Prius 75-91mpg

[Nathan jones]

I believe it is 7.16lb, removing it will give the same increase in acceleration as adding 1 bhp to the engine. I don't know the details, that was the rule. Everyone modifies in their own way. I just do things my way

[teoman]

F = m * a

Force = mass times acceleration


Assuming you can constantly kick with the same force, a pingpong ball will accelerate faster than a bowling ball.


In the formula mass is in kg, force in newtons and acceleration in m/s^2


The torque / hp curves complicate the exact calculations though.

[Vman455]

Originally Posted by California98Civic

If it is a law, then this comment will reveal my ignorance: if 7.6 lbs consumes 1bhp then how does my 106 hp engine propel my 2100 lb car? See what I mean? Clearly, I don't understand something here ....

It's better not to think about horsepower since "power" is a difficult concept to visualize and/or understand despite most people thinking they do. "Power" is the time derivative of energy (energy and torque are also, sometimes confusingly, measured in the same units; so, when we talk about horsepower in a car we're really talking about "the change in torque per unit time." One horsepower is equal to 550 lb-ft/s). What accelerates a car is, as teoman correctly points out, tractive force which is directly relatable to the rate of acceleration of the car, and what causes it to move. Reduce the mass and, with no change in tractive force (which isn't true in reality, as the available traction is proportional to the normal force acting on the tire which is equal to the load/weight on that tire), the magnitude of acceleration must increase. Rules of thumb like "7.6 lb = 1 hp" are generalities; you'll also hear drag racers use "100 lb reduction = 0.1 s reduction in quarter-mile time." But that depends on the car, the actual force produced over time, the actual mass of the car, where the mass was removed, the change in tire load because of the weight reduction, etc.

[Nathan jones]

Thanks for your replies, I should not have really introduced acceleration to an efficiency forum although I think a dare I say it rule of thumb weight to mpg could be generalized, limited also to variables even on the same vehicle. From tests it varies greatly depending on week pattern soc, ambient, ice temp, gradients, trip routes and traffic conditions, for my car 14-20kg worst/best per mpg seemed about right but I still maybe wrong. It's also very much work...

Also thanks yes I have custom tyres and pressures to compromise grip and efficiency although if you were on a limited budget reducing pressures works well

I decided as I have alloy wheels already, the net gains from replacing doors vs wheels, doors win as I only have limited time in January, plus my wheels do not rotate that rapidly





Hey guys just checking in 15/11, but I don't wanna modify the thread as such because not much has happened. My bumper was not a great success, I needed the car for work and removed it from the mould before it was properly set so in a couple of months I will buy a new one and use it as a die, the same as the doors, buy one at a time so I can still work and make new parts. The rear driver's door will be first. I will probably only use kevlar on the front drivers, four layers of 1000D with two impact bars. I will keep the wheels I have for next year, they are still very light and see the year after that. Passed with just corroded rear springs advise Saturday

Incidentally I rented a Hyundai in Canada last month and the best on a run I could get was 3.5l per 100km and that was a brand new car. Seemed like I filled up every other day so very pleased to be home!!



Hey folks, Merry Xmas. Another edit so I don't go to the top without anything useful to say...I did figure I will need spacers on the wheels to roughly correct offset as the fibre thickness will be about 40% less than the aluminum. Will have a go at that at some stage....

Hope everyone is doing ok. I was also wondering if anyone replaces their e-cvt magnets?? I figure they may lose flux with heat, mine sure have been heated from time to time...

[Nathan jones]

Just a quick question, I plan to remove my backbox and make a titanium exhaust with two resonators, does anyone know if this although noisier result in less dirty air in the compression stroke of the Atkinson like it does in Otto cycle engines?

[Ecky]

Originally Posted by Nathan jones

Just a quick question, I plan to remove my backbox and make a titanium exhaust with two resonators, does anyone know if this although noisier result in less dirty air in the compression stroke of the Atkinson like it does in Otto cycle engines?

Engine tuning often relies on valve overlap and exhaust back pressure to push exhaust gases back into the cylinder - it's a design feature, not a bug. Any exhaust gases that end up going back in displace fresh air and reduce pumping losses. It's both an economy and an emissions feature.

[freebeard]

Anti-reversionary headers are the opposite to EGR.

[Nathan jones]

Thanks, I'll copy the factory :0)

[alexshock]

Originally Posted by Nathan jones

Thanks, I'll copy the factory :0)

Have you already estimated weight gains of a titanium pipe?

[Nathan jones]

Hi, 10-15kg as a guess, it's only the perforated pipe, resonator, straight parts and backbox (muffler) that will be new materials, I cannot make the bends. I was surprised as Ecky said that after the pressure wave there is a vacuum (with quite a window) which helps clean the cylinder of burnt gases so I will have to keep the original layout and pipe diameter. I wrongly assumed back pressure was to suppress the noise rather than to help combustion