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 08-29-2021, 04:05 PM #231 (permalink) Master EcoModder   Join Date: Dec 2018 Location: england Posts: 279 Thanks: 31 Thanked 115 Times in 100 Posts 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
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 08-29-2021, 05:07 PM #232 (permalink) Master EcoModder     Join Date: Jan 2017 Location: Istanbul Posts: 1,243 A3 - '12 Audi A3 Thanks: 65 Thanked 225 Times in 186 Posts 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.
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 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.
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 01-11-2022, 06:12 PM #235 (permalink) Master EcoModder   Join Date: Dec 2018 Location: england Posts: 279 Thanks: 31 Thanked 115 Times in 100 Posts 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?
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Quote:
 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.

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 01-11-2022, 08:25 PM #237 (permalink) Master EcoModder     Join Date: Aug 2012 Location: northwest of normal Posts: 24,369 Thanks: 6,884 Thanked 7,751 Times in 6,339 Posts Anti-reversionary headers are the opposite to EGR. __________________ . . Without freedom of speech we wouldn't know who all the idiots are. -- anonymous poster ____________________ "Stuff just keeps on getting older...." -- Graham Hancock ____________________
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 01-14-2022, 05:54 PM #238 (permalink) Master EcoModder   Join Date: Dec 2018 Location: england Posts: 279 Thanks: 31 Thanked 115 Times in 100 Posts Thanks, I'll copy the factory :0)
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 Originally Posted by Nathan jones Thanks, I'll copy the factory :0)
Have you already estimated weight gains of a titanium pipe?
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 01-23-2022, 05:13 PM #240 (permalink) Master EcoModder   Join Date: Dec 2018 Location: england Posts: 279 Thanks: 31 Thanked 115 Times in 100 Posts 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