Rear gear ratio question
 

I am considering a different gear ratio for my truck. Currently has 3.73:1. Playing with an online calculator, I could go down to 4.56:1 and still be able to get to 135 mph in 3rd. My fastest trap was about 118 mph, and I can only add so much more power with my current setup, that I do not see me hitting 135 mph in the quarter.

So is there a reason not to go with the lower gear ratio? It should make the truck faster, correct? The only down side I can think of is traction,but their are ways to overcome that.

Re: Rear gear ratio question
 

You could go with a 5:14.

The math is there.:ito:

Re: Rear gear ratio question
 

A lot of things come into play on choosing the right gear. Tire size, transmission gear ratios, tq converter slip, max rpm etc.

Re: Rear gear ratio question
 

I am aiming to up my mph some. That would put me at "redline" at the stripe with the convertor locked




Tire is 29.5
Trans ratio would be 1:1
I have a lockup convertor, so slip could be zero
Max RPM is 7000

With those numbers it comes out to about 135 mph at 7000 rpm.

Re: Rear gear ratio question
 

I calculated that changing from 3.7 to 4.1 would give me a tenth or two. It made no difference at all, although it became more consistent. These trucks hit aero problems at the top end.

Re: Rear gear ratio question
 

I think 4.56 will work. Especially with the lockup converter.

Re: Rear gear ratio question
 

I run 4.88's daily with a Detroit locker in a 32" tire. Or a 285/65R17.

To me the biggest hold back of the combo is the TH700R4. If I had the money's to do over. A 4L80e would of been a more optimal choice.

Even though my engine is just a highly tuned gen2 LT1 it is a absolute blast to drive. I do miss the way bigger cam I had before. If I replace the cam it will be with a smog legal performance cam to get a little more out of her, but keep my drivibility.

My gear ratio, and Detroit effectively stop me from burning out. So that would be good for the 1/8 mile.

The same gear ratio hurts my top end charges a bit because my engine is more torquey vs 4500 rpm plus performance.

So with out mentioning engine specs or build list, and tire size.

Even 4.11's or 4.33's maybe a better split the difference overall combo.

Re: Rear gear ratio question
 

I ordered the 4.56s and a detroit locker last week. Can't wait till the Spring to try them out.

Re: Rear gear ratio question
 

:waah: I can't get no tire traction. I can't get no tire traction. Cause I try and I try and I try and I try. I can't get no, I can't get no

That is the theme song of the truck now. :burnout:

Re: Rear gear ratio question
 

Time to re-visit this...

Re: Rear gear ratio question
 

Flip for ya.

Attachment 2435801

Re: Rear gear ratio question
 

AND you hit 135 in the 1/4!

Re: Rear gear ratio question
 

That - uh - seems to have worked.

Good lookin' pass.

K

Re: Rear gear ratio question
 

That's after the gear change? If so it looks like it was a step in the right direction.

Re: Rear gear ratio question
 

I forgot to mention, it was bouncing off the rev limiter the last 100 feet or so.

I think over the winter I will go up a ratio to 4.30s.

That was with a lot of changes, with more yet to come.

Re: Rear gear ratio question
 

Ýou may already know about this calculator. If not it may help you or just use it to the pass time while waiting at the doctor's office. It does have a nice function to insert converter slip into the calculations.

https://www.blocklayer.com/rpm-gear

Re: Rear gear ratio question
 

Well, I got a 4.30 and spool to try out. Wait for it to warm up a bit, and I will get it swapped in.