7 replies to this topic

[phoenix1]

Hi can somebody confirm to me what will be the alledged top speed of a project I am just finishing. It is a 1380 MED engine with a 3/1 diff running on 13 inch 45 aspect ratio tyres . I work it out to be 130/140 mph am I in error or do I need 3/7 or 4/1 dff as I am not realy bothered about top speed.

[nicklouse]

missing so much info.

 

it depends on where you want to rev it to.

 

final drive kinda depends on the gearbox and the cam chosen.

 

have a play with the FD ratios

http://www.guess-wor.../Tech/ratio.htm

[Cooperman]

Hi can somebody confirm to me what will be the alledged top speed of a project I am just finishing. It is a 1380 MED engine with a 3/1 diff running on 13 inch 45 aspect ratio tyres . I work it out to be 130/140 mph am I in error or do I need 3/7 or 4/1 dff as I am not realy bothered about top speed.

What calculations did you do to work out a theoretical Vmax of 130 to 140?

 

You need to factor in the revs for maximum bhp, then gear it so that it will just pull those revs in top gear. However, since the aerodynamic drag increases as the square of the speed, that also needs to be factored in. It is a very complicated equation for which a lot of different data is needed.

 

The only other way of doing it is to complete the build aiming to get as close to the ideal as you can. Then you drive the car and see if it will pull to the revs for maximum power in top. If it won't, then it is over-geared and the FDR needs to be lowered and another measurement of revs at maximum speed noted. 

 

The problem is not just the power and gearing, it is the aerodynamic drag curve. Make sure you use an accurately calibrated speed measuring device when doing the test runs on your chosen straight (private) road and that the weather conditions are identical each time, so far as possible.

[hazpalmer14]

this might help someone worked out what power you need to get a top speed. I think this factors in aerodynamics, and if you look at high powered minis and there 1/4 mile times and terminal speed it tallies up.

 

Edit: Here are some previously calculated figures for BHP v top speed in a mini

General BHP needed for MPH for a mini
BHP____Speed
29.69___70
44.32___80
63.1____90
86.56___100
115.21__110
131.64__115
149.57__120
190.17__130
237.51__140
292.13__150
354.54__160
425.26__170
504.8___180
593.7___190
692.46__200

[nicklouse]

this might help someone worked out what power you need to get a top speed. I think this factors in aerodynamics, and if you look at high powered minis and there 1/4 mile times and terminal speed it tallies up.

 

Edit: Here are some previously calculated figures for BHP v top speed in a mini

General BHP needed for MPH for a mini
BHP____Speed
29.69___70
44.32___80
63.1____90
86.56___100
115.21__110
131.64__115
149.57__120
190.17__130
237.51__140
292.13__150
354.54__160
425.26__170
504.8___180
593.7___190
692.46__200

it is not in a Mini.

 

not that a reliant Kitten is much more Aero though.

 

like I said in my earlier post. so much info missing.

[Northernpower]

Hi can somebody confirm to me what will be the alledged top speed of a project I am just finishing. It is a 1380 MED engine with a 3/1 diff running on 13 inch 45 aspect ratio tyres . I work it out to be 130/140 mph am I in error or do I need 3/7 or 4/1 dff as I am not realy bothered about top speed.

I don't know what answer you're looking for, you say you want to know what the top speed will be then you say at the end you're not bothered about the top speed. Is it, you want maximum drivability and to redline in top? You need to supply more information than a simple engine capacity, also, who makes 13 inch tyres with a 45 aspect ratio?

[Retroman]

Project 64 did 156mph with a turbo'd 999cc S

 

280 ish BHP on pump fuel 325 on methanol

 

https://en.wikipedia...iki/Project_64_(Mini_Cooper)

 

Top speed is pretty irrelevant, its how fast you get there, wherever  'there'  is

 

You can do 120mph on a push bike, but it might take 3 miles and as many minutes to get there.

[Cooperman]

We have opened this can of worms before. 

Maximum speed is all saloon bar b******t anyway. It is unimportant when driving on a public road and on a race track it is lap time which is important.

Let's not go much further with this or we'll have folks with standard 998 Minis claiming they do 110 mph 

Edited by Cooperman, 27 February 2018 - 10:24 AM.