Need help with gears? 3.89

[Rt Jam]

There is NO one gear choice that will maximize acceleration and give you low rpms for comfortable highway cruising. Any choice will be a compromise. You will either have what you have now, too much rpm for highway OR give up some acceleration.

The only solution is an overdrive transmission. Think about any car made in the last 20 years, none of them have 3 gears with the top gear being 1:1.

 

[Ernest]

Perhaps this video will help determine whats right for you.

 

[Ribbedroof]

I have a car with a TH350 and 4.10 gear...IMO not a "good" highway gear...UNLESS I swap to an Overdrive. Which would really give the best of both worlds...the low end grunt of the 4.10s and an effective 2.7X gear in OD.

 

[Scubby13]

You might be happier with 3.55s if you go any higher geared than that you might find it sluggish off idle
If your pocket book will allow it install an overdrive transmission and keep the 3.89s
I’ve had 373s with a 700r4 and it was perfect fo

Perhaps this video will help determine whats right for you.

Thanks

 

[Scubby13]

I have a car with a TH350 and 4.10 gear...IMO not a "good" highway gear...UNLESS I swap to an Overdrive. Which would really give the best of both worlds...the low end grunt of the 4.10s and an effective 2.7X gear in OD.

Thanks

 

[Scubby13]

Just wanted to say thank you to each and everyone of you. Truly appreciate all of your help, advice and opinions

 

[Kamloops cutlass]

You’re welcome
I hope you found your answer among all the replies

 

[scoti]

Let me start by saying I am no expert when it comes to building cars this is my 1st project. I appreciate any advice or opinions that anyone has to give. Thank you in advance. I currently have a 84 cutlass with a 454 engine. Th350 with a 9in rear end with 3.89 gears. Originally I was told this would be a good gear for cruising on the highway as that is kinda what I want to do mostly. I just really want to be able to enjoy that car and spin the tires. Car seems to only have 2 gears and I was told that I need smaller gears to be able to cruise on the highway. Car is fine around 55 60 mph but then after that seems as tho it just revs and needs another gear. So I don't know if it is the transmission or if 3.42 or 3.55 or even 3.73 gears will work. Again I am new and learning every day and I appreciate any assistance or guidance. Thanks.

Just wanted to say thank you to each and everyone of you. Truly appreciate all of your help, advice and opinions

What size are the rear tires?

If one is assuming 255/60-15's @ ~27" tall, a th350 in 3rd w/3.89's yields 2905rpm @ 60mph w/no converter slippage w/a 1st gearing leverage ratio @ 9.80 (2.52 x 3.89).
Change the gearing to 3.70 = 2763rpm; 1st gear leverage ratio @ 9.324
Change the gearing to 3.60 = 2688rpm; 1st gear leverage ratio @ 9.072
Change the gearing to 3.50 = 2613rpm; 1st gear leverage ratio @ 8.820
Change the gearing to 3.40 = 2539rpm; 1st gear leverage ratio @ 8.568
Change the gearing to 3.25 = 2427rpm; 1st gear leverage ratio @ 8.19
Change the gearing to 3.00 = 2240rpm; 1st gear leverage ratio @ 7.56

Bigger cubes get away w/lower ratio gearing because they usually have more low end torque.
Bigger cubes w/a big cam however would be better suited for similar gearing to a smaller engine.

 

[motorheadmike]

What size are the rear tires?

If one is assuming 255/60-15's @ ~27" tall, a th350 in 3rd w/3.89's yields 2905rpm @ 60mph w/no converter slippage w/a 1st gearing leverage ratio @ 9.80 (2.52 x 3.89).
Change the gearing to 3.70 = 2763rpm; 1st gear leverage ratio @ 9.324
Change the gearing to 3.60 = 2688rpm; 1st gear leverage ratio @ 9.072
Change the gearing to 3.50 = 2613rpm; 1st gear leverage ratio @ 8.820
Change the gearing to 3.40 = 2539rpm; 1st gear leverage ratio @ 8.568
Change the gearing to 3.25 = 2427rpm; 1st gear leverage ratio @ 8.19
Change the gearing to 3.00 = 2240rpm; 1st gear leverage ratio @ 7.56

Bigger cubes get away w/lower ratio gearing because they usually have more low end torque.
Bigger cubes w/a big cam however would be better suited for similar gearing to a smaller engine.

True, but this also assumes the 454 is healthy enough to meet the conditions you laid out. We cannot confirm this.

Dropping the gearing could have knock-on effects of the cam and converter aren't in alignment. The driveability could go way down.

 

[scoti]

True, but this also assumes the 454 is healthy enough to meet the conditions you laid out. We cannot confirm this.

Dropping the gearing could have knock-on effects of the cam and converter aren't in alignment. The driveability could go way down.

Agreed..... My comments were based on the assumption the motor was in good working order & tune. Usually when someone pops for a 9" under their g-body, they did other items on a similar threshold of improvement.