Hello Hamb'ers.... I could use a little assistance....am trying to select the best gear ratio for my project. I will give all the info that I think is relevant and see what opinions we get back. Car : 37 Chevy Coupe Engne : LT1 with the GM aftermarket perf cam and fuel injection Tranny : 4L60E Rear end : Narrowed 9" Posi Tire size on rear: 255/70-15 Current ratio : 3.50 I have a new 4.11 ring gear set (given to me) that I am considering using...I was told that I could use the 4.11 and the overdrive would allow for good highway speed without the RPM going thru the roof. Since then I have been told the 4.11 will make me miserable and the 350 will stay wound up going down the road. This car will be a driver, but I do want good response off the line along with being able to travel down the road. Experience often tells the story......thanks for any help - Dogger
I personally would leave the 3.50. I have had 4.11, 3.55 and now 2.43 in my 51 chevy. I dont have overdrive, but the 2.43 is the best yet. I can cruise 70 at less than 2k rpms. With your overdrive trans, the 3.50 will probably be perfect.
Since the 3.50 is in the pumpkin now I would use that to get on the road. If you have problems launching and also have problems with bogging down in over drive switch gears. Changing the gears in a 9" pumpkin requires some additional parts and skilled labor. No point in incurring that expense unless you need to. Just because the 4.11 set was free does not make it right for your ride. A 3.76 set might be better.
I have pretty close to the same setup. 820 X15 on mine are a little taller. I'm running a 3.90 and i love it. 70 at 2k rpm and gets out of the whole really well. That 3.50 gear probably feels a little tall.
I run a 3.5:1 ratio with 235:75:15 rear tyres in my 35 Chevy. With a T700 it turns 2k rpm @ 60mph. You wouldn't want it turning over any less than 2K rpm so you don't labour the engine unnecessarily. 1st gear is still low enough to launch and with OD it drops the revs to an acceptable and economical level on the highway. Around town in traffic I may have to drop it back to D from OD.
Using 255/70-15's with the 4l60e and 3.50 gears your RPM will be 1845 at 65 MPH in 4rh gear.. With the 4.11;s the RPM will be 2166 at 65 MPH in 4th gear.. stay with the 3.50's...
Knew I had this somewhere, www.hotrodhotline.com/md/html/selecting_gear_ratio.php Rule of thumb, 60-65mph cruising speed with engine turning over between 1,800-2,100 rpm.
also, search online for: project33.com - click on calculators-will help you figure what you are thinking about.
3.50's should be about perfect with a over drive. Since the low gear in that tranny is lower than a 3 speed from the start ! I would stay there in less your going drag racing.
With 3.42 being the current rear ratio the GM factory uses with an OD trans I'd say your real close with our current gearing. Only reason I'd change is if you don't do any highway driving and want better acceleration. Frank
I ran 3:42's with a 3:27 first gear and a .76 overdrive. Mileage around town sucked but in overdrive drown the freeway, it was perfect. A friend of mine had a '33 Willys running a 4:10 rear with a 700R trans. It has a 33" tall tire. He took a trip from SoCal to Utah. He thought his gearing a trans were perfect.
go to www.ringpinion.com and they have calculators there and you can plug in your ratio, tire diameter, and speed, and it'll tell you how many revs you'll be turning, and other calcualators for other pertinent data. Great resource!
Considering the 4L60E has a 3.06 first gear I don't think launching would be any issue with 3.50 gears. I'd leave it alone personally. My TH350 has a 2.52 first gear and I'm running 3.73 gears with no problems launching.
Absolutely, DO NOT use the 4.11's. Bad things will happen. The car might even get a little sideways at sudden WOT! It'll be a freakin' death trap. Its common knowledge that big gears are a tool of satan. I had 4.56's and a T/A cheetah valve body in my old car, when you hit second @ wot, the glove box door would flop open, and hit anyone in the pass. seat on the knee! Oh the HUMANITY!
Would HATE the glovebox door to hit somebody in the knee....might hurt their feelings.....HMMMMMM...Big gears and weld the box shut ???!!!!
I was thinking about just taking it off, but then the 9/16 and 1/2 wrenches that I carry in there to drop the pipes would get lost under the front seat...
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