Gear Ratio help and understanding
07-28-2014, 05:57 PM
#41
Burning Brakes
Thread Starter
Mechanic installed tranny (twice). Currently out of car at different shop now.
I've had several people drive it. All commented that it seemed odd.
07-28-2014, 06:23 PM
#42
Instructor
What engine do you have? Where is 75% of your driving going to occur?
If you are just going to drive locally, around town, maybe an hour out of town for a show, the go with the 4:11 and clse ratio tranny.
If you are going to do mostly trips, then the 3:36 gears and the wide ratio box.
With the close ratio box, there is no cake and eat it to, more so if you have a bumpy cam. My 327/365 close ratio M-21 and 3:36 gear set is horrible for in town stop and go traffic. I have a second differential with 4:11 gearing I use. Great in town gear, not so much for long distance touring. I did a few long trips over a few year period and installed the 3:36 gears for that.
If you are just going to drive locally, around town, maybe an hour out of town for a show, the go with the 4:11 and clse ratio tranny.
If you are going to do mostly trips, then the 3:36 gears and the wide ratio box.
With the close ratio box, there is no cake and eat it to, more so if you have a bumpy cam. My 327/365 close ratio M-21 and 3:36 gear set is horrible for in town stop and go traffic. I have a second differential with 4:11 gearing I use. Great in town gear, not so much for long distance touring. I did a few long trips over a few year period and installed the 3:36 gears for that.
07-28-2014, 06:32 PM
#43
Drifting
3.55 is the best of both worlds.... Buuut I like the zip from a start sooo I have a 4.11 and love it!
Oh, here's a calculator for gear ratio/MPH & RPM's buuut you will need tire diameter: http://www.wallaceracing.com/gear-speed.php or simpler method: http://www.summitracing.com/expertad...tio-calculator
rustylugnuts
Oh, here's a calculator for gear ratio/MPH & RPM's buuut you will need tire diameter: http://www.wallaceracing.com/gear-speed.php or simpler method: http://www.summitracing.com/expertad...tio-calculator
rustylugnuts
Last edited by rustylugnuts; 07-28-2014 at 06:40 PM.
07-28-2014, 06:46 PM
#44
Team Owner
Member Since: Oct 2000
Location: Washington Michigan
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07-28-2014, 06:49 PM
#45
Team Owner
Member Since: Oct 2000
Location: Washington Michigan
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07-28-2014, 06:52 PM
#46
Burning Brakes
Thread Starter
If i had a Go-Pro camera I'd strap it to my head and go drive the 70 to demonstrate. The Professional shop is stumped as well.
We are all scratching our heads at the moment.
I'm desperately trying to find a local car with the same set up to drive. Kinda hard to find and then ask to drive their car.
Going over to drive another 63 tonight.
07-28-2014, 10:03 PM
#47
Instructor
07-28-2014, 10:51 PM
#48
Burning Brakes
Thread Starter
OK,
Connected up with Zoomin tonight for some testing Oklahoma style!!!
Zoomin was not sure exactly what his 63 SWC has for gears in the rear or the tranny so we set out to find out and do some test driving for shifting ease.
1. First I armed my self with my iphone with Speed GPS app, Ipad to punch data into the website so kindly provided by RustyLugNuts
http://www.wallaceracing.com/gear-speed.php and pad and paper. we also looked up the exact tire specs on the web for his diameter which was 26.89"
2. Next we went after determining his rear end. We ran the car up to known RPM settings and then I recorded the speed from the GPS (we quickly determined his speedo was just a little slow)
2,500 rpm = 58 mph
3,000 rpm = 68 mph
3,500 rpm = 79 mph
Punching into the calculator I got the respective gear ratio's, 3.45, 3.53, and 3.55. So it was very safe to say he has a 3.55 rear end.
