3:08 vs 3:73
Thread Starter
Racer
Joined: Jul 2004
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3:08 vs 3:73
I'm in the process of changing my differential from a 3:08 to a 3:73. The 3:08 housing was cracked and the spare differential I have is a 3:73. What can I expect in preformace ? The 3:08 did a good burnout in first gear but not second. How much will I lose on the top end ? I don't really care about gas mileage because I only drive it sometimes on weekends. Will It really be noticeable ?
Melting Slicks
Joined: Aug 2001
Posts: 2,043
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From: Elkhorn WI
The power-o-meter, "seat of the pants", will be through the roof. Stop light to stop light will be incredible. Standing burnouts should not be an issue. You should see tires breaking loose between gears, depending on your engine mods. When I swapped out my 3.08's for 3.70's it was like being in a different car. 
Safety Car
Joined: Aug 2001
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From: Waterford Mi
Race Director
Joined: Nov 2000
Posts: 11,872
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From: Waterloo ontario Canada
Your open road cruising will be poor. The motor will be buzzing at a high rpm while all the traffic goes around you.
One of our members in our little group had 3.55's and he had problems keeping up.
Without overdrive it is too steep for the few tenth's of a second you gain in the quarter.
One of our members in our little group had 3.55's and he had problems keeping up.
Without overdrive it is too steep for the few tenth's of a second you gain in the quarter.
Racer
Joined: Sep 2005
Posts: 359
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From: Shoemakersville Pa
Originally Posted by ylose
The power-o-meter, "seat of the pants", will be through the roof. Stop light to stop light will be incredible. Standing burnouts should not be an issue. You should see tires breaking loose between gears, depending on your engine mods. When I swapped out my 3.08's for 3.70's it was like being in a different car.
Burning Brakes
Joined: Feb 2005
Posts: 977
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From: wash. dc
i drive mostly around town so stop light to stop light is want i want... however when i'm on the highway, at 70 mph i'm screaming at 3200 rpm.. but i'm in a classic so i keep it at 60 and look at all the thumbs up as folks pass by... 
Pro
Joined: May 2005
Posts: 745
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From: Miami Florida
norval drives FAST. i enjoy 3.73's because my highway jaunts are usually in area's that i cant sustain 80+ for too long because of traffic. so for light to light and every day cruizin i go through the gears fast and back off. but for a 3hr trip they get a little old for several reasons. gas mileage drops off, and even though i love my sidepipes, after several hours your brain gets a bit buzzed. thats why almost 100% of us have a daily driver or two and our toy for fun.
Burning Brakes
Joined: Jun 2004
Posts: 936
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From: Tulsa OK
What kind of difference are you looking at assuming you have an OD trans? Right now I'm taching about 2100 at 75 or so with 2.87s. What'd 3.55 or 3.73 bump that too? Something like 2500ish maybe?
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Melting Slicks
Joined: Nov 2003
Posts: 2,362
Likes: 1
From: San Antonio TX
Originally Posted by Xakk
What kind of difference are you looking at assuming you have an OD trans? Right now I'm taching about 2100 at 75 or so with 2.87s. What'd 3.55 or 3.73 bump that too? Something like 2500ish maybe?
3.73 27 tire height at 75MPH is 3481 rpm
3.55 27 tire height at 75 Mph is 3313 rpm
Pro
Joined: Mar 2005
Posts: 559
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From: James Island South Carolina
Originally Posted by 71redskin
i drive mostly around town so stop light to stop light is want i want... however when i'm on the highway, at 70 mph i'm screaming at 3200 rpm.. but i'm in a classic so i keep it at 60 and look at all the thumbs up as folks pass by...
Le Mans Master
Joined: Jan 2004
Posts: 8,295
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From: one night in Bangkok you are never lonely
Originally Posted by norvalwilhelm
Your open road cruising will be poor. The motor will be buzzing at a high rpm while all the traffic goes around you.
One of our members in our little group had 3.55's and he had problems keeping up.
Without overdrive it is too steep for the few tenth's of a second you gain in the quarter.
One of our members in our little group had 3.55's and he had problems keeping up.
Without overdrive it is too steep for the few tenth's of a second you gain in the quarter.
I changed from 7.73 to 3.08 just for that reason. Driving on the highways here there is no speed enforcement so dump trucks were passing me at 90 I was screaming with my side pipes and tach up there. Now with the 3.08 it is reasonable to cruse at 90+ for 50 miles at a clip. Also with the 3.73 in first it was all over the place now it gets me going just fine. If I was drag racing the 3.73s would be OK but for everyday driving
Melting Slicks
Joined: Aug 2001
Posts: 2,043
Likes: 1
From: Elkhorn WI
Originally Posted by norvalwilhelm
Your open road cruising will be poor. The motor will be buzzing at a high rpm while all the traffic goes around you.
One of our members in our little group had 3.55's and he had problems keeping up.
Without overdrive it is too steep for the few tenth's of a second you gain in the quarter.
One of our members in our little group had 3.55's and he had problems keeping up.
Without overdrive it is too steep for the few tenth's of a second you gain in the quarter.
What speeds are you driving on the road? In my youth I drove an Old's Rocket 350/th350/3.73 rear wheel drive, year round in Wisconsin for near 10 years. Yes on the Xpressway I was pushing 3,000+ RPMs, but stop light to stop light is what mattered to me. Over 65 and you were on the side of road then anyways with Christmas lights behind you....and Santa was no where to be seen but gifts were, in the form of written court appearances and you had to pay them to accept your autograph. 
Must be nice not to have the Smokeys doing their job!
Here, they would love for me to drive those speeds, then when they impound my car they will have to take it out and 're-enact' the situation !
Anyone ever see the beginning of SuperTroopers? That would so be the case.
Last edited by ylose; Jan 30, 2006 at 12:16 PM.
Racer
Joined: Sep 2004
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I would go with 3.08's I had 4:10 in my 85 Mustang and went down to 3.08 and loved it. I also had 3.91 in my Challenger and went down to 3.23
Unless your not going on the Highways I'd say okay. Other than that 3.08 all the way
Unless your not going on the Highways I'd say okay. Other than that 3.08 all the way
Race Director
Joined: Jan 2003
Posts: 15,176
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From: State of Confusion
Originally Posted by rustbucket80
I'm in the process of changing my differential from a 3:08 to a 3:73. The 3:08 housing was cracked and the spare differential I have is a 3:73. What can I expect in preformace ? The 3:08 did a good burnout in first gear but not second. How much will I lose on the top end ? I don't really care about gas mileage because I only drive it sometimes on weekends. Will It really be noticeable ?
my '79 Z28 went from 14.40s @ 97 with 3.42s to 14-teens with 4.10s, with no change in trap-speed, if that is what you mean by 'how-much-will-I-lose-on-the-top-end' .....
Thread Starter
Racer
Joined: Jul 2004
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Originally Posted by 69/70vette
On my 69 BB I had Van Steel put 3.73 in the rear when they rebuilt (was 3.08) not back together yet. What kind of tire are you running so you don't spin tires everytime you pull out?
