Power to Weight

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Hoosier Dart

Hoosier Dart
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I've heard that fast vs faster basically comes down to power to weight ratio. By power I mean power to the ground in whatever package is used to do it. It seems logical to me that the more radical you go with an engine the reliability curve goes down somewhat. Not always and maybe not proportionally but some at least. The other side of the coin is removing weight. Free to a point and then probably just as costly as anything else. All else being equal what is weight removal worth in terms of performance. A more abstract question might be what is weight removal worth vs the same cost in reliability. By that I mean if you drop 800 bucks to remove 150 pounds are you better off to do that or leave the weight alone and put the 800 in the engine. These are just off the wall numbers by the way.
 
100 pounds weight loss is worth a tenth in the 1/4. I think as far as HP goes 10 HP will get you a tenth in the 1/4.
 
It's nearly impossible to say what is more beneficial without being more particular about the car/dollars. Generally, lighter is better. Power can be moved around rpm wise or added easy enough but the dollars to add depend on a ton of existing stuff.
 
There is absolutely no doubt that REGARDLESS of power to weight, lighter weight cars have an advantage. This was proved many many years ago in the Pro Stock wars of the '70's
 
Your question looks like you are asking if it's one or the other.

In reality your best bang often comes from a combination if weight reduction and power upgrades.
 
also in regard to weight there is only so far that u can go before you start cutting up the car...

rotating mass is the biggest thing to knock down, lighter rims/tires, brakes, axles, ring gear, so on and so forth
 
Great question.

As said early, lighter cars have an edge. Even if it is down on power compared to the other lane.

Removing weight from the car doesn't make the car less reliable, but more dangerous. If you start replacing doors with fiberglass, this is now a drive at your own risk for fear of lifeand/or limb. Street or track.

Things like bumpers, hood and deck lids are the norm. for lightening with fenders seen alot as weight reduction items. The cost can be reduced through resale of the replaced parts. This makes it a good spot to spend money. Paint optional cost of course.

With the lighter weight, getting off the line is easier and motoring on down the track is easier and quicker with the best bennifit yet, less strain on the engine/drivetrain. Since your engine is working less/not as hard I should say really, in order to move the weight, it shouldn't get so beat up....so to speak.

From my veiw, adding the like cost to the engine is the flip side of the coin with it's own cave eats. While the cars body is still strong and better in case of a fender bender, it'll still need to be stiffened for the increased power. Something a fiberglass car should do anyway.

Adding power to the engine in normal cases tends to move the power band up through cams, intakes, carb sizes etc.... and creates a harder running/charging engine. You still have the weight to overcome. Enter a higher stall converter and axle ratio.

The great equalizer to adding bigger cams and the like for more power would be to super charge the engine. RPM power curve stays the same. It just moves up alot in power while the RPM curve doesn't really change much.

At, oh, lets say, a $3500 cost for a enterly level Paxton and about a days work on the car, you can increase the power by 100 HP and lbs. of torque. For a street car to lose the equal amount of weight to power gained vs the Charger, it may be difficult to balance out. Once you move beyond a basic improved muscle car power upgrade to something considered radical (By the ave. guy walking around) you'll probably find most people went the engine route rather than weight savings.

1968FormulaS340 said:
In reality your best bang often comes from a combination if weight reduction and power upgrades.
Click to expand...

AS dually noted here, how true it is!
 
67Dart273 said:
There is absolutely no doubt that REGARDLESS of power to weight, lighter weight cars have an advantage. This was proved many many years ago in the Pro Stock wars of the '70's
Click to expand...

The thing that is not said is that the lighter cars were also smaller cars, especially in terms of frontal area. The A-body has less frontal area than the B-body. This creates an aerodynamic advantage that comes into play towards the top end.
 
hi, im shaving weight off for two reasons.have 440 and trying to get it to handle better and if makes it faster a bonus,i listed a post "will it ever handle" following me going b/b.amazing the replies on suggestions there to "cut back" on lbs,for instance i went fiberglass hood as mine rotten, my steel one weighed 30 kilos!!! fiberglass 5kg if that........along with ali rad,intake,headers etc ive lost well over 100lbs......regards to losing glass and going poly carbonate windows ,fiberglass doors etc??? my car a street car,you gotta draw the line i think, is it a drag car only? saftey a definate issue,i weigh 19 stone so if i wanted ultimate E T s id ultimatley have to go on a diet :bootysha:
 
I'd take a lighter car over more power any day. Want to know why?

Lighter car
-----------

Stops quicker
Turns better
Easier on drivetrain parts
Easier to hook


It's not just power to weight ratio that matters
 
If you are interested in the benefits of weight reduction Car Craft took a mid 80's Corvette and started cutting parts off it until it was nothing more than a frame, seat and drive train. At each step of the way they ran it around a road course and it was quite dramatic the improvement in performance until they got so much weight off that the suspension was so miss matched to the weight it started going slower.
 
I remember some magiaze a long way back got a ....could have been a Chrysler Impirail or something huge from MoPar. It had a 440/727 and ??? on gear set up. Probably a high way set up.

They also took body panels off and emptied the car down to a butchered hack jon. No ddors, trunk, hoodseats glass bumpers .... they just kept on going.

It ran low 12's though! All stock 440.
 
yellowdartdave said:
That was a mid 60s Caddy.
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"Caddy Hack" I believe was the name of that atricle. They did put a 440 in a Dart for another article. Used engine, 509 cam, single plane, headers, low gears. They finally got a "corrected for sea level" 12.90 something out of it.
 