3. Next we wanted to determine if he had a close ratio or wide ratio tranny. Using the basic formula of 2,200 rpm in first gear and then shifting to 4th and seeing if rpm dropped to 1,000 was not very accurate and we tried many times. It's pretty hard to determine by this was for sure because a wide ratio should drop to around 900 rpm.
We thought surely there is a better way so I went to the online calculator and sure enough there is a formula for calculating gearing and speed of a certain gear if you know some variables. So now we knew the rear end and we also know his tach is pretty darn accurate and we know the gear ratios for a CR and WR tranny.
So we picked the ratio for third gear on a CR tranny (which is 1.28) and put in a 3.55 rear. Out pops the chart for RPM and speed at that ratio tranny. we picked 2,500 rpm which should yield 44 mph. Our test was right on the money. Just to double check I punched in the WR third gear (1.48) and that chart shows that at 2,500 rpm the speed should be 38 mph. It was easy to see with my iphone GPS that we were at exactly 44 not 38.
So there we have it, Zoomin has a CR box with a 3.55 rear end.
How does it drive you ask. I thought great with no issues from gear to gear and the start from 1st was no big deal from a feather standpoint. I think a 3.36 might be a little more bothersome on the feathering.
I did not experience the same issues with his as I am with my 63.
I also talked with another local SWC owner and asked what he had. It's a CR and 3.70 rear.
Honestly, I'm leaning towards the CR and 3.70 right now and not worrying about fast highway speeds.
Still searching my brain as to what could be going on with my current box.
At any rate it was a beautiful evening and a lot of fun to get technical with a drive. Thanks ZOOMIN!!!
Connected up with Zoomin tonight for some testing Oklahoma style!!!
Zoomin was not sure exactly what his 63 SWC has for gears in the rear or the tranny so we set out to find out and do some test driving for shifting ease.
1. First I armed my self with my iphone with Speed GPS app, Ipad to punch data into the website so kindly provided by RustyLugNuts
http://www.wallaceracing.com/gear-speed.php and pad and paper. we also looked up the exact tire specs on the web for his diameter which was 26.89"
2. Next we went after determining his rear end. We ran the car up to known RPM settings and then I recorded the speed from the GPS (we quickly determined his speedo was just a little slow)
2,500 rpm = 58 mph
3,000 rpm = 68 mph
3,500 rpm = 79 mph
Punching into the calculator I got the respective gear ratio's, 3.45, 3.53, and 3.55. So it was very safe to say he has a 3.55 rear end.
3. Next we wanted to determine if he had a close ratio or wide ratio tranny. Using the basic formula of 2,200 rpm in first gear and then shifting to 4th and seeing if rpm dropped to 1,000 was not very accurate and we tried many times. It's pretty hard to determine by this was for sure because a wide ratio should drop to around 900 rpm.
We thought surely there is a better way so I went to the online calculator and sure enough there is a formula for calculating gearing and speed of a certain gear if you know some variables. So now we knew the rear end and we also know his tach is pretty darn accurate and we know the gear ratios for a CR and WR tranny.
So we picked the ratio for third gear on a CR tranny (which is 1.28) and put in a 3.55 rear. Out pops the chart for RPM and speed at that ratio tranny. we picked 2,500 rpm which should yield 44 mph. Our test was right on the money. Just to double check I punched in the WR third gear (1.48) and that chart shows that at 2,500 rpm the speed should be 38 mph. It was easy to see with my iphone GPS that we were at exactly 44 not 38.
So there we have it, Zoomin has a CR box with a 3.55 rear end.
How does it drive you ask. I thought great with no issues from gear to gear and the start from 1st was no big deal from a feather standpoint. I think a 3.36 might be a little more bothersome on the feathering.
I did not experience the same issues with his as I am with my 63.
I also talked with another local SWC owner and asked what he had. It's a CR and 3.70 rear.
Honestly, I'm leaning towards the CR and 3.70 right now and not worrying about fast highway speeds.
Still searching my brain as to what could be going on with my current box.
