How Much More HP Before You Can Actually Feel It?

With all the talk of adding a few HP here and there for low bux, I'm curious if you can actually FEEL a 10 HP increase? Or does it take more like 50 HP to notice the difference? The old rule of thumb in the computer world is that you need a 50% increase in computing power to really feel the difference. Any input?

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-Richard
'84 Carrera Cabriolet
'74 911 Widebody 3.6 Project

I doubt you could feel it. A 10 hp gain at high rpm might only shave (depending on total HP % change) a 10th of a second off your 0-60 times. You think you can detect 1/10th a second change? I doubt it. I don't think we can tell for 1/2 a second change really or more. So probably need 25 HP (again depending on how much % that 25 is, I'm assuming carrera type numbers, and it's an 1/8 or so change).
I could feel my weltmesiter chip, but it boasted around 20hp change for my year...


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Kurt B
'84 Carrera Cab.
carrera_cabriolet@yahoo.com

Horsepower is difficult to judge, TORQUE is what you can feel. Leave the engine alone and lower the tranny gears - you feel it even though no ponies were added.
SO - if you add something that enhances the torque ouput of your engine you are more likely to actually feel the difference. How many ft/lb? I don't know. In a small light car like a 911 you might be able to distinguish as little as a 15 ft/lb difference.

Food for thought-A/C compressors don't take lots of horsepower (5, maybe 10 on a really inefficient one) to turn, but we all notice when they cycle on and off when driving..(well, in most cars, anyway-it was really hard to tell in my 5.0 Mustang, and I drove that car for 11 years.)

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Clay McGuill '66 912, '97 Jeep Cherokee www.geocities.com/the912guy

I can tell you that I installed a K&N air filter and could definitely feel the difference (this was not on my 911, but on a daily driver Jeep Grand Cherokee V8). I doubt it was much more than 10 HP, but noticeable.

Originally posted by cegerer:
I can tell you that I installed a K&N air filter and could definitely feel the difference (this was not on my 911, but on a daily driver Jeep Grand Cherokee V8). I doubt it was much more than 10 HP, but noticeable.

Come on. The only thing you felt was money flying out of your wallet, another victim of the K&N marketing team.

K&N - Kooks and Nuts




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1988 black on black Coupe
www.cheaterswayside.com/911/gallery.asp?sort=0&userid=339

Originally posted by MarkY:
Come on. The only thing you felt was money flying out of your wallet, another victim of the K&N marketing team.

K&N - Kooks and Nuts

Not every car manufacture uses as high quality air filters as Porsche. On a Jeep it would make a noticable difference, on a Porsche no.



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Joshua Harrison
1968 912 Coupe

I don't know about you guys, but I can most definately feel the differance between 1/4th a tank, and a full tank of gas. Or having all 4 seats in the car, or only drivers seat.
Ahmet

Generally anything less than a 5% change in power output will not be felt by the driver.

Drivers tend to be able to pick up small handling differences quite easily though.
Which I think is the dominant effect felt by Ahmet, it's not the increase in power to weight that's being noticed with <1/4 tank, it's the improved handling.

Handling improvements will show straight away in your lap times, 5% power increase may or may not depending on the circuit.

Regards, Jon

'76 2.7S targa

My best 0-60 run was 5.35 seconds with a 170 lb. passenger in the car. My best solo run was 5.05 seconds. The lesson? Lose weight! It's cheaper than gaining horsepower.

Mike 94 C2 cab

Following this thread, and being engineering ignorant, I must ask: Can someone define both horsepower and torque for me? I know what horsepower represents and know how torque feels, but, what is the actual definition of each?



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Mark Howard
'88 Carrera
'62 356/B
'75 914 1.8 resto

1 horsepower is 550 ft lbs per second. Which really means, it's the energy equivalent of moving 1 lb mass 550 ft in 1 second.

Torque is RXF. It's the force applied at the end of a moment arm of length R.
So if you're putting out 192 lb ft of torque, that's equivalent to applying 192 lb force (note difference between lb mass and lb force!) at the end of a 1 ft arm lever.

A rice burner turning at 9000 rpms puts out a lot of energy per second, however, the force at the end of the lever arm is much less than a 911 engine because the 911 engine has much greater torque, or applies more force toward turning the wheels than does the 4 banger.
Which is why HP alone can be very misleading, and has little to do with launching your car from a dead stop.



