[Glock 18]

3.42 vs. 3.73 vs. 3.55 I'm searching for the best gear ratio for my '69 Chevelle. It has a 454 and 700R4 transmission, 12 bolt rear end with 26.97 " tires on back. I will be cruising on interstates (sometimes on trips) and want comfortble RPM's at 75 and 80 MPH. I want to keep RPM's well below 3000 at 80 MPH. I also want to keep good, strong low end power. And thanks to Ron for your input. Any suggestions from others with any of these setups is appreciated.

[Philip]

The El Camino had 3.73 gears, 700R4 and 28" tires. At 75 mph the engine was turning around 2300 rpms.

Use this calculator to compare the different gear ratios.

http://www.f-body.org/gears/

[WurlitzBurg]

Make sure you use the tire Revs/Mile or the rolling diameter. This info can usually be obtained from the tire manufacturer's website.

[BillyGman]

I'd use 4.10 gears. What good is having an overdrive transmission in a hi-perf car if you aren't getting the best of both worlds? With a 4.10 gear ratio, you'll be reving at about 2,950 RPM at 80 MPH. BTW, what are your cam specs and stall speed RPM?


http://www.richmondgear.com/101032.html

[Glock 18]

Thanks for the replies and input. I really want to stay at 2500 RPM or under at 80 MPH. Maybe the 3.73 is the better choice? I've heard big blocks have substantial torque at low end anyway without going to a very low rear end. This will be a street car. Maybe on the strip a time or two. It is being set up as pro-touring.

[Philip]

Shane With the low 1st gear ratio on the 700R4 the 3.73 may be the better choice.
My Nova has 3.73 gear, 27" tall tire and the OD is .64. I have a mild build 400 sb estimated at 500 lb ft of torque. I can shift to 5th gear at 45 mph and accelerate comfortably. Went to Phoenix Saturday was running 75 mph on the freeway turning 2200 rpm and averaged over 19 mpg on the 220 mile trip (used 11.37 gallons).

[Glock 18]

Thanks for the input about your Nova! That's the RPMs I hope mine cruises at.

[BillyGman]

Nothing would be wrong with 3.73's. To a certain extent it's mostly a matter of preference. Big blocks being low revers really depends on cam specs, but yeah, most big blocks will always have more torque down low than most small blocks will. More displacement + longer stroke= more torque.

[Glock 18]

I think 3.73 would be the logical choice for my driving needs. My cam is the Lunati Vodoo with 554 lift (part # 60204). However, the heads are stock for now.

[BillyGman]

Originally Posted by Glock 18

I think 3.73 would be the logical choice for my driving needs. My cam is the Lunati Vodoo with 554 lift (part # 60204). However, the heads are stock for now.

Yep, I think you'll be fine. Perhaps you already knew that anyway.