Board logo

Dilemma?
Northpole - 22/4/13 at 03:59 PM

I have a Hayabusa engine in Triumph Spitfire and before I test the car in full, I would like to have a estimate on the max speed.

- When I use the calculators on the web I get appr. 170 to 180 km/hrs as top speed with this setup, i.e. 4.11:1 diff ratio, final gear from gearbox 1.043 and tire size 185/70R13.

- Triumph Spitfire has 153 km/hrs at 6000 rpm and gearbox ratio in 4th 1.0 as standard, if the Hayabusa engine revs up to 11.000 rpm, should not the car have top speed according to this? Which gives appr 280 km/hrs (which is quite scary ) using the same setup i.e. 4.11:1 diff ratio, final gear from gearbox 1:1 and tire size 185/70R13.

Anyone have answer on this?

Minicooper - 22/4/13 at 04:11 PM

On a bike there is a primary reduction ratio to allow for as well, on the Hayabusa it is 1.596

I get 109mph using the bike ratios spreadsheet, which is 175kph

Cheers
David

cliftyhanger - 22/4/13 at 04:14 PM

You have assumed no change to air resistance. It is more about power than rpm, but assuming the hayabusa is 150bhp (guess) then that is double the original spitfire engine.
That would give a top speed approx 1.4 times the original cars top speed. About 215km/h. As a guess. The online calc may have a better idea than my simplistic approach, after all I have made some large assumptions.

EDIT, OK, I am looking at theoretical top speeds, nothing to do with RPM.
That 4.11 diff may not last very long, especially if it is the early version with the small quartershafts, see http://www.canleyclassics.com/?xhtml=xhtml/infodatabase/diff.html&xsl=infodatabase.xsl

[Edited on 22/4/13 by cliftyhanger]

Northpole - 22/4/13 at 04:42 PM

quote:
Originally posted by Minicooper
On a bike there is a primary reduction ratio to allow for as well, on the Hayabusa it is 1.596

I get 109mph using the bike ratios spreadsheet, which is 175kph

Cheers
David



Thanks David, I forgot the primary reduction ratio in the Hayabusa. This is much better both the tires and the driver will handle this more moderate speed
Can you please inform me what bike ratio spreadsheet you found?
Cheers
sigurjon

ReMan - 22/4/13 at 05:15 PM

This one :-)
http://www.locostbuilders.co.uk/forum/23/viewthread.php?tid=121319

snapper - 22/4/13 at 05:17 PM

Most people use a final drive of about 3.4 to 1
If your putting this in a Spitfire for god sake change the rear suspension
I had a MK3 when I was young and it tried to kill me several times when I lifted off the throttle in a corner

INDY BIRD - 22/4/13 at 05:19 PM

Or this thread

http://www.locostbuilders.co.uk/viewthread.php?tid=171831

Northpole - 22/4/13 at 05:33 PM

quote:
Originally posted by snapper
Most people use a final drive of about 3.4 to 1
If your putting this in a Spitfire for god sake change the rear suspension
I had a MK3 when I was young and it tried to kill me several times when I lifted off the throttle in a corner


Thank you for your consern I have done what is possible for it, the diff re-cond, new UV heavy duty and I have now Camber compensator, I hope this will help....
Can you recommend any other diff? I was thinking Subaro or Jaguar?

Andy S - 22/4/13 at 07:27 PM

Freelander

Northpole - 22/4/13 at 08:05 PM

quote:
Originally posted by Andy S
Freelander


Why is Freelander diff good for Spitfire?
Why not Jaguar, Subaro, Mercedes or BMW?
I need to do some modifications anyway...

bi22le - 22/4/13 at 08:22 PM

quote:
Originally posted by Northpole
quote:
Originally posted by Andy S
Freelander


Why is Freelander diff good for Spitfire?
Why not Jaguar, Subaro, Mercedes or BMW?
I need to do some modifications anyway...


Freelander is not specifically good for your spitfire, its just a commonly used one in the kit car scene. I think its a case of being common, LSD and sensible ratio.