Yeah I remember the HP per cubic inch debate before. No fair comparing the 100+ hp/ltr output from the smaller displacement engines. To make it fair I compared the output of a Lexus 4.0ltr v8 to a GM 5.7ltr LS1 v8 and the lexus made about 15 more hp per ltr than the LS1.

 

ok, torque is the only actual number. power is derived from torque, i.e. power =torque over time. the equation is
[torque(lb-ft) XRPM]/5250=hp
550 ft-lbs@3000 RPM/5250=314.3 hp@3000 rpms.
275 ft-lbs@6000 RPM/5250=314.3 hp@6000 rpms

you can see an import can make the same amount of power as a domestic provided it makes a decent amount of torque at higher rpm, versus the domestic not having to rev the **** out of it to make power. a flat torque curve is the most desirable. think about it, the first scenario allowed 550 lb-ft peak torque. supposing it drops off fairly slowly, and still makes 450 l-ft at 5000 Rpm.
450lb-ft@5000/5250=428.6 hp

a flat torque curve allows a higher measured power and a much broader powerband. displacement increase will not necessarily add more peak power, but it will increase torque over the band, allowing a much flatter torque curve and therefore adding more average power. peak power and torque is decieving, you only use that much power while youre at that rpm. what you want is a fairly uniform torqueband that is high. it will allow a higher measured power while simultaneously giving you a huge powerband, and reducing the engines neccessity to rev higher. it extends engine life, adds accelleration, and is more fun.

peak power is for bragging rights, average torque is for fun.
by the way, races are absolutely dependant on torque, theres no argument, it just is. where you make your torque, and how much, determines your hp. the horsepower versus torque argument is a ***** trait, the low rpm torque versus high rpm torque is the real debate.

hope you followed that. later, ssII

 

good move

you are right though


just want to quote one thing you said though
now this is all in an ideal world but...
I think of it as if I make 500 @2000 rpm and use a 2:1 gear ratio

that means I have 1000lbs/ft @ 2000
but a high rev motor can get away with more gear so if I make 400lbs/ft and use a 4:1 gear I get about 1600 lbs/ft

now again that is ideal world
´that doesn´t include drivetrain loss, friction, pumping losses and all that but I Think more torque up high helps out a lot

why else would F1, indy, nascar, top fuel and all those cars make SO much power up in the higher rpm range

I look at hp not as how fast you are but potential for speed.

think of an F1 car
900hp at about 17000rpms
if you do the math it is roughly about 200lbs/ft of torque but with the gearing they have b/c of there high revs allows them to use more gearing which can allow them to go faster



just my way of looking at things

 

Thanks guys, I finally SEE it! You know, you can hear things, and get a good idea of how they work, but when you can actually walk through the problem (thanks for the math examples too), it makes complete sense.

Basically, an engine with less torque (low end) has to rev higher to produce the same HP as an engine with more torque (low end). This would make the engine with less torque down low have a steeper torque/hp curve, right?

 

not always


my car has no low end whatso ever

but once you hit about 2500-3000 rpms the torque curve is VERY VERY FLAT


and you can´t always say torque is low end


torque can be high end or low end

just depends on where you place the majority of the torque

but yes if one motor has less torque then another but they both produced the same hp then the one with less torque has to rev higher to get the same hp rating


you can´t have hp without torque and the higher you move that torque in the rpm range the more hp you make

 

If torque can be high end or low end, then how do manufacturers decide where to put it? What parts of the engine (including displacement) relate to that?

Sorry if I'm sounding like an idiot, but its one of the things I've never had quite down pat.

Thanks again for the info!

