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Old 11-07-2002, 04:54 PM
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Question Weird question.

Hey All.
This is going to sound kinda goofy, but I have a question that I was curious about pretaining to my new engines low RPM performance.
Is a motor(like the 500) that makes a ton of horses and tourque at low rpms(like under 4600 rpm's) better, the same or worse than a motor that makes its horses and tourque at higher rpm's(like 6-7000 rpm's) or am I just a nut case for asking?
I was just curious as to if horsepower is horsepower no matter what rpm its working in, why does everyone spend boo koo money to get there engine to run extremely hi rpm's? Tnx, HG

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Old 11-07-2002, 05:24 PM
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For a typical street rod, you mainly will be under 4600rpm anyway. So, in my opinion, I would rather have the low rpm motor, so most of your power would be mainly off-idle to 4600 rpm. Someone correct me if I am wrong...
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Old 11-07-2002, 05:27 PM
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you are correct
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Old 11-07-2002, 05:31 PM
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depends what your after and your driving style , with torque and hp produced lower in the rev range you tend to find yourself with good launchs and the ability to climb small walls ,but running out of revs , coupled with good gearing you good probably get the thing going quite well , but by moving the torque/hp peak up the rpm scale you can run shorter gearing for a better launch and still keep the momentum up in the top end due to the extended rev range ....admitadly you have to keep higher rpms at the launch and induce a bit more driveline stress to keep the engine its it peak.

just my 2 cents
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Old 11-08-2002, 01:09 AM
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The way I see it is you have a motor that could pull a Mack truck out of mud.A car that weighs around 2800lbs and If I remember 4.56 rear gears(right??)I think you'll prolly have enough torque to boink the driver's front wheel off the ground and pull a nasty 1/8th mile but will prolly flatten out at like 1000'.

Just my $4,000,764,091 and .02cents.
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Old 11-08-2002, 07:29 AM
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Horsepower is horsepower no matter where it comes from. However, USEABLE horsepower is different in different situations. Horsepower can be calculated by the equation

HP = Torque * RPM / 5,252 .

Thus you are limited by the physics at low RPMs (street driving) to how much power you can achieve. The goal is to build a torque curve that is maximized at the proper RPM range for your purposes. A 700hp SBC probably has less USEABLE power in the 1800-3000RPM range than the wife's daily driver smog motor. However, above 5000RPM and up, the big motor can't be touched. The only way to get the BIG power output numbers is to spin fast. You get the benefit of the RPM factor of the equation, plus the tourque curve of an internal combustion engine is greatly improved at higher RPMs. Big cubic inch motors make torque very easily, thus don't need to scream to ultra RPM. Further, since the rotating/reciprocating parts are so much heavier, stress is high and engine life is compromised at very high RPM. Conversely, a SBC can't compete heads-up on a torque basis with a big block but since it has much lighter components, it can scream to +10,000RPM and yield similar big horsepower numbers as the slower rotating big inch engines. That is why you see SBCs very competitive with big block Chevies and Hemis in sportsmans classes in drag racing. They get the same power by spinning faster. In the pro classes, the guys spend a LOT of money to keep their HUGE displacement big blocks alive at the extreme RPMS so the little engines lose that advantage and drop out of the competition.

[ November 08, 2002: Message edited by: willys36@aol.com ]</p>
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Old 11-08-2002, 07:00 PM
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So does that mean theoreticly I could get my Push Mower Briggs and Straton to make 1000 HP by spinning it to a gazillion rpms?
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Old 11-08-2002, 08:29 PM
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That equation says you can but you must apply some other pertinent equations to see where it's limits are. Other physics take over and limit what any engine can output. An IC engine is a heat engine and power comes from using the potential energy from the cmbustion of fuel. Air and fuel flow equations show the amount of fuel and air you can shove through an engine is a function of it's size so your 3-1/2 horse Briggs and Straton will reach it's limit of what you can shove thru it long B4 you reach the 6000hp you need to be competitive in top fuel.
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Old 11-08-2002, 08:35 PM
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i think the main reason people think about HP is cause they never heard of torque. that's usually all they see in the headlines.
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Old 11-09-2002, 03:45 AM
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OK, I guess I need to add my two cents worth to this horsepower/ torque/ rpm question.
While I will readily admit I am empressed by those big block, tire smoking, torque monsters, I am still a screaming/high reving/small block fan.
I keep hearing the old addage that there is no substitute for cubic inches and while this does carry some wieght(no pun intended) I think most are overlooking a very important part of the equation. What has allways impressed me with the small blocks was how fast you could get one to those "high" rpm's. That is to say how "quick they are. On the drag strip "quick" means lower et's. Of course the car has to be matched to the engine in order to achieve those low et's.
But that is on the drag strip, where small blocks really come into thier own is on the road racing side of the sport. It blows me away to watch how fast these cars can come into a turn and accelerate back out. These cars are perfectly matched and balanced to handle the varibles on the road race track and to me the small block properly matched to the car will provide a much better handling package on the street as well, unless all you do is drive in a striaght line and like to smoke your tires a lot.
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Old 11-10-2002, 05:59 PM
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Ok i'll try. what you want in a street engine is a wide, flat torque band.

A screaming smallblock is great, so is an 800+ hp 3.0 liter formula 1 engine @ 15000 rpm. Trouble is that this type of engine tends to be a bit less than reliable and peaky, the torque band is small, what this means is that you have to maintain the narrow xxxx rpm torque band.

Street driving precludes this, the engine has to work from idle to a reasonible red line, say 5000/5500 max. this is accomplished thru long stroke big block motor. The torque band on this type of motor tends to be wide and rather flat throught the rpm range.

This makes the combo much more pleasant to street drive.
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