would it be safe to say that speed os based on the ability to overcome the amount of drag. i am pretty much saying that in theory if your transmission could be a perfect match for max speed, would horsepower be the only thing left to have any effect on speed? thanks

barfing smilies are the best smilies!!! :U :U :U

 

I would say rpm more then HP....HP is only a calculation of torque in a motor, which is essentually the power of the motor. to me most of it would rely in the tranny, TQ(at what RPM), the weight of the car, the amount of drag on the car, and the size of the tires...I would think those are the factors that react to MPH....those to me are the biggies, there are obviously lots of others like amount of room, and time it takes to get up to speed before you have to slow down to make a corner, and so forth....

Just some thoughts

Daniel

 

Well...on a theoretical level (God if my aerodynamics professor ever knew I was saying that he'd laugh for hours!), if you lump all of the different "forces" trying to slow your car down together and call them "drag", you're kind of right. One Horsepower is just another way of expressing the amount 550 foot-lbs per second (those are pounds force, not to be confused with pounds mass--aren't you glad you asked). Horsepower in a car is not actually measured, but rather computed by multiplying the Torque the engine produces (which is easily and cheaply measured) and multiplying it by the rpm of the engine at the time the torque was measured, then dividing by a constant to get all the units in order. Okay this is hurting my head now, too, so one of you real engineers take over.

There's much more to speed in the car context than engine horsepower-- gear ratios, aerodynamics, to name two big things. All else being equal, more HP equals more :D

Now excuse me while I go :U .

 

Ok,,,Since everyone here is talking greatly above my head....I'll just say; "Ditto" :D :D :D

 

I didn't see your g sub c term in your calculations! :D I agree. You must draw a FBD (Free Body Diagram) showing all forces acting on the vehicle. You must also determine how many RPM's you must turn to achieve a certain speed. Then determine how much power your engine must produce in order to provide the necessary forward force (derived from your free body diagram) to achieve that number of RPM's at the specific conditions created due to your chosen speed. Bottom line. Top speed is limited by RPM's. If your engine is only turning so fast, your tires can only turn at some given ratio based on your tranny, rear end, and tire size. Get your engine to handle more RPM's, and you'll go faster.

 

I saw this the other day and thought it was a pretty good description. You may want to check it out. http://www.vettenet.org/torquehp.html

 

Actually, I was watching a Speedvision show recently on Bonneville. Some of the REALLY fast guys (400+), were saying that traction is a big problem. They explained that they had the horsepower/gear combo necessary to go faster, but at some point the aerodynamic drag becomes greater than the traction available to push it out of the way. 'Course that's on salt, I suppose if they had a paved runway long enough they could go a lot faster.

 

Gearing for maximum speed would be matching your gears so that your hp peak corresponds with the speed you want to go. If you do and the engine will still exceed its peak hp rpm, a taller gear (lower number) will permit you to go even faster. On the other hand, if you can't reach your peak hp rpm, you need to go to a somewhat higher numerical gear.

The best simple explanation I have heard regarding the difference between hp and torque was found on this forum. It goes something like this: If two people could each lift a 100 pound sack of flour they each have the same torque, but if the first man can lift two 100 pound sacks per minute and the second man can only lift one sack per minute, the 1st man has twice the horse power rating compared to the 2nd man even though they have the same torque.

This is why torque is the key to acceleration and hp the key to top end.

Chuck




[Modified by Chuck Harmon, 1:16 PM 10/25/2001]

 

Chuck, could that be backwards? :confused: I think torque would be the ability to lift the sack, and horsepower would be how many times you can do it in a minute. Or something like that...

-Joe


[Modified by Flareside, 1:30 PM 10/25/2001]

 

As stated before you gear to achieve the power peak at the speed where drag horsepower equals available power, but it's important to remember that the power required to overcome total drag is a function of speed cubed, so if you add ten percent more power, you don't change to a ten percent taller gear. A ten percent improvement in power will increase top speed 3.2 percent if gearing is ideal.

Most vintage Corvettes, especially those with SHP engines are geared too short to achieve top speed potential. If the engine will rev to above the power peak in top gear, the car is geared too short to achieve top speed potential with its available power.

Duke

 

[QUOTE]Chuck, could that be backwards? :confused: I think torque would be the ability to lift the sack, and horsepower would be how many times you can do it in a minute. Or something like that...

-Joe


Umm, !dluoc ti sey :bb

Chuck

p.s. Joe, my uncorrected explanation was a sack of something else! :conehead


[Modified by Chuck Harmon, 1:26 PM 10/25/2001]

 

ok. i know a few of you guys have done this so.....what if i went to a scrap yard and tried to get a wrecked vette's engine. i am refering to a newer vette (C-5 or so). would this be a good idea. why would this be good and why would this be bad? in referance to power and torque and max speed and such what should i know? thanks.

if it doesn't work.....:U :U :U


[Modified by wigi93, 11:23 PM 10/25/2001]

 

The hot rodder's maxim:

"Speed costs money. How fast do you want to go?"

Chuck

 

I put a 98 motor from a wrecking yard in my blown motor 90. The big crowd pleasers this summer in the car shows were the imaculate 61 ans 62's on ZO6's chassis. There is some company in the L.A. area that will take a 2001 ZO6 and put your body on it.

For less money go to Merlins 522's web page and see how a 1200+ hp car is put together. Then your only talking $80,000 or so ready to drive. Or if you want to go cheaper talk to Monty at $55K+ I have an old beater only insured for $36K.

What I'm saying is you can spend what ever you like. Modern electronics are very nice. But any day of the week I would buy one of our old C-3's with super power and handling over spendiing $50+ on a brand new Vette.


Salt flat cars add weight. weight does not limit top speed it only takes you longer to get there. Wings add drag. Which would take more hp to get to max speed. Cars at the salt flats have three miles to hit the flying timed mile. So I have noticed that these running on the edge cars and bikes take off slow and don't even really hit it until a mile or less from the timed mile. The other problem is traction on the salt. 2000+ hp cars were smoking the tires at 300+ mph. Kind of like the top fuel dragsters smoking the tires at 300+ on sticky pavement through the end of the quarter.

The only thing that made this car fast is less than 2 pounds per hp. It would be like putting 1800+ hp in our 3400 pound Vettes


[Modified by gkull, 12:43 AM 10/26/2001]

 

After re-reading the article in my last post, I realized it was written by a guy whose first name is Bruce. Unfortunately, I can't take credit for it. Didn't want to give anyone the idea I was smarter than I was. Bruce is my last name, anyway! :flag