Hey all,
 
I'm pretty new to the MR2 scene, I have just bought a 1990 SW20 with the standard MT box (S54?).
 
The car has had an engine transplant from a honda S2000, it's a very tidy job but the diff ratio is all wrong.  Currently the car doesn't hit redline in first gear until approximately 90 km/h and in second gear the Vtec doesn't kick in until around 80 km/h.  As the intake and exhaust is specifically setup for optimum output with the Vtec engaged, the car is extremely gutless until it kicks in.
 
I'm sure I can improve things a little by manipulating the point at which the Vtec kicks in but doubt I would gain more than 1500 - 2000 rpm as a best case scenario.
 
The diff ratio most certainly needs to be changed, I want the Vtec well and truly doing it's job at 60 km/h in 2nd.
 
Please somebody/anybody!  What are my options, and are there any affordable LSD options that I may consider?
 
Thanks

If it is an E153 as used in the MR2 Turbo it's final drive ratio will be 4.285.
That is the lowest ratio available that I'm aware of.
Honda transmission ??

If this is the one from Queensland, I am fairly certain this has an S54 transmission (The N/A MT)

OK. In that case it's final drive is most likely 3.944 to 1.
Where are you located? Which transmission do you actually have?
E153 or S54 ?

If you are unsure on which gearbox you have, the easiest way to check is to look under the gearbox on the front side (cabin side) and look for a pipe that is in a "U" Shape. 

If it has this pipe, it is an E153.

This is Thomas Cran's old car, it's an F20C motor fitted to an S54 gearbox via an adaptor plate. 
Build thread here: https://www.mr2australia...mr2play/tm.aspx?m=96882

Thanks guys.
 
Yes, this is Thomas Crans' old car so looks like I'm running an S54.  Is the E153 a direct bolt up alternative for the S54?  
 
4.285 is heading in the right direction but I may have to look at going custom, I worked out 5.8:1 is what I need...  If it's even possible!  (or I could run 13 inch wheels....  Or not!).  I was really hoping someone knew of a low range application that was compatible.  :(
 
I may have to get REALLY creative.  If I simulate 0.7 psi intake vacuum pressure from 3000 rpm onward and tune the Vtec to that range then the 4.285 may get very close.
 
If anyone has any creative solutions I'm keen to hear them.  The more outlandish the better :) 

I've done some quick calcs on an online gear/tyre/rpm calculator and come up with the following results, assuming your rev limiter is 9000 and rolling tyre diameter is 620mm (235/40/17):
 
Current S54 - 3.944 Final Drive
1st - 3.285 - 80kmh
2nd - 1.96 - 135kmh
3rd - 1.322 - 200kmh

This is roughly in line with your first quoted figure of 90 in first.

Turbo Gearbox - 4.285 Final Drive
1st - 3.23 - 75kmh
2nd - 1.913 - 127kmh
3rd - 1.258 - 194kmh
 
Still much higher than the s2000 gearbox's top speed of 106kmh for 2nd. Remember, that's a 6 speed box though. I did a quick google and found a link of all K series gearboxes and their ratios. (http://img.photobucket.com/albums/v504/MJ23FE/Tranny%20Gear%20Calculations/K-SeriesTransmissionTablev3-28-08re.jpg)
Using the same tyre size and limiter, I used a K20A Y2M3:

Final Drive 4.764
1st - 3.266 - 67kmh
2nd - 2.13 - 103kmh
3rd - 1.517 - 144kmh

From memory, I think you can buy adapter plates to put a K series box on a F20C. Currently it is looking to be your best bet
 
As far as I am aware, no one makes a custom final drive off the shelf. Hope this helps!
 

Thanks!  That is VERY useful... I didn't consider the K series boxes, will have to check and see how that impacts the mounts.  
 
In the meantime I will attack from another angle and start experimenting with Vtec activation points and see how much I can increase the active range.  I believe there is a SuperSprint event at QR soon, probably be a good opportunity to have a play around.  Purely scientific purposes, no intention whatsoever of enjoying myself.  ;)
 
A turbo or supercharger would fix this but I really want to keep this an NA setup if I can.
 
 

If you wanted to keep the current gearbox, to save on ****ing about, i believe someone 3 or so years ago sent an s54 final drive assembly to PAR engineering to have some 4.866 final drives made up. Maybe email them to see if they can make onr up for you. It would probably cost around 1-1100 to have made, and then there is the cost of fitting it. But, an e series swap is not great, its heavy and slow shifting, and you need a box, linkages, shafts. A k series box has you up for an adapter plate, box, custom shafts (byp could probably point you in the right direction)

So either way your probably a few thousand in, id freshen up the s54, fit an lsd and a 4.866 final drive and that would be the best bang for buck.