 

i agree, and thats the point behind racings differences. do i want low end torque and power with lower gears or high end torque with higher gears. yes i agree about the f1 analysis, and its reaaly just forming the right package with the right parts. i would tend to believe that for the purpose of reliability i would rather have the lower rpm motor, given the lower frictional damage of 5000 rpm versus 16000. for all out drags, top fuelers run 10-12k rpm on 500 cid nitrometh aluminum blocks pushing 7k horse, so if thats what we use as control i would sooner choose that, particularly if it wasnt a reliability issue. in other words, the argument on the street is what do iwant? a low rpm monstrosity, or ahigh winding chainsaw on n20. and which is less likely to grenade itself. its all personal opinion. i was merely stating that someone who argues power versus torque usually doesn't know the principles behind what they are arguing and thus are not prepared to make a valid argument, i.e., i get a better launch with this triple decker wing on my civic dx, cuz racecars have 'em.

Afterburn-- the parts that determine a motor's torque band are as varied as automakers themselves, but really it comes down to cam, heads, intake setup, compression, rod-to-stroke ratio, and bore-to-stroke ratio.
cam- a high lift cam, or high duration, will have a hard time from idle to as high as 3k rpm, versus a mild cam or "rv" cam being more towards the bottom end of the rpm range. the cam is in essence what controls your rpm range. if you have everything else setup for high rpm but have a small cam, you'll never burn past 5k, andyoull probably make little torque and power. VTEC and others are ways of making the best of both worlds, offering a small cam until it engages at 4+k rpm and shifts the cam profiles to a higher lift, allowing a better torque curve, and thats how hondas have stumbled upon the dual personality of its motors. at idle, its smooth and provides a decent economy feel, but when it engages the motor becomes much more agressive and raucous, although 170-200 hp really is still nothing exciting.
Heads- large valve large port large combustion chamber heads simply move more air, and the more air you move the better youll do at higher rpm. think of it this way, say at 4000 rpm you need 20000 cubic feet of air to fill the cylinders every minute. at 8000 rpm youll need twice as much air to fill the same time, as your going to cycle through twice as many times in a minute. and, heads are one of the parts that will benefit any combo, at least the ports and valves. lets just say you want the smallest combustion chamber you can get away with while having the largest ports and valves possible. the larger your combustion chamber the lower your compression.
Intake setup- Again, moving air and in this case, air fuel mixture, is the key to higher rpm. more volume gets you higher rpm, more velocity gets you lower. big short runners will support a higher rpm versus skinny long runners. again, one of the parts that will benefit almost any package, which can be mismatched, but the results will be much less drastic than a mismatched cam.
compression- low compression just wont support high rpm torque, it doesnt work. as a general rule, each point of compression is worth about a 4 percent increase in power.
rod-stroke ratio- more rod less stroke, allows higher compression on a small stroke
bore-stroke ratio- if your displacement is more dependant on bore youll have an easier time pulling higher rpms without compromising much in the way of reliability. the longer the stroke, the more contact with the cylinder lining and the more friction, more heat, etc. bigger bores allow for displacement increase without the added friction. unfortunately, stroking a motor is easier, cheaper, and usually less work than siamese boring the cylinders, re-lining, etc. etc.

one more thing rex.... i think the reason nascar f1 etc rev so high is to make power out of a displacement cap, which with f1 has tended to be 3.5 liters, and 5.8 liters in nascar. nascar has displacement enough to pull low end torque, and the restrictor plate keeps them from making really high rpm torque like f1. f1 doesnt have the displacement to make low end torque, so they tech it up and pull 16-17k rpm. think of a nascar 5.8 withy all of f1's toys and no restrictor plate....2000 horse anyone?
i say higher rpm is better for racing, as its no secret that the higher rpm you buzz the more power youll make to a point, but reliability definately suffers.

 

Nice pic Da Vincci. As far as what is better, fwd vs rwd vs awd. Look at the applications. Fwd on family cars and econo-boxes, rwd on sports couples, awd on ralley cars. Drag cars used rwd btw.

 

excellent write up silver. I enjoyed it.

You're absolutely right, it all gets down to moving air (and fuel). The more mixture you have in the chamber for each stroke the more torque you'll make. So, large displacement motors always have more potential (assuming an indestructible block) than the same small displacement motor. Also, the more you can effectively use in the least amount of time the more potential you have (rpm). If you're still getting the same amount of air for each stroke at high rpm you will make more power than at low rpm.

