DSM at 180mph

Alright you sunsabitches, I went through the trouble of looking up the CD and frontal drag figures for a 2G DSM, and did the math before I realized that thread was closed :mad: :biggrin: and that's too much work to just drop it, so here you go. Assuming you had the gears for it, a stock bodied Eclipse would need 241.514784 hp to the wheels to reach exactly 180mph. This doesn't include the amount of power needed to overcome rolling resistance to start moving in the 1st place, so about 260 hp to the wheels. AWD would then need to make even more power than a FWD, because of more drivetrain loss.

Of course a stock bodied DSM would never even stick to the road at that speed, and by the time you've added the aerodynamic aids to keep it down, you've increased the amount of power you'll need. So blah.

I'd like to see the equation you used to come up with that figure.

260hp thats seems very low.

My R32 has about 310 to the wheels and she will only get to 160ish. You did mention gears, that does play a big factor, but if the gears are that high, 0-60 sure would sux.

How long would it take to reach that top speed?

Originally posted by YogsVR4
I'd like to see the equation you used to come up with that figure.

so owuld i .. im 15 and this looks fishy.. i think thers a problem

From August '01 Sport Compact Car:

Frontal Area: Amount of Frontal Area (large hood scoops, mirrors and bumper openings add to this and decrease your top speed.

Cd: Coefficient Drag.

Speed: In MPH

HP at the wheels = 0.000007 x Frontal Area x Cd x Speed(cubed)




And from this site http://home.earthlink.net/~jonaa/cd.html which took the figure from Car and Driver:

Car--------------Cd----------Frontal Area
Eclipse/Talon---.29----------20.4




So if you have any gripes about it, don't blame me, blame Dave Coleman. :lol:

i THINK i posted up a vid of a DSM hittin 180+. the whole video is 1:08 minutes long. and the guy who reached it, reached it less than a minute. i dunno how many horses it is to take a DSM to hit 180 mph, but for sure has to be over 240 hp, unless the car weighs like a GEO METRO (not sure bout geo metro weight with DSM power??).

Weight shouldn't change the top speed, just make it take longer to get there.

And with 260hp, it will take a while...

yeah, ya posted that video, but the only time it was confirmed to do 180 was in the title of the video.

if you're talking about the run across the desert, there is no proof from the car's speedo, or onboard ecu, or from a radar gun.

all it is is a video of a car going across the desert.

also.

that car was featured in the fwd vs. awd vs. rwd shoot out in sport compact car about 2 years ago, and it was making 400+hp.

it better have hit that kinda speed with that kinda power.

i don't doubt that car did it, but there's not any proof in the video...

If you had some NO2 you could spray and get their pretty quick even with the long gears.

Originally posted by ldelaysionl
Weight shouldn't change the top speed, just make it take longer to get there.

And with 260hp, it will take a while...

weight does affect top speed because it robs horsepower. if you put a civic engine in a semi with a full trailer i dont think it could even hit business district speed limit (35mph)..

The Nissan 350Z is electronically limited to 160 or 165 but according to gear ratio calculations it can hit 180 in 6th gear.

Originally posted by 90gs


weight does affect top speed because it robs horsepower. if you put a civic engine in a semi with a full trailer i dont think it could even hit business district speed limit (35mph)..

First-off, the motor would blow its tranny and/or itself apart before that tractor-trailer even moves 2-feet. But that doesn't have anything to do with top-speed.

Top-speed is more reliant on a car's drag coefficient(cd), available power, and gearing, so it can punch through the thickening wall of air as the speed rises.

Check this out:

http://www.sportcompactcarweb.com/features/0212scc_speedweek/index.html

The Vortech/Progress Civic Si that hit 204.3MPH in that article had a stock engine with a Vortech blower with about 274FWHP. I say had, because that motor blew during testing...though it ran at a max of 186MPH with it. The motor they had for the 200MPH run was the rebuilt version of the old one, with newer rods and pistons. Either way, it's a motor that somebody from the street can potentially have.

There were weight-reductions done to the car, mostly to the interior, and aerodynamic-enhancements...real ones. The gearing, obviously, was altered, the suspension revised, and the tire size was customized.

