Right now Im running with a 2 series 2.56. I want to have a mid gear for my car. Im have a 3000 stall and the 2.56s are killer with it keeping the trans temps hot. The 3.42s are about $20 bucks cheaper than the 3.55s.
My car is street driven daily driver. I will occasionally take it down the strip but not often. Please help with my decision.
My tires are 25.5" Tall, I will stay with around a 26" tire.

Im no expert but i dont think you would notice any difference between the 2...either one would feel alot better than what you have..Sean

Go for the 3.42's

Go for the 3.42's

Without overdrive I would not go to the 355's in a daily driver. On the open road they suck and being a bigblock you don't want to rev it all the time.
Even the 3.42 suck on the open road.
Given the 2 choices I would pick the 3.42 but how about 308's?

I've had 308 331 355 373 390 410 433 gears. The gear I liked with the best overall performance with tire size you have is the 355. If you plan on installing a 4spd some day I would opt for the 355's. I agree with sonk. You will never be able to tell the difference it's only about 3%. Either way you will love the change, but when cruising down the highway you will be looking to see if it is in drive instead of second gear.

I'm going to go with the 3.55 but I have a 28" tire.

Without od trans & being a daily driver with alomst no strip time i would opt for used 3:31's or the 3:42 gear at max for street,no 3;55's.

With no strip time and being a daily driver 3:55's are not nedded IMHO and used 331's or new 342's (MAX) will be more street friendly rpm wise since this is not a pure perf car. The 402/bbc trq will handle the 331 or 342 gear just fine with good perf when getting into it vs streetability for cruise rpms.

I just saw a used set of 331s go for $130 on ebay,the 331s i bought used from ebay are still fine 3yrs later and cost me $125.

Scott

I just went with 3.42 but mine will be more of a driver and does have a auto trans.

what rpm do you run at, at 75mph?

I had 3:73's with a BB and TH400, sucked driving on the freeway. Now, I'm switching to 3:08's in hope's of a little more comfort, and less wear and tear on the Drivetrain. In my first Chevelle many years ago, I had a SB, M-22 with 3:31's, was the best all around combo I ever rode in.

3.42

regardless of driving style a mid 3 range gear is great. 3.42's for my vote even though i have 3.73's.

where can I get 3.31s except ebay?

No where,331's are not produced NEW anymore.

My friend and myself both bought used sets of 331s a few yrs ago for approx $125 off ebay and have had no problems after having them installed by a qualified shop,not everyone selling on ebay is a thief unloading junk.

I just saw a good looking set of 331s sell on ebay last wk for $130 and i see used 331s pop on ebay every 1-3 months so just kee watching.

I have seen 2-3 NEW GM NOS 331 ring & pinion sets sell for approx $250-$325 on ebay over the last 1.5-2yrs.

IMHO 331s are the best all around gear for perf vs streetability GM put in a muscle car that doesnt have some kind of an O/D trans.

So be patient and you will eventually find a good used or NOS set of 331's on Ebay or maybe even here in the T/Chevelle sales section,its worth the wait.

Scott

I voted 3.42 since you said it is a DD. Here are my results.

I have 3.55 in mine, but I like a lot of gear, I actually prefer a 3.73; but I do need to drive on the highway. I did the calculations for you so you can compare the 2 different gears. I used a 26" tire as the standard, and a 5500 redline.

3.55 Gear :
1st gear redline: 48 mph
2nd gear redline : 81 mph
3rd gear redline : 120 mph
60mph rpm : 2750..... 55mph rpm : 2550

3.42 Gear :
1st gear redline : 50 mph
2nd gear redline : 84 mph
3rd gear redline : 124 mph
60mph rpm : 2650......55mph rpm 2450

Here is the link I used to do the calculations, you can play with it and find what you think you may like. http://www.f-body.org/gears/ Let me know if you need to know the gear ratios for a th400. - Mike R

Thanks the 3.42s seem appealing, I might see if I can get a tad bigger tire.

Mike,no disrespect but the rpm cal your using is not accurate,it shows rpms too low for sure.

For example,when i was running the stock setup 307 gear/m20,and 26" tires like you used for your calc my motor turns 2,400 rpm @ 60mph and your calc is 2,450 rpms (only 50 rpms more)for 342's @ 60mph with same tires and a lot more gear,thats incorrect.

When i changed to 331's with correct speedo gear,26" tires & m20 the rpm is 2,600 @ 60mph and you state 355 is less rpm 2,550 @ 60mph with more gear which is incorrect.

I have the correct speedo gear installed for each ring & pinion i was running so i know that was correct.

Again,my rpm #'s are real world what i got with same 26" tires with the correct speedo gears & M20 for each of the 2 gear ratios i used & i know my speedo is correct because i also clocked it against my wifes new car a while back and we were 1mph dif @ 60mph.

