Decisions, Decisions? What rear gear to use?

[hurst1979olds]

I want to change the rear gear. Currently my car is a 7.5 with a tight posi and 3.08 gears. So all I'm looking to do it replace ring and pinion. I'd like to go up to a 3.73's but I do drive my car to work which is 50 miles one way. With about 12 miles on the highway and the rest cruising at 50mph. So I've also been leaning towards 3.42's.

I have a th350 trans and would like to keep it like that. So I guess I'm a little torn at which to use. The added fuel consumption is not an issue as its not my daily driver and i get low gas mileage as it is. I do plan on upgrading in the next year or some to 16" ZQ8 rims and alittle bit taller tire.

I pretty much know what I want, I just want to hear other people experiences to help with my decision.

 

[khan0165]

I recently went thru the same exercise... Tho I can't match your combo, I will explain some of the questions I asked myself.
I have a 700r4, 3.42 gears, and 25.6" tall tires. I have a Chevy 350, which likes revs

with the above combo, I was holding 2000rpm at 60mph, 1800rpm in lockup. At the track it sucked, only pulling 4900rpm thru the traps with a 27" tire.

I imagine in 3rd, you will see around 2800rpm with 3.42s and 26" tire size. The thing I struggled with is at 2000rpm, my car was on the edge of the cam range, so it was never fully happy (or fuel efficient), and it also sacrificed at the top end.

... so going bigger was almost a no-brainer. And after some maths, I was shocked at how much tire size can contribute.

with my combo, if I jump to a 4.11 but use 28" tires on the road, I can maintain almost the same rpms I have now on the highway (2100rpm, up from the current 1800rpm in lockup). So I don't have to worry about high rpm cruising. And if I continue to use my 27" slicks, I will see 5400rpms thru the traps... win win

In my opinion, I think you have the best of both worlds with your 3.08s... I have found this to be the best combo for non-O/D cars. I believe with a 26" tires, you're likely seeing 2500rpm at 60mph? Which to me is very sensible for the use of that car. If you plan on track use, I could see the reasoning for 3.42s or 3.73s , putting you at the buzzing 3000rpm mark for highway cruising.

you really have to consider your motor combo as well... your olds probably doesn't like the high rpms my chevy does. An a buzzing 3000rpm Olds cruising on the highway can get annoying. Unless you're plans are for huge 28" tires, I can't see you being happy with 3.42s

thanks for listening,

 

[GhettoRacingKid]

Wait you drive the car to work but its not a daily driver and you dont care about bad gas mileage? kind of make no sense.


With gearing you need to look at what you want, and the drive train set up.

I personally. I would still drive it to work once in a while and go with teh 3.73 not great on teh highway but managable. youll feel it in the seat of your pants.

I was running 3.42s and a 28inch tire it wasnt bad on the street at all but I wish I had 3.73s or 4.11.

 

[hurst1979olds]

I dont drive it everyday to work. I will occassionally, about 3 times a month, drive it to work. (collector car insurance says only I can only once a month). With my car now you can feel it in the seat of your pants with the 3.08s.

Khan, I see what your saying right now cruising at 60 its about 2500rpm. which is tolerable. Even if I went with 3.42s being closer to 3000rpm would still be somewhat tolerable. Having a loud exhaust doesn't help much. Considering its a small block Olds it likes the RPMs. The thing really sounds good and healthy at 6000rpm, it gets there effortlessly and sounds like it wants more.

I want something to were I feel the difference and if I were to take it to the track I wouldnt be a complete dog, considering the engine I got. Thats why I'm considering the 3.42 or 3.73 instead of the 3.23. Going to those hardly seems worth the time and money.

 

[khan0165]

I agree, going to 3.23s would not be worth the effort.

I can see where you're coming from. I just worry, because I've done the "th350, 3.90gear, 3000rpm highway" thing before... it was great the first few weeks, but after that it was a nightmare. This was with a shorty header, single 2.5" exhaust (about as quiet as you can get with a V8)

the noise on long commutes was hugely annoying. But worse, 3000rpms sustained over long drives kept the engine always hot (around 200-210 F*). You would have to have a cooling system to match that kinda regular driving.

now let's talk 3.42s... I know several Buick guys using these for their th350 street/strip cars. Being Buicks, the 3.42s are a good match for low range broad torque bands. But these guys drive their cars a handful of times during the summer, so the highway rpms become more bearable.

they use 275/60R15 tires, and run mid 12s with nearly stock motors (stock intake, Qjets, and even manifolds, maybe a mild cam and that's it)... So there's plenty of GO with a mild compromise in street manners.

