2.78 gear to a 3.55 gear

j's69stang · 03-28-2001, 05:51 PM

i get 16 mpg right now with the setup i have which is a 2.78 or so gear somewhere in that range. how much would my gas mileage decrease and how much would my et increase with the gear swap???? thanks

red · 03-28-2001, 08:07 PM

I did the swap and didn't notice a change in gas milage. I don't really drive long distances though. If I remember right 60 used to be at about 2400 rpm and now it pretty high, about 3K. I have 14" rims with 60 series tires so that hurts the gas milage too. Overdrive would be nice! I don't regret the change one bit.

The et will depend alot on traction. It is hard to get traction with a '65, I think the 69's hook up a little better.

DO it

-JON

j's69stang · 03-28-2001, 10:28 PM

i have got 14 inch rims and 60 series tires too. I dont drive long distances just drive everyday. The parts cost 188 out of jeggs, are they cheaper anywhere else? but the et should be higher if i can hook and i should be able to spin the tires a whole lot easier right?

Jaydee · 03-29-2001, 09:06 AM

You will love the change. The seat of ter pants feel will be very noticible, the ET will drop and yeah, smokin em up will be easier. I have 3.50's in my 65 and they are IMO just about a perfect steet gear with my four speed. I have 14" wheels and a 25.5" tall tire and turn about 2,800 rpm at 60 mph. And you will lose some mpg due to both the higher cruise rpm and (the biggest factor) not being able to resist urge to press down the Go pedal harder and more frequently.

------------------
1965 K code coupe - numbers matching - restoration ongoing. 1987 LX notch, 5 spd, stock heads (minor porting) and intake, 65mmTB, 3.55's, ram air, pulleys, shorty's, 2.5" exhaust with cats 13.89@100.25

j's69stang · 03-29-2001, 02:42 PM

well the problem im going to have is i have a c-4 so i might get some crappy gas mileage i just didnt know if i wanted to do it with that being my only car and gas at 1.55 a gallon.

Fostang · 03-29-2001, 03:48 PM

Only a dollar 55. Why are you complaining? I haven't seen those prices in a while.

------------------
67'fastback- Edelbrock carb, intake, cam, valve springs. Road lifters, Comp Cam rocker arms, windage tray, cerama coated headers, dual flows with H-pipe, modded c-4, tci stall converter, perma cool electric fan, aluminum water pump, griffen aluminum radiator, accel 8.8 cable, wide cap distriburator, magnetic pick up, manley valves, v-matic hurst shifter, edelbrock performer nitrous, carter electric fuel pump, ignitor coil, solid motor mounts, magna racing suspension, poly urathane bushings, und

j's69stang · 03-29-2001, 04:21 PM

well ever since i got the motor rebiult i have had to put the good stuff in it and i thought it was kinda expensive but i guess not. well thanks for the info but how much did your gas mileage fo down 2-3 mpg or what?

Jaydee · 03-30-2001, 09:32 AM

I think that the biggest factor determining you mileage after this change will be in how you actually drive the car. The natural tendency for most people after making a change like this is to get on the car more often because it feels so much stronger which is why people change gears and being more aggresive with the go pedal obviously drops the gas mileage. If you drove the car in a conservetive fashion after making the change, your mileage would likely not change much at all from what you are now getting. In normal driving, the better gear multiplication will require less throttle opening to get the car up to normal operating speed, which in day in day out driving helps to balance out the increased cruising rpm. This assumes that you do not do a lot of higher speed highway driving - if you do your mileage will likely drop by 2 or 3 mpg. As mentioned, IMO the use of your right foot will be the biggest factor

------------------
1965 K code coupe - numbers matching - restoration ongoing. 1987 LX notch, 5 spd, stock heads (minor porting) and intake, 65mmTB, 3.55's, ram air, pulleys, shorty's, 2.5" exhaust with cats 13.89@100.25

j's69stang · 03-30-2001, 12:11 PM

well then i guess im gonna have to order that gear from jegs real soon and put it in there and see if i fall in love with it

Tom351 · 04-02-2001, 08:51 AM

You may want to find a rear axle center-section with the gear already installed. This way, you can swap back to 2.79's in about an hour or less if you ever need it for road trips.

