calculating top speed , drop gears , cwp etc
Turbo Mini Forums

Right guys the mini tops out around 94mph , that's shown on the rollers , gps speedo and that's the speed it did over the line at the drag strip on the limiter lol.

So its not long enough , but the calculations ive had done say my set up should be 107 ish !!! so theres a problem

jkd sccr gear set , 3.76 cwp 1:1 drops , 165 70 10

the only thing I could think is that the drops weren't 1:1 (it has been 15 yrs since I got them ) that I thought they were , so ive got the motor out and stripped it. the drops have jkd and 1:1 stamped on them , I have 24 31 24 .

So stripped the diff out , 64 / 17 teeth

ive been on the guess works site and done calculations on there and no matter what gear kit I put in with the 1:1 drops and 3.7 with my 10" tyres says 106 mph !

So whats going wrong , I'm puzzled , any help

thanks men

Edited by cossierick on 1st Nov, 2016.

Tyres. Not all 165/70s will have the same circumference. I suspect you have them on quite wide rims which will reduce circumference slightly and gear you down

Really 12mph difference ! If i put 13" wheel in the calculator it alters the too speed 2mph !
I understand what your saying but thats a big jump

What I would suggest is find a nice flat piece of tarmac/road/drive (whatever), put a chalk mark on one of the front tyres pointing at the ground and a corresponding mark on the ground and push it in a dead straight line for, say, ten revolutions of the wheel until the chalk mark is pointing at the ground again and measure the actual distance travelled.
That is the only accurate way to calculate what the actual rolling circumference of the tyre is.
It takes wheel width, tyre pressure, and almost everything else out of the equation and gives you the most accurate figure to calculate back to RPM.

EDIT - typo

Edited by Rod S on 2nd Nov, 2016.

Schrödinger's cat - so which one am I ???

Using a 1:1 4th gear, 1:1 drops, 3.76 FD, 1540mm tyre circ and 7000 rpm (you don't mention what rpm the limiter is supposed to be set at) I get 107 mph.

I measured 165/70-10 008 and 032R myself new at 1540 / 1541mm (@ 2.0 bar) respectively.

Wide rims make very little difference on a steel belted radial tyre as far as circ goes, but even going to 1500mm circ (which is a massive change) only brings the top speed to 104 mph.

N.B. The running / dynamic circumference won't be exactly the same as I have measured statically here but nothing like as big as a 40mm show as an example

You stated you have GPS, dyno rollers and the strip speed all agreeing on 94 mph (ish) - so several checks of top speed.

You have physically counted all the teeth on the necessary components

All I can think is the limiter isn't set to what you think? Or the measurement of RPM for the limiter is incorrect?

Edited by Aubrey_Boy on 2nd Nov, 2016.

Why did you choose that cwp?

Seems a bit low to me.

Rick, have a look at the graph from Johns, what were the engine revs showing on the limiter?

Ha thanks jonny , it was in the box years ago when i got it.

Rev limit 7200 , running a032's but even with the mig slicks on makes very little difference . The drag strip runs were years ago and on 12 inch wheels, i can understand everything being a few mph out tire size , psi etc but loosing over 10 is bugging me!
Or the next problem is is i need more top speed, so do i put the 3.4 in i have , i think that was calculating 115mph but if im not going to acctually achieve that

Tom , from memory 7200 ! , so thats as acurate as we need hopfully !

My other thought is idler gear !, mine has 31 teeth , minispares say 30 but i carnt find anywhere else to see how many teeth they should have or doesnt it matter so long as the other two are the same

Edited by cossierick on 2nd Nov, 2016.

Shouldn't matter if the other two are the same Rick.

If something is worth doing, it's worth doing half of.

It sounds like you have a 4.2 diff in there to me Rick but if you have counted the teeth on the pinion then bugger knows!

If something is worth doing, it's worth doing half of.

strange one; given the fixed info from the hardware, I'd have to wonder if the rev limiter is accurate. Have you any way of checking the revs independently of the limiter? data logging or something perhaps give you another indication? The info would suggest your topping out at 6500rpm which I think you'd have been aware of in reality

a couple of thoughts,

is the rev limiter hard or soft cut, if its soft it may be pulling advance out before 7200 so it cuts at 7200, so not actually hitting 7200 under load?

also do a tyre rolling circumferance measurment if you havent already. mark the tyre and floor, roll it forward one revoluton, mark the floor, measure it, althioug I'm sure you worked that out already.

I haven't done a tyre rolling circumference yet but will do, il also check the graph from the rolling road.

thanks

only 94 mph, Rubarb!!, I have a timing ticket form York raceway showing just over 90mph for the DON in second gear, so that's at least 400 mph in top.lol

carl

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

Yes but you are THE carl austin !!! Lol

You have 1.1x drops, geuss works and your info gives 95mph at 7200rpm change drops out for some 1.1's or under driven drops

Drives
-Ford S-max Mk2 Ecoboost
-Rover 100 VVC #2 - track project

Searching is all you need on TurboMinis

1.1364:1 22/25, jkd gear set, 3.7xx diff gives 93mph @7k

Drives
-Ford S-max Mk2 Ecoboost
-Rover 100 VVC #2 - track project

Searching is all you need on TurboMinis

Rick mine topped out at 108 with a 3.44 diff and 1:1 drops and 165/10's 032's, guesswork's calc says 115 so there must be some variables.

Paul are you on crack !!

Neil , the brilliant info , thankyou very much 👍🏻

And don't you forget it ,lol

WWW.FORCE-RACING.CO.UK PLEASE CLICK HERE

No I'm not, just had a look through the drop ratios, information given and change drops to the other set gave the speed at rpm you gave, makes sence for the low top speed you are experiencing.

It's obviously not final drive if you have counted the teeth and worked out the ratio, gear set is highly unlikely to have a special short 4th rev limit has most likely been seen on a tach or ecu checked leaving the drops.

Drives
-Ford S-max Mk2 Ecoboost
-Rover 100 VVC #2 - track project

Searching is all you need on TurboMinis

he's already stated that the primary and input gear have the same no of teeth you fucknugget

Did not see that.

Drives
-Ford S-max Mk2 Ecoboost
-Rover 100 VVC #2 - track project

Searching is all you need on TurboMinis

Thats my new word of the day!

On 3rd Nov, 2016 Joe C said:
fucknugget