If two cars were to race, both with 7.6 lb/hp ,one weighing 3300 lbs with 425 flywheel hp and the other 4300 lbs and 565 flywheel hp. What would be the effect of moving the extra 1000lbs even though they're putting the same power to the ground.
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If two cars were to race, both with 7.6 lb/hp ,one weighing 3300 lbs with 425 flywheel hp and the other 4300 lbs and 565 flywheel hp. What would be the effect of moving the extra 1000lbs even though they're putting the same power to the ground.
Not that simple. A lot depends on how the two cars hook and launch, and the torque put out by the two different engines. HP is what we all talk about, but torque is what wins races.
The old rule of thumb was, for every 100 lbs you remove from a car you pick up one tenth second et, so 1000 lbs less equals 1 second faster time. Beyond that, my mathmatical skills run out. :)
Don
I'm not a pro drag racer, but have been around it all of my life.
Another thought that occurs to me... besides simply increasing power... is that the tires are gripping the asphalt, trying to accelerate the car's mass. But as weight increases, you may approach or surpass the limit of the tires "gripping" ability.
...of course there may be the option of bigger tires... :-)
Other advantages to light weight are the decreased stress on the drivetrain, and the potential to go even faster, when the power is increased... as you did in the heavier example.
If you are talking moving weight..... The more weight of the car, highest percentage, you can put on the rear the better. Better weight transfer, in theory, the better the car will hook up. Of course there are so many varriables it's hard to say. Like don said torque, torque, and you got to get it to the ground. You could have a 7hp per lb advantage over another car and if you blow the tires off......well guess who will come out ahead. Of course that's a drastic exageration, but you get the point. With any race car the lighter the better. Then if you have a weight minium you put it where you want it. And with a very light car, and no weight minium, you may find that adding weight to the rear, will make car hook up better and better et's.
There was a time when a "small amount" of wheel spin was to be expected .........Quote:
Originally Posted by HOTRODPAINT
Procedures do change!
Why did this work as well as it did?
Jim
I have a Suzuki Samurai and a Jeep. The Jeep is 180hp 4k lbs and the Sanurai is 60hp 2300lbs. The Jeep runs a 33x15.50 and the Samurai runs a 31x11.50. Both are the same brand of tire, Super Swamper TSL. Now this aint drag racing but the Samurai will definately climb a muddy hill (level, no ruts just slick greasy) the Jeep will spin the tires more and will definately accelerate better. But the little light weight Samurai will climb better, hold a line better and not slide in off camber situtions. Weight plays a huge factor in how a car performs. I think in a weight distributing, traction perfect world, a 2300lb 7.9hp per lb car won't accelerate like a 400lb 7.9hp per lb. I have no scientific or mathmatical evidence but I would assume that the hp per lb would have to increase slightly. Maybe a small percent, like 7.9 to 8.1.
Dont forget the other factor....age.
Since I got old and fat, I cant run 1/4 mile without having
a heart attack!
mike in tucson
The 100 Lbs 10th of a second rule applies only if bothcars are making the same HP.
If both cars hook well and launch hard (within .002 @ 60 ft) they should theoretically run the same ET although the MPH may be different.
Why not just run them and find out?
:3dSMILE:
i sold my old bbc 572 to some guys that ran it in a samurai :eek:they ran it in a mud pit with alot of Nos i would hate to see that run down the trackQuote:
Originally Posted by joe_and_jeep
I have mine geared way down for RockCrawling, I'd like to put a ported rotary in it but the complete lack of lowend torque would suck in a crawling situation. Or a turbo EcoTec... But my 1.3L motors are dirt cheap :)Quote:
Originally Posted by pat mccarthy
so .. would an elephant pulling a deisel truck out run a man pulling a pickup truck ?
yep i did a eco tec were he lean abit to much on it with a blower blocks need a up grade on sleeves but rods and crank look goodQuote:
Originally Posted by joe_and_jeep
We always thought losing 100lbs was equal to 10hp.And that to lose 100lbs was a whole lot cheaper than to build 10hp.
