transmission gear selection questions

Whizbang · 09-24-2008, 07:23 AM

Here is the data i processed:

I used an assumed shift point of about 9600 rpms. The true shift point may be lower (about 9000) once i finish my engine build, but generally, this gets the point across.

Mazda 12a Gearbox w/ 4.78 Final Drive on 205/50 R15 Tires
9600 rpm shift point (assuming bridge ported engine)

70mph = 4136 rpm

*Top gear yields 16.9 MPH / 1000 rpms and top speed of 162.5 mph ( @ 9600 rpms)
*Top speed in 1st gear = 36.48 mph
-Changes into 2nd gear at 5793 rpm dropping 3807 rpm
*Top speed in 2nd gear = 60.45 mph
-Changes into 3rd gear at 6201 rpm dropping 3399 rpm
*Top speed in 3rd gear = 93.60 mph
-Changes into 4th gear at 6704 rpm dropping 2896 rpm
*Top speed in 4th gear = 134.035 mph
-Changes into 5th gear at 7920 rpm dropping 1680 rpm
*Top speed in 5th gear = 162.467 mph

Mazda Miata Gearbox w/ 4.78 Final Drive on 205/50 R15 Tires
9600 rpm shift point (assuming bridge ported engine)\

70 mph = 4081 rpm

*Top gear yields 17.152 MPH / 1000 rpms and top speed of 164.662 mph ( @ 9600 rpms)
*Top speed in 1st gear = 42.74 mph
-Changes into 2nd gear at 5780 rpm dropping 3820 rpm
*Top speed in 2nd gear = 70.993 mph
-Changes into 3rd gear at 6763 rpm dropping 2837 rpm
*Top speed in 3rd gear = 100.778 mph
-Changes into 4th gear at 7218 rpm dropping 2382 rpm
*Top speed in 4th gear = 134.035 mph
-Changes into 5th gear at 7814 rpm dropping 1786 rpm
*Top speed in 5th gear = 164.662 mph

09-24-2008, 07:23 AM	#10
Whizbang Respecognize! Join Date: Jul 2008 Location: Δx = ħ/2Δp Posts: 3,190 Rep Power: 21	Here is the data i processed: I used an assumed shift point of about 9600 rpms. The true shift point may be lower (about 9000) once i finish my engine build, but generally, this gets the point across. Mazda 12a Gearbox w/ 4.78 Final Drive on 205/50 R15 Tires 9600 rpm shift point (assuming bridge ported engine) 70mph = 4136 rpm Top gear yields 16.9 MPH / 1000 rpms and top speed of 162.5 mph ( @ 9600 rpms) Top speed in 1st gear = 36.48 mph -Changes into 2nd gear at 5793 rpm dropping 3807 rpm Top speed in 2nd gear = 60.45 mph -Changes into 3rd gear at 6201 rpm dropping 3399 rpm Top speed in 3rd gear = 93.60 mph -Changes into 4th gear at 6704 rpm dropping 2896 rpm Top speed in 4th gear = 134.035 mph -Changes into 5th gear at 7920 rpm dropping 1680 rpm Top speed in 5th gear = 162.467 mph Mazda Miata Gearbox w/ 4.78 Final Drive on 205/50 R15 Tires 9600 rpm shift point (assuming bridge ported engine)\ 70 mph = 4081 rpm Top gear yields 17.152 MPH / 1000 rpms and top speed of 164.662 mph ( @ 9600 rpms) Top speed in 1st gear = 42.74 mph -Changes into 2nd gear at 5780 rpm dropping 3820 rpm Top speed in 2nd gear = 70.993 mph -Changes into 3rd gear at 6763 rpm dropping 2837 rpm Top speed in 3rd gear = 100.778 mph -Changes into 4th gear at 7218 rpm dropping 2382 rpm Top speed in 4th gear = 134.035 mph -Changes into 5th gear at 7814 rpm dropping 1786 rpm Top speed in 5th gear = 164.662 mph __________________ For current updates and event coverage check out Follow on Twitter! @WhizbangRally Whizbang Rally's Webpage \| Facebook Last edited by Whizbang; 09-24-2008 at 07:26 AM.