I calc the rpms for 342 & 355 gear @ 60mph with 26" tires and here is what got which i feel is right on or very close within 50rpm + - @ 60mph.

342 @ 60mph = 2,650 rpm

355 @ 60mph = 2,750 rpm

355 is too much gear for a daily driver with todays fuel prices IMHO. Even the 342s are pushing it for a daily driver esp with bbc that has good trq and can easily handle gear like 331 which is what gets my vote,but 342 max without an overdrive trans for daily use & even thats pushing it.

Scott

I voted 3:42's because that what I just put in my Camaro. In my ElCamino I have 3:73's hate it on the highway I should have put 3:42's in it.

Im thinking the 3.42s might be the highest gear I get but it also depends on what I decide with the tranny later on. Id like a 5 or 6 speed overdrive manual but they seem pricey to swap.
I had 4.10s for a while and I could only go on the highway at 60 for about 3 miles before engine temps started climbing high.

I got 3.42s with a 28 inch tire its a little much on the open road.

3.55 is a little stiff for highway use lucky we have rural roads and 50 mph speed limit it would be hell on the real freeway I'm 2200 rpm @ 50 mph with 454.

3:55's with a bigger tire. Do the the speed limit and maybe slightly less.
Put on a smaller tire at the track and get better et's.
Either gear will not make that much difference but myself acceleration is why I luv musclecars. To each his own.

Check out this link so you can determine the pros and cons of each ratio for yourself. It's real easy to use. Just enter your tire size, rear end gear ratio and your tranny gear ratios.

Vince
'66 SS clone


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

With 26" tires you want a 342---if you drive on the HWY at all. That is
about 26/2700 @60 MPH like you have been shown. At 70 you will be
doing almost 3000 that gets old in a hurry if you trying to keep up in traffic
and you are going more then a few miles. Pete

Mike,no disrespect but the rpm cal your using is not accurate,it shows rpms too low for sure.

you state 355 is less rpm 2,550 @ 60mph with more gear which is incorrect.


342 @ 60mph = 2,650 rpm

355 @ 60mph = 2,750 rpm

Scott

No disrespect taken at all, I value you opinion; you seem to be on the same page as me on most topics (including this one).
We actually have the same results, I think you got confused how I posted them, I have 2750 RPM at 60 with a 3.55 gear, I put 2550 @55 MPH (which is most likley closer to 2600)to show that you can still "get by" without turning a ridiculous RPM.


3.55 Gear :
1st gear redline: 48 mph
2nd gear redline : 81 mph
3rd gear redline : 120 mph
60mph rpm : 2750..... 55mph rpm : 2550

3.42 Gear :
1st gear redline : 50 mph
2nd gear redline : 84 mph
3rd gear redline : 124 mph
60mph rpm : 2650......55mph rpm 2450


Hope that cleared things up a bit, sorry for the confusion guys.

My stock 3.31's and stock about 25.3" to 25.5" tall D-70 Redline tires ran right at 3070 to 3050 rpm at 70 mph w/ my M-20 way back then.

I added a pair of skinny 29.5" tall M&S tire's and I hit 145 mph at like 5500 rpm or so and still had more motor years ago..

pdq67

You wont notice much of a diference between 3.42 or 3.55 like eveyone is saying. But that 3000 stall is too much for the gears u are using now for the street. When i do my set up i usually go from the rear end back up to the engine. Example small gears in the rear = small stall and small cam and thats important if your driving it daily and considering the cost of fuel. Now if u have big gears in the rear u can go with a higher stall for an auto and a much bigger cam too. Your combo selection is critical for overall happiness of driving and performance expectations.

I have 26" tire and 3.42, but overdrive tranny which is perfect for a DD imo.

However I had to drive home from college with a broken shifter cable and I had to get under the car and put it in 3rd for a patch of steep hills and ended up not pulling over to put it back in OD. It got old in a hurry. If you can't get an OD tranny soon I would wait or consider a higher gear if you do a lot of driving over 50mph.

My old 442 clone has a built Olds 455 (Edelbrock heads,240/246 @.050 cam)3.31 gears,10" convertor (about 3500 flash) and 28" tall tires.
Runs high 11's and is totally streetable..scoots on the highway too

Even the 3.42 suck on the open road.

I agree completely. I had 3.42's with a TH350 and hated it for driving on the freeway. Unless you have overdrive, IMHO 3.08 is about as steep as you want to go if you want to drive over 60MPH.

