Best gearing?

[ccautoupholstery]

So im trying to figure out what gears will be best in my 67 and would love some input. I had an inline 6 with 4 on the floor...1st was pretty much useless. Well i now have a 350 with th350 and dont plan on racing or high hp anytime soon...wanting it to be my daily driver which means freeway speeds regularly. Thanks in advance for the help

[trac209]

I've just in process of doing a rear swap from 3.73 to 3.07 posi. At the same time swapping to 5 lug to match the front. With a th350 a 3.07 gear will be your best balance between city and highway driving. Your truck now most likely has 3.73 or possibly even 4.10

[ajviper]

I have both 3.08 in a Blazer and 3.73 in a Truck and Suburban. I prefer the 3.07 for extended highway driving but my 3.73 trucks have no issues running down the highway either. In all my vehicles I have a mix from 2.73 all the way to 4.10 which I still don't find horrible on the highway.

[tsetsaf]

Wheel size is an important factor too. I have 3.73 behind a 4l60 with 245 65 17. Stays under 2k rpm on the highway and gets a reliable 18 mpg.

[Mike C]

GM thought the 3.07 was the right choice for the 350/350 combo and for a driver you will probably feel the same. If you tow a bunch or want performance then not so much.

One of the reason new vehicles have such high levels of performance is the transmission. Deep first gear and a 30% overdrive lets you do both.

[demian5]

1970 1/2 ton 2wd, small block, TH350 with 31" tires, Went from 3.73 to 3.07. Best decision ever.

[trac209]

Originally Posted by Mike C

GM thought the 3.07 was the right choice for the 350/350 combo and for a driver you will probably feel the same. If you tow a bunch or want performance then not so much.

One of the reason new vehicles have such high levels of performance is the transmission. Deep first gear and a 30% overdrive lets you do both.

Very true now it's all about the trans,although in most cases using a 700r4 or even a 4l60 towing in od is a no-no and then your still stuck towing in drive and if you've got 3.73 gears you're going to be holding up traffic unless you like 3000rpm. I tow with my truck and I absolutely hate single lane highways due to the fact nobody goes 55-60 anymore. The only truck that will have issue towing with a 3.07 gear is probably trying to tow more than he should with one of these. Engine aside if you really want best of both worlds use a 6 speed or a gear vendors.

[Orence1]

72 LWB with a 402 BB and 350 TH. Old set-up (350/350) with 3:73's was turning 3000 RPM at 65 on 15" wheels. Wanted to keep the RPM's down on the same tire set up so switched to 3:07. Now at about 2700 at 70 MPH. Not the screamer off the line that it would be with the 3:73 but as my primary concern is longevity the 3:07 meets my need.

[68Stepbed]

3.07 or 3.08 will probably be optimal, and you might luck up and find a whole rearend with the right gearing. However, you could always go middle of the road, and go 3.42. Just run a 28-30" tire, and you'll still be happy with it.

[Alex V.]

Whatever puts it at about 2,500 RPM @ 60 miles per hour - the math ain't rocket science.

[nevada]

72 C20 350 TH350 with 4.1 gears, 30 inch tires, not bad at freeway speeds but would like to lower rpm a little, no tach. was going to pay big $$$ in a few years for 700r but since have seen I only drive it about 2000 miles/yr so seems dumb to invest that much...I would think 3.07 gears would make it a dog off the line or suck towing so now thinking of keeping transmission and changing gears to 3.54

[JMC1965]

this is useful

https://www.ringpinion.com/calculators/Calc_RPM.aspx

[jocko]

Since you mention mostly highway driving, 3.07 would be the logical choice and be very drivable. Rear end swap isn't free, but it's less expensive than a new trans. And I realize you mentioned you just swapped the TH350 in - but if you want the best of both worlds, leave your 3.73 where it is and stick a 700R4 in there. There's a reason this has been a common setup (o/d with 3.73) in modern GM 1/2 ton trucks. If you're ever gonna tow, 3.07 isn't really the way to go. Having said all that - first step is to confirm what you actually have. I'm betting 3.73 also, but ya gotta know before spending $! If you give us your tire diameter, we can calculate some stuff for you. Also, keep in mind that your speedometer can be way off if tire dia, rear, trans, etc have been changed out (although the 4-spd to TH350 won't be any different rpm at highway speeds, same 1:1 final drive), so if you tell us the rpm you're seeing at 65 mph, for example, make sure it's from a GPS, not the speedo. That can also allow you to figure out the rear end ratio without much head scratchin. Again, assuming you just shelled out for the TH350, completely understand if this isn't even an option, but just wanted to mention in case it was perhaps a long-term goal - you'd save money (in the long run) and enjoy best drivability at both ends of the spectrum.