Using a simplistic 1 cylinder engine as a model, I like to think of torque as the force the motor can exert in one power stroke and power as the cumulative of the force exerted in a given period of time.

If the engine were perfect at attaining the same air/fuel at any rpm, the engine would still have the same force per stroke, but it has a whole lot more strokes in the same amount of time.

This explains why, while in the same gear, a car running with 76.16 hp at 2000 rpm would accelerate a car exactly as hard as the same care with the same gear running at 304.64 hp at 8000 rpm. Can this be right? It is. Both cars are making 200 lb-ft of tq, and since the one at higher rpm isn't taking advantage of gearing it accelerates at the same rate. That said, the car at 8000 rpm is going 4 times the velocity of the first car. (air resistance and all other friction resisting the movement of teh car is assumed negligable for the purpose of understanding the point of the model).

Chris

 

Besides the physics lesson (sorry, I had that @ NJIT years ago0, the factors that impact top-end acceleration are simple:

Aerodynamics
Gearing (transmission and differential)
Power (curve and total TQ and HP)
Friction (things like tires, awd losses, suspension...)

Aerodynamics are a simple one - the slicker the car is, the higher top speed it can attain (theoretically)

Gearing (transmission) is a big one - if the gearspread in the top gears is too large, acceleration will be negatively affected

Gearing (rearend) determines the engine rpm at a certain speed

Friction is a factor simply because it robs power beyond aerodynamic drag. Things like tire drag become more prevalent at high speeds (that is why you pump ups the pressure at high speeds-not to mention possible overheating and failure). AWD doubles (if not more) the drivetrain friction, which is mostly linear, but can suck power out as well. Suspension is a tricky issue to explain, but in really fast cars (200+ mph) you don't want the alignment to be off so it scrubs off speed (or wears the tire edge out) - you want it to articulate freely without adding drag. You also don't want to align a car with positive downforce at rest - the alignment will be off at high speeds.

If you think about it, imports have no advantage then:

They might punch a smaller hole in the air, but the CD is typically higher due to physical limitations.

Power - there aren't too many 4 cylinder motors making 400hp, but the Z06 does (from the factory with a warranty)

Gearing - everyone is kinda stuck with the stock transmission ratios, but domestic cars are easy to change gears (not to mention availability)

Friction hurts everone just as much, although a Civic on 205 tires will have less tire drag than a Viper with 335 tires.

 

all i can say is wow

 

Thanks silver (and everyone else who has helped me out)!

I just feel I should mention one thing...they moved the F1 displacement cap to 3.0L in 2000, or 2001 I believe.

 

I don't wanna sound like a a$$hole but that has a double meaning. Sounds like your saying a Z06 is a 4-cylinder. Also sounds like and I know what your getting at...Is that their aren't too many cars you can buy out there from the show room floor with a little over 400hp.
Sorry just thought I'd bring that to attention because that kinda confused me. No biggie.

 

know which car has the lowest CD out there right now?


thought a lot of imports are fairly close to the .34 range
least the ones that are supposed to kinda fast

and I wish I could get more gears for my car

only options are 3.90,4.10, and 4.30

but the 4.1 is good for about 170-180mph or so

 

silverstreakII

wouldn´t you have more friction by boring out the cyl wall?

maybe less per area of ring due to less movement but now since you upped the area that is in contact that should up total friction right?


and nascar only runs rest plates at two races right?


I would type more but having a brain fart

 

while it is true that more surface area is contacted by boring, more friction is created by movement. try this--press two fingers into your palm. keep your palm flat. slide your fingertips quickly back and forth in short strokes. now do the same thing in long strokes at the same speed, but with one finger. which one gets hotter? which is harder to do. speed would be constant as it must cycle the piston up and down in the same amount of time per rpm. motion is what causes more friction, surface area plays a lesser part. now, more friction would make the motor work harder at higher rpm. another test? run your palm across a table a foot, quickly. now run a fingertip across a tabletop about two feet. try and cover the distance in the same time as it took to move your palm over a foot. your palm will get warm. your finger is gonna be shiny.

