General Top speed RR vs Track.

[Rustbucket]

Fiddling with the beast Friday and ran it down the local track with timing gear etc. Did 140 on the board which is very close to the speedo reading in the car.

However just had it on the RR for some fiddling and the guys are adamant that the top speed is around 125(!) according to their magic rolling machine.

Who's taking the P*? 125 isn't a million miles off the balls out figure for a standard 130 Hp Barchetta and mine puts 200Hp down on the road.

 

[dave]

what does satnav say?

 

[bumble]

Sounds evasofast to me. I did nearly 55mph today.

 

[Rustbucket]

Legal speed is huge fun..curiously 140 in car feels extremely quick (arse twitching) when you get the corner or braking combo wrong and watch the world come at you ..sideways.

Curiously 250mph in our club Cessa turbine feels awful slow...

 

[Nino_1975]

Car Speedos are less accurate the faster you go, especially over 100mph. SatNav will not give a correct reading ether.

If you have a cover over the KPH then you are more than likely driving 10mph less than shown. Mine showed 145mph and my friend who kept up with me said his car showed 135mph.

I would say the B can do 125 - 130. This also depends on Air flow, exhaust etc. Mine can do slightly more due to some mods, but 145 is max, down hill with the wind behind me.

 

[Rustbucket]

Just curious to see what the top end is with an extra 70Hp through the existing gearbox/drivetrain. 16VT coupe engine has a top end around 140Mph in a body weighing 1.3T. I'd have though that in the B shell, being small and lighter, should be good for 150? WikiP lists a standard B top whack at 120 altho I think this is low?

Maybe just not getting the power down? I've already noticed an appetite for front tyres and I don't push it any harder than before the conversion.

 

[Nino_1975]

Just curious to see what the top end is with an extra 70Hp through the existing gearbox/drivetrain. 16VT coupe engine has a top end around 140Mph in a body weighing 1.3T. I'd have though that in the B shell, being small and lighter, should be good for 150?

Maybe just not getting the power down? I've already noticed an appetite for front tyres and I don't push it any harder than before the conversion.

Well not really. The Lotus elise is 118 BHP, power to weight makes it quick, but the top speed is only 140mph.

I had a 5ltr American car which was slow as BEEEEP.

VW have a 1.4ltr 170BHP Polo.

Just because you increase the BHP does not mean it will be quicker. Down force, Traction, Weight and the list goes on.

 

[Rustbucket]

Interesting. In this case I suspect its weight/traction. Acceleration is now very good, boot in the bum jobbie when the turbo comes in. Downside is doing anything energetic in the wet results in the back end flicking out and a trip sideways to the hedge.

I'm going to investigate some form of traction control..got any ideas without doing a complete drivetrain rebuild?

 

[Nino_1975]

OOOOO Forms of traction would be good, let me know how you get on.

Main issue it getting the front to stick.

The cars handling is the 1st thing to upgrade, down force and weight, breaks suspension. Spoilers slow the car down going in a straight line; they are only for cornering only.

Without my hard top I have got my car weighing in at 990kgs.

 

[s130]

GPS based speed is accurate to 0.1mph

So a quality hand help GPS unit sitting on the dash is accurate. e.g. Garmin GPS12 (now an old model)

A decent Sat Nav system uses GPS & internal gyro. In theory a decent Sat Nat spped signal should be accurate to 0.1mph as well.

The only other alternative to to drive down the motorway at an indicated 60mph and count the 100m markers passing the windscreen A post. Stop watch time 16 markers.

This the will be a mile distance so for ever second over or under will be about 1mph error. If there is a large error like 10 seconds then things get a little more complicated to calculated. The contast is the 1600m. After that is is down to time and calculation.

If you are feeling brave then try the mile run at 60mph and 120mph (in Germany) to check linearity.

Failing that hire a calibrated 5th wheel.

 

[s130]

Forces like drag, wind resistance, rolling losses etc. tend to follow a square law so putting 50% more BHP (say 150bhp to 200bhp) is not going to make a massive difference to top speed.

e.g if a 100bhp car tops out at 100mph then the same car with 150bhp will top out are approx. 122.5 mph.

At this end of the scale we a talking pure rate of doing work against a square law load.

Zimples

 

[desert rat]

Have checked my speedo using a Garmin GPS unit... at normal high highway speeds it seems to read about 5 mph slower than the speedo reading..

 

[s130]

This is pretty normal for most cars. The speedo will tent to read 5 to 10% low at or around 70mph.

This is good becuase if you do 100mph on your speedo then you will definately be on the safe side to 70+30mph = 100 mph tue or +30 over a limit side of getting an automatic court appearance and almost certain ban.

I set the speed warning beep on my Croma to 85mph. I know this to be about 77mph which is 70 + 10%. When it beeps I know I'm entering the danger zone and need to accordingly "scan" more seriously/aggresively.

 

[afroking]

Just curious to see what the top end is with an extra 70Hp through the existing gearbox/drivetrain. 16VT coupe engine has a top end around 140Mph in a body weighing 1.3T. I'd have though that in the B shell, being small and lighter, should be good for 150? WikiP lists a standard B top whack at 120 altho I think this is low?

Maybe just not getting the power down? I've already noticed an appetite for front tyres and I don't push it any harder than before the conversion.

What gearbox are you using? If it is the Barchetta gearbox you won't manage a higher top speed without changing the ratios. More HP will not increase the top speed if it not geared to reach higher speeds.

 

[Nino_1975]

This is pretty normal for most cars. The speedo will tent to read 5 to 10% low at or around 70mph.

This is good becuase if you do 100mph on your speedo then you will definately be on the safe side to 70+30mph = 100 mph tue or +30 over a limit side of getting an automatic court appearance and almost certain ban.

I set the speed warning beep on my Croma to 85mph. I know this to be about 77mph which is 70 + 10%. When it beeps I know I'm entering the danger zone and need to accordingly "scan" more seriously/aggresively.

WOW - Good stuff this thank you (What do you do for a job?) I

have an expensive SAT NAV well £300 Garmin. And this reads ok. I think people have issues when their car is an import, they put the MPH sticker over the KPH, then the speedo is not totally correct say <70 5mph out, and anything over >100 can be as much as 10mph out. I do use my SAT NAV as a back up, work the mean between the two.

 

[s130]

Me, a job....actually I'm a Chartered Engineer (electrical/electronic/software world as opposed to mechanical) and retired early this August

A small number of people who have data logging GPS units have successfully overturned speeding fines because they can prove they we not speeding. Has to be done in court though I believe. The GPS log confirms you were where the police/camera say you were and at the time they say but your logged speed is less than the reported speed.

Don't know what else you have to do regarding handing over the logger to a solicitor for safe keeping etc..

 

[KC3]

Hiya, all,

Rustbucket. When i had my turbo B, it rolling road at 188bhp,
on a run up a track, it hit 140mph on the spedo..

with my present B, 153bhp, on the german autobhan i clocked 132mph from the sat nav, have a pic somewhere..

hope this helps..

 

[Rustbucket]

Thanks..I was wondering about the speed on the rollers vs the track speedo...The car should manage a similar speed to the 16vt coupe original. I'd hope for a bit more as its smaller / lighter etc. 140mph sounds about right.

 

[afroking]

Thanks..I was wondering about the speed on the rollers vs the track speedo...The car should manage a similar speed to the 16vt coupe original. I'd hope for a bit more as its smaller / lighter etc. 140mph sounds about right.

Which gearbox are you using?

 

[Rustbucket]

Original gearbox.