# Better gas mileage



## Rich1967GTO (3 mo ago)

I currently have a 400 ci with the three speed automatic tranny, I have 4.11 or lower gears at this time. Can I run 2.56's or what higher gear can I use to not have to tac 3k rpm at 65 mph? I'd like to tac around 2k rpm at 65mph.

thanks


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## armyadarkness (Dec 7, 2020)

Rich1967GTO said:


> I currently have a 400 ci with the three speed automatic tranny, I have 4.11 or lower gears at this time. Can I run 2.56's or what higher gear can I use to not have to tac 3k rpm at 65 mph? I'd like to tac around 2k rpm at 65mph.
> 
> thanks


You can switch to 336 for a big improvement... but keep in mind that changing too drastically would require a new carrier. 336 is the best all around.

My 67 400 with 336's, tachd about 3200 rpms at 80 mph. Now I have a manual with overdrive.

No 67 GTO is ever going to be great on gas, unless you get overdrive. Also, if you go numerically lower than 336, the fun goes away fast!


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## ponchonlefty (8 mo ago)

Rich1967GTO said:


> I currently have a 400 ci with the three speed automatic tranny, I have 4.11 or lower gears at this time. Can I run 2.56's or what higher gear can I use to not have to tac 3k rpm at 65 mph? I'd like to tac around 2k rpm at 65mph.
> 
> thanks


2.41 gear but i dont know if you can get them. a 3.08 with a overdrive transmission is a good option. and maybe easier to find.


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## Sick467 (Oct 29, 2019)

I had a 2.56 in a 67 GTO with a TH400 (maybe 400hp with a cam, port matched, and headers), and at 55 mph it would get around 17 mpg. It was a single peel rearend and was a slow take-off off the line, but was a rather hellacious punch in a down shift at 45 mph. it would do 50 plus in first gear and chirp into second. 140mph was as fast as my old self had the guts to take it. I can't say what the RPM's where...I didn't have a tach.


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## Baaad65 (Aug 29, 2019)

Sick467 said:


> I had a 2.56 in a 67 GTO with a TH400 (maybe 400hp with a cam, port matched, and headers), and at 55 mph it would get around 17 mpg. It was a single peel rearend and was a slow take-off off the line, but was a rather hellacious punch in a down shift at 45 mph. it would do 50 plus in first gear and chirp into second. 140mph was as fast as my old self had the guts to take it. I can't say what the RPM's where...I didn't have a tach.


140 ? whoa I hope you were at Bonneville ...how stable was the car? And if you had a tach I wouldn't be taking my eyes off the road to look at it 😳


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## armyadarkness (Dec 7, 2020)

My car with 336's and a similar setup, would easily hit 120 mph and still had plenty-o-pull. Now with the new cam and TKX, it would scream past there.

It's a rocket off the line and cruises at 80mph, barely touching the gas. It's stable as Hell because of all the Global West stuff... but I did de-laminate a back tire, last week, and that wasnt pretty.

This is one of those times when Im okay to just assume what me abilities are. Obviously the car handles and hold terrific, but there're too many other things to go wrong on a 55 year old car. The milage is way better with the TKX.


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## Sick467 (Oct 29, 2019)

Baaad65 said:


> 140 ? whoa I hope you were at Bonneville ...how stable was the car? And if you had a tach I wouldn't be taking my eyes off the road to look at it 😳


Stability started to wain at about 80 mph and got worse from there, but but my stupidity just got more firm. Young and dumb...with God on my side!


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## 66COUPE (Jul 23, 2021)

Rich1967GTO said:


> I currently have a 400 ci with the three speed automatic tranny, I have 4.11 or lower gears at this time. Can I run 2.56's or what higher gear can I use to not have to tac 3k rpm at 65 mph? I'd like to tac around 2k rpm at 65mph.
> 
> thanks


You knew GTO meant gas, tires & oil… right? 🤣


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