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01-23-2008, 08:56 PM | #1 |
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How to measure an Engine's ability to Rev Quickly?
In looking at the performance of the E92 M3, there are things that can easily be measured.... HP, Torque, Area-under-the curve.....
But my question is that one of the beautiful design elements of the S65 V8 is how freely it revs and how quickly it revs. As you know Revs determine the output of an engine. The higher the revs, the more power an engine produces. If want to understand the basics of the how horsepower is calculated, please do a search..... So my questions are....
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01-23-2008, 09:25 PM | #2 | |
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Quyci revving vs. acceleration
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01-23-2008, 10:05 PM | #3 |
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what greg said, but add torque.
on the other hand there is also throttle response. the M3 should have great throttle responce with the 8 individual throttles.
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01-23-2008, 10:32 PM | #4 | |
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This is what is troubling me..... An engine with a heavy crankshaft can have the same power output as an engine with a lighter crankshaft at steady RPM but the engine with a lighter crankshaft will change revs faster over a period of time since there is less inertia to fight....this would mean it will get in the power band quicker, which means faster acceleration. Anyone else want to chime in? I am truly confused.
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01-23-2008, 10:38 PM | #5 |
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Rotational inertia is just another type of load the engine experiences. It is not any different than hauling a trailer, climbing a hill, or pushing through air in the sense that they are all loads the engine needs to oppose. The only difference is that rotational inertia only becomes a load during acceleration. It is a non-issue if the engine is running at a steady rpm. An engine accelerates/revs faster when it experiences less "total" load.
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01-23-2008, 10:42 PM | #6 |
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yes - the less weight of the rotational mass of the engine parts will result in faster acceleration and that will also show up as higher HP and TQ.
you are not confused. you are on the right track. but the actual measurement is still HP and TQ.
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01-23-2008, 10:47 PM | #7 | |
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Understood.....using the heavy vs. light crankshaft example below....we are talking about the rate of change in revs. At a steady RPM, the only thing the engine is fighting is internal engine friction (plus the load on the drivetrain). At a steady RPM, it is not dealing with the inertia of say heavier components. When constantly changing RPMs, the air-fuel charge would be better used to accelerate rather than overcome inertia caused by heavier internal parts. Not trying to argue, I would like to get a better understanding....
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01-23-2008, 10:55 PM | #8 | |
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01-24-2008, 11:33 AM | #9 | |
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01-24-2008, 01:15 PM | #10 |
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An engine with less internal inertia will be a quicker engine if all other factors are equal(HP& Torque) as it will have less resitance to change speed.I know this from 1st hand experiance with a E30 race car many years ago.We went from a 30 lb flywheel to a 12 lb one in combination with a 3 puck lightweight clutch setup.The car was a joy to drive with the lightweight setup and the speed of the shifts and braking was improved greatly.In quanitive terms we picked about a second in lap times on a 1.30 lap and over 7kph at the end of a 1 km straight.But on a dyno (not a dynojet) it showed no difference in RWHP or torque.A reduction of rotational weight is almost is a free lunch!
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01-24-2008, 02:51 PM | #11 | ||
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Chonko, any comments on Gearhead999s response? Are all 400 hp engines equal?
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01-24-2008, 06:26 PM | #14 | |
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I understand what you are saying and is absolutely correct but these are second degree variables. Fundamentally, engines do not generate HP, they are actually generate Torque. The torque generated at any rpm is what drives the shaft. Power is how fast that Torque can be applied within a time frame, ie torque applied per unit time. So HP relates to efficiency of the engine, how fast the engine takes in fuel, and how it quickly expels the burnt fuel. If an engine can perform this cycle faster than another with the same amount of fuel intake, then that engine will naturally have more Power. Like you rightly pointed out, at the engine the mass of the components(piston+cylinder heads etc) in the combustion chamber does affect the amount of energy(torque) that is required to initiate motion. |
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01-24-2008, 06:42 PM | #15 | |
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1. 3.0 litre V6 with 200 ft.lbs with 300 HP 2. 3.0 litre V6 with 200 ft.lbs with 250 HP Engine (1) will be the faster revving engine. All 400 HP engines are not equal as you will have normalize for the displacement- the engine with the higher HP/litre will be the faster revving engine. I will say the engine with the higher HP/litre is the most optimized engine. |
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01-24-2008, 06:47 PM | #16 | |
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Very interesting discussion....can you please explain your statement above?
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01-24-2008, 07:18 PM | #17 | |
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A good example to my statement is the RS4 engine and the M3 engine. 1. 4.2 litre V8 with 414 HP 2. 40 litre V8 with 414 HP. Just looking at the HP numbers will tell you nothing about the engines, however when you normalize for the displacement: 1. 414/4.2 = 98.57 HP/litre 2. 414/4.0 = 103.5 HP/litre After normalizing for the displacement you can see the difference in the engines- this is purely from the engine perspective decoupling gearing and transmission. The second (m3) engine is a more optimized than the first (RS4) engine. |
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01-24-2008, 07:46 PM | #18 | |
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I have been around hottrodded V8's most of my adult life and I can not wait to get my hands on M3 engine as it is an engine that I have allways tried to get emulate with modding.Geez over 100bhp litre normally aspirated and with warranty! |
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