Gear Ratio

[DOOM]

After I posted I talked to Frank and he has me down to a 355 .That sounds way better. 430 did'nt sound right..

[GregWeld]

Originally Posted by DOOM

After I posted I talked to Frank and he has me down to a 355 .That sounds way better. 430 did'nt sound right..

Mario -- You still need to KNOW - not GUESS - at the tire diameter... final drive ratio... (there are multiple ratios available!) and your desired cruise RPM's for the given combination.


For comparison sake using ASSumed numbers:

Using a 355 x 30 19 tire - and the final drive of the T56 (700 torque - 1st gear is 2.97) and a 3:55 rear end -- @ 2000 rpms your speed is 106 MPH

Nice - as long as you can get away with it!

Using all the above but substitute a 3:73 - you're at 87 MPH

Using all the above but substitute a 4:56 - you're at 71 MPH

Drop the cruise RPM's to 1800

Speeds would be 83 - 79 - 64

Raise the RPM's to 2200 - which is about where it probably should be...

Speeds would be 101 - 96 - 79

NOW HERE'S WHERE YOU CAN'T JUST GUESS.... IF you use the Tremec with the 2.66 First gear look what happens using the 2200 rpm cruise and same tires... There's almost a 20 mph difference!

3:55's -- 81
3:73's -- 78
4:56's -- 63

[DOOM]

Sorry for the thread hyjack Swain!! Greg I'm running a 345-30-19 tire..

[GregWeld]

Right! Sorry SWAIN!! Sheeeesh -- I have a bad habit of doing that! My bad!

Mario -- tire size is close enough for the purpose I was trying to demonstrate... a couple 10th of an inch diameter isn't going to change the basic tech session I was running there...

My point was really more about how critical - or really - about how much difference there is between all these seemingly 'simple' factors. Tire size - final drive ratio - desired cruise RPMs.

A buddy has a 454 bbc Imagine Injected 56 Chevy with 3:55's and a 700r4 -- My 56 runs a 427 sbc 700r4 with 3:73's... I can hear the difference and I like mine better... and I've ridden in both (DOH!) and my 3:73's seem to put a little more bounce into the step. Would I like something in the 4:10 range? NO WAY... Do I care about gas milage? NOPE! I do like to drive my stuff - but also want relatively snappy performance so life is a trade off. :>)

[GregWeld]

Swain and Mario --

I just read the other post about gearing and Frank makes some very good points. This also brought to mind the recent Optima Challenge - it was so "obvious" which cars could actually put the power to the ground... they were MUCH quicker! The cars that just went up in smoke off the line... looked cool... sounded good... made lots of "furry" but went nowhere in a hurry. I've always referred to my tire size as my "slow blow fuse"... my car doesn't hook for poo... with the 3:73's... and too narrow tire... guys love it - and I'm not going to change 'em - and would need major mods to get more tire under it... With a motor that throws down torque like a 572 - mid 3's should get 'er done! And maybe a 5 speed instead of the 6?

[Vegas69]

Come on Greg, that's what traction control is for. That would be your left and right foot on the clutch and gas. I wouldn't want a deeper gear in my car. I run a 3.73 with a tko600 and it's about right. 1st gear is plenty short and traction is a huge issue if you don't slip the clutch or modulate the gas pedal. It also allows me to run all my autocrosses in 2nd gear and not need to shift. Which version on the t56 are you running Mario?

[GregWeld]

Originally Posted by Vegas69

Come on Greg, that's what traction control is for. That would be your left and right foot on the clutch and gas. I wouldn't want a deeper gear in my car. I run a 3.73 with a tko600 and it's about right. 1st gear is plenty short and traction is a huge issue if you don't slip the clutch or modulate the gas pedal. It also allows me to run all my autocrosses in 2nd gear and not need to shift. Which version on the t56 are you running Mario?

WELL THAT SETTLES IT -- We both run 3:73's -- so then -- so should everyone else!!

LOL

Hard to modulate my torque converter... and I wear magnetic shoes and the floor is made of metal. It'll hook up when it gets done spinning!!

[DOOM]

Originally Posted by Vegas69

Come on Greg, that's what traction control is for. That would be your left and right foot on the clutch and gas. I wouldn't want a deeper gear in my car. I run a 3.73 with a tko600 and it's about right. 1st gear is plenty short and traction is a huge issue if you don't slip the clutch or modulate the gas pedal. It also allows me to run all my autocrosses in 2nd gear and not need to shift. Which version on the t56 are you running Mario?

Todd I have'nt worked out my trans choise yet I'm going to get with Frank and have a little pow wow about this . I want the strongest and the best........ I know that much....

[awr68]

I will be using a 3.89 with my SBC-T56-9"-335/30/18 combo. I should be at 1800 rpm @ 65mph