How much horsepower when you can feel a difference?

[RyRy210]

There has been talk with my friend about what amount of horsepower can actually be felt from the driver's seat. I know sometimes its just pure speculation, but I would imagine an increase of just 1-5 won't be noticeable at all. My friend pretty much feels that unless its at least a 20hp increase, u won't be able to tell. Any comments? Opinions?

Ryan

 

[cojones]

depends on how you define "feel"

Do you feel a noticeable difference with:
- full tank versus empty
- full trunk versus empty
- passenger vs no-passenger
I think I FEEL a noticeble difference with empty trunk, fuel tank and pass seat -- thats about the equivalent of 15-20 hp, no ?

 

[TigerNSX]

I thought that the actual feel of being "fast" or "accelerating" comes from torque, not horse power. So having 5-10hp increase will not make you feel as if your car has become faster. I don't know exactly how this works, but I remember this physicist talking about the difference between hp and torque..

 

[MYNSX]

I would think(although your comparing the apple to the orange)take out the passenger/ empty the tank /and empty the trunk would "feel" like 20-30 hp difference .,although that is extremely subjective.....
PS... I have a 420 friend who has been a passenger and it "feels" like a hundred HP increase when I drop him off at home.He barely fits in the passenger seat.

------------------

 

[nsxtasy]

Adding and removing ballast is a good approximation of the effect of adding hp, and it's an easy test to see what you can feel.

On the NSX, adding 20 hp will improve acceleration slightly more than removing 200 pounds (as noted in the "Gears" section of the FAQ). So I would approximate that the effect of adding one hp would be roughly the same as removing 11 pounds (which just happens to be the same as the power-to-weight ratio of the '91).

The gas tank holds 18.5 gallons, and each gallon weighs about 6 pounds. Of course, even if you have it close to empty, you still have some gas left.

 

[nsx4fun]

The difference between horsepower and torque is an equation. Given one curve, you can calculate the other, so in effect they are the same thing, they just report it differently. Horsepower = torque * RPM * some constant I don't have on the top of my head. The real curves that will tell you the whole story are torque vs speed with a line for each gear of the car. This will tell you exactly what RPM to shift at for each gear change. Basically when the torque at the wheel drops below the next gears curve, you need to shift.

Fritz

 

[MAJOR STONER]

I like the way my car drives after I fill up the tank, but I can't understand those guys that say they can feel a one psi change in tire pressure. I don't know if the same rule applies to cars, but in motorcycle circles, every eight pounds in weight loss equals the performance gain of one horsepower.

 

[sjs]

Originally posted by MAJOR STONER:
... I don't know if the same rule applies to cars, but in motorcycle circles, every eight pounds in weight loss equals the performance gain of one horsepower.

That's because a quick bike weighs about 8 pounds for each HP w/driver. A stock NSX is about 12 lb/hp with driver, give or take, so shedding 12 pounds is like adding one HP in terms of off the line acceleration. That becomes less true the faster you go because the effect of weight is quickly overshadowed by drag. Of course, the more you shed the more each pound is worth because it then represents a larger percent of the remaining mass.

 

[Lud]

I believe some eggheads have determined that the least noticeable difference for most things like this (weight, light, movement, time, etc.) is 2% under optimal conditions with quick A/B comparisons. Below that people just do not perceive the difference.

An NSX which increased in peak power 2% over 270 HP would be 275 HP. And remember that is a PEAK increase; the increase in the rest of the RPM band will be lower.

But since a car is not an optimal lab environment with instant A/B comparisons - the car comparisons necessarily have some elapsed time between them - the least noticeable difference is certainly a little higher.

 

[nsxtasy]

Originally posted by Lud:
An NSX which increased in peak power 2% over 270 HP would be 275 HP. And remember that is a PEAK increase; the increase in the rest of the RPM band will be lower.

Not necessarily. The peak of the before-change curve is at 270 hp, at some RPM. The peak of the after-change curve is at 275 hp, which may be at the same RPM or a different RPM. The increase at any specific part of the revband (other than the point(s) where those peaks occur) may be more than, or less than, 5 hp. (It could even decrease at some RPM points.)

 

[sjs]

But since the idea is a 2% change and 5hp was just the result of applying that factor to the simplest benchmark, the actual amount that might be discernable parallels the power curve.

 

[nsxtasy]

Right - IF the 2 percent increase applies uniformly throughout the revband. It rarely does.

 

[skim83]

Who cares about all this technical 2% babble; this is America folks where the award goes to the man with the most ponies

 

[nsxtasy]

No,

this is America folks where the award goes to the man with the most

...money.

 

[sjs]

Originally posted by nsxtasy:
Right - IF the 2 percent increase applies uniformly throughout the revband. It rarely does.

Never suggested it was. On the contrary, I was just picking nits by suggesting that if 2% were the threshold, then the numeric value that could be detected depends on the RPM and “parallels the power curve” (2%above it, whatever the shape).

I'm not sure we can pick this nit much smaller, but feel free to try. Everyone else has already left or fallen asleep.

[This message has been edited by sjs (edited 30 March 2002).]

 

[wildbill846]

The how much do you need in order to "feel" it depends on many factors including where you put it and the manner of the power added. For instance adding more low and mid range torque is probably easier to feel than high end power. That's what gives the off the line pull. Of course, increased torque is best come by with increased displacement, although I know small displacement motorcycles often have the timing advanced to boost the mid-range. I also have a little theory that a very peaky torque curve "feels" faster than a broad, flat torque curve. Remember, velocity is the rate of change in location, acceleration is the rate of change in velocity, and "jerk" is the rate of change in acceleration. The NSX with the long broad torque band gives a relatively constant acceleration throughout the RPM range and that's why it often feels slower than many other cars despite producing the same numbers for the quartermile, for instance. Those other cars have a high rate of change in acceleration as they approach peak power. While it feels faster, it doesn't necessarily mean better performance. In fact, it can have a adverse effect on handling.

 

[nsx1164]

Originally posted by wildbill846:
The how much do you need in order to "feel" it depends on many factors including where you put it and the manner of the power added.

Well said... the only way to achieve a full "curve shift" is IMO to increase displacement (at the expense of weight and possibly complexity). Other means tend to compromise, and this isn't necessarily a bad thing

- superchargers tend to favor certain "sweet spots" throughout the powerband where they add more value, less in others (BBSC more top-end, CTSC more bottom-to-mid)
- how its applied -- a more gradual effect with superchargers, versus the sometimes-more-abrupt boost that follows lag/spool-time associated with most earlier (and single) turbo setups, or the extreme upper-end pop with NOS

Beyond a certain bump level you have to watch out for requisite driveline, transmission, suspension and tires (lets not forget braking) to make sure all that increase is converted to forward acceleration.