WHAT THE #$%$%^ IS HORSEPOWER ANYWAY??

[grumpyvette]

first thing to keep in mind is that theres no such "thing" as horsepower, horsepower is a TERM USED TO EXPRESS a mathmatical formula for the RATE, at which rotational TORQUE can be applied ......... the formula for hp is (tq x rpm/5252=hp example
450 ft lbs of torque at 3000rpm=257hp
450 ft lbs of torque at 6000rpm=514hp
because the torque at the higher rpm useing gearing can be applied faster
here read this

keep in mind a great deal of performance is related to the HORSEPOWER TOO WEIGHT RATIO, it takes a great deal more hp to move a heavy car than a lighter weight one to similar speeds, removing weight is just as effective as adding hp toward increasing performance, naturally the amount necesary varies with the application but on the average street car removing 20-25 lbs will do just as much or more as adding 1 hp

READ THESE CAREFULLY

http://en.wikipedia.org/wiki/Horsepower

http://www.69mustang.com/hp_torque.htm

http://craig.backfire.ca/pages/autos/horsepower

http://www.wallaceracing.com/et-hp-mph.php

http://craig.backfire.ca/pages/autos/co ... wer-curves

http://www.datsuns.com/Tech/torquehp.htm

http://www.ubermensch.org/Cars/Technical/hp-tq/

http://vette.ohioracing.com/hp.html

http://www.howstuffworks.com/horsepower.htm

where most guys go wrong is in not correctly matching the cars stall speed and gearing to the cars tq curve, if you mod the engine for increased high rpm performance but fail to also match the stall speed and gearing to that higher rpm tq curve much of the potential improvement is wasted.
example

in the close to stock engine above, the engine should be geared to stay in the 3500rpm-5000rpm range for max acceleration (lower in the rpm range if mileage is a big factor)

in the moded engine above the rpm range moved to 4000rpm-6500rpm requireing differant rear gears and slightly higher stall speeds to gain max acceleration in the same car,
you should readily see that a trans that shifts at 5000rpm will work in the first example but would waste most of the power curve in the second example,where shifting at 6500rpm under full power acelleration would make more sence.
a 3.08 rear gear and 700r4 trans matches the first example well but it would take a swap to a 3.73-4.11 gear to allow the engine in the second example to keep its most effective power band matching that second power curve well.
ok basics
horsepower (in our context)is a term used to describe the RATE at which rotational torque can be applied, as force from the engine to the drive train

viewtopic.php?f=50&t=558

http://www.epi-eng.com/piston_engine_te ... ciency.htm

http://tunertools.com/articles/volumetr ... ciency.asp

http://www.ztechz.net/id2.html

http://www.auto-ware.com/combust_bytes/eng_sci.htm



as the RPMS increase the amount of TIME AVAILABLE PER INTAKE STROKE DECREASES, up to some point, thats determined by the ports,runners and cam lift and the engines displacement,as the rpms increase the number of power strokes per second increase and power goes up,but at some point the time necessary to fully fill the cylinders starts to limit the flow into the cylinders and the volumetric efficiency falls off in relation to the rpm increase, this decrease in the amount of fuel air mix burning per power stroke tends to lower the torque produced PER POWER STROKE, but as the rpms increase its a trade off , of more power strokes, but less effective ones, so the power tends to increase for a bit higher in the rpm range than the torque peak, (WHICH TENDS TO FOLLOW THE VOLUMETRIC EFFIENCY CURVE VERY CLOSELY)



links youll need to figure out correct rear gear ratios

http://www.geocities.com/z_design_studi ... zx_tt.html


http://www.miata.net/garage/tirecalc.html

http://www.wallaceracing.com/reargear.htm

http://users.erols.com/srweiss/calcmph.htm

http://users.erols.com/srweiss/calcrpm.htm

http://users.erols.com/srweiss/calcrgr.htm

http://www.prestage.com/Car+Math/Ge...io/default.aspx

http://www.geocities.com/z28esser/speed.html

http://server3003.freeyellow.com/gparts/speedo.htm

http://www.pontiacracing.net/trannyratios.htm

http://www.tciauto.com/tech_info/gear_ratios.htm

 

[grumpyvette]

http://www.geocities.com/z_design_studio/transmission_300zx_tt.html

this calculator is very handy, just remember to keep the engine in its ideal power band, you want to spend as much time as you can in any gear in the area centered between the torque and hp peaks, naturally youll need to rpm the engine above and below the peaks at times but try to concentrate the engines power band rpms with the sellected trans and rear gear choices
it makes no sence to build an engine that potentially produces 500 hp at 6700rpm, if your rear gear and trans keep the engine in the 2500rpm-5000rpm band most of the time or if your auto trans shifts at 5500rpm.
I constantly tell people that its critical that the MATCHED components be used in a combo to maximize the results.
adding 3.73:1 rear gears and a 3000rpm stall converter to a combo like a decent 383-427 sbc with a cam and heads designed to effectively run up into the 6500rpm band makes a HUGE differance.
one of the more comon mistakes is adding a killer cam and decent heads to a stock or nearly stock low compression engine combo with a restrictive exhaust and then when it runs like crap they blame the cam, not understanding that the cam will do exactly what its designed to do only with the correctly matched components.
yet almost everyone that actually follows that advice is amazed at the results, quotes like (WOW,ITS LIKE A NEW CAR) are comon!