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Kurt B
'84 Carrera Cab.
carrera_cabriolet@yahoo.com

Thanks Kurt. I understand better now.

Horsepower is calculated using the amount of torque at a given RPM.

HP = Torque(@RPM) X RPM/5252

That is why HP and Torque curves always cross at 5252 RPM. In my opinion, for street driving, the HP is a useless number. A torque curve is a better indication of how a car will perform over a range of RPM's.

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Bill Krause
'79 911SC Euro

Mike is right-on with his comment about weight loss as the cheapest route to gain speed. Like Ahmet, I can surely feel the difference carrying less fuel, and driving solo.

There is an SC in my club whose owner has stripped out *everything* you can imagine...carpets, undercoat, rear seats, radio, fans, electric windows, a/c, bratwurst muffler, cat, etc, etc. I feel sorry for this "shell" of a car, but it goes like blazes!

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Doug
'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
members.home.net/zielke/911SC.htm

Peak HP and peak torque numbers are simply general indicators of an engine's power characteristics. An engine that develops lots of hp but not so much torque can be quite formidable if the *gearing* is set up right. Also it is important to realize that in performance driving, the area under the power curve that is most often swept by the tach is what matters most. A Honda S2000 will have a weak launch in 1st, wind it out and the rest of the gears will stay in its power band and the thing will MOVE because it is operating between the rpms of say 6000-9000 rpm (i.e. bottom end doesn't matter). Also 1st gear in these types of cars are typically very steep to get the car moving in its powerband quickly. Keep in mind for impromptu-testosterone-driven-street-racing you'd have to really be aware in that car and be in the right gear, a car with a big fat low torque curve is *already* in its power band when they're just cruising along and they have an advantage in a suprise attack

Brad

p.s. - also keep in mind that most 911s (except turbos) produce much more HP relative to their torque numbers (especially the early cars) so our babies are definitely more HP cars than torque cars IMHO.

To put them in terms easier to understand..(When talking about engines)

Torque is the AMOUNT of work an engine can do.

Horsepower is a calculated MEASUREMENT of how quickly it can perform that work.

Model airplane engines (and Honda motors) can produce impressive horsepower numbers (at high RPM) for their size...but they don't make much torque.
Diesels make tons of torque (at a low RPM), but are hardly ever spun fast enough to generate huge horsepower numbers-they don't need to (and probably wouldn't stay together very long).


My 5.0 Mustang only made 225 HP-not bad, but it was the 300+ ft-lbs of torque that shoved my ass back in the seat when I opened the throttle. Damn, I miss that car...

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Clay McGuill '66 912, '97 Jeep Cherokee www.geocities.com/the912guy

for what it's worth:

i tweaked a few things in my 924 engine to extract a horsepower here and there. the way i could tell if anything made a difference is by driving up a certain hill in 4th gear. if i made a positive difference, the car would not bog down from 3000rpm in 4th gear. if something i did made a difference, then the car would stay at RPM or gain speed going up this long, big hill.

the same rules will apply to your 911, or to any car for small changes. you may not "FEEL" it instantly, but if you made a difference your car will be able to climb certain hills faster.

obin

Think of doing some dumbell arm curls.

Torque = How much (say 20lbs) you can lift.

HP = HOW FAST you can lift that same 20lbs.

Those TNN shows are good for something.

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Nick Hromyak
'85 Carrera 7 & 9 Fuchs
Havin' Fun in Sacramento

Excellent discussion of HP and Torque. Restating what the others have said, Acceleration is a funciton of Torque and Weight. Improving either improves acceleration (0-60 times). Since Torque is a rotational force, you can change it by changing the gearing, although the top end speed will suffer. Always a tradeoff.

Top end speed is a function of HP and Drag Coefficient (Cd). That is why a big Mercedes with lots of HP will eventually reach the same top-end speed as a lighter Porsche, although the Mercedes usually gets killed from a standing start (assuming similar Cd)

One other little thing to check that I found on my car. Lift your car and make sure your brake calipers are fully retracting. Other than a slight vibration, you would never know unless you checked and this was having an effect on my acceleration.