Best gear for .82 OD
Race Director
Joined: Jan 2003
Posts: 15,177
Likes: 90
From: State of Confusion
..... 'assuming' a 27"-tall tire is used, 85 MPH with .82:1 OD ratio is:
2.72 - 2340 RPM
2.87 - 2470
3.08 - 2650
3.31 - 2850
3.55 - 3050
3.73 - 3200
3.90 - 3350
4.10 - 3535
Formula is: MPH x GR (Gear Ratio ) div/by .006 div/by 1/2 TH (Tire Height ) x OD-ratio
85 x 2.72 div/by .006 div/by 13.5 x .82 = 2340 RPM (see-above )
2.72 - 2340 RPM
2.87 - 2470
3.08 - 2650
3.31 - 2850
3.55 - 3050
3.73 - 3200
3.90 - 3350
4.10 - 3535
Formula is: MPH x GR (Gear Ratio ) div/by .006 div/by 1/2 TH (Tire Height ) x OD-ratio
85 x 2.72 div/by .006 div/by 13.5 x .82 = 2340 RPM (see-above )
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
I presently have 4.11 rear X .64 = 2.6304 effective ratio. I have enough TQ to pull and even higher gear so my plan is to 3.08 X .82 = 2.5256
I'm always doing way too many RPM driving the local freeways. I glance down at the tach and I'm often way over 4000 rpm cruising.
Le Mans Master
Joined: Jan 2006
Posts: 6,506
Likes: 139
From: Butler Pa
On my list of things to do is change my 5th gear OD ratio from .64 to .82
I presently have 4.11 rear X .64 = 2.6304 effective ratio. I have enough TQ to pull and even higher gear so my plan is to 3.08 X .82 = 2.5256
I'm always doing way too many RPM driving the local freeways. I glance down at the tach and I'm often way over 4000 rpm cruising.
I presently have 4.11 rear X .64 = 2.6304 effective ratio. I have enough TQ to pull and even higher gear so my plan is to 3.08 X .82 = 2.5256
I'm always doing way too many RPM driving the local freeways. I glance down at the tach and I'm often way over 4000 rpm cruising.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
I forgot to add that i have a fear of being rearended!
This picture was taken after I slowed down to about 4200 rpm. I just didn't feel safe fumbling with a camera when my speedo needle was straight down off past 140 mph. It was curvy road through a canyon following a small river
I also have some on track videos doing a 4-5 shift at near 140 mph and track radar gun had me at 156 mph just before the braking zone.
Years ago at Bonneville Salt Flats I was able to do 7000 rpm with 28 inch 300 mph tires using a .70 OD and 4.11 rear.
This picture was taken after I slowed down to about 4200 rpm. I just didn't feel safe fumbling with a camera when my speedo needle was straight down off past 140 mph. It was curvy road through a canyon following a small river
I also have some on track videos doing a 4-5 shift at near 140 mph and track radar gun had me at 156 mph just before the braking zone.
Years ago at Bonneville Salt Flats I was able to do 7000 rpm with 28 inch 300 mph tires using a .70 OD and 4.11 rear.
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Burning Brakes
Joined: Dec 2003
Posts: 1,004
Likes: 7
From: Adelaide South Australia
On my list of things to do is change my 5th gear OD ratio from .64 to .82
I presently have 4.11 rear X .64 = 2.6304 effective ratio. I have enough TQ to pull and even higher gear so my plan is to 3.08 X .82 = 2.5256
I'm always doing way too many RPM driving the local freeways. I glance down at the tach and I'm often way over 4000 rpm cruising.
I presently have 4.11 rear X .64 = 2.6304 effective ratio. I have enough TQ to pull and even higher gear so my plan is to 3.08 X .82 = 2.5256
I'm always doing way too many RPM driving the local freeways. I glance down at the tach and I'm often way over 4000 rpm cruising.
Why do you want to change the OD ratio?
It is much better for keeping rpm down at highway speeds in your situation.
Give it some more thought: I'd be sticking with the 0.64 ratio OD, but change the diff to ~ 3.9 or even 3.73.
That way you still keep a good 1st gear ratio for take offs, and 4th gear will carry you over the qtr mile at around the right rpm for best utilisation of power, and 5th is your high speed cruising gear.
I have a 3.36:1 diff, and the 2.87 1st gear is about as tall as I would want (overall 9.64) A 3.08 diff ratio will make your overall 1st gear lug a bit on takeoff..... you'll be riding that clutch a bit in traffic (if it is used as a driver)
but then if your spending time at the salt flats..... go for the 3.08 with the .64, and add a bit of N2O.... that'll wind the needle off the clock
Racer
Joined: Apr 2007
Posts: 361
Likes: 0
From: Sacramento (Citrus Heights) California
I forgot to add that i have a fear of being rearended!
This picture was taken after I slowed down to about 4200 rpm. I just didn't feel safe fumbling with a camera when my speedo needle was straight down off past 140 mph. It was curvy road through a canyon following a small river
I also have some on track videos doing a 4-5 shift at near 140 mph and track radar gun had me at 156 mph just before the braking zone.
