After some searching here and through Google, I wasn't able to find what I was looking for - at least in the form I needed to understand it, anyway. Forgive this non-gearhead.

I am considering a swap to make highway driving better in the mpg department and to possibly have less wear on my 43 year old motor. How much effect would a swap from a 3.08 to a 2.41 have on long, interstate trips?

I saw where 2.41 was available in a '67 cutlass with a 6 cyl engine. Who might have those gears? I guess JY Dog might be the place to look, huh?

 

 

I really would not bother.Those 2:41's are going to make the engine work harder to get it moving,so you will use a little more gas in that area.The 3:08 is a good gear for the highway.If you are still determined to do that,I have 2:56's & 2:78's for the 12-bolt O-axle,& I have the matching 2-series carrier to go with them.These are for the 12-bolt O-axle.Is that what you have,or do you have the 8.2" 10-bolt? The early 67's came with the 8.2". I have a 67 4-door parts car that I can check too.

 

Math is your friend...

With everything else the same (same tires, for example) the new engine RPM at a given speed will be 2.41/3.08 times the old RPM.

 

Thanks for not roasting me - I love cars, but after 43 years, I am finally deciding I want to know more.

Thank for the formula and the chart is great.

So I guess, for the cost/benefit analysis - all things involved - swapping the SuperTurbine300/Jetaway for a 200-4r or swapping for lower gears wouldn't really be much of a pay-off in reducing engine wear and increasing mpg. I don't anticipate driving it on the interstate often - maybe one or two trips overnight a year - so any increase would be offset by the cost unless amortized over a long term, probably longer than I will own the car. I am fine with the way it drives now, but some extra MPG on the highway and less RPM would be nice - I have no illusions that the car is anything but a crusier, anyway - I don't plan on racing it or anything.

So then, why do people do it?

 

if you want, I have a spreadsheet that can estimate fuel economy pretty accuratly using the gear ratio, BMEP ect ect... I have a BMEP estimate for a 71 350, which would probably scale down well for a 6 cyl engine. Let me know if you are interested, and I can change around the model, and estimate your current fuel economy, and verify that the model is accurate, and use it to estimate your fuel economy with the lower gears. Based on experience and other cars I have analyzed, I would say you would see probably 1-3 mpg better, however your car would feel slower, meaning you would probably put your foot into it more to accelerate at the same rate you were used to, which would probably make everything equal out.

 

My car has a 330 - I was just stating the 2.41 rewar-end was available on the 6 cyl 67 Cutlass

actually, the spread sheet would be great

 

Actually, in my opinion you'd be miles ahead in both economy and performance to keep the 3.08 and get rid of the Jetaway. Put a 200-4R in there and get the best of both worlds.

 

Put a 200-4R,or at least go with a TH350 to get an extra gear.

 

Are you sure about the 2.41 gear ratio? Some even had 2.29...lol I am almost certain that was a FULL size car ratio only in the 1967 day. Not till the 8.5 came to being that we had the 2.41 in the cars...

8.2 10 bolt in the cutlas Buick and ponitac all basically had the same ratios 2.56 2.78 2.93 3.08 3.23 3.36 3.42(buick/ olds) 3.55 3.64 (68-70B) 3.90 4.33 and up to crazy numbers 4.66 etc.

Jim
J D Race

 

leave the gears as they are get larger tires for your hi-way trips,watch your speed it will read slower then you are traveling.