How much does horsepower weigh?
#16
03-06-2009, 09:22 AM
Depends on sprung vs. unsprung weight. I think the factor is something like 10x as great an impact for unsprung / rotational (vs. sprung - or general weight in the car), thus my relating 1 lb lost at the wheels / tires / rotors to be so much. Therefore, 100 lbs of sprung weight lost might be about equivalent to finding 10 hp. But finding 10 lbs of unsprung / rotational mass is like finding 10 hp worth of performance gain.
#17
03-06-2009, 10:01 AM
Traction Limited?
Another key factor in acceleration is whether the car is already traction limited or not. Adding horsepower to a traction limited car will not help the 0-60 times much, but will help at points in the acceleration curve where traction is not a problem.
This is especially true of cars with traction control where power is applied to the limit of adhesion, and that's it.
The previous post regarding weight reduction is spot on. There are many benefits to reducing weight, especially unsprung weight; Acceleration, braking, cornering speed, ride quality, reduced wear, etc.
Lightweight forged wheels anyone?
This is especially true of cars with traction control where power is applied to the limit of adhesion, and that's it.
The previous post regarding weight reduction is spot on. There are many benefits to reducing weight, especially unsprung weight; Acceleration, braking, cornering speed, ride quality, reduced wear, etc.
Lightweight forged wheels anyone?
#18
03-06-2009, 10:02 AM
To my mind this requires no magic formula to appoximate. If a 997s has 1 hp for every 8.5 lbs (do the maths) then reducing weight by 8.5 lbs should give an increase the equivalent of one hp, no? The unsprung weight issue complicates this as Ron points out due to the issue of rotating mass. As I read the question it pertains more to straight line performance however. For a significant improvement in straight line performance it is cheaper to add horsepower than reduce weight.
Last edited by Gpjli; 03-06-2009 at 10:09 AM.
#19
03-06-2009, 10:21 AM
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Take a look at this. HeavyChevy started a thread on the 996tt and it took off quite well. The car will not be the same, but it should give you some idea of an answer to the question that the OP is asking.
https://www.6speedonline.com/forums/...urbo-list.html
The chart is of particular interest based on the calc. that he provides. I will just go ahead and post it:
This above thread has been the most interesting that I have come across addressing weight reduction since I joined the 6.
https://www.6speedonline.com/forums/...urbo-list.html
The chart is of particular interest based on the calc. that he provides. I will just go ahead and post it:
WHY IS WEIGHT LOSS IMPORTANT?!?!?!?!?!?!
Ive been wondering how weight loss translates in terms of hp so I did some rough calculations that might be interesting to you all. If you assume a 3500 lb car with 500 hp, each 100 lbs of weight loss translates to this amount of power. Math experts please correct me if im wrong.
Weight....actual HP.........lbs/hp.............relative power
3500.......500.................7.0................ .500
3400.......500.................6.8................ .514.7
3300.......500.................6.6................ .530.3
3200.......500.................6.4................ .546.9
3100.......500.................6.2................ .564.5
3000.......500.................6.0................ .583.3
So a 300lb weight loss is the equivalent of adding 47 hp if my calculations are correct. Interesting to note that going from 3500 to 3400 is only equivalent to 14.7 hp and going from 3100 to 3000 is equivalent to gaining 18.8 hp. It would be interesting to make tables like this for cars with 600hp and 700 hp and so on. (rwm514)
Ive been wondering how weight loss translates in terms of hp so I did some rough calculations that might be interesting to you all. If you assume a 3500 lb car with 500 hp, each 100 lbs of weight loss translates to this amount of power. Math experts please correct me if im wrong.
Weight....actual HP.........lbs/hp.............relative power
3500.......500.................7.0................ .500
3400.......500.................6.8................ .514.7
3300.......500.................6.6................ .530.3
3200.......500.................6.4................ .546.9
3100.......500.................6.2................ .564.5
3000.......500.................6.0................ .583.3
So a 300lb weight loss is the equivalent of adding 47 hp if my calculations are correct. Interesting to note that going from 3500 to 3400 is only equivalent to 14.7 hp and going from 3100 to 3000 is equivalent to gaining 18.8 hp. It would be interesting to make tables like this for cars with 600hp and 700 hp and so on. (rwm514)
#20
03-06-2009, 11:08 AM
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YES! That is the sort of table I had in my head. To make it more actionable, I wanted to add another chart that lists the value of relative power. So, we would need to chart the cost of each mod and compare it with the relative power gain. This chart would list both HP and Weight mods. As I said, most mod discussions seem to address the HP equation. Who knows, lighter wheels could be the best 'power' mod...dollar for dollar.
Nick
Nick
Take a look at this. HeavyChevy started a thread on the 996tt and it took off quite well. The car will not be the same, but it should give you some idea of an answer to the question that the OP is asking.
https://www.6speedonline.com/forums/...urbo-list.html
The chart is of particular interest based on the calc. that he provides. I will just go ahead and post it:
This above thread has been the most interesting that I have come across addressing weight reduction since I joined the 6.
https://www.6speedonline.com/forums/...urbo-list.html
The chart is of particular interest based on the calc. that he provides. I will just go ahead and post it:
This above thread has been the most interesting that I have come across addressing weight reduction since I joined the 6.