Years ago at Bonneville Salt Flats I was able to do 7000 rpm with 28 inch 300 mph tires using a .70 OD and 4.11 rear.
This picture was taken after I slowed down to about 4200 rpm. I just didn't feel safe fumbling with a camera when my speedo needle was straight down off past 140 mph. It was curvy road through a canyon following a small river
I also have some on track videos doing a 4-5 shift at near 140 mph and track radar gun had me at 156 mph just before the braking zone.
Years ago at Bonneville Salt Flats I was able to do 7000 rpm with 28 inch 300 mph tires using a .70 OD and 4.11 rear.
Holy crap, where'd you do that?
The only place I feel really safe opening it up is on I-5 between Buttonwillow and Stockton.
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
You can do a Ford T5 retrofit for about $1200 depending on your parts finding skills. You can pick up a low mile T5 for $500 to $700. The T5 is a great five speed manual to look at when you're on a budget.
If you like automatics, then a TH200R4 is very easy to find for about the same price as above. Drop a few hundred into a rebuild that you perform yourself, and you can have OD either way, for under $1500.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
gkull, if you have the 0.64 OD ratio, I'm assuming you have a TKO-600.
Why do you want to change the OD ratio?
It is much better for keeping rpm down at highway speeds in your situation.
Give it some more thought: I'd be sticking with the 0.64 ratio OD, but change the diff to ~ 3.9 or even 3.73.
That way you still keep a good 1st gear ratio for take offs, and 4th gear will carry you over the qtr mile at around the right rpm for best utilisation of power, and 5th is your high speed cruising gear.
I have a 3.36:1 diff, and the 2.87 1st gear is about as tall as I would want (overall 9.64) A 3.08 diff ratio will make your overall 1st gear lug a bit on takeoff..... you'll be riding that clutch a bit in traffic (if it is used as a driver)
but then if your spending time at the salt flats..... go for the 3.08 with the .64, and add a bit of N2O.... that'll wind the needle off the clock
Why do you want to change the OD ratio?
It is much better for keeping rpm down at highway speeds in your situation.
Give it some more thought: I'd be sticking with the 0.64 ratio OD, but change the diff to ~ 3.9 or even 3.73.
That way you still keep a good 1st gear ratio for take offs, and 4th gear will carry you over the qtr mile at around the right rpm for best utilisation of power, and 5th is your high speed cruising gear.
I have a 3.36:1 diff, and the 2.87 1st gear is about as tall as I would want (overall 9.64) A 3.08 diff ratio will make your overall 1st gear lug a bit on takeoff..... you'll be riding that clutch a bit in traffic (if it is used as a driver)
but then if your spending time at the salt flats..... go for the 3.08 with the .64, and add a bit of N2O.... that'll wind the needle off the clock
The jump from 1.00 to .64 is way to much.
I am much more interested in making first and second gear more usable.
Burning Brakes
Joined: Dec 2003
Posts: 1,004
Likes: 7
From: Adelaide South Australia
I agree, the gap IS too wide from 1.00 to 0.64 to make it useful for anything other than highway cruise.
Burning Brakes
Joined: Dec 2003
Posts: 1,004
Likes: 7
From: Adelaide South Australia
First opportunity to run my vette on a longer cruise today with the new motor and gearbox.
I have the 0.82 OD ratio with a 3.36:1 diff.
I am happy with my choice.
I sat on 65~70 mph and car drops 500 rpm from 4th to 5th.
Noise level is markedly lower at 2400rpm compared to 2900 rpm, and motor (383) still pulls strong in 5th up hills....
It is a very usable 5th gear.
cheers
tom
I have the 0.82 OD ratio with a 3.36:1 diff.
I am happy with my choice.
I sat on 65~70 mph and car drops 500 rpm from 4th to 5th.
Noise level is markedly lower at 2400rpm compared to 2900 rpm, and motor (383) still pulls strong in 5th up hills....
It is a very usable 5th gear.
cheers
tom
Racer
Joined: Apr 2007
Posts: 364
Likes: 1
From: Dane Wisconsin
First opportunity to run my vette on a longer cruise today with the new motor and gearbox.
I have the 0.82 OD ratio with a 3.36:1 diff.
I am happy with my choice.
I sat on 65~70 mph and car drops 500 rpm from 4th to 5th.
Noise level is markedly lower at 2400rpm compared to 2900 rpm, and motor (383) still pulls strong in 5th up hills....
It is a very usable 5th gear.
cheers
tom
I have the 0.82 OD ratio with a 3.36:1 diff.
I am happy with my choice.
I sat on 65~70 mph and car drops 500 rpm from 4th to 5th.
Noise level is markedly lower at 2400rpm compared to 2900 rpm, and motor (383) still pulls strong in 5th up hills....
It is a very usable 5th gear.
cheers
tom
Burning Brakes
Joined: Dec 2003
Posts: 1,004
Likes: 7
From: Adelaide South Australia
How did you determine that ratio?
standard ratios in chrome bumper vettes that I am aware of were....
3.08, 3.36, 3.55, 3.73 and 4.11
In any case..... a big block should pull tall gearing without issues.
