41 replies to this topic

[998dave]

I think thats what the drag coefficent takes into account.

Correct,
For this reason the bottle nose Cd is 0.51, and the clubman apparantly 0.53.
So got that bit covered.

Am aware of deseaming - that is in Vizard, and will be taken into account, along with wheel size, lowering, etc, etc...

[Jammy]

Does that 0.02 make much of a difference between the two styles?!

Looking at your calculation I can't imagine it does?!

[Jackman]

I dont understand what you are on about but i know of this webpage which could be helpfull to you. By the sounds of it someone has tested the drag of a mini.

Drag Mini

[mattvallins]

Thats the idea! No stupidly wide tyres because unless they are VERY low profile then they just add to the rotating mass of the car. That slows acceleration a LOT, and unless they are a better compound of rubber (ie softer) then they give NO performance upgrade due to grip levels! They just look "bling".

[lewis]

i dont fully understand this, does it mean that once its gone over 78mph it begins to lag whereas newer cars would basically beat this due to newer aerodynamics?

[998dave]

my calcs mean that the max speed of a standard 998 should be 78 mph, but this is wrong, so there's an error in either Cd or A, but i don't know which.

I could do with some values for standard cars or known values, e.g. standard mk3 mini with 73 bhp, etc, etc...

Dave

[Pavel]

Seems okay to me... Haven't seen a 28kw mini go faster than that...

[lewis]

my calcs mean that the max speed of a standard 998 should be 78 mph, but this is wrong, so there's an error in either Cd or A, but i don't know which.

I could do with some values for standard cars or known values, e.g. standard mk3 mini with 73 bhp, etc, etc...

Dave

Thank you now i understand, it was a bit too clever for me you see lol

[Leonard]

i agree with pavel. 37bhp is the very early 998's. try it for a 76bhp coopers and see what you get. the official figure was 98mph i think. The 850's were 38bhp, and their official top speed was 78mph

[998dave]

Seems okay to me... Haven't seen a 28kw mini go faster than that...

What is the supposed power figure for a 998 then? cas mine goes far more then 78, did even before the stage 1 kit...

[998dave]

i agree with pavel. 37bhp is the very early 998's. try it for a 76bhp coopers and see what you get. the official figure was 98mph i think. The 850's were 38bhp, and their official top speed was 78mph

Useful stuff,
Using the above calc and assumptions then I got a 76bhp cooper going at Vmax at 107 mph.
Remember the assumptions aren't accurate yet, but that's not bad for a starting point.... is it?

Dave

[Leonard]

about right. if the cooper s was geared right it'd probably get close to that.

[Leonard]

my calcs mean that the max speed of a standard 998 should be 78 mph,

just thought of something obvious. the maximum power and torque of an engine isnt at maximum revs. a 998 at 78mph will be doing nearly 500rpm, which is around where maximum power is

[pdaykin]

the top speed quoted by lots of articles/brochures (including top trumps !!!) for a 998 mini is 75 mph - so you arent far wrong

Your transmission efficiency may be too high. The mini's box isnt particularly efficient. You should exepct to lose between 25 and 33% of the engines grunt.

[Ricewind]

the top speed quoted by lots of articles/brochures (including top trumps !!!) for a 998 mini is 75 mph - so you arent far wrong

Your transmission efficiency may be too high. The mini's box isnt particularly efficient. You should exepct to lose between 25 and 33% of the engines grunt.

I think that estimate for energy loss through the gearbox may be a little too high. Imagine for arguments sake we have a 100 bhp engine, the loss is converted to heat generation. that would be equivalent to having between ten and twelve 2kw kettle elements in your gearbox. One reason to exaggerate transmission loss may be because engine tuners have historically had a problem with over optimistic power output figures quoted by manufacturers. The manufacturers would have obtained their figures from a blue printed engine in ideal circumstances on a test bed, which does not accurately represent what came off the production line. So when you put your go faster goodies on your pride and joy and take it to an engine tuner, it makes a lot of sense for the engine tuner to exaggerate the transmission losses rather than explain how they have tuned 2% off of the original power that was never there in the first place.  

 

 

 

I think thats what the drag coefficent takes into account.

Correct,
For this reason the bottle nose Cd is 0.51, and the clubman apparantly 0.53.
So got that bit covered.

Am aware of deseaming - that is in Vizard, and will be taken into account, along with wheel size, lowering, etc, etc...

 

 

 

 

Does that 0.02 make much of a difference between the two styles?!

Looking at your calculation I can't imagine it does?!

That is about 3.8% less efficient cd . I think that would be noticeable.