HP & Torque Seem Wrong

[two40]

I'm a bit curious about some figures and was hoping you guys can shed some light on them. It just seems wrong to me when I apply the formulas found here http://forums.hybridz.org/showthread.php?t=75985

 

Fresh chev making around 490hp on an engine dyno and on average 450 torque. The torque peeks at 480. What is going on? Is something holding the hp back?

[grumpyvette]

this is an old post with some insight,and the links have good info

 

we have all heard it, " you need massive low rpm tq" "you need a screaming high rpm hp peak" well heres some info,

More in-depth description:

http://www.revsearch.com/dynamometer/torque_vs_horsepower.html

http://vettenet.org/torquehp.html

http://auto.howstuffworks.com/horsepower4.htm

http://homepage.mac.com/dgiessel/engine/hpvstq.html

 

first thing to keep in mind is that theres no such "thing" as horsepower,...... horsepower is a mathmatical term to express the results of the formula explaining the RATE at which TORQUE (rational force ) can be applied increasing the torque at a given RPM or increasing the RPMS with a given torque increases THE RATE(HORSEPOWER AVAILABLE TO DO WORK)GEARING ALLOWS YOU TO APPLIE THAT FORCE at a given force level but not at a RATE APPLICATION LEVEL that exceeds the engines peak power.

put a differant way, if we ignore drive line friction loss,if an engine puts out 400 ft lbs at 6000rpm (400 x 6000/5252equals (457 hp)we can gear it to apply 1600 ft lbs at the wheels by running the gearing at 4:1 but that also cuts the application rate by 4:1 so the HP applied stays constant at the 1500rpm at the rear wheels 1600 x 1500/5252 equals (457 hp)

 

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 is available at that higher RPM RATE and at the higher rpm useing gearing the rotational force the engine supplied can be applied faster or slower to the rear tires

 

here read these ALL CAREFULLY

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

 

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

 

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

 

http://auto.howstuffworks.com/engine1.htm

 

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

 

http://auto.howstuffworks.com/question622.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.

 

links youll need to figure out correct rear gear ratios

 

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

[two40]

Looks like I have a bit of reading to do. Thanks