------------------
67 Fastback - Arctic White Pearl paint
351W ,Trick Flow Aluminum Heads, Edelbrock TorkerII, Carter 750 CFM, Comp. Cam 477/510 219/233@.050, Performance Automatic C-4 Trans, 3.55 gears, Front Disc Brakes, 1-1/8" Fr. 3/4" rear sway bars.

My 351W Fastback

Fostang · 04-02-2001, 04:24 PM

Thats exactly what I would do Tom 351.

------------------
67'fastback- Edelbrock carb, intake, cam, valve springs. Road lifters, Comp Cam rocker arms, windage tray, cerama coated headers, dual flows with H-pipe, modded c-4, tci stall converter, perma cool electric fan, aluminum water pump, griffen aluminum radiator, accel 8.8 cable, wide cap distriburator, magnetic pick up, manley valves, v-matic hurst shifter, edelbrock performer nitrous, carter electric fuel pump, ignitor coil, solid motor mounts, magna racing suspension, poly urathane bushings, und

Rev · 04-02-2001, 04:34 PM

Tom 351, you're a better man than me if you can do that in an hour. Drive shaft, brakes, and axles and then do it all over again plus refill takes me several hours. But then again, I don't really hurry. Of course us old peckerwoods are known to be slow. LOL.

Rev

------------------
'66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph
1/4 mi.

Fostang · 04-02-2001, 09:02 PM

peckerwood lol. Well if you find that an hour is a whooping time to change a 3 rd member then you'll get mind blown that my dad have a team effort record for a gear swap change in under 30 minutes and I changed my whole carrier in under 2 hrs. These changes were done with basic tools, some jack stands, and floor jack. Carburator change over in 4.34 minutes is my record. I use to love timing myself. Gave the pit crew feel.

It's better to take your time if your not sure if it's going to work.

------------------
67'fastback- Edelbrock carb, intake, cam, valve springs. Road lifters, Comp Cam rocker arms, windage tray, cerama coated headers, dual flows with H-pipe, modded c-4, tci stall converter, perma cool electric fan, aluminum water pump, griffen aluminum radiator, accel 8.8 cable, wide cap distriburator, magnetic pick up, manley valves, v-matic hurst shifter, edelbrock performer nitrous, carter electric fuel pump, ignitor coil, solid motor mounts, magna racing suspension, poly urathane bushings, und

j's69stang · 04-02-2001, 11:52 PM

wow you might be a gearhead if you time yourself changing parts out on your car!!!!!!!!!!!!! im in no hurry to do anything on my car everytime i try to do something fast something else screws up so thanks anyway for the advice

Tom351 · 04-03-2001, 08:37 AM

Well, I was using a lift and air tools when I did it in under an hour, but 1.5 hours max on jackstands unless your just takin' your time having fun.

------------------
67 Fastback - Arctic White Pearl paint
351W ,Trick Flow Aluminum Heads, Edelbrock TorkerII, Carter 750 CFM, Comp. Cam 477/510 219/233@.050, Performance Automatic C-4 Trans, 3.55 gears, Front Disc Brakes, 1-1/8" Fr. 3/4" rear sway bars.

My 351W Fastback

Fostang · 04-03-2001, 04:45 PM

J's69STANG where are you from? I have a 9 inch rear with 3.50 gears it's an open unit. I'm asking $85 for it. I have some other sizes if interested send me a message. Also the whole 9 inch rear end for $180.

------------------
67'fastback- Edelbrock carb, intake, cam, valve springs. Road lifters, Comp Cam rocker arms, windage tray, cerama coated headers, dual flows with H-pipe, modded c-4, tci stall converter, perma cool electric fan, aluminum water pump, griffen aluminum radiator, accel 8.8 cable, wide cap distriburator, magnetic pick up, manley valves, v-matic hurst shifter, edelbrock performer nitrous, carter electric fuel pump, ignitor coil, solid motor mounts, magna racing suspension, poly urathane bushings, und

j's69stang · 04-03-2001, 10:00 PM

i have an 8 inch right now so and i live in memphis TN

Fostang · 04-03-2001, 10:41 PM

Well I can get you an 8 inch also thats not a problem.