At any rate it was a beautiful evening and a lot of fun to get technical with a drive. Thanks ZOOMIN!!!
12-08-2014, 11:28 AM
#51
Sorry to see you going through such hoop-jumping; but anytime you can jump in a classic Vette for "Okie road testing"; is a good time!
I saw this on the first page; the close- vs wide- ratio has nothing to do with the physical gap from 1st to 2nd. You use the same synchronizer, 1st gear and 2nd gear, shift forks, sidecover and shift system from an M21 or 20. "Close" and "Wide" refers to the percentage of ratio drop between the gears. Also as alluded to previously, the M20 and the M21/22 have the same essential ratio drops from 1-2 and 2-3, with the M20 falling on its nose between the 3 and 4. In a street car, its no big deal, same in Autocross. Road Racing ( or GT-style driving) might benefit from the Italian aftermarket M22W gearset with its 2.56/1.75/1.36/1.00 spread.
To be honest; a Muncie M20 wide ratio would be a close ratio by todays standards, case in point the T56 close ratio is a 2.66, the TKO is a 2.87 and a T5 is a 2.95). Also note that "M20", "M21" and "M22" are RPO codes. In 1978 an M20 was not your Muncie M20, it was a B/Warner ST10 with most likely a 2.88 1st, and the close ratio was the 2.64.
When I help someone spec out a new production gear box; assuming the customer has a 26-26.5" rear tire, we take the number '9' and divide it by their rear axle choices to settle on the 1st gear they need. Corvettes, can certainly be a little less than "9", but I wouldn't stray too far.
Some of you may know there is an aftermarket, Italian M22Z gearset which has a 2.98 1st, a 2.04 2nd and a 1.46 3rd; which will fit in a 1" countershaft Muncie case; OR a 2.88 1st gear SuperT10. For GENERAL driving, or perhaps "spirited acceleration testing"; I often recommend these with rear gears between 3.08s and 3.36's. Be careful with the ST10 and the 2.88 1st, there was a version which had a 1.75 second, and that would be a complete trainwreck to put behind a mild 327.
I saw this on the first page; the close- vs wide- ratio has nothing to do with the physical gap from 1st to 2nd. You use the same synchronizer, 1st gear and 2nd gear, shift forks, sidecover and shift system from an M21 or 20. "Close" and "Wide" refers to the percentage of ratio drop between the gears. Also as alluded to previously, the M20 and the M21/22 have the same essential ratio drops from 1-2 and 2-3, with the M20 falling on its nose between the 3 and 4. In a street car, its no big deal, same in Autocross. Road Racing ( or GT-style driving) might benefit from the Italian aftermarket M22W gearset with its 2.56/1.75/1.36/1.00 spread.
To be honest; a Muncie M20 wide ratio would be a close ratio by todays standards, case in point the T56 close ratio is a 2.66, the TKO is a 2.87 and a T5 is a 2.95). Also note that "M20", "M21" and "M22" are RPO codes. In 1978 an M20 was not your Muncie M20, it was a B/Warner ST10 with most likely a 2.88 1st, and the close ratio was the 2.64.
When I help someone spec out a new production gear box; assuming the customer has a 26-26.5" rear tire, we take the number '9' and divide it by their rear axle choices to settle on the 1st gear they need. Corvettes, can certainly be a little less than "9", but I wouldn't stray too far.
Some of you may know there is an aftermarket, Italian M22Z gearset which has a 2.98 1st, a 2.04 2nd and a 1.46 3rd; which will fit in a 1" countershaft Muncie case; OR a 2.88 1st gear SuperT10. For GENERAL driving, or perhaps "spirited acceleration testing"; I often recommend these with rear gears between 3.08s and 3.36's. Be careful with the ST10 and the 2.88 1st, there was a version which had a 1.75 second, and that would be a complete trainwreck to put behind a mild 327.
Last edited by Auto Gear; 12-08-2014 at 11:40 AM.