The point is, the weight on that car was the least of their worries.

How can you be sure that the major factor was not the weight-reduction?

Originally posted by igor@af
How can you be sure that the major factor was not the weight-reduction?

I have the actual magazine article somewhere and have seen the pics of the interior. Yes, it was gutted, but they couldn't have taken off more than 400 to 500lbs, if that, which still leaves most of the car intact.

They also had a naturally-aspirated car that was street-legal, and mostly stock outside of the engine. With bolt-ons and the right tire combo, that car ran close to 160MPH or more, if I remember right.

I don't know man .. maybe the 400-500 lb weight did act as a major factor. I am going scientific here.

Originally posted by igor@af
I don't know man .. maybe the 400-500 lb weight did act as a major factor. I am going scientific here.

Nah. I doubt it.

Take the case of a GS-R motor in a 2200lb hatch.

Take that same motor in a.........GS-R.

Even though the hatch might get there a bit faster, since it's lighter(weight is a MAJOR factor in acceleration), if they have the exact same mods, tune and wheel sizes, both cars will top out at the exact same spot and stay there. This is with the Integra weighing in at about 400-500lbs more than the hatch.

This is because they have similar frontal areas, and similar power. We are talking about top-end here.

Think gravity. We were all taught in elementary school that two objects, no matter how different their masses are, will always have the EXACT same acceleration when falling, with wind resistance the ONLY variable.

Example: a marble and a bowling ball. Even though the other is much heavier, when dropped, they will accelerate similarly.

Why? Due to their shape, they have similar wind resistance, regardless of their size difference. Because the force causing their acceleration towards the ground is constant and equal(gravity).

Now, if you change the force between them...say you drop the marble from the exact same distance, at the exact same time, on the moon, and the bowling ball on earth.

This configuration is more reminiscent of the top speed factor. The marble, which is lighter, and has no air resistance to speak of, is going to drop a lot slower than the heavier, atmosphere-resisted ball, because, as we all know, the power behind(or underneath) the bowling ball is greater.






There.:biggrin:

Theory is great, you can sit there and talk about it all day long:rolleyes:

Screw theory, Like Nike say's just do it:biggrin:

In a nutshell using those numbers I get 255 hp needed to go 180 mph. But more realistically you need about 300 hp at the wheels. The long story is below.

Vehicle drag is slightly dependent on weight (because of rolling resistance) and independent of gearing. It simply takes a certain amount of power to move a vehicle a certain speed, regardless of gearing.

Let me explain.

There are two parts to figuring out how much power it takes to move a car a certain speed. Here's how you calculate the drag force (using metric units).


========================================
1. Aerodynamic drag (call it D)
========================================

Assuming ambient air temperature (and therefore density) at about 77 F (25 degrees C) and no wind the equation is then

D = 0.5 x Air Density x Cd x Frontal Area x (Velocity^2)

Air Density at ambient is 1.184 kg/m^3

So D = 0.592 x Cd x Area x (Velocity^2)

========================================
2. Rolling resistance (call it R)
========================================

Assuming passenger car tires at 30 psi on concrete.

R = fr x Weight

fr depends on velocity and is calculated with this equation, which was determined from experiments at the Institute of Technology of Stuttgart:

fr = fzero + 3.24 x fs x (Velocity/100)^2.5

From a chart in my textbook fzero and fs are roughly 0.01 and 0.005. So all you have to do is plug in your velocity, frontal area, and drag coefficient and you'll know how much power it THEORETICALLY takes.

So fr = 0.01 + 0.0162 x (Velocity/100)^2.5

Now, different cars are limited by different factors. Some are drag limited, some are gear limited. This equation simply tells you how much power it would take a vehicle to go a certain speed. If the engine and gearing in that car don't make enough power at that speed, then the car is gearing limited.

