Limited?

As far as I am aware the only limiters fitted are those that restrict higher end cars at 155 mph.

There is a new kind of limiter on the E60 M5 that has a "second limit" of about 167mph though.

I assume the revlimiter is set at 6500 in which case when your doing 3.25 in 5th multiply it by 2 then that's your theoretical top speed.. Mind you since the power band drops off dramatically I'd assume you wouldn't have enough power to go much faster then the 149 anyway.. however down very long straight hill wind assisted... you never know...

Starfury, a cars top speed is determined by it's gearing and aerodynamics. A car will not go much past it's peak power, depending on how quickly power drops off after this. Top speed will probably be how fast the car is going in top gear at around peak power RPM. Even if you doubled the power output, if it's developed at the same RPM you will not increase the top speed. However once you reach a certain speed the wind resistance also will stop the car getting any faster. Wind resistance is very hard to overcome and normally determines how fast a car will ever go regardless of power or gearing. For example a mark 1 Escort hits a wall of wind resitance at 140mph. Even with a 400bhp cossie motor it will not go any faster.

The Honda Civic has a similar top speed, because of it's gearing and power curve. Also it may only have a 2.0 engine, but it does have a higher power output than the 2.8. The weight difference will affect acceleration but have very little effect on top speed. 

Finally speedos are nor very accuruate. This inaccuracy increases the faster you go. As a rule of thumb it reads 10% positive, so if it reads 150mph, you may only be doing 135mph.

As has been mentioned, it comes down to power, resistance, gearing and weight. The required power squares with the increase of resistance (if i remember right), so doubling the speed requires four times the grunt.

The gearing comes into it when you hit the redline/limiter or whatever and where abouts in the powerband you are.

My M3 is limited to 155, but it would probably go slightly higher (maybe close to 160) before you hit the redline. That's (on paper) got about 290bhp, delivered at 7k rpm.

My wife's Leon Cupra isn't limited - book speed 142ish - and when you get close you just hit a wall where the resistance from air/road cannot be outweighed by the power available. And it's still a way off the redline. That one's about 180bhp at 6.5k rpm(ish) and a LOT lighter than the M3.

So two cars - 110bhp between them, and probably 18mph difference in the top speed! But it's an unfair comparison as the M3 weighs about 300kg more, is a different shape and geared differently. 

brybusa - I'd be surprised if the 330 could get that high, but as has been correctly stated any model that can exceed 155 is limited to that anyway. An agreement between BMW and Mercedes IIRC.

Peter Fenwick wrote:   Finally speedos are nor very accuruate. This inaccuracy increases the faster you go. As a rule of thumb it reads 10% positive, so if it reads 150mph, you may only be doing 135mph.

as a genral rule of thumb ..id agree with you on this one ..but i was amazed to see 190 mph on the clock of a motorbike of mine while doing some track days in the past ...and i thought yeah what a load of old tosh .the bikes only tested at 182mph..so i thought just another over happy speedo...but the speed gun on the start /finish straight had me clocked going through at 188mph to 189.4 mph ...so upon untill that day i would agree with you ..but .on that particlure track day ..id have to disagree with you pete .lol

Bike speedos generally are far more accurate than car ones, especially the newer digital ones...if the bike in case was good for a true 182MPH, 190MPH on the clock is a good level of accuracy id say.

the most recents tests of the new Ducatis have showed a near 100% accuracy

Anyway, e46 330 coupes,whaddya reckon they would do with no limiter?..Im guessing 155.5MPH...!

NewBMWOwner wrote: I've managed 140mph from my 323 Saloon, with a little left, that's from a 170bhp engine, I would imagine the 328 would easily reach 150 and behond with 193bhp on tap???

It takes a lot of extra power to go another 10mph. The top speed of the 328 is determined by the gearing and the RPM that the power peaks at. Since power dies off quite quickly once you get past 5000rpm it ain going to go much past 5k in top. If that equates to 145mph or so then that is as far as it's going to go. As I have said before it doesn't matter if you have 193bhp or 1093bhp, if it peaks at 5K rpm then top speed will be determined by how fast that equates to in top gear.