------------------
67'fastback- Edelbrock carb, intake, cam, valve springs. Road lifters, Comp Cam rocker arms, windage tray, cerama coated headers, dual flows with H-pipe, modded c-4, tci stall converter, perma cool electric fan, aluminum water pump, griffen aluminum radiator, accel 8.8 cable, wide cap distriburator, magnetic pick up, manley valves, v-matic hurst shifter, edelbrock performer nitrous, carter electric fuel pump, ignitor coil, solid motor mounts, magna racing suspension, poly urathane bushings, und

j's69stang · 04-04-2001, 07:54 AM

do you have an 8 inch posi center section with 3.50 gears in it? if so how much

Fostang · 04-04-2001, 04:37 PM

Limit slip 8 inch units are hard to come by. No I don't have one right now. I'm currently looking for one also. All the ones I have are open units.

03-28-2001, 05:51 PM	#1
j's69stang Registered Member Join Date: Apr 2000 Posts: 102	2.78 gear to a 3.55 gear i get 16 mpg right now with the setup i have which is a 2.78 or so gear somewhere in that range. how much would my gas mileage decrease and how much would my et increase with the gear swap???? thanks

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03-28-2001, 08:07 PM	#2
red Registered Member Join Date: Sep 1998 Location: Millburn, NJ Posts: 310	I did the swap and didn't notice a change in gas milage. I don't really drive long distances though. If I remember right 60 used to be at about 2400 rpm and now it pretty high, about 3K. I have 14" rims with 60 series tires so that hurts the gas milage too. Overdrive would be nice! I don't regret the change one bit. The et will depend alot on traction. It is hard to get traction with a '65, I think the 69's hook up a little better. DO it -JON

03-28-2001, 10:28 PM	#3
j's69stang Registered Member Join Date: Apr 2000 Posts: 102	i have got 14 inch rims and 60 series tires too. I dont drive long distances just drive everyday. The parts cost 188 out of jeggs, are they cheaper anywhere else? but the et should be higher if i can hook and i should be able to spin the tires a whole lot easier right?

03-29-2001, 09:06 AM	#4
Jaydee Registered Member Join Date: Sep 2000 Location: Conn. Posts: 220	You will love the change. The seat of ter pants feel will be very noticible, the ET will drop and yeah, smokin em up will be easier. I have 3.50's in my 65 and they are IMO just about a perfect steet gear with my four speed. I have 14" wheels and a 25.5" tall tire and turn about 2,800 rpm at 60 mph. And you will lose some mpg due to both the higher cruise rpm and (the biggest factor) not being able to resist urge to press down the Go pedal harder and more frequently. ------------------ 1965 K code coupe - numbers matching - restoration ongoing. 1987 LX notch, 5 spd, stock heads (minor porting) and intake, 65mmTB, 3.55's, ram air, pulleys, shorty's, 2.5" exhaust with cats 13.89@100.25

03-29-2001, 02:42 PM	#5
j's69stang Registered Member Join Date: Apr 2000 Posts: 102	well the problem im going to have is i have a c-4 so i might get some crappy gas mileage i just didnt know if i wanted to do it with that being my only car and gas at 1.55 a gallon.