#21
03-06-2009, 01:41 PM
YES! That is the sort of table I had in my head. To make it more actionable, I wanted to add another chart that lists the value of relative power. So, we would need to chart the cost of each mod and compare it with the relative power gain. This chart would list both HP and Weight mods. As I said, most mod discussions seem to address the HP equation. Who knows, lighter wheels could be the best 'power' mod...dollar for dollar.
Nick
Nick
#22
03-06-2009, 01:48 PM
Can my daily driver go on a Diet?? Or will I be loosing a lot of creature comfort?
I have been thinking about the CF hood and CF roof. Would be sooo sick! but I dont want to loose my sunroof
I have been thinking about the CF hood and CF roof. Would be sooo sick! but I dont want to loose my sunroof
#23
03-06-2009, 02:13 PM
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A lot of this stuff sounds good for weight loss, but to lose a few hundred lbs would be very very expensive and still maintain stock drivability. That is why the modders usually increase power first, because it is the cheapest path to a faster car. Then the people who are obsessive about modding spend the serious money to drop weight. This is because the law of diminishing returns kicks in much more quickly on weight than power. This is the reason why weight loss threads usually focus on the most expensive P cars. If you are going to drop some serious money you might as well start with the absolute best, because it will just be a drop in the bucket.
Still a very cool thread and I just want to say that I am not trying to rain on anyones parade.
#24
03-06-2009, 03:22 PM
I think it's reasonable to look at the stock power/weight ratio and say something like "if stock is 9lbs/HP, then 90lbs = 10hp, more or less".
Ouch. Kinda takes the sails out of the cost/benefit - HP is MUCH cheaper and easier to live with. Try to gain 30hp - eh, that's doable on a C2 or C2S without losing much if any driveability and without going crazy on cost. Try to lose 270lbs - yikes. Lose the rear seats, swap wheels/tires, start throwing carbon fiber . . . I doubt you've made it yet, and spent a LOT while reducing your car's functionality.
Ouch. Kinda takes the sails out of the cost/benefit - HP is MUCH cheaper and easier to live with. Try to gain 30hp - eh, that's doable on a C2 or C2S without losing much if any driveability and without going crazy on cost. Try to lose 270lbs - yikes. Lose the rear seats, swap wheels/tires, start throwing carbon fiber . . . I doubt you've made it yet, and spent a LOT while reducing your car's functionality.
#25
03-06-2009, 04:14 PM
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I want to know the mod list to get rid of over 600lbs on the 996tt that is on the top of the list... Seems like you could just get rid of the back 1/4 of the car. 
#26
03-06-2009, 05:17 PM
As mentioned, the hood on the 911 is small and pretty light (24lbs for CF doesn't justify it IMO). The roof is likely not worth the hassle. Your quick and easy weight items (that I can tell thus far with the car) are: Bypass Pipes instead of Mufflers = 40lbs (or so) & Rear seats removed = 90lbs (iirc someone weighed them). Next would be GT3RS Lexan rear window (glass is heavy). Those are 3 big ones on the good end of the car to lose weight on. I doubt there is a lot to be had up front, i guess you could pull out the tire kit and the carpeting and the CD Changer, drain the windsheild washer to as low as wont' set off the warning (if it has one).
After that it gets expensive I imagine. Lighter wheels (OEM aren't that bad IMO, but there are lighter to be found). Lightweight battery (doubt there's much there).
After that it gets expensive I imagine. Lighter wheels (OEM aren't that bad IMO, but there are lighter to be found). Lightweight battery (doubt there's much there).
#28
03-07-2009, 09:04 AM
I think it would be a lot more expensive to reduce weight rather than just add mods which increase torque/horsepower. One good example is the M3 CSL which is about twice as expensive as the standard M3 namely for its use of carbon fiber/weight reduction+reinforcement on top of other add ons.
On the 911 there would be a few obvious options, namely lighter seats rather than the heavy leather ones, removal of the back seats, air conditioning unit, replacement of exterior body panels with carbon fiber components, and lighter titanium exhaust components. Cost would be upwards of $15k. Now, take that $15k and put it towards some performance mods, and now your talking.
On the 911 there would be a few obvious options, namely lighter seats rather than the heavy leather ones, removal of the back seats, air conditioning unit, replacement of exterior body panels with carbon fiber components, and lighter titanium exhaust components. Cost would be upwards of $15k. Now, take that $15k and put it towards some performance mods, and now your talking.
#29
03-07-2009, 09:46 AM
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I was thinking and there are two Top Gear Episodes that come to mind when I think of this thread. The first is the one where they slim down a xj12 to bare bones and do 0-60 and 0-100 tests:
http://www.topgear.com/us/videos/mor...12-slims-down/
And then there was this one where they take a Renault Avantime and try to modify it to make it a faster track car. The results were fairly interesting:
http://videos.streetfire.net/video/T...ime_199780.htm
It would be interesting to know how much difference it would make to just add items to stiffen the chassis. If you just added better strut bars and braces, anti-roll bars and a new suspension how much faster you could make the car.
http://www.topgear.com/us/videos/mor...12-slims-down/
And then there was this one where they take a Renault Avantime and try to modify it to make it a faster track car. The results were fairly interesting:
http://videos.streetfire.net/video/T...ime_199780.htm
It would be interesting to know how much difference it would make to just add items to stiffen the chassis. If you just added better strut bars and braces, anti-roll bars and a new suspension how much faster you could make the car.
