Old School vs. New School Differential Gearing

[robbie_d68]

So, I have driven my truck for a little while. I have read up a little on the gearing and such. I found out that I have 3.07 gears by turning my wheel and counting the number of revolutions of the drive shaft. I am 90% sure my problems are with my Carb and the other 10% are with the engine. When I get some money I will get the carb looked at and I think that will change everything about how this truck runs.

[jocko]

Ah, well that sheds a little more light on this. As I read the prev page of posts, I was about to tell you that you have a great combo - sbc, 700R4 and 3.73 - something the factory replicated in the 2000's in 1/2 tons it worked so well. 3.07 is a different story. Take all the previous advice and follow it, because the motor probably needs a tune up and, considering its vintage, is likely low compression anyway. So, normally, a 3.07 stinks off the line - but with a 700R4, you're in a little bit better spot. Not MUCH better, but still. If you're just still figuring out what you have, that takes a while, so enjoy it, you'll learn a lot more about it as you spend more time with it. A 3.73 and a modern crate motor will bring a dramatic difference in your performance. I think you'll eventually want both. I'd focus on the motor 1st, get what you have to peak performance, and be ready for some disappointment soup! It's all good though. Then, between a new rear gear or a new(er) or rebuilt with a little higher compression engine - a modern crate is a good place to start. Funds are always an issue, I know. A Jeg's 260 hp engine is a good honest truck motor and they are usually around $1300-1500. Use your current accessories and brackets, etc. Or, if $ permit, a ZZ3 or a little bit more of a perf engine would be money well spent. THEN see how you like the perf with your 3.07. If still a little sluggish, then maybe save up for a 3.73. Your trans is already optimum for your application, so hang onto it and keep it in good shape. And enjoy driving it! Welcome to the site!

[James the III]

Problem, is that most build there classic with the wrong parts..

to big a cam, to big a carb, never bothers to tune the carb and ign timing curve.

Then one must remember a '92 crate 350 might have 200 gross h/p

Newer vehicles the transmission gearing is set to use the engines power band.. and keep it in the meat of it..

Many I'm sure have added overdrive, and used a 7004r or the electronic twin 4l60e that has a low 1st gear designed back when v8's had 145hp , to get it off the line, then shifts to 2nd with a HUGE rpm drop.. The gear splits are designed for epa mpg ratings, not performance..
The 2004r has better gear splits.. and so does the 4l80e..
Todays vehicles are very smooth, where as the older stuff was a bull in a china shop, it felt fast as it was loud, harsh , and YOU controlled the power, new vehicles, comtrol it.. you push the gass pedal, and the ecu decides how much you get and when.. torque management..

[68 P.O.S.]

Hmmm, very interesting. So with all of this being said, I wonder if anyone has done the research to figure out which gear splits would be optimum to keep our trucks in the power band like a modern vehicle. Probably wouldn't be worth it as I assume you'd probably have to have custom tranny gears made. Would be cool though.

[James the III]

Originally Posted by 68 P.O.S.

Hmmm, very interesting. So with all of this being said, I wonder if anyone has done the research to figure out which gear splits would be optimum to keep our trucks in the power band like a modern vehicle. Probably wouldn't be worth it as I assume you'd probably have to have custom tranny gears made. Would be cool though.

Look at todays trucks 6-10 speed automatics..
The problem is these use the powertrain module and ecu and all the vehicle sensors to make gear choices.. An engine that is at the same rpm gets better mpg than one going up and down..

The 7004r gear splits would be great with a 3.08 rear gear and a engine with big low end torque (think big block) problem is the trans will not live behind an engine like that.. without a bucket of cash thrown at it..

Most over think this. as most older trucks are not getting 100k miles on them in 4-5 years. like todays trucks are..

Most bought into the thinking of building an engine that makes power at 6500+ rpm.. and need rear gears as it has no balls down low..
then never use it. and need o/d to run the highway.. as they needed 450hp 350 sbc
long flat torque curve is your friend..

One, has to remember that todays trucks will need all those gears , as the oem's are forced to put smaller c.i.d. engines in them..

[jeffahart]

Ford Edge! Hell, I had doofus on a bicycle smoke me off the line the other day. He even beat me to the next stop light. I should of ran him over!