i honestly dont know how many races they use the plates at, but my analogy was more based on f1's tech advantage overcoming displacement. fi, turbo, dohc, versus nascars pushrod carbed motors.
Paul, not to dis you or anything, but the discussion was centered on poweband and that was the question regarding top end, not top speed. had that been the question you would be absolutely correct, but we were discussing what determined high rpm torque versus low rpm torque. just info. later

 

see your points just more or less being a smart a<x>ss saying that having more surface area will also create friction

but your right have what a whole .060 of a inch is not going to do as much as making a 4in diam piston move another .25 and inch

and at the speeds they are moving at..... well boy howdy will that suck

also don't think F1 use turbo's not sure though
think indy does or cart
I can't remember just know I want to drive F1



still does anybody know what car right now has the lowest CD

 

youre right, .06 vs. .25 is a big difference. but suppose you destroked a 350 to a 327, then siamese bored the cylinders to accommodate a 4.25inch bore. a 366 that'll rev like nobodys business, provided the rest of the motor could support it, a 10k rpm short block reliably, or at least more reliable than a 7000 rpm 383, with essentially square bore geometry. 4.03 inch bore, 3.875 inch stroke.
366= 4.25 inch bore and 3.25 inch stroke. add 12:1 compression and shake vigorously. some huge port heads, super stiff springs and a high lift cam, high rise manifold and a 750 cfm carb, and youre probably close to 500 lb-ft at 7000, which comes out to 666 horse, aka the evil mouse. and im not sure which is turbo, but the one that is is faster. anyway, just sayin that the friction coefficient will determine your rev limit due to heat and thermal breakdown, hence the reason for the term redline. the highest point your motor is rated to operate. not to say it wont rev higher, but youre takin a chance. ps, rotary's are friggin cool

and im not sure what the slipperiest car is out there, but its probably not anything with downforce. no adjustable wings a la porsche or lambo, low and sleek. probably something like a buick. remember chevy's old corsica ad? more aerodynamic than an f1 racecar.... trouble is those wings make a whole hell of a lot of drag. at speed they put down like 1.6 g's of downforce. you can drive them upside down. hell yeah. might actually be a bentley sedan. probably somethin no one would expect, even a vette coupe has a really low one, like .24 i think. the hatch, front clip, and super abrupt tail really make it slip. but im not sure what the lowest actually is.
oh and a lot of places can make a custom gearset, check out reider racing, they might be able to help you, but im not sure. probably pay more, but a rotary can spin for days so itd definately be worthwhile. or you could just get a 9 inch in there with a set of 5.11's =)

 

think the vette is high 20 range

around .28-30 maybe


the lowest one I know of is the honda insight

.24

and frontal area.... first off you have to find the car

that thing is so damn small

 

i remember something from a couple of years ago i saw an ad for gm's ev1, said it was the lowest ever, but i dont recall the actual number.

 

Exactly why I'm moving up to the v8, LOL. (Still pondering if it's gonna be another 3rd gen camaro or 3rd gen 5.0 stang)

what in the ****ing hell are you mother ****ing thinking? you can't seriously ****ing be thinking of buying a mother ****ing mustang peice of ****. who the **** really ****in wants a mother ****in rustang? and a five slow at that. and of all mother ****ing places, in a mother ****ing CHEVROLET sanctuary, a sanctum of CAMARO owners. Go **** yourself you ****ing ****er of ****s. take your **** *** mustang fantasy and blow it out your mother ****ing *** *** damnit. I don't wanna ****ing see that ****. BRAND LOYALTY MOTHER ****ER.

 

um dude you need some serious help and if you want to swear then f<x>ucking swear ok. but don't go here bashing on the mustang owners or the ones who want to buy a mustang. they can be fast cars just as fast as whatever you want to own and going about here trying to pull something like that is going to either get you banned or your are going to **** off just about EVERYONE here buy saying that


so calm down ok.... not saying you need to like mustangs but don't go about bashing ppl like that just b/c they want one

 

I'm still trying to understand what he was trying to say from that blabber