[Dave]

So a Overdrive tranny, or a Gearvendors are out of the question at the moment, and I want to make driving the Chevelle a little more enjoyable. Most all of my driving is backroads, and the Interstate. I live about 20 miles out of town, and would like to drive the Chevelle a little more often. I've currently got 3:73's in it now, thinking that changing gears for awhile might be the most cost effective way to bring the cruise RPM's down. Yet I don't want to kill the acceleration I got right now......I kinda like it the way it is. Anybody out there switched from 3:73's to 3:08's, what did you think? Anybody running 3:08's in a 425 HP 468, with a TH400 and a B&M 2400 holeshot? Thank's for looking, Dave.

 

[big gear head]

Your engine should pull those 3.08 gears just fine. You should have enough torque to light up the tires whenever you want. An overdrive would be best, but the 3.08 gears should give you what you want for now.

 

[Dave]

I was PM'ing you while you were responding to my post. I'll be talking to ya soon.

 

[mr 4 speed]

Anybody running 3:08's in a 425 HP 468, with a TH400 and a B&M 2400 holeshot? Thank's for looking, Dave.

Dave,I ran 2.56's and now 3.31's with a 450 HP 454 and the B+M 2400
It was fun to drive even with 2.56's so 3.08's will be fine.

 

[charbilly2001]

A larger diameter tire would accomplish the same thing with out all the work

 

[mr 4 speed]

A larger diameter tire would accomplish the same thing with out all the work

That is correct.
My 3.31's and a 26" tall tires probably cruises at what a 28" tall/3.73 combo cruises at RPM wise in drive.

 

[Dave]

A larger diameter tire would accomplish the same thing with out all the work

That would mess with the look of the car, which I don't wanna do. Plus, new tire's would probably be more then the $300 to put in new gears.

 

[The Collector]

A FRIEND OF MINE RUNS 3.42s. in his 71 ss 468. Its seems to be perfect all around gear.

 

[artmalibu]

I've got 3.42s and 28 inch tires, I love the combo!!!! But if I did as much open road driving as 71metbu I would want the 3.08s. IMO it revs a little much to cruise at 65mph for any period of time.

BTW remember, less gear = less acceleration

 

[mr 4 speed]

BTW remember, less gear = less acceleration

But you'll have a higher top speed with 3.08's than 3.73's

 

[69-CHVL]

I've got 3.31's w/28" tire, and I think thats too much on the highway. Most of my driving is around town/backroads, and I'm in 4th gear most of the time.

I think you need to be honest and decide what the primary use for the car is. If your doing alot of highway, 3.08 are probably the steepest I would use.

 

[SWHEATON]

If seat of the perf is still important go with some 3:31's (can find used and once in a while NOS on ebay) which will give you a decent reduction in cruise rpms comming from 373's but stillperf decent esp with bbc.

But the 3:08s will also work fine with your motor/setup if reducing cruise rpm is more important to youthen seat of the pants perf,thst the decision you have to make for yourself. I went from 3:;08 to 3:31 in my 69 for a little extra umph and it did wake up the perf some for sure without killing me at crusing speeds either.

My 69 with m20/26' tires/3;31 12bolt turns approx 2,800rpm @ 65mph on the open road with 331's which is the most gear i could stand for longer cruising times.

The 3:31's are about the best all around compramise for perf vs cruise rpm/streetability you can find for a BBC muscle car which is likely why GM went with that gear ratio for those applications.

3;31's are enough gear to still have some fun but its not turning 3,200-3,300rpm @ 65mph like 373's with 26' tires would do in a NON OD trans car which is too much gear for street if not racing on the track a lot IMHO.

I know there are people here in T/C that think/state 373's are a good street gear for crusing in NON OD cars but i dont agree with that at all. The 373's have too high of a cruise rpm in NON OD cars wasting fuel along with creating more motor noise/heat/wear,etc which i am sure your already aware of wanting to get away from the 373's on the street,smart move.

Scott

 

[Dave]

By my calculation's, with My 26.5 tall tires, going to the 3:08's would reduce my RPM's by about 650 at 70 MPH. It's an awfully long way to the track from my house, and I really built the car to DRIVE. So I'm really leaning towards doing it. I will in the future upgrade to a overdrive tranny , 4l80 or such, but for the mean time, I think this is the best way to go. One possibility that is avaliable, is a friend has another 12 bolt at his house. Get that, put some 2:73's in it, put my 4:10's in mine, and get one of those quick disconnect brake hose adapters. But by the time I get the other rear all set up, I could probably just do the OD tranny. Decisions, decisions, Thanks all.

