How do you find horsepower in car?

Answer 1

First thing is an engine doesn't make HP, it makes torque. Horsepower is only a calculation of torque over time - (TQ xrpm)/5250. Torque is what gives you that push into the seat on acceleration, that "jump" when you tap the throttle. Torque is all about cylinder pressure and displacement. This is why larger engines and forced induction engines make the most torque.

To increase horsepower, you need to increase one of three things: CYLINDER PRESSURE, RPMS or DISPLACEMENT. There are different ways to increase the horsepower of an engine. You can do one or more of the following, depending on where in the rpm range you want the extra power and the amount of money you want to spend.

Stroker kits- are the only way to increase displacement, boring the cylinders only adds a few cubic inches and the other option is swapping to an engine with more cylinders. Stroker kits will add the most low-end power of any mod, save forced induction. It can be expensive in parts and labor especially if you also want to increase the rpm range of the engine. The length of the stroke has a direct bearing on the maximum safe engine speed, mainly due to piston speed and connecting rod/rod bolt strength. Rpms-If you are able to increase and/or maintain the torque curve to higher rpms the Horsepower will always increase as the revs climb. Without increasing displacement or boost, it is the only way to gain a significant amount of horsepower. There is a limit though, because the stress on the engine's internals increases 4x when the rpm doubles. An example: raising the redline on a v8 from say 5000rpms to 7500rpm, doubles the stress on the engine. Stronger /lighter / more expensive materials are need to deal with the tension loads on the connecting rods/pistons/rod bolts and stresses on the valvetrain. Pushrod engines are "generally" limited <6000-7000rpms and OHC 7000-9000rpms. Increasing the powerband range usually reduces low-end power. The exception is an engine with variable timing. On an engine without VVT, you compromise low-end power to gain top-end, it is like a see-saw when choosing intake manifolds, camshafts etc they usually favor a side. Durability and emissions are also compromised when increasing the power-band. Last modification is cylinder pressure, It can be increased with supercharger/ turbos / NOS or by increasing an engine VE (volumetric efficiency), how well an engine breathes. Turbos/superchargers/NOS all increase power by forcing more air into the engine, thereby increasing cylinder pressure.

The screw/roots supercharger is mechanically driven and always forces the same amount of air/fuel into engine, at a given rpm. This can be a good thing if you want low rpm power due to the "instant" boost of a screw type or positive displacement blowers, plus it is easier to tune. It's the closest thing to dropping in a bigger engine. With say 8psi any engine will produce 50% more power or act like an engine 50% bigger than stock. The downside is they are bulky/expensive/ less efficient at higher rpms than centrifugal superchargers and turbos.

Centrifugal superchargers have the efficiency off a turbo, but belt driven so it can make big top-end power. The down side is they give little or no increase to low-end power, the belts "will" slip/need servicing. An upside is the power is predictable and the units are smaller easier to fit than screw superchargers/blowers.

Turbochargers provide boost only when it is needed and the engine can operate like a N/A (normally aspirated) engine when cruising around. Turbochargers will also give better fuel economy than superchargers on cars due to the fact that turbochargers are driven off the exhaust (don't use as much HP to be driven like a supercharger). They are not free, as many believe because they do cause a restriction/pumping loss, still 25hp is less than the 50-100 for a supercharger. With turbochargers available in different sizes the horsepower level available is only limited by where you want the power and how much you want to spend. They can be side for low end power, but more than often only give additional power above 3000rpms. The downsides to turbocharging are that there is turbo lag. Lag is a delay between when you floor it and when the turbos start to make boost. It can be small if the turbos are small or if you are at a higher rpm but there will always be some. Turbos are more complex/difficult to tune and usually more expensive than superchargers. Turbocharging like camshafts are selected by where and how much power you want for a given engine. An example: A factory turbo car, will have small turbos to reduce lag and improve lowend torque, but will be limited on the possible top-end power. Standard turbos require selecting a size that will flow enough air for a given engine at a given rpm. If big HP #s are wanted, the turbos will be laggier, produce less low-end power. Some vehicle have variable turbos that offer quick response and high HP with low backpressure, but are complex and are not used in aftermarket kits. NOS adds additional air into the engine through a chemical reaction. It is really only a viable option at the drag strip as a tank only last a few runs depending on the shot size. A typical 100hp "shot" will use up a 10lb tank in 9-10 runs. It isn't street legal in any state I know of and is only used at wide open throttle above a set rpm to prevent engine damage. It is also damaging to the engine/pistons when it doesn't operate correctly, sooner or later it always backfires.