FWIW, there are classes where cars go by weight-to-cubic inch. i.e.: At 8 lbs ber cubic inch, one can build a 300 ci engine and weigh a minimum of 2,400 lbs. Or one can build a 350 ci engine and weigh a minimum of 2,800 lbs.

If both engines are built and optimized to the same level, the smaller engine will likely be faster because it's more efficient and make more HP per cubic inch. This can only go so far. But Modified Production-type cars, from what I recall, run between 270 and 305 ci. for best results.

Older Pro Stock rules once had weight to cubic inch rules and many went smaller when they figured out they could go faster with less inches but also less weight. There were even approx. 366-394 Hemis based on modified low deck big blocks before they all went to 500 cubic inches at the same weight.

Power-to-weight is important. But everything in the vehicle has to work together to get that power to the ground as efficiently as possible. (i.e.: gears, converter, suspension, traction, etc.)
 
hypermite said:
I think you meant the opposite right? I believe the Mopar chassis book says that removing 1 pound of sprung weight is like removing 4 pounds of unsprung weight.
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Are you sure that's not talking about rotating weight, like wheels? But even those numbers have been quoted as being anywhere from 3-10x. Depends who you talk to. Just my opinion, but I don't believe there is that much difference between unsprung and sprung weight on a drag car. A 440-6 Challenger racer in Stock tested an 8 3/4 and Dana 60 back-to-back while equalizing the weight difference with ballast. I forgot the actual weight difference, but he didn't see any definite ET difference. However, the Dana 60 is suppose to be more efficient and take a little less HP to turn also.

Unsprung weight would probably make the most difference in a circle track/road race car because the suspension has a lot more work to do than on a drag car. Weight would be a big factor with the constant up-n-down movement of the unsprung wheels, tires and and rear end throughout the course.
 
Locomotion said:
Are you sure that's not talking about rotating weight, like wheels? But even those numbers have been quoted as being anywhere from 3-10x. Depends who you talk to. Just my opinion, but I don't believe there is that much difference between unsprung and sprung weight on a drag car. A 440-6 Challenger racer in Stock tested an 8 3/4 and Dana 60 back-to-back while equalizing the weight difference with ballast. I forgot the actual weight difference, but he didn't see any definite ET difference. However, the Dana 60 is suppose to be more efficient and take a little less HP to turn also.

Unsprung weight would probably make the most difference in a circle track/road race car because the suspension has a lot more work to do than on a drag car. Weight would be a big factor with the constant up-n-down movement of the unsprung wheels, tires and and rear end throughout the course.[/QUO

All I can be certain of is my experience. ( I'm pretty sure wheels are unsprung weight) I took off the super heavy hideous aftermarket wheels my Mustang had on it( saving 14.6 lbs per wheel/tire combo !) & my 1/4 mile times & traps were improved, fuel economy went up by an average of 25-30 miles per tank. No way to be 100% certain, but I would say that braking & cornering improved as well. I'm no expert but I dont think removing 60 lbs of interior/sheetmetal would have the same effect. Again, I'm not trying to start anything, just relaying my experiences.:toothy10:
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Hypermite,

No problem. Your experience makes sense because the weight of wheels is not only "unsprung" weight, but also "rotating" weight. Big difference between 30 lbs in rear end housings and 30 lbs in wheel/tire weight.
 
It really Depends on what you are doing with your car. Drag racing is very different than roadracing or circle track.

Quick over-view of the different types of weight and how they affect performance.

Sprung (regular) weight- This weight is most of the weight in an average car. This weight determines the center of gravity height, the loading of the tires, most of the percentage of the power to weight ratio, and most of the weight you are trying to accelerate.

Un-sprung weight- This is the weight that controls how fast your suspension reacts, the ride quality, and the capability of your shock control and such.

Rotating mass- This is anything that actually spins. Engine components, flywheel, transmission gears, drive shaft, rear gears, brakes, wheels tires etc. This weight actually does double duty. It uses engine power to spin and acts as part of the weight that is being moved around.

Now as you can see by the above descriptions it is much more important to reduce rotating mass than any other weight. Especially from a pure acceleration standpoint. The components that spin at engine speed are most important, then transmission speed and so on. But you also have to consider how far out the wight is spinning. The wheels and tires, as others have mentioned have a lot of effect on the braking is huge.

Un-sprung weight is much more important to those corner people(like me) than to straight line only racers. fast suspension reaction is really important in a situation like a mid-corner bump leading onto a straight where you can't really afford to loose grip or cornering speed. Also a Big factor in ride quality for those concerned about that.

Sprung weight is everything else. The weight that limits the maximum cornering, the maximum acceleration and braking, and the stress put on all your components.

After all that, The only thing I can say is that every case is different, and most likely, you will find that a mix of engine mods and weight loss is the best thing in your case(again, like others have mentioned).

Hopefully That somewhat long winded reply makes things a little bit clearer.
 
Mopar-Man said:
I'd take a lighter car over more power any day. Want to know why?

Lighter car
-----------

Stops quicker
Turns better
Easier on drivetrain parts
Easier to hook


It's not just power to weight ratio that matters
Click to expand...

What he said and a lighter car don't need all that HP to go fast.. A car that heavy with more HP could be slower than a car with less hp and lighter..
 
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