rpms at 70, confused...
Thread Starter
Melting Slicks
Joined: Jan 2008
Posts: 2,065
Likes: 1
From: Jasper Texas
rpms at 70, confused...
so...I know alot of people around here run in the 2000s range at 70 mph. I, however, turn 3200 rpms at 70 mph. The speedo is right, so is the tach. I thought I used the calculator before and came up with 3.75 for the rear gear, but now I'm pretty sure I'm wrong.
With stock size tires on the back, what should my rear ratio be? Seems to be around 4.10 to me, did they make that for a dana 36?
I figured I ask this since my car is down right now, I'm bored!
With stock size tires on the back, what should my rear ratio be? Seems to be around 4.10 to me, did they make that for a dana 36?
I figured I ask this since my car is down right now, I'm bored!
Team Owner
Joined: Sep 2001
Posts: 62,160
Likes: 1,733
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
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Never seen lower than 3.73 for a D36, thats probably what you have.
Stock, it wouldnt have had lower than 3.07.
Stock, it wouldnt have had lower than 3.07.
Thread Starter
Melting Slicks
Joined: Jan 2008
Posts: 2,065
Likes: 1
From: Jasper Texas
I thought I saw 3.75s for the 36, could be wrong, not really a difference there. the rpo list indicates it had 3.07s stock, but something still doesn't add up...
I'll be changing rims and tires soon, I'll do the check then.
I'll be changing rims and tires soon, I'll do the check then.
Melting Slicks
Joined: Nov 2002
Posts: 2,471
Likes: 2
From: 1993 Quasar Blue 'vert Scottsdale AZ
With 3.54's, I run 2500 rpm at 75 mph. You must have 3.73's or something is amiss. Are you sure that you have a D36? P.S. Vader86, I thought that you had fallen off the face of the Earth or something worse.
Thread Starter
Melting Slicks
Joined: Jan 2008
Posts: 2,065
Likes: 1
From: Jasper Texas
When I bought it, I was told it had an upgrade rear end with 4.10 gears (I figured he meant a d44). When I got under the car, however, I could swear that I saw a third top bolt on the diff. housing. Maybe I imagined it??? When I get my car back next week, I'll check into it.
The other things I can think of that could affect my cruising rpms would be the torque converter, its a 2800 stall, but it does lock up properly. I've been having that injector problem too; 500 horses hasn't felt like 500 horses since the injectors have been acting up, could that affect cruising rpms any?
The other things I can think of that could affect my cruising rpms would be the torque converter, its a 2800 stall, but it does lock up properly. I've been having that injector problem too; 500 horses hasn't felt like 500 horses since the injectors have been acting up, could that affect cruising rpms any?
Last edited by cwyates4; Jun 27, 2008 at 11:42 PM.
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Le Mans Master
Joined: Dec 2002
Posts: 5,270
Likes: 3
From: Seattle Area WA
Whats stock size? 255 50 16?
With those tires measuring at 26.04 inches tall. I have you at 3200 RPMs turning 70mph in 3rd (1.0) with 3.54s, 100mph in 4th (0.7)
Turning 3200 RPMs and 70.8mph in 4th, would require you to have a rear gear of 5.
So either you are in 3rd gear or someone has changed your gear ratios.
With those tires measuring at 26.04 inches tall. I have you at 3200 RPMs turning 70mph in 3rd (1.0) with 3.54s, 100mph in 4th (0.7)
Turning 3200 RPMs and 70.8mph in 4th, would require you to have a rear gear of 5.
So either you are in 3rd gear or someone has changed your gear ratios.
Thread Starter
Melting Slicks
Joined: Jan 2008
Posts: 2,065
Likes: 1
From: Jasper Texas
I'm definitely in overdrive, no doubt about that.
Here's my shift points, maybe this will help.
1st= 6500 rpms, 42-43 mph
2nd=6300-6500, 78-81 mph
3rd=never got that far, scared
Yep, thats the tire size I have; Will soon be switching to 315/35/17s though.
Here's my shift points, maybe this will help.
1st= 6500 rpms, 42-43 mph
2nd=6300-6500, 78-81 mph
3rd=never got that far, scared
Yep, thats the tire size I have; Will soon be switching to 315/35/17s though.
Le Mans Master
Joined: Dec 2002
Posts: 5,270
Likes: 3
From: Seattle Area WA
So with the stock 700r4 gear ratios (3.06, 1.63, 1, 0.7)
6500rpm
4.10's:
40.1 mph
75.3 mph
122.8 mph
175.4 mph
3.73's:
44.1 mph
82.8 mph
135.0 mph
192.8 mph
3.54's:
46.5 mph
87.3 mph
142.2 mph
203.2 mph
3.07's:
53.6 mph
100.6 mph
164.0 mph
234.3 mph
2.59's:
63.5 mph
119.3 mph
194.4 mph
277.7 mph
70mph: 3rd RPM // 4th RPM
4.10: 3705 // 2594
3.73: 3371 // 2359
3.54: 3199 // 2239
3.07: 2774 // 1942
2.59: 2340 // 1638
Keep in mind, this is with an assumed tire height, so while pretty accurate, expect some variance.
The easy solution to ?'s about ratios and D44/D36 is to jack up the car when you get it back. Put a piece of tape on the inside of the tire and a piece of tape on the drive shaft by the rear yoke. Lie on your back so you can watch both and spin the rear tire by hand. Count the revolutions it takes for the drive shaft to make 1 rev.
6500rpm
4.10's:
40.1 mph
75.3 mph
122.8 mph
175.4 mph
3.73's:
44.1 mph
82.8 mph
135.0 mph
192.8 mph
3.54's:
46.5 mph
87.3 mph
142.2 mph
203.2 mph
3.07's:
53.6 mph
100.6 mph
164.0 mph
234.3 mph
2.59's:
63.5 mph
119.3 mph
194.4 mph
277.7 mph
70mph: 3rd RPM // 4th RPM
4.10: 3705 // 2594
3.73: 3371 // 2359
3.54: 3199 // 2239
3.07: 2774 // 1942
2.59: 2340 // 1638
Keep in mind, this is with an assumed tire height, so while pretty accurate, expect some variance.
The easy solution to ?'s about ratios and D44/D36 is to jack up the car when you get it back. Put a piece of tape on the inside of the tire and a piece of tape on the drive shaft by the rear yoke. Lie on your back so you can watch both and spin the rear tire by hand. Count the revolutions it takes for the drive shaft to make 1 rev.
Last edited by USAsOnlyWay; Jun 28, 2008 at 03:49 AM.
Team Owner
Joined: Dec 2000
Posts: 21,094
Likes: 282
From: Phila., PA burbs
The easy solution to ?'s about ratios and D44/D36 is to jack up the car when you get it back. Put a piece of tape on the inside of the tire and a piece of tape on the drive shaft by the rear yoke. Lie on your back so you can watch both and spin the rear tire by hand. Count the revolutions it takes for the drive shaft to make 1 rev.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Another possibility is that the tach readout is FOBAR for some reason.
My "new" '88 IROC-Z shows a much higher RPM on the analog tach than my scanner shows the ECM is seeing.
My "new" '88 IROC-Z shows a much higher RPM on the analog tach than my scanner shows the ECM is seeing.
Le Mans Master
Joined: Dec 2004
Posts: 5,488
Likes: 1,352
The 3.75 is the thick gear set for a 2 series carrier, Richmond makes them. I run a 3.75 in mine and am nowhere near 3200 @ 70 more like 2400 sounds like you are stuck in third gear to me.