against it has nowhere to go. The air can be blown off outside of the car or further upstream in the intake tract for later use.

[Cappy]

Why Power is important:

Acceleration - How quickly speed can be changed. Engines obviously create forward acceleration, while brakes create rearward acceleration (deceleration).

Force - A push or pull on an object. Force is what causes acceleration. The goal of an engine is to provide much acceleration by providing as much force pushing the car forward as possible.

Torque - A sort of rotational (as opposed to linear) force. Since rotating wheels are used to provide acceleration, the goal of the engine is to provide forward force by providing as much torque spinning the wheels as possible.

Gears - Useful simple machines that can perform several fuctions. They can change linear into rotational motion and vice-versa. They can change the direction of rotational motion. Finally, they can increase the speed of rotation for a sacrafice in torque, or decrease the speed of rotation for more torque. The multiplication of torque achieved by reducing rotational speed is useful in cars.

Peak Torque - The maximum torque a given engine makes. This maximum occurs at a certain rotational speed (in revolutions per minute).

The function of the engine is to turn the chemical energy of fuel into mechanical energy (movement). At peak torque, the engine is operating at a rotational speed that allows it to intake a lot of air and burn a lot of fuel. At lower or higher rotational speeds, slightly less torque is made. However, at higher engine speeds torque multiplication is able to be taken advantage of to a greater degree.

Power - A measure of an engines ability to do work at a high rate. It is the multiplication of torque and rotational speed.

"Strong" engine rotates at one third the rpm as "Fast" engine, and "Strong" engine has three times the torque as "Fast" engine. If both engines are geared to provide the same rotational speed at the wheels, they will provide equal torque at the wheels. These two engines have equal power.

Peak Power - The engine speed at which the best combination of engine torque and rotational speed are created. It occurs at an engine speed above peak torque, where the increase in engine speed can no longer compete with the drop in torque.

Power is a useful way to compare the ability of engines to accelerate cars. It is easy to see that greater power means greater torque at the wheels. However, torque at the wheels also depends on the required speed at the wheels. If greater rotational speed is required at the wheels, less gear torque multiplication can be used and therefore less torque will be created at the wheels EVEN THOUGH THE ENGINE IS WORKING JUST AS HARD. This is why a car that can do a burnout in first gear at peak power can't spin the tires in top gear at peak power.

Besides the forward force of torque at the wheels, acceleration depends on mass. An 18-wheeler has more "stuff" to push than a motorcycle, and requires a greater push to accelerate at the same rate.

Formula for acceleration: Acceleration = Force / Mass
Formula using Force = Power / Wheelspeed: Acceleration = (Power / Wheelspeed) / Mass

Engine power can be measured in several ways. Manufacturers typically measure it at the flywheel in order to brag about higher numbers. However most dynamometers (instruments used to measure power) measure power at the wheels. This is more useful, but is hard to compare with flywheel power since it is slightly lower in the same car.

[megotmea7]

nice use of a search engine and the copy-paste function of your computer buddy too bad the questions hav already been covered and some of the info you posted wasnt entirely correct...

[Cappy]

LOL, no actually that was all from my head. I just organized it like that so it wouldn't be as intimidating. By the way, what is incorrect?

[Cappy]

Scavenging

When piston moves down during the intake stroke, atmospheric pressure pushes the air to fill the cylinder vacuum. By the time the cylinder is nearly full, the air has accumulated some speed. Even though the cylinder is full at atmopheric pressure, air may continue cramming into it because nothing is there to slow the air down. This requires the intake valve to remain open after the piston has reached the end of the intake stroke. Achieving greater than 100% volumetric efficiency by this method is called scavenging.

Note: Scavenging also depends on pressure waves, exhaust valve timing, intake charge velocity, etc. The above is a simplified explanation.

[-datsun 1600-]

Ok i know most stuff about cars but WHY DO YOU ENLARGE VALVE SIZE