I also picked up a set of 3:31's off ebay they are in great shape I will be running a 26 to 28 tall tire that would bring me down around a 3:08 ratio. If you go to richmondgear.com on the left side there is a gear calculator go there then to the street performance icon you can enter different ratios, tire size and desired mph to see what your rpm's will be at. You can change things around like tire sizes ratio's ect to see how your rpms will change. The reason I went the way I did is living in NY if your doing less that 70 you will get run over and I did not want to be screaming the motor while out trying to enjoying a nice cruise. :thumbsup:

It all comes down to how much rpm's you are willing to live with on the highway. If you do way more street than strip I say 3.08's. 3.42's are still
gonna buzz pretty good down the highway compared to your 2.56's.

Man all this talk about running on the highway with those gears, i run on the highway with 4.10's. At 60mph i'm running about 3200. Its not that bad. I put different exhaust on it and its a lot quieter now at that rpm.

I would try to find a 3.31 gear, you can still find them on e-bay or swap meets, other than that the 3.42 gear won't be to bad with the right size tire.

Well Im looking to get 15x8 or 15x10 rear SS rims and put in a 295 wide tire with a 27-28 inch height. Im also trying to find stuff to swap to the t5 5 speed tranny. So I think 3.42s will be fine will all that.

Assume, 12 bolt and 25.5" tires:

3.07s ...RPM in
MPH 1st.. 2nd.. 3rd
45.0 4589 2768 1821
47.5 4844 2922 1922
50.0 5099 3076 2023
52.5 5354 3229 2125
55.0 ...... 3383 2226
57.5 ...... 3537 2327
60.0 ...... 3691 2428
62.5 ...... 3844 2529
65.0 ...... 3998 2630
67.5 ...... 4152 2732
70.0 ...... 4306 2833
72.5 ...... 4460 2934
75.0 ...... 4613 3035
77.5 ...... 4767 3136
80.0 ...... 4921 3237

3.31s ...RPM in
MPH 1st.. 2nd.. 3rd
45.0 4948 2984 1963
47.5 5223 3150 2073
50.0 5498 3316 2182
52.5 ...... 3482 2291
55.0 ...... 3648 2400
57.5 ...... 3813 2509
60.0 ...... 3979 2618
62.5 ...... 4145 2727
65.0 ...... 4311 2836
67.5 ...... 4477 2945
70.0 ...... 4642 3054
72.5 ...... 4808 3163
75.0 ...... 4974 3272
77.5 ...... 5140 3381
80.0 ...... 5306 3491

3.42s ...RPM in
MPH 1st.. 2nd.. 3rd
45.0 5112 3084 2029
47.5 5396 3255 2141
50.0 ...... 3426 2254
52.5 ...... 3598 2367
55.0 ...... 3769 2479
57.5 ...... 3940 2592
60.0 ...... 4111 2705
62.5 ...... 4283 2818
65.0 ...... 4454 2930
67.5 ...... 4625 3043
70.0 ...... 4797 3156
72.5 ...... 4968 3268
75.0 ...... 5139 3381
77.5 ...... 5311 3494
80.0 ...... 5482 3607

3.55s ...RPM in
MPH 1st.. 2nd.. 3rd
45.0 5307 3201 2106
47.5 ...... 3379 2223
50.0 ...... 3556 2340
52.5 ...... 3734 2457
55.0 ...... 3912 2574
57.5 ...... 4090 2691
60.0 ...... 4268 2808
62.5 ...... 4446 2925
65.0 ...... 4623 3042
67.5 ...... 4801 3159
70.0 ...... 4979 3276
72.5 ...... 5157 3393
75.0 ...... 5335 3510
77.5 ...... ...... 3627
80.0 ...... ...... 3744

FWIW, I drive with a 26.5" toire and 4.10s. I love it, but do almost no highway driving, not a daily driver. I'd hate if it was a daily. I had 2.56s and thought it was great - but lacked perforamnce I wanted. I think 3.07s or 3.31s are teh way to go for daily car unless you have limited highway, then... maybe, 3.42s if no OD.

I intend to change to 3.55s with an OD ....some day.

If you have MS Excel, I can send you a spreadsheet that lets you choose transmission and tires size and gear size to see your MPH/RPM comparison from 10 to 120 MPH ....

ron, i use your spread sheet all the time. i have even passed it on to other gear heads. great work with that. do you have a new one with even more trannies in it? tom

I vote for the 3:42's :thumbsup:

I just did a rearend swap in my car. The above mentioned formulas I used just today to determine my speed by rpm. I don't yet know for sure what gear I took. I did put in 3.07. I know my speedo is off now, about 12 mph under @70. Is there a formula to determine the correct speedo gear?

May not be the answer you were looking for, but if I had to do it over again, I would keep the 2.56 gear. I swapped a 2.56 for a 3.42 and was disappointed at the acceleration gain. It certainly is quicker, but not worth the high rpm on the highway. I would put $1000 toward more engine power and keep the highway gears. Dave.

