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All motor vs supercharged vs turbocharged

Old 01-16-04, 02:15 PM
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All motor vs supercharged vs turbocharged

Okay I had a general question thats been lingering in my mind for the past week regarding how horsepower is produced from different applications, and which is the best in terms of speed. And mainly this question refers to a scenerio that would apply in a straightaway.

If I had 3 vehicles all the same weight and each producing exactly 300 hp at the wheels ungoverned, and all the drivers performed exactly the same. One was an all motor high compression car, the other was supercharged and the last was turbo charged would they produce almost the same exact 1/4 times, and would they be almost exact all the way down the line.

Obviously there are going to be differences in terms of torque and rpm peak power. Which I would also expect to be duiscussed here. But I am basically trying to get an idea as what would out perform what, or if that would even be the case.
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Old 01-16-04, 02:43 PM
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Well, there's a LOT of factors that would have to be determined.
The size of the turbo, motor, and supercharger would determine the actual "area under the curve" which is what really determines the maximum acceleration.
The truth is- whichever motor produces the largest area under the curve through the RPM band that you're concerned with will win.
Assuming the areas are identical (a near impossibility), the N/A car should win because it lacks the turbo lag (as insignificantly small as it may be). Even 1/100th of a second of lag will be more than the N/A car has- and thus the N/A car will win. Again- given identical HP and TQ curves which is NEVER going to happen.
Vague enough for you?
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Old 01-16-04, 02:49 PM
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Re: All motor vs supercharged vs turbocharged

Originally posted by lopedl
If I had 3 vehicles all the same weight and each producing exactly 300 hp at the wheels ungoverned, and all the drivers performed exactly the same

It doesn't matter. All the motors make the same power.

In the real world the motor that can get to it's power curve more quickly and stay in it the longest will win. We always talk of peak hp but that's only a small story. A motor that can make nearly its peak power over a much wider rpm band will always have advantages, not the least of which is being easier to drive and gear.

THis sketch represents a simple dyno plot. Both motors make the same peak hp, but the one at the bottom has a much wider power band and is preferable in every case. It's normally a good trade off to give up a little peak hp for a wider powerband; dragracing being a possible exception. Again given the context of your question though the motor with the wider power band will be easier to balance on the edge of tire adhesion and will not bog as easily at gear changes.

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Old 01-16-04, 03:31 PM
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I see so the wideband will actually get you ahead while the other guy is still shifting to the next gear after he reaches his peak on a shortband.

Which would also apply to rpm peaks if I'm correct because if your able to rev up to your peak say 9,000 without dropping off of the band, that can put you ahead as well while the other guy is having to shift on another gear because of his peak at 6,500.
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Old 01-16-04, 03:47 PM
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Originally posted by lopedl
I see so the wideband will actually get you ahead while the other guy is still shifting to the next gear after he reaches his peak on a shortband.

Which would also apply to rpm peaks if I'm correct because if your able to rev up to your peak say 9,000 without dropping off of the band, that can put you ahead as well while the other guy is having to shift on another gear because of his peak at 6,500.
Correct on both accounts. The area under the curve is the deciding factor.
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Old 01-16-04, 03:48 PM
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Old 01-24-04, 04:03 PM
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It is also going to depend on the car. If they are al the same car then its just the power band that you will have to take into consideration. If they are not the same car then you have erodynamic issues. Also you have gearing, hp is hp, how you get it to the ground makes a diff if you 293 gears it will take you longer to get thru you gears putting more load on the motor compared to 456 gears.
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Old 01-24-04, 05:59 PM
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It doesn't matter. All the motors make the same power
so you say that if I put a 500Bhp motor in a 100lb go-kart, and another in a 10,000lb tank - it wouldn't matter?

Can you tell I'm being awkward?
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Old 01-24-04, 08:56 PM
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You're not measuiring HP/weight, you're measuring acceleration.

Acceleration is affected by the inertia of the entire system - including all the mass that has to be accelerated.

Rotating inertia goes up with the square of the RPM. Or to put it another way, there is twice as much rotating inertia at X rpm as there is a .707X rpm. (Twice as much at 10,000 as there is at ~7000, twice as much at 8000 as there is at ~5700, do math as you see fit) What that means for us is that if you can bring the powerband lower in the RPM range, even by a thousand RPM, the engine will be able to better accelerate the car because it isn't wasting as much energy in accelerating itself. Plus, the lower gears generally visited with higher RPM engines means that the engine has to change its speed
more drastically. (easier to accelerate an engine from 5000 to 10000, or from 2000 to 4000? Either one is doubling speed. Just as an example...)

Also note that the "engines" rotational inertia applies to everything whose RPM is affected by engine speed and not road speed - the clutch, the trans input shaft, the countershaft, all of the gears on the output shaft... also all the accessories on the front of the engine....

Saying "a turbocharged car" or "a supercharged car" that makes 300hp is a bit vague - at what RPM? But my guy feeling is, given proper gearing for each individual case involved, and a 300hp limit, the engine that revs the lowest will be the quickest.
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Old 01-24-04, 10:36 PM
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Originally posted by chairchild
so you say that if I put a 500Bhp motor in a 100lb go-kart, and another in a 10,000lb tank - it wouldn't matter?

Can you tell I'm being awkward?
I believe we were assuming equal chassis for each engine... The idea was to compare engines.
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Old 01-25-04, 08:28 AM
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Originally posted by chairchild
so you say that if I put a 500Bhp motor in a 100lb go-kart, and another in a 10,000lb tank - it wouldn't matter?
I'm saying I read the guy's question and found it clearly says "If I had 3 vehicles all the same weight ..."
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