Help me understand, does weight play a HUGE role in top speed?

[DaTT]

A guy told me that his 2000lbs Honda Civic with 450 FWHP would do 180 Mph. I don't believe him. I figure aerodynamics would play a much larger role than weight in top speed.

[Doppel]

It actually plays zero role in top speed, at least once you remove any impact on rolling resistance (which would increase as weight does). It's all about aerodynamics.

I don't know the specific math of what it would take an S2k to hit 180 mph but if his car really has that much horsepower it's probably not far off.

Stock car does about 149 according to a link I found with 237 horsepower, so doubling that I think 180 sounds pretty doable.

[jmarti445]

Gear and Final Drive ratio, Engine RPMs, and Horsepower have a lot to do with top speed. Other things such as co-efficient of drag and surface area also affect top speed. Making a car lighter may have an effect if the Engine RPMs are able to overcome the weight difference but weight has more to do with quickness vs top speed.

[Demo24]

Originally Posted by Doppel

It actually plays zero role in top speed, at least once you remove any impact on rolling resistance (which would increase as weight does). It's all about aerodynamics.

I don't know the specific math of what it would take an S2k to hit 180 mph but if his car really has that much horsepower it's probably not far off.

Stock car does about 149 according to a link I found with 237 horsepower, so doubling that I think 180 sounds pretty doable.

Its a civic, not an s2k.

The limiting factor here is going to be aerodynamics, followed by gearing. All depends on if he put in longer ratios to even have the possibility of spinning the wheels to 180mph, which I kind of doubt. Most likely it probably does closer to 130, give or take some (I have no idea what a stock civic is geared to in 5th, pretty low from my experiences in Honda manuals so maybe more like 115).

[LTC8K6]

Back in the mid 80's, those Nascar cars were hitting 230 mph in testing at Talladega.

Tim Richmond took a Nascar Monte Carlo to over 240mph at a top speed comparo with Al Holbert's Porsche 962LMP, which could only manage 228 on the same track.

The main reason was that the Porsche had a lot of downforce, and the Monte Carlo had comparatively little. Aerodynamics.

The Porsche only hit 212 initially, then managed 228 with a lot of downforce removed, but it still had more df than the Monte Carlo.

Most people think the Nascar cars are "bricks", but in fact they really aren't. And they weren't, even back then.

Had the test been at Watkins Glen for lap times, the 962 would have cleaned the Monte's clock.

[jmarti445]

If it has 450HP and a lower final drive on the transmission it may do 180MPH. The civic is a light car, my 2008 EX does close to a buck 130 stock, I believe the governor is set to 127MPH and I've seen cars without governors do close to 230 kilometers per hour. The Si's rev to 8500 RPMs. The RSX was a great example of this.

[jmarti445]

Get the guy to prove it, talk is cheap

[twinrider1]

Originally Posted by Doppel

It actually plays zero role in top speed,...

This thread should have been locked after the first 8 words.

Zero effect on top speed. It affects the time needed to get to top speed.

[skyking]

zero is a really small number so I'd rather say not much
Here is a handy calculator that will give you the horsepower used by rolling resistance and aerodynamic resistance, all the way to 200 MPH!

http://ecomodder.com/forum/tool-aero...resistance.php
Drop some numbers in and you can see as that Aero drag rises exponentially, the rolling resistance drag just moseys along up a shallow slope.
At the end at 200 MPH with the example numbers, aero is 370 hp and rolling resistance is 7.81 hp

You can find numbers for your car on the web, take a guesstimate on crr. I use .011 for typical tires.

[JCH13]

Taking a known comparable:

MS3 = 263hp,155mph top speed (gear-limited, so this is conservative)

Power required for aero drag is quadratically related to speed: (180mph^2)/(155mph^2) = 135% power requirement to go 180mph

263hp*1.35 = 355hp

Should be doable with 450hp assuming the car is not gear-limited.

[JulesMaximus]

Would that car even be stable enough to drive safely at that speed?

[skyking]

Race cars generate a shit-ton of downforce for handling. That induces even more drag.
I'd say no, not safe in any stock aero form.

[JCH13]

A little bird told me it wouldn't be crash-worthy at 3x the design speed (8x the energy) of the crumple zones...

[skyking]

Fatality!

[DaTT]

I had a hard time believing him because he also told me a 400hp civic can do low 8's. 1/4

[JackBurton]

Originally Posted by DaTT

I had a hard time believing him because he also told me a 400hp civic can do low 8's. 1/4

lol!

[Throckmorton]

Weight is irrelevant but why wouldn't it do 180mph? 450hp is a lot of horsepower and Civics are very aerodynamic.

But I'm guessing his tires aren't rated for that speed, and the aerodynamics will make it dangerous. No, a wing on the trunk doesn't help!

[Pulsar]

Originally Posted by JulesMaximus

Would that car even be stable enough to drive safely at that speed?

Hard to say. Probably not. The problem is usually rear downforce. The front usually has a pretty decent amount just because of the hood slope. Most cars at that speed form a suction as the air flow lifts off the rear window (Bernoulli number, no longer laminar flow, etc...).

The '04 era Mustangs are limited to the speed they are exactly because of that reason.

[Pulsar]

Originally Posted by Throckmorton

Weight is irrelevant but why wouldn't it do 180mph? 450hp is a lot of horsepower and Civics are very aerodynamic.

But I'm guessing his tires aren't rated for that speed, and the aerodynamics will make it dangerous. No, a wing on the trunk doesn't help!

Um... actually a wing on the trunk DOES help.

[JulesMaximus]

Originally Posted by Pulsar

Hard to say. Probably not. The problem is usually rear downforce. The front usually has a pretty decent amount just because of the hood slope. Most cars at that speed form a suction as the air flow lifts off the rear window (Bernoulli number, no longer laminar flow, etc...).

The '04 era Mustangs are limited to the speed they are exactly because of that reason.

I've owned 2 Mustangs and neither one of them felt safe at speeds over 130mph. They get really light in the rear.

Adding a rear wing will help but also creates drag that will further limit top speed.

[Doppel]

Originally Posted by DaTT

I had a hard time believing him because he also told me a 400hp civic can do low 8's. 1/4

V-TEC, anything is possible, crate motor from Japan [overnighted], double-clutching, beef the welds on the manifold etc. it might happen!

In truth can a FWD on the planet even do 8's? Obviously it would need literally magnitudes more than 400 horsepower, but I question whether it could get the traction. A 1000 HP bugatti veyron with AWD does 1/4 in 10 flat.

[Ferzerp]

Originally Posted by Doppel

beef the welds on the manifold

Gotta avoid that danger to manifold.

[JulesMaximus]

Originally Posted by Doppel

V-TEC, anything is possible, crate motor from Japan [overnighted], double-clutching, beef the welds on the manifold etc. it might happen!

In truth can a FWD on the planet even do 8's? Obviously it would need literally magnitudes more than 400 horsepower, but I question whether it could get the traction. A 1000 HP bugatti veyron with AWD does 1/4 in 10 flat.

Apparently they can.

http://www.youtube.com/watch?v=ct36IUKaP5w

[LTC8K6]

Originally Posted by Pulsar

Um... actually a wing on the trunk DOES help.

The trunk lid is not the place for a lot of weight.

[Throckmorton]

Originally Posted by Pulsar

Um... actually a wing on the trunk DOES help.

Yes, it helps traction at the rear, but it will also lift the front