Right now Im running with a 2 series 2.56. I want to have a mid gear for my car. Im have a 3000 stall and the 2.56s are killer with it keeping the trans temps hot. The 3.42s are about $20 bucks cheaper than the 3.55s.
My car is street driven daily driver. I will occasionally take it down the strip but not often. Please help with my decision.
My tires are 25.5" Tall, I will stay with around a 26" tire.


Do yourself a favor and keep the 2.56's. The first couple days with the 3.42 you'll be stoked (especially behind a 3000 stall) but after awhile you'll hate them. I've got 3.31's behind a 502/T400 combo and driving on the freeway is murder. I would swap out the converter though, something around 2200 stall. Good luck...Pat

If you are planning on installing a six cylinder, keep the 2.56's.

I ran 3.55s in my car for almost 20 years. Great gear. 3.42 or the 3.31 too. If you are going to see some track time, 3.55. No track time, 3.31. If you plan to get an OD, then 4.10s.

And a 28" tire (275-60-15 fit great). Anything smaller, IMHO, just doesn't fill up the rear wheel well enough. I had some 26" tires on mine one time, and they did not look good. Might make a difference how low your car sits. Maybe if the rear is low enough, the 26" tires would look okay.

Daily driver? 3.42. Dont they still have a 3.23? Or was that a 10 bolt item only? My 71 Velle has a 3.55 posi 12 bolt but is a weekend warrior. My 75 short step has 3.07s and are nice for highway driving and still get a 2nd gear scratch with 295/50/15 tires.. 3.07 to 3.42 would be my choice. I assume you have a 12 bolt?

I had 3:73's with a BB and TH400, sucked driving on the freeway. Now, I'm switching to 3:08's in hope's of a little more comfort, and less wear and tear on the Drivetrain. In my first Chevelle many years ago, I had a SB, M-22 with 3:31's, was the best all around combo I ever rode in.


2nd the 3:08.If I want to hear my engin screeming all day Ill keep it in 2nd gear.

3.42.

I love my 3.08's but I have a 700r4 with that hotter 1st gear.:beers:

I have 26" tire and 3.42, but overdrive tranny which is perfect for a DD imo.

However I had to drive home from college with a broken shifter cable and I had to get under the car and put it in 3rd for a patch of steep hills and ended up not pulling over to put it back in OD. It got old in a hurry. If you can't get an OD tranny soon I would wait or consider a higher gear if you do a lot of driving over 50mph.


I agree, 3.42 is a good match for 0.70 OD in 4L60-E but I couldn't imagine it in a non-OD tranny.

I found 3.73 too much with 4L60-E, turning 2400-2600 at highway speeds (between 70-80)

I ended up with 3.31s and a 28" tire

I ended up with 3.31s and a 28" tire

I bet you'll like them. Good compromise between drivability and performance! :hurray:

Another thing that makes a big difference in cruising comfort is how your exhaust is routed. I've had mine out the side in front of the tires, all the way to the bumper, and right now I have dumps in front of the rear end. 3" pipe and race mufflers, so noise isn't really a concern for me.

Out the side and the dumps are WAY louder. If I drove my car more, I'd have tailpipes on it. But with mainly racing, it makes it easy to take the exhaust off if I need to drop the trans.

rough estimates:

Ratio RPM @ 60 MPH
2.56 2025
3.08 2440
3.31 2620
3.42 2705
3.55 2810
3.73 2950

As noted, not much difference at all between 3.42s and 3.55s ( ~100 RPMs on the highway)... "race difference probably similar, but would also depend on lots of other variables (cam, convertor, weight, etc)...

IMO, since its mostly street, I'd go with the 3.42s... I ran these before, and liked them...


3.31 vs 3.42, again very little difference ( 85 RPM at 60)... IMO, I'd NEVER get a set of USED 3.31s, unless you can see them/know what to look for and/or know/trust the seller... JMO, but too much risk in used gears, with very little benefit... Now, IF you have an installer/shop, that has a set of 3.31 they'll guarantee, maybe... But still, its a used gear ( just because its GM, doesn't mean it perfect)...

I always wonder why the aftermarket came out with 3.42, when 3.55s were already available. Why didn't they just make a 3.31 or similar?

I bought my used GM 3.31 gears with an open carrier off ebay. I traded the carrier to a friend who set up the rear end in exchange. probably got 5000+ miles on them and hunderds of track runs no problems or noises other than a leaking pinion seal (due to the pinion itself, ive changed the seal multiple times)
I like the 3.31s with the 28" tire I can cruise all day on the highway and I still run low to mid 12s on street tires and mid to high 11s with slicks.