Is this even possible??
Thread Starter
Supreme Member
Joined: Dec 2000
Posts: 1,536
Likes: 0
From: Springfield, MO, USA
Car: 1986 Trans Am, 1991 Firebird
Engine: 355 TPI, 3.1L V6
Transmission: 700R4 in both
Is this even possible??
My friend just recently upgraded his rear end from 2.73s to 3.73s and now he says that he's getting MORE gas mileage than before. He said he was getting about 17mpg with the 2.73s and now he says he's getting 21mpg with the 3.73s. Has anyone ever heard of this happening??
Supreme Member
Joined: Dec 1999
Posts: 1,237
Likes: 1
From: Reno, NV
Car: yep
Engine: uhuh
Transmission: sure does
Could be, its like putting a 4 barrel on where a 2 barrel was will get better mileage sometimes...
The reason being the engine doesn't have to work as hard to achieve the same speeds.
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ASE Mechanic/Machinist/Smog Tech
1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R
and 2 POS commuters...
R.I.P. #3
"He can see air"
The reason being the engine doesn't have to work as hard to achieve the same speeds.
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ASE Mechanic/Machinist/Smog Tech
1999 NBM Trans Am
1986 Chevy 3/4 ton pick up
1981 corvette
1995 Kawi ZX6R
and 2 POS commuters...
R.I.P. #3
"He can see air"
Supreme Member
Joined: Jan 2001
Posts: 7,164
Likes: 1
From: Someone owes me 10,000 posts
Car: 99 Formula
Engine: LS1
Transmission: T56
Axle/Gears: 342
No, he's not getting better gas milage. Did he change the speedo gears, if not then if he really goes 100 miles then his odometer probably says he has gone like 150, hence giving better gas milage.
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'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
3" Hooker CatBack w/Aero Chamber muffler
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
160* Stat
3:73 Posi
Rebuilt 700R4
B&M Megashifter, 5" Autometer Tach w/shift lite
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'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
3" Hooker CatBack w/Aero Chamber muffler
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
160* Stat
3:73 Posi
Rebuilt 700R4
B&M Megashifter, 5" Autometer Tach w/shift lite
Joined: Mar 2000
Posts: 43,187
Likes: 43
From: Littleton, CO USA
Car: 82 Berlinetta/57 Bel Air
Engine: L92/LQ4 (both w/4" stroke)
Transmission: 4L80E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
I like Mark's answer.
17 * (3.73/2.73) = 23.2.
If he didn't recalibrate his speedometer, then in fact his mileage has gone down, which isn't too surprising.
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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. 2-1/2" cat-back, ZZ3 intake, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 CC system w/'87 LB9 block, ZZ3 cam, ported World 305 heads, Hooker 2055 headers, 3" Catco cat & 3" catback, restalled TC, Spohn SFCs).
57 Bel Air, my 1st car. '66 396, 9.7 CR forged TRWs, Weiand Action+, Holley 750VS w/4150 conversion, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 600 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).
17 * (3.73/2.73) = 23.2.
If he didn't recalibrate his speedometer, then in fact his mileage has gone down, which isn't too surprising.
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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4. 2.93 limited slip. 2-1/2" cat-back, ZZ3 intake, Accel HEI SuperCoil. AMSOIL syn lubes bumper-to-bumper. Daily driver, work-in-progress (LG4 CC system w/'87 LB9 block, ZZ3 cam, ported World 305 heads, Hooker 2055 headers, 3" Catco cat & 3" catback, restalled TC, Spohn SFCs).
57 Bel Air, my 1st car. '66 396, 9.7 CR forged TRWs, Weiand Action+, Holley 750VS w/4150 conversion, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 600 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).
Thread Starter
Supreme Member
Joined: Dec 2000
Posts: 1,536
Likes: 0
From: Springfield, MO, USA
Car: 1986 Trans Am, 1991 Firebird
Engine: 355 TPI, 3.1L V6
Transmission: 700R4 in both
That makes sense. He has NOT changed his speedo gear yet. I'll have to let him know about that.
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Supreme Member
Joined: Nov 1999
Posts: 2,860
Likes: 3
From: NE
Car: 82 camaro SC
Engine: 350
Transmission: 700r4
Correct, madmax. For example, on the extreme side, suppose you had a radical engine with a killer cam that has a powerband of 2700-6500 rpm. You have 2.73 gears and your cruise rpm is well below the point where the engine becomes efficient. Deeper gears would, in that case, help.
With those deep gears and a way off speedo he probably thinks he is going really fast as well as getting better mileage.
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350 with stealth intake, holley carb, 470 lift cam. 700r4 with .5 boost valve, vette servo, tci lock-up kit, B&M megashifter. Richmond 3.73 gears, powertrax locker, timkin bearings, synthetic lube. Custom 3 inch single into 2 2.5 pipes. 1 1/2 drop springs, 1 5/16 solid front sway bar, 1 inch rear bar, custom subframe connectors, custom LCA relocation brackets. Kobel ground FX, currant red metallic paint. Lots of other stuff...
82camaro
With those deep gears and a way off speedo he probably thinks he is going really fast as well as getting better mileage.
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350 with stealth intake, holley carb, 470 lift cam. 700r4 with .5 boost valve, vette servo, tci lock-up kit, B&M megashifter. Richmond 3.73 gears, powertrax locker, timkin bearings, synthetic lube. Custom 3 inch single into 2 2.5 pipes. 1 1/2 drop springs, 1 5/16 solid front sway bar, 1 inch rear bar, custom subframe connectors, custom LCA relocation brackets. Kobel ground FX, currant red metallic paint. Lots of other stuff...
82camaro