03-29-2001, 03:48 PM	#6
Fostang Registered Member Join Date: Feb 2001 Location: Stockton, Ca Posts: 599	Only a dollar 55. Why are you complaining? I haven't seen those prices in a while. ------------------ 67'fastback- Edelbrock carb, intake, cam, valve springs. Road lifters, Comp Cam rocker arms, windage tray, cerama coated headers, dual flows with H-pipe, modded c-4, tci stall converter, perma cool electric fan, aluminum water pump, griffen aluminum radiator, accel 8.8 cable, wide cap distriburator, magnetic pick up, manley valves, v-matic hurst shifter, edelbrock performer nitrous, carter electric fuel pump, ignitor coil, solid motor mounts, magna racing suspension, poly urathane bushings, und

03-29-2001, 04:21 PM	#7
j's69stang Registered Member Join Date: Apr 2000 Posts: 102	well ever since i got the motor rebiult i have had to put the good stuff in it and i thought it was kinda expensive but i guess not. well thanks for the info but how much did your gas mileage fo down 2-3 mpg or what?

03-30-2001, 09:32 AM	#8
Jaydee Registered Member Join Date: Sep 2000 Location: Conn. Posts: 220	I think that the biggest factor determining you mileage after this change will be in how you actually drive the car. The natural tendency for most people after making a change like this is to get on the car more often because it feels so much stronger which is why people change gears and being more aggresive with the go pedal obviously drops the gas mileage. If you drove the car in a conservetive fashion after making the change, your mileage would likely not change much at all from what you are now getting. In normal driving, the better gear multiplication will require less throttle opening to get the car up to normal operating speed, which in day in day out driving helps to balance out the increased cruising rpm. This assumes that you do not do a lot of higher speed highway driving - if you do your mileage will likely drop by 2 or 3 mpg. As mentioned, IMO the use of your right foot will be the biggest factor ------------------ 1965 K code coupe - numbers matching - restoration ongoing. 1987 LX notch, 5 spd, stock heads (minor porting) and intake, 65mmTB, 3.55's, ram air, pulleys, shorty's, 2.5" exhaust with cats 13.89@100.25

03-30-2001, 12:11 PM	#9
j's69stang Registered Member Join Date: Apr 2000 Posts: 102	well then i guess im gonna have to order that gear from jegs real soon and put it in there and see if i fall in love with it

04-02-2001, 08:51 AM	#10
Tom351 Registered Member Join Date: Oct 2000 Location: Atlanta,GA,USA Posts: 278	You may want to find a rear axle center-section with the gear already installed. This way, you can swap back to 2.79's in about an hour or less if you ever need it for road trips. ------------------ 67 Fastback - Arctic White Pearl paint 351W ,Trick Flow Aluminum Heads, Edelbrock TorkerII, Carter 750 CFM, Comp. Cam 477/510 219/233@.050, Performance Automatic C-4 Trans, 3.55 gears, Front Disc Brakes, 1-1/8" Fr. 3/4" rear sway bars. My 351W Fastback

04-02-2001, 04:24 PM	#11
Fostang Registered Member Join Date: Feb 2001 Location: Stockton, Ca Posts: 599	Thats exactly what I would do Tom 351. ------------------ 67'fastback- Edelbrock carb, intake, cam, valve springs. Road lifters, Comp Cam rocker arms, windage tray, cerama coated headers, dual flows with H-pipe, modded c-4, tci stall converter, perma cool electric fan, aluminum water pump, griffen aluminum radiator, accel 8.8 cable, wide cap distriburator, magnetic pick up, manley valves, v-matic hurst shifter, edelbrock performer nitrous, carter electric fuel pump, ignitor coil, solid motor mounts, magna racing suspension, poly urathane bushings, und

04-02-2001, 04:34 PM	#12
Rev Registered Member Join Date: Nov 1998 Location: Houston, Tx. Posts: 3,887	Tom 351, you're a better man than me if you can do that in an hour. Drive shaft, brakes, and axles and then do it all over again plus refill takes me several hours. But then again, I don't really hurry. Of course us old peckerwoods are known to be slow. LOL. Rev ------------------ '66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph 1/4 mi.