 

[GhettoRacingKid]

for the track the 3.73 would suit you just right. but it would be a compromise with the when you are cuising.

I would say if your really torn. try to find a 3.73 monte ss rear. pop it on the car and see how it is. you could pick one up for around $100 if you like it you saved yourself a few bucks. if not you know where to go for the gearing.

 

[hurst1979olds]

the noise on long commutes was hugely annoying. But worse, 3000rpms sustained over long drives kept the engine always hot (around 200-210 F*). You would have to have a cooling system to match that kinda regular driving.

now let's talk 3.42s... I know several Buick guys using these for their th350 street/strip cars. Being Buicks, the 3.42s are a good match for low range broad torque bands. But these guys drive their cars a handful of times during the summer, so the highway rpms become more bearable.

they use 275/60R15 tires, and run mid 12s with nearly stock motors (stock intake, Qjets, and even manifolds, maybe a mild cam and that's it)... So there's plenty of GO with a mild compromise in street manners.

Noise wont bother me so much. I was fighting an cooling issue when I first put the engine in. I had a New factory 3 row radiator with stock pulleys and water pump. It would be fine cruising and everything only pulling hills it would climb over 200. So I put aluminum radiator in, took out the stat and now won't run over 180. I'm also putting in a March pulley kit and a milodon waterpump in a couple weeks, so hopefully cooling wont be an issue again.

I was pretty much going to go with a 3.42 but if someone would talk me into 3.73 i would go with those. So I guess 3.42s it is.

Khan, I know your good with the tire sizes and I know Ive asked before but forgot, Whats the biggest tire for a 16" rim I can fit in the back. I want to use the ZQ8 rims.

 

[khan0165]

with an aluminum rad, I think you'll be good. So if noise isn't an issue, and cooling is sorted out, I'm still rooting for the 3.42s

245/50/16 is most common size.
255/50/16 is pretty common as well.
but me, I like the taller look on these cars. And there's a nice 255/55/16 I was considering before I got my 15s.

this will put you at the 28" tall (like my big 275/60/15s)... so you'll see comfier rpms on the highway

and you could go with some even 225/60/15s or 245/50/15s for the fronts

 

[mebe007]

ill be running a 3.42 rear ratio on my car with a muncie m20 trans. i was planning on a 275/60/15 on the rear as i love the tall rear tire look. im hoping this will be ok with the ratios i have.

i would stick with the 3.42 if you dont plan on taking it to the track much if at all. i was back and forth 3.42, 3.73, 3.90 gears and still somewhat am as the axle is sitting in the floor next to the car as of right now, but it already has 3.42 in it so i figure i might as well try it out first lol. mine is mainly a street car with a couple trips to the track a year. ill prolly keep nitto 555r or the M &H drag radial on it year round though.

 

[dogsht]

IMO 3.08 with a common 26.0" tire is probably the best compromise or all around gear for a three speed. If you go to the 255/55/16 ie a taller 28.0" tire and the 3.42 you will get a little lower gearing or better quarter mile gearing than what you have now but should still be tall enough for driving to work. One other thing to think about or ask yourself is how much better is my quarter mile times going to be going from a 3.08 to 3.42 and is that worth it to me ie the expense and drive ability change. The drop in et is not going to be as dramatic as say coming from 2.29 to 3.08. There becomes a point of diminishing returns. You eventually start to give up a lot more to get a little more. Not saying you are there yet for how you use the car just saying it is something to consider and keep in context with how you actually use the car.

I think the 3.42 & 28" would be a pretty good combo for how you use the car and with the 16s would look good and have a good stance. Any lower might get a bit over the top for enjoying the car off the race track. I know a sbo likes to rev but I also see you have a stroker with good size so unless its cammed to the moon it has to make a lot of torque down low. I don't think I would want to not take advantage of that. I wouldn't change the gear for behind that motor and how you use the car without going to a 28" tire or an overdrive transmission.