this is a perfect example of why SFO is THE mega dork......
this is a perfect example of why SFO is THE mega dork......
ProDarwin wrote: SFO: I have a spreadsheet I built for calculating what you really want to know here... what's your email?
Neato!
Celicahalftrac at gmail dot com
Just as a forewarning, i had my rear end ratios messed up.
And i'm now confused about all this, because it would seem that the math isn't explaining my question. Looking at this dyno chart, if the "torque is everything" sect is correct, then this car would be fastest through the quarter mile short shifting at around 4500-5000rpms. (MX6, and yes, i realize that this is not a 600hp motor, nor are we comparing it to one.)
It's not. It's fastest shifting at redline, which doesn't even drop down far enough to ever hit peak torque. Why is this?
oldeskewltoy wrote: this is a perfect example of why SFO is THE mega dork......
This is my own personal "Ignore" thread. 
I can't answer your last question...
Torque is an instantaneous unit of measure. It does nothing for "accelerating". Horsepower is taking torque and adding in teh "time" element. Therefore, Horsepower is the item you seek.
However, instantaneous horsepower is not relavant to answering your question either. This is because you are at that horsepower value only during that short time you are at that rpm.
If you had a CVT, "instantaneous horsepower" would mean everything.
Because of the above, you need to look at the entire picture of the engines operating range. Computing the area under the curve gives you an idea of how much "overall horsepower" the engine is making.
Let me know if this is making sense.
Rob R.
Let me change something...
If you really wanted to compare the two engines, you would only look at the area under the curve where the usable rpm is.
What I mean is that if you shift from 1st to 2nd at 6000rpm, and the rpms drop down to only 4000 rpm, that is the range I would be looking at.
The other engine, using the same gears, may only use 6700 rpm to 8500 rpm. Take the area under those parts of the horsepower chart and compare them.
The larger area is the faster accelerating car.
Rob R.
An interesting way to look at torque and horsepower:
Torque is how much weight you can pick up.
Horsepower is how quickly you can pick it up.
Swank Force One wrote: We know the transmission ratios (posted earlier this page) and the drag will be the same, since they're the same car.
Then you can get as far as which cod ranges would make which car top out faster, the cod at which they will both go equally fast, etc, but not the actual speed.
wvumtnbkr wrote: Let me change something... If you really wanted to compare the two engines, you would only look at the area under the curve where the usable rpm is. What I mean is that if you shift from 1st to 2nd at 6000rpm, and the rpms drop down to only 4000 rpm, that is the range I would be looking at. The other engine, using the same gears, may only use 6700 rpm to 8500 rpm. Take the area under those parts of the horsepower chart and compare them. The larger area is the faster accelerating car. Rob R.
More rhetorical things, but here's example:
Car A makes a flat 600hp from 7000-9500. This covers the RPM drop each time shifting at redline.
Car B makes a flat 600hp from 5500-7500. This covers the RPM drop each time shifting at redline.
Car A has a shorter gear due to higher RPM to keep target top ground speed equal.
Do they accelerate at the same rate?
I think that would come back to bradyzq's post on the first page:
bradyzq wrote: Car B is accelerating harder at 6500 than Car A is at 8500RPM. A: 600 *5252/8500 = 371 torques @ flywheel * 3.9:1 rear end ratio = 1447 lb*ft at the wheels B: 600*5252/6500 = 485 torques @ flywheel * 3.23:1 rear end ratio = 1566 lb*ft at the wheels So, Car B is accelerating 8% quicker.
In reply to Swank Force One:
Yes.
In reply to Swank Force One:
Yes! Yes they do! Spot on!
I am ignoring drivetrain losses, time spent shifting, etc... Just confirming that if they each are making a steady 600hp during the acceleration contest, they will accelerate equally.
Well.... i suppose that makes sense, but it doesn't make me happy.
Kenny_McCormic wrote:Flight Service wrote: I am gonna be the ass here. Faster as a noun infers top speed. B given traction can be obtained as the same as A. B is Quicker and FasterWe don't know the coefficient of drag, or the transmission ratios, thus we cannot know that either.
Everything else is the same, I thought. Tire traction is the only that comes to mind that would be able to be in the middle.
Either way I think we have determined the lower RPM engine is stronger
or after reading the other posts they are the same.
Let me give a good example of why Torque is what we should be looking at not the HP.
A push boat has 1200 hp. Some fishing boats have that and more.
Will a 1200 hp outboard fishing boat push a barge the same as a 1200 hp push boat? No.
Why? smaller props? Well that is partly to blame but the torque is different as well. One is 1200 hp at 1900 while the other is at 6000.
Which is the higher performance engine? outboard hands down.
We have simplified this to the point of being almost useless but B will accelerate faster, because if it follows the normal automotive torque curve it will have more power over more of the power band meaning it will have less drop in power over the assumed "equal" RPM drop during gear changes.
Swank Force One wrote: More rhetorical things, but here's example: Car A makes a flat 600hp from 7000-9500. This covers the RPM drop each time shifting at redline. Car B makes a flat 600hp from 5500-7500. This covers the RPM drop each time shifting at redline. Car A has a shorter gear due to higher RPM to keep target top ground speed equal. Do they accelerate at the same rate?
Yes.
The good news is that Car A is less likely to assplode the transmission. Although the synchros may work harder due to the larger speed differential.
oldeskewltoy wrote: this is a perfect example of why SFO is THE mega dork......
Well of course! Why do you think im posting in here? Im just bumping my post count for higher dork status! It's certainly not like my factually correct arguments are swaying opinions or anything productive like that!!
In reply to Flight Service:
We can't know which will have a higher top speed because we cannot know if one or the other will run out of gears first, or if drag will reach equilibrium with power before then. Remember that most 6 speed Corvettes top out in 5th.We can only calculate things like limits of drag for one or the other to win out, or when both will top out at the same speed. There are too many variables and not enough equations.
10 engineers walk into a bar...
To the optimist, the glass is half full. To the pessimist, the glass is half empty. To the engineer, the glass is twice as big as it needs to be.
Normal people believe that if it ain't broke, don't fix it.
Engineers believe that if it ain't broke, it doesn't have enough features yet.
luv you guys.
Swank Force One wrote: Well.... i suppose that makes sense, but it doesn't make me happy.
Welcome to my world. Just wait until you start doing stupid things like running lower final drives and shorter tires just because you have some inertia advantage with that setup over more gear and more a heavier wheel/tire. It gets nutty really fast.
Stop thinking and just turn the boost up 2psi. It'll do exactly what you think it will do.
Hey Swanky:
What is the real question?
Forget HP, torque, and ratios.
Are you trying to go faster? Off the line, or top end in the quarter mile?
Or are you trying to increase the rpms at peak?
Are you trying to size the rear end to accomplish something?
Are you trying to build a motor to match a particular profile?
Or are you trying to pick up a hot babe on this site who goes crazy when you talk about power and rear ends?
Based on his other thread, that girl digs high revs too.
I'd just gear it to match what the engine in question is more "naturally" capable of and avoid exotic custom rods and such. The F2T is going to be happier living with a ~7200 RPM redline, it makes good torque, I say gear it around 3.50ish at the rear end and focus on other things.
Kenny_McCormic wrote: In reply to Flight Service: We can't know which will have a higher top speed because we cannot know if one or the other will run out of gears first, or if drag will reach equilibrium with power before then. Remember that most 6 speed Corvettes top out in 5th.We can only calculate things like limits of drag for one or the other to win out, or when both will top out at the same speed. There are too many variables and not enough equations.
Everything is the same was listed as the original statement. The only difference is the power curve of the two engines.
The final drives are different.
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