Assuming the DSM car has a Cd of 0.29 and Frontal area of 20.4 square feet (which is equal to 1.895 m^2) and weighs 3,000 lbs (13,351 N at sea level) then total drag at 180 mph (which is 80.5 m/s) is:

F = [0.592 x 0.29 x 1.895 x 80.5^2] + [(0.01 + 0.0162 x (80.5/100)^2.5) x 13,351] = 2,108 + 259 = 2,367 N (N is Newtons)

========================================
To calculate Power
========================================

Power is Force x Velocity

W = F x v = 2,367 x 80.5 = 190,544 Watts = 190.5 kW (kiloWatts)

1 kW = 1.34 hp so at 180 mph you need 255 hp

Which is all fine and dandy but this is under ideal conditions based on assumptions of drag coefficient, frontal area, tire drag and such.

If I'm not mistaken, drag figures are calculated from wind tunnel models without side mirrors, gaps in the windows and body panels, and smooth wheel covers. These things all contribute to Cd and can increase frontal area. So I think a more realistic Cd estimate for a real world DSM would be more like 0.35 which would bump the HP needed up to around 300. That seems more reasonable.

Most of the drag on a car is the aero, almost 10 times as much as rolling resistance. Hope this clears things up a bit. By the way, these figures are from a textbook called "Fundamentals of Vehicle Dynamics" by Thomas D. Gillespie.

Nice write-up:bigthumb:.


There is rolling resistance, where a heavier body will always exert more stress on it's moving parts, therefore increasing the friction resisting against it's movement (lube up!).

But, just like you said...and especially with modern automotive designs...the impact to ultimate top-speed is minimal, around ten-percent.

The biggest enemy at those speeds is atmosphere. If you have the power to push it despite your frontal area, and have the gearing to take you there, then you're set.

Also, the 300whp claim you made is quite valid. The Civic in my example had over 270 to the wheels when it made it's 186mph run. That's with some weight reduction, and major aerodynamic enhancements.

The heavier, less aerodynamic Eclipse would need at least that.

Thanks for the compliments.....

You went 186 in a Civic?! Wow. Balls out!

I think a Civic has less frontal area than a DSM... do you know what your Cd is?

Hey, here's an idea. If there's enough interest I'll try to put together a script to calculate this so that we can run "what if" scenarios quickly.

What do you all think?

the vid that i put up, im not even sure if that was a DSM. Like wat Flywsi said too. if u want weight reduction for sure if u wanna go 180+, u gotta have down force....then the math part comes i think. Even with 250 some hp, u wont hit 180. im GUESSING around the 350 to 450 hp range, and DSM that can hit 11s could do 180....I THINK

davewin,

Very good post.

I like your idea, as well :bigthumb:

Originally posted by davewin
Thanks for the compliments.....

You went 186 in a Civic?! Wow. Balls out!

I think a Civic has less frontal area than a DSM... do you know what your Cd is?

Hey, here's an idea. If there's enough interest I'll try to put together a script to calculate this so that we can run "what if" scenarios quickly.

What do you all think?

LOL. I wish.

Nah...in a previous post, I used the Vortech Civic that went 186mph on its first motor as an example, then 204mph after they rebuilt it.

Fastest I've ever gone is 159-160 bouncing off the rev-limiter in a Chevy Beretta of all things. The speed was confirmed by my ex-roommate pacing me with his GSX-R 750 on the highway to California just right before Blythe.

I did go close to that in a 1990 Integra with a modified JDM-spec motor, keeping up with an old co-workers YZF. He claimed that he only pulled-away after he hit 160mph (he didn't downshift). I can't confirm that though, so I can't really claim it.

a stock awd dsm can go 160 with 210 hp

Originally posted by tino
a stock awd dsm can go 160 with 210 hp

And a lighter, more powerful SRT-4 can only go to 153MPH radar-verified?

AWD DSM:
3200lbs/210HP to the crank

SRT-4:
2800lbs/220 to the wheels

Weight effects on drag are negligible.

What's important is to know the actual frontal area and drag coefficient of each car, as well as power to the wheels.

And remember that every manufacturer tends to be optimistic on their numbers.

Originally posted by davewin
Weight effects on drag are negligible.

What's important is to know the actual frontal area and drag coefficient of each car, as well as power to the wheels.

And remember that every manufacturer tends to be optimistic on their numbers.

True. I even said so myself above:bigthumb:.

