S2 won't go faster than 265 km/h

[quattrostyle]

anybody got an idea what could stop my S2 from reaching 280 km/h like it should?

it goes fine till 200 km/h then it crawls towards the 265 km/h where it ends.

Vids are in this thread: http://www.s2forum.com/forum/showthread.php?t=37234

[EspenW]

Hmmmm... perhaps inadequate level of brake horsepower compared to what is required to reach such rapid velocity?

[quattrostyle]

the webmaster of the Dutch S2 forum did 270 with his unchipped S2 and with broken wgfv. A chipped one should do 280 quite easy.

[Key Walshe]

For those wondering what that is in mph it's roughly 165mph (265/100 x 62.1).

Correct me if I'm wrong, but a standard S2 is pretty much flat out at that sort of speed, so would struggle to pull that extra 15kmh (9mph) you're expecting it too. My Nothelle would struggle to pull that sort of speed and that has an extra 70-80bhp over a standard motor. If it's pulling strong to 200kmh (124mph) and then steadily making its way up to 250 or so then that sounds correct from my perspective.

If your car is not standard, and it isn't 'pulling' like it should, then check for a possible small boost leak.

[Sonic]

sounds right to me unless its has some serious mods done to it?

[S2central.net]

Sounds fine to me too... I did some rough calcs for a 280bhp version S2 and it only went to 160mph something from memory. Aero losses are significant at that speed. An extra 50bhp does not mean an extra 50mph or even 50kph. I'd have to dig up some old maths on this one. Never had a chance to redline mine in 6th - would be quite awesome - but saving that for a nice big fat Autobahn one day.

[quattrostyle]

as can be seen in the intro thread, nothing major. Produces 298 HP and 424 Nm of torque. I don't think it's a big problem that it won't go faster because of the completely stock drivetrain incl. brakes. Well I'll leave it this way then

[Rusty]

Peak power and top speed don't necessarily occur at the same point! If you really want to go faster then just stick a big WG spring in and run 1.5 bar to redline, turbo won't last too long but you should see a bit more speed

[Jonas_R]

Is this measured with GPS or on the speedo?

[Keeper of The Kitten]

265kph seems pretty fast to me! I make that a sniff under 165mph.

I usually explain to people about the drag increasing by the square of the speed.

So if you think of going 35mph as a baseline...

At 70mph, double the speed, the drag will be four times as much.

At 105mph, three times the speed, the drag will be nine times as much.

At 140mph, fours times the speed, the drag will be sixteen times as much.

At 175mph, five times the speed, the drag will be twenty five times as much.

I know this is probably well known amongst many people but it bears repeating.

[quattrostyle]

@Jonas on the speedo as you can see in the video http://www.youtube.com/watch?v=_wTdY3QpN88 in one of the other vids you can see that it goes allright on lower speeds.

The Dutch forum members keep telling me that it should go faster than 265 on the speedo though...

@Rusty that's a nice idea, but honestly I don't even know if I do want to go faster really, the car becomes a bit light in the front at 260.

[UrS4boy]

Speed vs Hp

Further to what Martin suggests, overall, the hp required to push the car through the air goes up with the cube of the velocity. As you pass peak power, you have less and less available power to accelerate the car on its way to the final terminal velocity.

Graphically, it looks something like this:

[quattrostyle]

yeah I do understand that part, but I can't understand why other chipped 3B's do 260+ much easier, don't think speedo's differ between S2's do they?

[quattro84]

Further to what Martin suggests, overall, the hp required to push the car through the air goes up with the cube of the velocity. As you pass peak power, you have less and less available power to accelerate the car on its way to the final terminal velocity.

Graphically, it looks something like this:

Yup, and it's even worse! it's an thirth order function.
Force required to overcome windresistance: Fw = 1/2*Cw*A*rho*v^2
And Power equals: P=F*v
That makes Pw=Fw*v
=1/2*Cw*A*rho*v^2 *v
=1/2*Cw*A*rho*v^3
~1/2*0,32*1,89*1,29*74^3
At 265km/h (~74m/s) makes 158kW which is about 215Hp.

[Jamo]

Your top speed is determined by the gearbox ratios, Have you got a 5 speed of 6 speed?