04-02-2001, 09:02 PM	#13
Fostang Registered Member Join Date: Feb 2001 Location: Stockton, Ca Posts: 599	peckerwood lol. Well if you find that an hour is a whooping time to change a 3 rd member then you'll get mind blown that my dad have a team effort record for a gear swap change in under 30 minutes and I changed my whole carrier in under 2 hrs. These changes were done with basic tools, some jack stands, and floor jack. Carburator change over in 4.34 minutes is my record. I use to love timing myself. Gave the pit crew feel. It's better to take your time if your not sure if it's going to work. ------------------ 67'fastback- Edelbrock carb, intake, cam, valve springs. Road lifters, Comp Cam rocker arms, windage tray, cerama coated headers, dual flows with H-pipe, modded c-4, tci stall converter, perma cool electric fan, aluminum water pump, griffen aluminum radiator, accel 8.8 cable, wide cap distriburator, magnetic pick up, manley valves, v-matic hurst shifter, edelbrock performer nitrous, carter electric fuel pump, ignitor coil, solid motor mounts, magna racing suspension, poly urathane bushings, und

04-02-2001, 11:52 PM	#14
j's69stang Registered Member Join Date: Apr 2000 Posts: 102	wow you might be a gearhead if you time yourself changing parts out on your car!!!!!!!!!!!!! im in no hurry to do anything on my car everytime i try to do something fast something else screws up so thanks anyway for the advice

04-03-2001, 08:37 AM	#15
Tom351 Registered Member Join Date: Oct 2000 Location: Atlanta,GA,USA Posts: 278	Well, I was using a lift and air tools when I did it in under an hour, but 1.5 hours max on jackstands unless your just takin' your time having fun. ------------------ 67 Fastback - Arctic White Pearl paint 351W ,Trick Flow Aluminum Heads, Edelbrock TorkerII, Carter 750 CFM, Comp. Cam 477/510 219/233@.050, Performance Automatic C-4 Trans, 3.55 gears, Front Disc Brakes, 1-1/8" Fr. 3/4" rear sway bars. My 351W Fastback

04-03-2001, 04:45 PM	#16
Fostang Registered Member Join Date: Feb 2001 Location: Stockton, Ca Posts: 599	J's69STANG where are you from? I have a 9 inch rear with 3.50 gears it's an open unit. I'm asking $85 for it. I have some other sizes if interested send me a message. Also the whole 9 inch rear end for $180. ------------------ 67'fastback- Edelbrock carb, intake, cam, valve springs. Road lifters, Comp Cam rocker arms, windage tray, cerama coated headers, dual flows with H-pipe, modded c-4, tci stall converter, perma cool electric fan, aluminum water pump, griffen aluminum radiator, accel 8.8 cable, wide cap distriburator, magnetic pick up, manley valves, v-matic hurst shifter, edelbrock performer nitrous, carter electric fuel pump, ignitor coil, solid motor mounts, magna racing suspension, poly urathane bushings, und

04-03-2001, 10:00 PM	#17
j's69stang Registered Member Join Date: Apr 2000 Posts: 102	i have an 8 inch right now so and i live in memphis TN

04-03-2001, 10:41 PM	#18
Fostang Registered Member Join Date: Feb 2001 Location: Stockton, Ca Posts: 599	Well I can get you an 8 inch also thats not a problem. ------------------ 67'fastback- Edelbrock carb, intake, cam, valve springs. Road lifters, Comp Cam rocker arms, windage tray, cerama coated headers, dual flows with H-pipe, modded c-4, tci stall converter, perma cool electric fan, aluminum water pump, griffen aluminum radiator, accel 8.8 cable, wide cap distriburator, magnetic pick up, manley valves, v-matic hurst shifter, edelbrock performer nitrous, carter electric fuel pump, ignitor coil, solid motor mounts, magna racing suspension, poly urathane bushings, und

04-04-2001, 07:54 AM	#19
j's69stang Registered Member Join Date: Apr 2000 Posts: 102	do you have an 8 inch posi center section with 3.50 gears in it? if so how much

04-04-2001, 04:37 PM	#20
Fostang Registered Member Join Date: Feb 2001 Location: Stockton, Ca Posts: 599	Limit slip 8 inch units are hard to come by. No I don't have one right now. I'm currently looking for one also. All the ones I have are open units.