Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Theoretical gains from weight reduction and aero improvements

saand · 10-26-2010, 07:53 PM

cr45 thanks for picking up some naming errors i appreciate your time in looking through the calculations, they are fixed now.

I also agree with frank lee, the EM performance calculator generates more information and it is a valuable tool for theoretically evaluating some modifications. The methods and equations for my methods in the wiki and the EM performance calculator are likely the same and i have also checked the results of the wiki calculator against the EM performance calculator and they match closely.

zerohour, it might be worth taking this conversation off this thread so we dont clutter up the thread (we can start a different thread something like "problems with assumptions for theoretical calculations").
Note the EM performance calculator i believe makes all the same assumptions when it is calculating weight influence (someone please correct me if you actually know the equations used in that calculator)
Anyway regarding your last comment
firstly i take no offense at your comments and i am happy to have the discussion about the calculations in the hopes that any errors will be found and others can use the calcs as a useful tool.
secondly regarding the
yes agreed every car is different, the calculations assume the drive train (manual/auto trans) is 95% efficient so if anyone has a better approximation of efficiency of transmissions i would love to put these numbers in.
I agree to an extent with your comment on engine efficiency being different for different power outputs. However i disagree with the comment that when looking at a very powerful engine like a v6 or v8 that the fact there is excessive power means that weight reduction will have no effect. As far as i see it the more powerful engine has a different percentage of efficiency for converting the chemical energy in petrol to energy for movement. So the V8 still has to put out less energy to accelerate less mass and assuming the car is still driven the same way with the same throttle position the V8 will use less energy with less weight.

as a side comment it is my impression that auto makers reduce weight not just for the gains in not accelerating the extra weight but also the gains had by reducing the size of the engine and associated systems. The gains in reducing the engine and associated systems probably out weigh the effect from accelerating the extra weight. It is very hard for ecomodders to reduce the engine and other system sizes so we will always get less improvement than the car manufacturers will when reducing weight.

10-26-2010, 07:53 PM	#13 (permalink)
saand Wiki Writer Join Date: Jul 2010 Location: Melbourne, Australia Posts: 236 bugler - '91 Mazda 626 90 day: 35.89 mpg (US) Thanks: 15 Thanked 25 Times in 22 Posts	cr45 thanks for picking up some naming errors i appreciate your time in looking through the calculations, they are fixed now. I also agree with frank lee, the EM performance calculator generates more information and it is a valuable tool for theoretically evaluating some modifications. The methods and equations for my methods in the wiki and the EM performance calculator are likely the same and i have also checked the results of the wiki calculator against the EM performance calculator and they match closely. zerohour, it might be worth taking this conversation off this thread so we dont clutter up the thread (we can start a different thread something like "problems with assumptions for theoretical calculations"). Note the EM performance calculator i believe makes all the same assumptions when it is calculating weight influence (someone please correct me if you actually know the equations used in that calculator) Anyway regarding your last comment firstly i take no offense at your comments and i am happy to have the discussion about the calculations in the hopes that any errors will be found and others can use the calcs as a useful tool. secondly regarding the yes agreed every car is different, the calculations assume the drive train (manual/auto trans) is 95% efficient so if anyone has a better approximation of efficiency of transmissions i would love to put these numbers in. I agree to an extent with your comment on engine efficiency being different for different power outputs. However i disagree with the comment that when looking at a very powerful engine like a v6 or v8 that the fact there is excessive power means that weight reduction will have no effect. As far as i see it the more powerful engine has a different percentage of efficiency for converting the chemical energy in petrol to energy for movement. So the V8 still has to put out less energy to accelerate less mass and assuming the car is still driven the same way with the same throttle position the V8 will use less energy with less weight. as a side comment it is my impression that auto makers reduce weight not just for the gains in not accelerating the extra weight but also the gains had by reducing the size of the engine and associated systems. The gains in reducing the engine and associated systems probably out weigh the effect from accelerating the extra weight. It is very hard for ecomodders to reduce the engine and other system sizes so we will always get less improvement than the car manufacturers will when reducing weight.