The B/Modified roadster that my partners, John and Shirley Ryan, and I raced in the late fifties and early sixties was heavy for its class.
You can tell that by lookin'.
The frame was water pipe (heavy) and the engine a 354" Chrysler (read that heavy, too).
That (along with a degree of driver ineptitude) didn't exactly give us an advantage over our competition, most of which consisted of light tube chassis running 265 and 283 Chevys.
We all had the same cubic inches to weight ratio but when the flag dropped, we had a lot more inertia to overcome than they did. By the time the Chrysler figured out what it was there for, it was usually too late.
We had some very good top speed numbers. That's okay, but the object is to win the race.
We just had more to get moving.
Say you got two cars on the line, identical in every way, and both set up and tuned by the same person. One has a driver that weighs three hundred pounds and the other has a driver that weighs one hundred pounds. I'll put my money on the skinny guy.
Anything wrong with that thinking?
Jim
So your saying fat drivers should be on the Tv show "The Biggest Loser"???.:LOL::LOL::LOL:Quote:
Originally Posted by Big Tracks
Me and my wallet have found out lately that it is not just h.p./torque, but a particular combo that gets the car dialed in. The guy that gets his car on a chassis dyno, and spends the time and money to get the car set up right, should have an advantage. Proper tire size/axle ratio, tuning, and a torque converter that allows one to launch at peak torque wins races. Power to weight ratio is very important, but only a starting place when getting a car to run well.
I read something years ago regarding making a car lighter that always stuck with me. It said "instead of looking for one place to eliminate 1000 pounds, find 1,000 items that weigh 1 pound and eliminate those." There are a lot of things on a car that aren't needed on a drag car, so if you find enough of those little items (window winders, wiper motors, dash brackets, dome lights, etc.) you can make a real difference in the overall weight. There are ALWAYS unnecessary parts you can remove if you look hard enough. (and putting the skinniest driver in there doesn't hurt either :D)
Don
To address the original thought experiment of 7.6lb/hp in 3300lb car vs. a 4300lb car... assuming perfect or identical traction and ignoring any aerodynamic differences, the two cars will run the same ET at the same speed... 11.45@117mph according to one racing calculator. (BTW: 3300/7.6 = 434.2HP, 4300/7.6 = 565.8HP)
"horsepower" or "power" in general is a measure of "work" over "time". "work" being movement of a mass (weight) over distance. If both cars have 7.6lb/hp doesn't matter if one car is 1000lb and the other is 10,000lb, the answer will be the same.
Now I'm talking about HP to the wheels with ideal traction... not HP at the crank. In the heavier vehicle, you may expect higher losses through the drivetrain.
As mentioned above, a good rule of thumb is that removing 100lbs will reduce ET about a tenth.
Here's the racing calculator I used this time (there are several out there):
http://www.wallaceracing.com/et-hp-mph.php
-Chris
The effect would be your still moving 1000 pounds extra down the track. Forget the effects for a moment of moving the thousand lbs. and concentrate on getting from Point A to point B with the quickest ET. More effect would also be putting more strain on your parts, 1000 LBS worth. The question is pretty vague.Quote:
Originally Posted by hhaywoodjr
From pure physics, both cars would accellerate identically. But as many have already said, there's more to racing.
On the TV show "Trucks" this weekend they were demonstrating a new power tuner from Bully Dog that will control lots of different vehicles. So they put the tuner on the pickup truck and towed a new Camaro to the track. Then they put the same tuner on the Camaro and made several runs down the dragstrip. Then they loaded a "football player sized cameraman" in the car to get some action shots. With the addition of 200+ pounds, the car was 0.2 seconds faster in the quarter mile! The only thing that suffered was the top speed. That just goes to show you that there is more to racing than horsepower and weight.
I agree theres more too racing and the TV show was probably more advertisement then anything else.Quote:
Originally Posted by Mark in Memphis
For me, it's the overall % of weight lost and wheelbase (balance). Static #'s don't mean anything. It's all about that 60 FT.