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fedorfan
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Ive got a question, which is more powerful and better to have in auto racing, torque or horsepower? I've gotten mixed answers and wanted to ask some people who know their stuff.
No, the engine that is able to to deliver more torque will be able to kick your butt to the finish line faster.cesiumfrog said:Sure, but in the ideal world (where no energy is lost in the gearbox), if two engines (with different torque) output equal horsepower, than both should accelerate at the exact same rate (even if one does have to shift gears at 2kph) and reach the same top speed (if both cars have the same aerodynamics). Right?
No. Every time you shift gears the torque delivered to the wheels drops, so the acceleration drops. Those two cars will only have the same acceleration for about a tenth of a second.cesiumfrog said:Sure, but in the ideal world (where no energy is lost in the gearbox), if two engines (with different torque) output equal horsepower, than both should accelerate at the exact same rate (even if one does have to shift gears at 2kph) and reach the same top speed (if both cars have the same aerodynamics). Right?
What you're saying seems to be that I'm correct (noting the ideal situation I specified, think massless continuous variable transmission); the only difference is the losses that occur between the engine and the wheels (obviously from real life experience, time lost on the clutch early-on is a major factor).russ_watters said:Even in the ideal case, you still have to account for it because it has a huge impact.
Uh, ok... I guess if your incorrect scenario were correct, you'd be correct. :uhh:cesiumfrog said:What you're saying seems to be that I'm correct (noting the ideal situation I specified, think massless continuous variable transmission); the only difference is the losses that occur between the engine and the wheels (obviously from real life experience, time lost on the clutch early-on is a major factor).
That much is true.This is interesting because it seems to demonstrate horsepower governs maximum speed (circular track), but torque influences acceleration (drag racing).
joema said:This is a frequently-debated topic in automotive performance circles.
fedorfan said:Ive gotten torque=acceleration and hp=top speed. Well, I want to ask something, if you have a lot of torque all over the powerband especially up on the top end does that mean while one car is topped out on the top end you`re still accelerating?
The problem is on many engines the hp rpm peak is above the torque rpm peak.TGarzarella said:...TQ and HP are proportional to each other, so it makes no sense to speak of them as if they're independent...
joema said:The problem is on many engines the hp rpm peak is above the torque rpm peak.
This raises the question, is optimal acceleration at hp peak or torque peak. Also we must define "acceleration". Do we mean momentary acceleration, as from 60-61 mph. Or do we mean sustained average acceleration, as in lowest time from 0-60 mph or 1/4 mile? Also transmission type is a factor: traditional geared transmissions vs CVT.
You might want to visit a few drag tracks and buy a pit pass so you can rub elbows with the racers. One of the most incredible performers in the NE in the early 80's was a Canadian driving a Camaro called Mouse Trick. He ran pro-built small-block Chevy engines and he said that he was dumping the clutch at 10,000 rpm off the line. I don't know if that was true, but I have no reason to doubt him. He had reliability problems because of this "pushing the envelope", and I recall him and his crew at Pembroke, NB one year scouring the camped-out drag crews for clutch parts, so that he could advance to the Sunday eliminations. My buddy was running a 340 Duster (eventually the US champion in his class for a couple of years) and he was dumping the clutch at 6000 rpm - only after a lot of efforts lightning the rods, grinding off piston skirts, etc. 340 Mopar parts are a lot more massive than small-block Chevy parts and he had a lot of work to do to overcome that differential.5.0stang said:Even in a drag race, (let's say a 6,000 rpm limit) you are below 3,000 rpm (intial launch) for a short period of time (probably 5% for example). The upper rpm horsepower is crucial here. You can have "gobs" of torque below 3,000 rpm...but if you have trouble breathing up top - no horsepower output...the car with less torque and more horsepower (equivalent vice versa situation) is going to take you. The 95% of the time, he is in his "sweet spot."
fedorfan said:So hypothetically, if you had an engine that had unlimited revs or unlimited gears would it have infinite top speed?
But without that friction (and with limitless gearing) every engine could have "infinite speed", trivially (regardless of power etc).fedorfan said:What, why doesn't infinite revs=infinite speed? I am talking like there's no wind or air or anything and no universal speed limit like the speed of light.
turbo-1 said:You might want to visit a few drag tracks and buy a pit pass so you can rub elbows with the racers. One of the most incredible performers in the NE in the early 80's was a Canadian driving a Camaro called Mouse Trick. He ran pro-built small-block Chevy engines and he said that he was dumping the clutch at 10,000 rpm off the line. I don't know if that was true, but I have no reason to doubt him. He had reliability problems because of this "pushing the envelope", and I recall him and his crew at Pembroke, NB one year scouring the camped-out drag crews for clutch parts, so that he could advance to the Sunday eliminations. My buddy was running a 340 Duster (eventually the US champion in his class for a couple of years) and he was dumping the clutch at 6000 rpm - only after a lot of efforts lightning the rods, grinding off piston skirts, etc. 340 Mopar parts are a lot more massive than small-block Chevy parts and he had a lot of work to do to overcome that differential.
My point is that if you go to the track and ask the successful drag racers how they're tuning their cars, you will find that they want their torque (powerband) optimized for the higher rpms and they want the powerband wide enough to cover their shift points. They launch pretty hot and flog 'em down the stretch and they want to continue to accelerate strongly in each gear, so the torque has to be available over a range of RPMs that exceeds the RPM drop caused by shifting to each higher gear. Peak horsepower is a "nice to know" number, but to continuously accelerate, you need to deliver that power effectively over a usable range of RPMs. That's the importance of the torque vs RPM curve on a dynamometer plot. If the absolute value of your car's torque is relatively high and the high portion of the curve is wide enough to cover your shift points (gearbox dependent), you will outperform a competitor with higher absolute torque values if his curve does not adequately span the RPM differential at his shift points. His acceleration will not be consistent because his torque curve is narrow and peaky and since acceleration adds cumulatively to velocity, your car, with a slightly lower but broader torque vs RPM curve will win out.5.0stang said:So again, I do not know what you were getting at. I'm quite familiar with the track
fedorfan said:Not infinite power, I am saying if you have endless gears or an endless revs then your car wouldn`t stop accelerating. Not acknowledging wind resistance, gravity resistance, and whatever else restricting it. Its just a stupid little meaningless waste of 2 minutes and feel free not to answer it. Thank you if you do or did.
polar said:At 5252 rpm all engines have the same torque (ft-lbs) as horsepower.
Stingray said:That's just a statement about the system of units commonly used in the US. It has no physical meaning.
Thank you. That strategy not only gets you off the line the quickest, but it assures that you enjoy continuous acceleration that maximizes your speed through the traps as long as you observe your shift-points, and adjust for temperature/humidity, etc.. It took me a while to learn this, with a modified HD '85 Wide Glide with head-work by Perewitz - a master builder. When competing against later 5-speeds (mine was a 4-speed), I had to optimize for a wider power-band than the 5-speeds, but I managed to kick their butts regularly. One big factor was the installation of a Yost Power Tube (atomizer) over the main jet of the S&S Super E racing carb, which made the bike more drivable at low RPMs, gave a wider power band and boosted the fuel economy from 45 MPG to 50 MPG two-up. Raw horsepower cannot hold a candle to usable torque.polar said:At 5252 rpm all engines have the same torque (ft-lbs) as horsepower.
:)
P.S. I agree with post #29 from Turbo as an answer to what will get you off the line quickest.