All bolt ons/modifications are done to increase the engine's efficiency (get more air in and out per revolution). Most people start with bolt ons as they are the cheapest modifications, but in general, the more pricey the mod the more you get.

1.cold air intakes- with a larger/low restriction filters is the Best bang for the buck(most gain per dollar). It should be the first modification one does. Only buy a kit that has the filter sealed off from under hood heat, not just a tube with a filter located near the radiator. A ram air setup or cowl induction/hood scoop that takes air from outside the engine bay are the best. The colder the air the entering the engine the more power you'll get. A general rule is, for every 10 degrees you lower the intake air temperature you gain 1% in horsepower. On a stock v8 you can see up to 10-20hp from one of these 5-7% increase.

2. Under drive pullies free up alot of hp and is probably the second "best bang for the buck" mods. You just need to make sure you don't get ones that under-drive the alternator if you daily drive it as it can cause charging issues.

3.For new cars, a programmer would be a good next step, if you tune it to run on premium fuel(91+) you can get a 5-7% increase in power. It can also adjust for different tire sizes, remove speed limiter, adjust rev limiters and in some cases increase fuel economy. 4.Cat-back exhausts are usually changed early by most people, but on a newer car it doesn't show much if any gains on a near stock engine. They usually only provide a different sound for the customer. The money would be better spent else where and a header and other parts should be installed before the cat-back setup. On a stock engine made after 2000 or so, a cat-back "generally" is worth 0-5hp while a header would be worth 5-10hp increase. On older cars the gains would be more significant and would be worthwhile earlier in the modification steps. Older systems are small by todays standards and almost always compression bent restricting air flow and a change will show more of a gain vs. stock than on newer cars. 5. Modern cars have good cylinder heads, so changing them isn't worth the cost until you are near 30% over stock hp. Higher flowing heads will 99% of the time reduce low end power and should only be done after/with camshafts, intakes and other mods. 6. hi-performance camshafts offer more, lift = more power throughout the powerband duration= can be shortened for more towing/ lowend power and economy or increased to move the powerband higher in the rpm range. Higher compression piston/with great valve clearance will be need on big camshafts. High compression pistons restore cranking pressure with larger camshafts but will require running high octane fuels.

Lobe seperation angles= tigher angles (106-110)- can give that rumpety rump idle, old muscle cars had. It gives higher peak HP/TQ#s while building power quicker in a narrower powerband. A Narrower angle's downside is poorer idle quality and fuel economy. Wider lobe angles (114-116) allow for smoother idling and wider powerbands at the expense of slightly lower peak HP/TQ #s. Wider angles are need for fuel injected equipped cars than ones with a carburetor. Wider angles are also needed when running turbochargers as they prevent exhaust gas contaminating the intake charge.

7. (On pushrod engines) A cheaper alternative/addition to, a camshaft is to install higher lift Roller rocker. If the valvetrain has the proper springs and clearance, they offer additional lift(horsepower) and reduced friction. On a V8 they can add 10-20 more horsepower over a stock ratio on a stock camshaft equipped engine.

8. Aftermarket intakes are usually seperated in two categories:

Single plane/short runner manifolds- allow more topend HP will a drop in lowend torque, usually more for racing and high rpm engines.

Dual plane manifolds- like edelbrock rpm allow an increase in a more street oriented rpm range upto 6000- 6500rpm range. They "usually" only give up 10hp at the topend vs. a single but give you 20 lb/ft over the single in the lowend.

9. Larger throttle bodies will allow more air into the engine and give a HP increase but "usually" only after intake manifold and/or camshafts have already been installed.

10. Ingition sysems on newer cars don't usually need modification until the rpm is raise with camshafts,etc. or if the engine is boosted with a supercharger/turbo. Older vehicles <2000 can see idle/ hp/ fuel economy and emission improvements with the installation of aftermarket ignition systems.

Depending of they vehicle you are working on some parts maybe plentiful and others will not but you need to be realistic in what you want/can expect. You also will need to keep in mind that transmissions, gears and fuel systems will also need to be modified if HP levels exceed what the stock equipment is rated for. Tires are also speed rated for saftey and should be changed accordingly.