 

[SWHEATON]

If your going to o/d trans later for sure then go with the 3;31 now and not 308 so you can possibly avoid another gear change later on as the 308 are very tall for od trans,somthing to ponder for sure.

scott

 

[Dave]

So I did alittle research:

TH400 3rd gear 3:73's 70mph 26.5 tall tire = 3310 RPM's

TH400 3rd gear 3:08's 70mph 26.5 tall tire = 2733 RPM's

but if I changed the tire size to a 2" taller tire,

TH400 3rd gear 3:73's 70mph 28.5 tall tire = 3100 RPM's.

So I think the taller tire idea is out. Got all the stuff here to do the gear swap. Just need the Beam style in/lbs torque wrench.

So my cruise speed will still be above my stall speed, but it will be under my cam's reccommended cruise rpm. Cam calls for a 3200-3500 cruise rpm, is that going to bother it, to be 500 RPM under?

 

[658Chevy]

My mild daily-driver 461 has 27" tires, stock TH400, and 2.73's -- it's a lot of fun to drive. The BBC torque will still make the car float sideways on spinning tires if you stomp on it, and it cruises at a comfortable 2100 rmp's at 60 mph. Also, due to the highway gears the tranny will downshift as high as 65 mph and sling-shot the car past whatever's in front of you.

The combination of highway gears and a torquey big-block seems to be perfect for the street. It's easier to hook it up and actually get going instead of spinning the tires needlessly. Burnouts may be impressive, but not as much as actually going fast.

I don't race the car -- on the track or on the street -- so take that into consideration. But since it is a big-block muscle car there are times that I don't act my age (37).

 

[DZAUTO]

I must agree with the above, if you have that big of an engine, I would SERIOUSLY consider a 2.73, or, maybe, even a 2.56. Oh ya, and I'd dump the 2400 stall converter! Get one back down to a much lower rpm.
But to answer your immediate question, you will be just fine with a 3.08 (ALTHOUGH, if your rear is a 12bolt, it is NOT 3.08, in a 10bolt its 3.08 and in a 12bolt its 3.07). I have a healthy SB400 in my 70 conv with a wide ratio Muncie (M20) and 3.07 posi and really like the combo. At Chevellabration, it will also hold its own with that combo (that's the ONLY time in its life that it sees the strip).

 

[mr 4 speed]

My mild daily-driver 461 has 27" tires, stock TH400, and 2.73's -- it's a lot of fun to drive. The BBC torque will still make the car float sideways on spinning tires if you stomp on it, and it cruises at a comfortable 2100 rmp's at 60 mph. Also, due to the highway gears the tranny will downshift as high as 65 mph and sling-shot the car past whatever's in front of you.

The combination of highway gears and a torquey big-block seems to be perfect for the street. It's easier to hook it up and actually get going instead of spinning the tires needlessly. Burnouts may be impressive, but not as much as actually going fast.

I don't race the car -- on the track or on the street -- so take that into consideration. But since it is a big-block muscle car there are times that I don't act my age (37).

I agree
I used to have 2.56's with my 454 and while it was fun for a number of years and actually ran a 12.99 thru the exhaust on drag radials going to 3.31's was perfect for my combo.
I not rule out putting together another big block and running 2.73 or 2.56 gears for a driver.

 

[MikeN]

I used to run 3.42's with a TH350 and 28" tires, and driving on the interstate for extended periods pretty much sucked. People tend to drive at least 75-80mph on the freeway now, so you're turning 3500-4000 to keep up. I like your plan to go to 3.08's. I'm planning the same swap myself later.

 

[Chief fat nutz]

I've got some BFG drag radials in a 295/65R15 which are 29.5" tall, 3.73 gears and freeway cruzing is actually pretty good at 60mph. I drive around everywhere now with these tires since they are a bit taller than my 325/50R15's(28" tall)

I'd keep the gears you have,get a bigger tire and cruise around. 60mph is around 2600rpms. Its pretty mellow and you've got a big block,no problem turning those 29.5 BFG's for you!

Tirerack.com has the 295/65R15's on clearance for $115 a piece,thats why I bought them,so I could cruise to work 20miles away some days.