Gear Ratio

[DOOM]

I was just going to post about this very subject. I just got off the phone with Strange . Mike in tech told me I should be going with a 4.30 with my 572 6 speed .I told him I was running 19's . Man I thought that was a high gear. Does this sound okay guy's???

[waynieZ]

Mario won't that make you shift out of first aweful quick .They have a formular (which I forget right now ) but with a 2.66 first gear and 4:10's It was already on the high end of the scale for being too short. Someone will know the formular.

[E.rodz]

food for thought what do you plan on using the car for ?do you plan on autocrossing?taking it on long road trips?weekend drag racing.thats the first ? the second is what motor and howmuch hp.tq.have had many cars with 411 gears and they work good for a auto but not as well for a stick you just have to shift to much and gas milage suffers bad.I would give up a little hole shot for some extra milage and drivability for the street.but an autocross car for a short track would be a different story.you might be at the top of your preformance level of that t56 and with a deaper gear you will put more stress on the tranny.and fry tires alot easier..I think greg is on track with his calculations need more info before gearing can be figured for your optimum fun factor.

[Vegas69]

Originally Posted by Vegas69

Look at your intended application and normal cruise speeds in your daily driver and play with the calculators. You also need to take into consideration your engine. How large is the camshaft, what type of fuel delivery?

Man that's a good idea.....

[Flash68]

Originally Posted by DOOM

I was just going to post about this very subject. I just got off the phone with Strange . Mike in tech told me I should be going with a 4.30 with my 572 6 speed .I told him I was running 19's . Man I thought that was a high gear. Does this sound okay guy's???

Damn! You're already gonna have traction issues I imagine with the 572... those 4.30s ain't gonna help! LOL

I would think 3.73, 3.90, or 4.10 tops.

[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?