Home / Toyota Supra Forums

Go Back   Toyota Supra Forums! Join the Supra forum! > Performance, Modification, and Maintenance Forums - for generation specific discussions > MKIII Supra > MKIII FAQ

Reply
 
Thread Tools Display Modes
Old 06-03-2010, 03:43 AM   #1
cre

Toyota
Racing
Development
 
cre's Avatar
 
Join Date: Apr 2007
Posts: 5,036
cre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond repute
Default Speedometor / Ma70 Gear ratio

There were three different gear ratios used for the MA70's 4.30:1 3.91:1 and 3.73:1. All three were available in LSD, the latter two were ONLY available in LSD and the 4.30:1 was ONLY available in the non turbo. If you spin one wheel with the back end jacked up and the other side moves in the OPPOSITE direction it's an open LSD and thus it's 4.30:1. If both move the same way it's an LSD. If it's an LSD you may look at the charts below to easily find which one it probably is. The minor difference in gearing will make for a small offset.. so will the MASSIVE margin of error in the stock spedometer and tachometer. Best way to check is to roll the car along a measured lengthof road and check against the odometer.

75's right for 5th gear in a N/A at about 3300RPM.

W58: (that's the non-turbo transmission)

Attachment 3095

R154's:
Pre89 (3.91:1)
Attachment 3096

89+ (3.73:1)
Attachment 3097
Attached Thumbnails
Click image for larger version

Name:	5spd4[1].jpg
Views:	335
Size:	65.3 KB
ID:	3345   Click image for larger version

Name:	R154-3.91.jpg
Views:	446
Size:	91.0 KB
ID:	3346   Click image for larger version

Name:	R154-3.73.jpg
Views:	272
Size:	90.7 KB
ID:	3347  
__________________
If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum.

If you're so inclined I'm always more than happy to accept tips via PayPal.
Tip Jar --->
cre is offline   Reply With Quote
Old 06-05-2010, 02:56 AM   #2
cre

Toyota
Racing
Development
 
cre's Avatar
 
Join Date: Apr 2007
Posts: 5,036
cre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond repute
Default

Quote:
Originally Posted by fullthrottlesrqsupra View Post
yep sounds right i did my first highway drive today and at 70 i was right on 3000 i think the chart might be just a little off for 3rd though because i was in 3rd at 87mph not redlining (track reading not my speedo i wasnt looking at it to know) and the chart shows that being impossible my tires are actually 1/4inch or so smaller than stock too hmmmm wonder whats up

or maybe not my car is an 86.5 so its not supposed to be a turbo but my mph to rpm match the pre 89 r154 perfect hmmmmmmmmmmm????? i know it not though because i just did a clutch on it im puzzled
It's simple... first off that chart is for a PERFECTLY dialed in FACTORY, BONE STOCK setup... even a difference in air pressure will start it moving off... second, the factory speedometer SUCKS. It can be calibrated but will not be terribly accurate except for the speed at which it was calibrated. and Third... the stock tachometer SUCKS... miles off. Mine is off by about 150RPM at idle and it gets worse the higher you rev... this could be modified so you could calibrate it, but it's not worth it in the least. Also, if you're running a R154 the numbers will be off too... their gearing is a bit different for each gear.
__________________
If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum.

If you're so inclined I'm always more than happy to accept tips via PayPal.
Tip Jar --->
cre is offline   Reply With Quote
Old 06-06-2010, 05:28 AM   #3
cre

Toyota
Racing
Development
 
cre's Avatar
 
Join Date: Apr 2007
Posts: 5,036
cre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond repute
Default

Get it on a dyno and REALLY measure the speed; While you're there get a comparison on the tach readings.

Otherwise, you need to just start measuring things; pull the speedometer drive gear and cross reference the part number and find out what you REALLY have in the car. There are too many variables. If things are so far off your car's had something swapped and possibly more than one part.

You can't base any conclusions entirely on the ECU's response in most circumstances in my opinion either... Leaking capacitors, 5% tolerance resistors... skewed tachometers and speedometers...




There are two different types of offset you will see with the stock speedometer: linear and logarithmic.

I'm not going to cover how it all works... the short and simple of it is that if the speedometer is off by a constant amount regardless of speed it is due to one of the following: tire size, end gear ratio, transmission gearing, speedometer drive gear.

If it is off by a percentage it is the speedometer (the clock/tension spring inside can be used to adjust this to a degree, but it will never be accurate over the entire speedometer's scale... choose the rage where you want it accurate and accept that there will be some shift at other speeds).

If both are off it's not fun to calibrate... best is to start with physically identifying components such as the speedo drive gear and counting wheel revolutions to ID the diff.




I'm not guaranteeing the numbers in that chart are correct, but they're the output from a spreadsheet based on very simple math... if they're off I'd be very surprised, but it is possible.
__________________
If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum.

If you're so inclined I'm always more than happy to accept tips via PayPal.
Tip Jar --->
cre is offline   Reply With Quote
Old 06-06-2010, 05:34 PM   #4
cre

Toyota
Racing
Development
 
cre's Avatar
 
Join Date: Apr 2007
Posts: 5,036
cre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond repute
Default

If the speedo's only a constant 2MPH off then your tach's screwy or your igniter is... Roll the car slowly across a measured one mile segment of road and see if the odometer is reading accurately. If it's right on the mark just move the speedo needle to set everything right.

And if your speedo is 2 MPH off at 10MPH and still only 2MPH off at 100MPH feel lucky, the speedo was blessed by god himself.

Last edited by cre; 03-11-2012 at 04:57 AM.
cre is offline   Reply With Quote
Old 08-24-2010, 05:14 AM   #5
cre

Toyota
Racing
Development
 
cre's Avatar
 
Join Date: Apr 2007
Posts: 5,036
cre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond reputecre has a reputation beyond repute
Default

If the speedometer is off but all the gearing is right you can recalibrate the gauge. There is an arm behind the face which adjusts it my percentage and flat out moving the needle is what you'll do fix a constant offset (ie: it's ALWAYS 5 MPH low).

If the gearing does NOT match you may swap out the speedometer driven gear or worst case swap out the diff to make everything right.

You may recalibrate the gauge to make the speed report accurately without changing any gearing (diff or speedo drive gear) BUT the odometer will still be off.

When changing to a different diff the proper course of action is to change the speedometer drive gear for one the appropriate size or to install small gear box which changes rate at which the speedometer cable spins (there are actually shops that do just this).


EDIT: Here's a picture showing the adjustment arm which you may use to calibrate a speedometer which is off by a percentage (ie, you're doing 30 but it reports 33 and then when doing 60 it reports 66).
Click image for larger version

Name:	speedo_adjustment2[1].jpg
Views:	227
Size:	102.6 KB
ID:	4498
__________________
If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum.

If you're so inclined I'm always more than happy to accept tips via PayPal.
Tip Jar --->

Last edited by cre; 03-11-2012 at 04:55 AM.
cre is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
harmonic balancer came off crank shaft help? wishiknewmore MKIII Supra 3 04-15-2011 12:04 PM
1st gear jumping out, 4th gear crunching, how do I fix it without changing gearbox wcrispino Non-Generation Specific Questions 7 01-31-2010 11:13 AM
Clutch wont go into gear... Help?! Conga1991 Non-Generation Specific Questions 4 07-26-2009 10:17 PM
wats the gear ratio on an mk3 rear end? suprabilly21 Non-Generation Specific Questions 3 05-08-2007 01:01 AM
quick question blacksheep Non-Generation Specific Questions 10 01-01-2007 08:19 PM


All times are GMT. The time now is 08:59 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.

1986



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86