But, it doesn't deny the fact that the SRT-4 has power over-all, stock-for-stock, and has less rolling resistance, since it only has to power two wheels.

His claims are for a stock car, plus I doubt if the SRT's CD is that much worse than the Eclipse's, if at all.

Yeah, I would guess an SRT and the DSM are not all too different in Cd and frontal area. DSM might have slightly less frontal because it's lower (I think) though it seems a bit wider.

Here's another curiosity. What would the true power difference between the 2 cars be if they were dynoed on the same machine under the same conditions?

Does anyone know of a list of Cd and area figures for street cars? I know there's one that covers some sports racing cars and a few sports cars (you'd be surprised how many generate lift instead of downforce, ahem, 911), but I haven't seen one for most regular cars.

http://www.mulsannescorner.com/data.htm

I can get my GTR's speedo to read 200mph. Therefore I must be going 200mph. Speedos are very inaccurate. I have seen Ferrari's read as much a 30mph off at top speed. Speedo 199mph, actually 169mph.

quote:
Example: a marble and a bowling ball. Even though the other is much heavier, when dropped, they will accelerate similarly.

Why? Due to their shape, they have similar wind resistance, regardless of their size difference. Because the force causing their acceleration towards the ground is constant and equal(gravity).


well the shape thing is pretty much right, but the bowling ball would still drag more through the air because of it's size.

The reason two objects of different mass and similar shape fall at the at the same acceleration (9.81 m/s[squared]) is different. The force on the bowling ball is much greater, which is why it weighs more - remember weight is a measure of force, not necessarily mass. However, because the bowling ball is of much greater mass, it takes a proportionally greater force to accelerate it at 9.81 m/s(squared).

So, when the two objects hit the ground, the bowling ball will be at the same velocity as the marble, but it's kinetic energy (M x V[squared]) will be greater.

I also saw some comment on weight/mass robbing hp???
I dont see mass in the equation Torque x RPM / 5250.

Regarding lateral acceleration and top speed, Increased mass will ONLY make it take longer to get there. What we're concerned with is the point that the force of wind resistance equals the force the engine can supply - this does not change with mass.

Look at us, we're in a CAR forum discussing Newton's Laws...

Stay tuned for tomorrows discussion: Does E=mc(squared)?

LOL

a marble will hit the ground before a bowling ball because there is less wind resistance on the marble :biggrin: ...therefore... the bowling ball will hit the ground after the marble:bigthumb:

Don't be dissin' Einstien, Lancaster. :biggrin:

You guys are funny:bigthumb: And smart, I think:confused:

Originally posted by LancasterWannaBe
I also saw some comment on weight/mass robbing hp???
I dont see mass in the equation Torque x RPM / 5250.

Regarding lateral acceleration and top speed, Increased mass will ONLY make it take longer to get there. What we're concerned with is the point that the force of wind resistance equals the force the engine can supply - this does not change with mass.

What I was trying to say :bigthumb:

Not to nitpick, just noticed this after I'd already clicked reply, but it's 5252, not 5250... right? :confused:

5252????
Havn't heard that before....
but hey it's not nitpicking, dude I want to know if I'm wrong....
Anyway, serriously let me know (anyone) what the correct constant is.

Oh yeah SkylineUSA ,
Einstien is du shit man, fo real :bigthumb:

Einstien is du shit man, fo real Agreed

I got around to making the aero drag calculator. Just input frontal area, drag coefficient, vehicle weight and speed and it spits out how much horsepower is needed.

http://www.davewin.com/tech/horsepower_calc.shtml

This is all based on the little write up I did earlier in this thread. Let me know what you guys think.

sweet man, very cool

Originally posted by davewin
I got around to making the aero drag calculator. Just input frontal area, drag coefficient, vehicle weight and speed and it spits out how much horsepower is needed.

http://www.davewin.com/tech/horsepower_calc.shtml

This is all based on the little write up I did earlier in this thread. Let me know what you guys think.

:bigthumb:

Excellent scripting, and awesome site, I might add. My only complaint about your site? No links to AF:eek:.

You should talk to Igor about some kind of partnership. Maybe one of the tech forums or something.