picking rear ratio

[BB BELLA]

trying to pick a rear gear for the zf s6-40 which has double OD. car will see lots of highway and I like not constantly pulling gears on the street! what gear 3.91/ 4.10 or ?
833 2.66/1.91/1.39/1.00
zf 2.68/1.80/1.29/1.00/.75/.50
500+ci alumhead 11/1

 

[69L48Z27]

3:73 to 3:91 would be my preferred range.

 

[1 Wild R/T]

trying to pick a rear gear for the zf s6-40 which has double OD. car will see lots of highway and I like not constantly pulling gears on the street! what gear 3.91/ 4.10 or ?
833 2.66/1.91/1.39/1.00
zf 2.68/1.80/1.29/1.00/.75/.50
500+ci alumhead 11/1

View attachment 814250

Sorry but you've out cooled yourself... Your comment "I like not constantly pulling gears on the street!" but you've got a 6 speed trans...

The reason modern cars are going to 6-10 speed transmissions is engines with limited torque & a narrow band where the engine is efficient...

You on the other hand have 500CI of torque that does not really care what gear it's gonna pull...

5th gear is .75 so a 3.73 or 3.91 gear would be fine... But 6th gear is .5... You've never need it

You could jump to 4.56 so 6th gear is 2.28 but then 1st & 2nd are worthless unless your hauling a heavy load....

Yup, plain & simple you've out cooled yourself..

 

[Jerry Hall]

3.91 is my choice. It has great performance 1-4 and right around 2000-2200 rpm at 75-80 on the interstate. In contrast my 66 with 6.i Hemi and 727 is 3500 at 68-70 with 3.55 gears.
Torque and HP is what is going to keep down rowing gears.

 

[Slap Stick]

I think what was meant by, "pulling gears" was referring to the 3rd member.
Do the math using tire diameter, etc to find engine rpm at the desired speed in OD.

 

[Hey-O]

I thought he was talking about changing gears in the rear end also. I would go 3.91

 

[R413]

Info not disclosed:
-rear tire height 25” or 31” ?
-desired RPM, cruise and top speed?

Are you considering driveshaft RPM?

 

[toolmanmike]

Ya with 500 cubes you could get buy with a 3 speed and 2.87's.

 

[Slap Stick]

Driveshaft rpm I think is irrelevant. Its engine rpm at x mph in high gear. Don't over think it.

 

[Budnicks]

trying to pick a rear gear for the zf s6-40 which has double OD. car will see lots of highway and I like not constantly pulling gears on the street! what gear 3.91/ 4.10 or ?
833 2.66/1.91/1.39/1.00
zf 2.68/1.80/1.29/1.00/.75/.50
500+ci alumhead 11/1

View attachment 814250

http://www.wallaceracing.com/calc-gear-tire-rpm-mph.php

1 3.73 gear
in 6th with a 0.50% OD
with a 28" tall tire it's like
@ 65 mph it's like 1,455 rpm
@ 70 mph it's like 1,567 rpm


a 3.91 gear same other stuff
@ 65 mph it's 1,525 rpms
@ 70 mph it's 1,642 rpm

a 4.10 same other stuff
@ 65 mph it's about 1,599 rpms
@ 70 it's 1,722 rpm

or try other calculators there to figure out what you need

good luck

 

[BB BELLA]

.
thinking 3.91 is the gear!Don't forget I'm in Canada and it's quite common for traffic to be moving 130kph+19kph before dangerous driving!that's 92mph.
1wild r/t is correct about my not wanting to row gears. now that I see the term "rowing"! I prefer longer hard pulls that keep you back in the seat instead of jostling around in the car!

 

[Hey-O]

http://www.wallaceracing.com/calc-gear-tire-rpm-mph.php

1 3.73 gear
in 6th with a 0.50% OD
with a 28" tall tire it's like
@ 65 mph it's like 1,455 rpm
@ 70 mph it's like 1,567 rpm


a 3.91 gear same other stuff
@ 65 mph it's 1,525 rpms
@ 70 mph it's 1,642 rpm

a 4.10 same other stuff
@ 65 mph it's about 1,599 rpms
@ 70 it's 1,722 rpm

or try other calculators there to figure out what you need

good luck

Well done!!

 

[BB BELLA]

forgot to mention this tranny was sitting in the shop destined for the 6/71 blown gen6 big block 80 2 wd blazer with much more tire , my son decided it might not be tough enough for the truck and s/c motor so it goes in the mopar!picked up a richmond 5 speed for the blazer.
It'll all be together soon and we'll see if we know anything about anything!maybe we'll have a lot of scrap!

 

[Cranky]

With a .5 OD.......4.10's at least and being me, 4.30's! Geez. Do the math with the 4.10's and a .5 OD and see what your rpm is at 90 mph. Heck, I've run 4.56's on the street and some short highway stuff with a small block and no OD! Yeah, 60 MPH is getting up there but for short hops, no big deal. And no one and I mean no one took me off the line!

 

[BB BELLA]

it's not tubbed!keeping the tires hooked is #1 in my opinion! these cars won't fit much rubber under them! that's why I'm thinking longer pulls with less tire contact disruption!