MX-3.com

ok i got a new speed record for my mx3 the other night...230km/hr...i was going over the burlington skyway,,for those who know where that is...

-126mph with the DOHC B6. Just intake and exhaust, no A/C or power steering.
-165mph on my Stealth TT (that sold though so yeah) lol
-BP with ITBs + less weight = who knows? will see soon

ElectricEnergy wrote:Why does everyone seem to think your top speed has anything at all to do with how much work you put into the engine? Its just the gearing. If you give it enough time, a K8 will max out at the rev limiter (I know, I've done it :p). Unless you've modified the engine to allow you to rev higher, or modified the transmission with taller gears, everyones top speed on this site should be the same.

I don't see that being the case. My old K8, despite I was running out of road, was steady at a max of 190km/h

My ZE, my top speed depended on the weight. I could hit 240km/h just myself, but when I had my not-so-lightweight-girlfriend (of the time) with me, loaded with my car-show gear, she couldn't go faster than 220km/h. Once was racing a Prelude on the QEW and I couldn't catch up to him, the other was a Civic that I destroyed on the Burlington Skyway, than I backed-off since obviously I was speeding excessively and figured I showed him, than he had the nerve to fly by me and flash his 4-ways.

dunno if i posted here.. but i reached 140 in my mx3 klze turbo and it was FAKING SCARY and I tought my engine was going to blow up...


it ea like at 7k rpms. I beat the hell out of a dude who was picking on me for a few months


since then i have the engine out for clutch and other work and it seem pretty fine..

I dont recommend 140!

No matter how much people say it, weight has nothing to do with top speed.... because weight itself is a downward force, and downward forces do not affect lateral forces.... Friction is also neglible, when talking between the bearings.

So that's why [drag] race cars are made of only steel & glass, and they don't spend ANY money on carbon fiber, Lexan, Aluminum, Titanium, Microporous Ceramic, Thermal plastics, Fiberglass..... And Olympic bicycles weigh about 16 lbs, and cost $100,000, and they put gas in the tires that is lighter than air. If you say it's for accelleration.. Drag racing is just top speed within parameters.

Drag cars are all about changing their speed. Bikes also change speed (with every pedal you accelerate a little bit, and when your legs are at top and bottom, you're slowing)

Top speed does not equal acceleration. Drag racing has everything to do with acceleration, and few cars who drag race ever hit their top speed. Why doesn't anyone understand? lol...

I suppose, if you're talking the top speed achieved in a drag race (with distance constraint), then yes, mass matters. But if you have an infinitely long road, your top speed will be the same wether you poured concrete in the trunk or not.

Ryan wrote:But if you have an infinitely long road, your top speed will be the same wether you poured concrete in the trunk or not.

but don't you need more HP to pull more weight?

I challenge anyone to find, anywhere, any intelligent source, aside from their own brain, that says/proves that weight affects ultimate top speed in any significant manner. We're talking wheels here, too. Flat ground, in an atmosphere.

The only thing more HP would get you is more speed. The main factor working against top speed (I would say 99%) is wind resistance. The more HP you have, the harder you can push against the wind, the higher your top speed.

Simple rule of physics - Horizontal and vertical forces do not affect eachother. (although friction is a force that works horizontally (usually) but changes based on the normal force.) Friction doesn't play a big role here. I bet you you could spin the tire of your car with your tongue.

Ryan speaks the truth. Top speed is when the magnitude of the force of aerodynamic drag is equal to the magnitude of the applied force, or when you simply don't have enough revs to keep accelerating. Now if I remember physics class from last year correctly, Fnet=ma (Fnet is the net force, m is mass, a is acceleration) when acceleration stops (all forces in equilibrium) Fnet=0m, therefore Fnet=0. No matter what the mass is, Fnet will always be zero. So no matter what the mass is, you'll still need the same amount of applied force to reach equilibrium.

I hope this makes sense, if not, I'll just leave to to Ryan and just back him up.

C'mon, right?

Trust the guys who are still in Physics classes

It's been a while since i've been in school, and we've mentioned this already in the 1000mph car thread, but it doesn't make sence. I know an extra ~300lbs shaves about 20km/h off my top speed. I understand your formulas, but I believe your arguments are fundamentally flawed for the fact that it's impossible to hit your top speed instantly. Your formulas balance themselves out because your talking about a vehicle sustaining a specific speed, but it doesn't matter if your trying to increase your speed by 100, 10, 1, 0.1 etc km/h, you still need to accelerate from the previous speed to your new speed. A change in speed in a positive manner, no matter the amount, is still an acceleration.

So yes, your HP is irrelevant in determining your top speed, but you need horsepower to overcome all the forces to accelerate to that specific speed, which involve wind resistance and weight. A good example would be when Fieromx3 put a DE mated to his automatic tranny. I had calculated (and correct me if i'm wrong) that the theoretical top speed would be, if I remember right, about 174mph @ 7000rpms, because of the long gearing of the 4-speed, if I did the math right. An Mx-3 would never hit that speed no matter how much road you gave it, K8 and probably not even a DE/ZE. Even if you watch the top gear episode where James tested the top speed of the Veyron, it has to use everything of it's 1001hp to Even in that same video, James mentions that it takes only 270hp for the Veyron to get to 155mph, and you need another 730hp to hit 250mph. By your math, technically the Veyron should be able to hit 253mph with just that 270hp...and you watch how hard it is for that car to hit 407km/h from 400, and hitting 407, it still looks to have a few hundred rpm left before it hit it's "redline" (I don't know what the rev limiter is however).

En bref; yes your math is right, but regardless, you always have to accelerate to your speed.

But the acceleration will always happen. The more weight will make it slowler, but you'll still get there. Just because he doesn't hit the rev limiter, just means his engine physically can't overcome the wind resistance. Exactly how it is with the veyron, the first 150mph is easy, but the ratio isn't the same throughout the spectrum... Air resistance is very complicated, so I won't bother trying to explain the calculations (mainly because I've never bothered the learn them) but I know, the resistance at 100mph is not doulbed at 200mph, its most likely squared.

We're talking top speed, meaning no acceleration. As soon as the forward force applied by the engine matches the wind resistance, it levels out, and thee force on the car boils down to 0 laterally. To get to that top speed, yes, you need to accelerate. Losing weight will make the process faster, but not matter what you weigh, your surface area/drag coefficient is what limits your utimate top speed.

This really is the same thory of dropping a flat piece of paper, and a crumpled one off of a tall building. Or dropping a regular golf ball, or one with lead injected into it. Its been proven hundreds of years ago.

Air resistance is more logarithmic, it's far from linear. At very high speeds, power is used almost completely to fight air resistance, since acceleration is so low not much force is used to fight inertia. Ryan just reminded me, no matter what the object is, it will fall at the same speed in a vacuum (no air resistance). That also reminds me of how we combined some equations and eventually the variables for mass were simply removed during simplifying because they canceled each other out. Again I don't remember the specifics, sadly.

I know it's a hard concept to grasp, took me a while to get around it too because you grow up for so long assuming the opposite.

Ryan wrote:No matter how much people say it, weight has nothing to do with top speed.... because weight itself is a downward force, and downward forces do not affect lateral forces.... Friction is also neglible, when talking between the bearings.

actually it does. It takes more torque to propel your fat friend, gf, mom etc.