just found out i have 4.56 gears but....

[mj42]

like the title says i just found out that i have 4.56 gears....

here is a little backround of my 04 cobra:

gears: 4.56

rearend: SRA swaped

engine mods: mainly stock with a 2.8 pulley

trans: (tr 3650 previous owner) will swap back to t-56 as soon as i can.

my question is since i have no idea about gears are they worth keeping. i have searched and i cant get really any input of what i should do.

I will mostly be DD, with some track time highway pulls maybe. as of right now i dont notice any problem besides 1st gear being short, but what about mpg's as well.

Any help would be greatly appreciated

 

[cobracide]

I would go back to the IRS with T56 and stock 3.55 gears since mostly a DD.

 

[04svtsnke]

What he said

 

[tt335ci03cobra]

Keep your combo for now but put a 3.55 in the rear, and then when money allows, do a t56 swap. If you drag race a lot at the strip on nights/weekends, the solid is a great mod to keep but if you love twisties and comfort, swap to a modded IRS with bushings/shim kit, axels, hubs, Detroit true trac or other diff, and a diff brace.

Anyways, a 3.55 rear should do wonders for traction/economy and is easy plus you can keep the 3.55 if you do go back to an IRS in the future.


You're probably seeing 2600+ rpms on the freeway, this will be painful at the gas pump...

Here are t56 ratios:

T3650 Specs:

1st gear – 2.66

2nd gear – 1.78

3rd gear – 1.30

4th gear – 1

5th gear – .80

6th gear - .63

Here are T3650 Specs:

1st gear – 3.38

2nd gear – 2

3rd gear – 1.32

4th gear – 1

5th gear – .62

Reverse – 3.28

The big difference is 1st and second vs a t56, so with 4.56 gears, 1st is literally going to feel like a creeper gear in a diesel truck.

Here's a great website to play around with different combos. Try the numbers with each transmissions gearing numbers incase you keep the t3650 or swap.

http://www.wallaceracing.com/calcmph.php


First enter an rpm you'd like to know the speed you'll be able to cruise around at, say 2000 rpms, which is ideal for freeway economy.

Next enter the tire height. This is as easy as simply measuring the height from bottom to top of the tire or doing it mathematically.

Tire height is likely 25.x" but if it's an aftermarket tire, just do the following math to get the height. Let's say you have a 315/35/17 rear tire...

Multiply 315 x .35 and you'll get 110.25, meaning the side wall of the tire is 110.25mm tall. Multiply that by two since a tire has its sidewall around the top and bottom of the rim. Now we know there is 220.5mm of tire and 17" of rim. Now convert the sidewall height of 220.5mm into inches by dividing 220.5 by 25.2 (25.2mm in an inch) and you get 8.75". Now add 17+8.75 and you get 25.75" of tire height.


Next, Enter your current rear gear ratio of 4.56 (or experiment with other options:
-4.30
-4.10
-3.90
-3.73
-3.55
-3.27
-3.08
-2.95

And test out different setups, I did this and ended up going from 4.10's to 3.55 with stock t56 gears to my new combo of a 3.08 with viper spec .72 5th and .50 6th gears because I swapped to the torquey 5.4 motor so I can get away with lugging at 1300rpms and turbos love long gears for load and spool plus traction was impossible with 3.55 and 9xx wtq at 3900 rpms haha. 1st goes to 65+ so traction is now very manageable. I played with ratios for an hour or so before picking my combo on a 28" tire, play around with the stats and I'm sure you'll find a combo that is perfect for your build and maximizes performance and economy.

Last, enter the gear you want to see the speed of. Here's a full example.

Rpm: 1300
Tire: 28 ( I run a 315/40/18, yours is prob 25.5 or so)
Rear gear: 3.08 (you have 4.56's now)
Transmission gear: .50 (my 6th, yours is a .62, t56's have a .63)

Then hit enter, I got 70.35mph.

I did the same with your current setup (4.56 and 3650) assuming a 25.5" tire height and got these speeds for 2000rpms and 6750rpms plus played around and got about what rpm you're going at 70mph in 60th.


2000rpms in each gear (ideal shift point for economy in most cases)

1st. 9.8 mph
2nd 16.64mph
3rd. 25.22mph
4th. 33.29
5th. 53.69

Also here's roughly your rpm at 70mph

70mph: 2,606 rpms



6750rpms in each gear (racy shift point)

1st. 33.24mph
2nd. 56.17mph
3rd. 85.11mph
4th. 112.34mph
5th. 181.2mph

I'd do a 3.55 rear. It'll give you much more run in any gear plus boost your economy by at least 3-4mpg on the freeway-huge difference.

Also, assuming 500hp or more, I can't see you getting much traction wit the current 4.56's unless you're in 3rd gear, a 3.55 rear should help tremendously.

Good luck!

 

[mj42]

man that is some extremely great insight. i never imagined anything close to what you have given me im going to use it.

ill see what tire size im running, and as far as gas i thought i was ok with a 1/4 tank im almost at like 80 miles, so if 3:55's will increase 3-4 mpg.

**** IN A PERFECT WORLD PERFECT ECONOMY SHIFTING IM NOT IMPLYING ANYTHING IM JUST DOING SOME QUICK MATH**********


so theoretically if i get 80 miles at a 1/4 roughly 20 mpg then for a full tank i should get about 320. which is highly improbable all with 4:56 gears

so with 3:55, ill be getting 23-24 mpg @ 1/4 tank will be 90-94.2 so a full tank would come out to 376.

**** AGAIN IN A PERFECT WORLD PERFECT ECONOMY SHIFTING IM NOT IMPLYING ANYTHING IM JUST DOING SOME QUICK MATH WHICH WOULD BE INSANE **********

it will be interesting to see what i can get since i never recorded my miles from full to when the low fule light comes on.

ALSO I JUST RELIZED WITH THE GEARS BEING CHANGED WHO KNOW IF IT IS CORRECT IN THE FIRST PLACE SINCE MY SPEEDOMETER IS A LIL OFF. ALSO ME AND MY FRIEND THINK IT MAY HAVE A TUNE.

just so many variables but sorry for the tangent, ill just have to wait and see once i figure out all the small details but 3:55's sound like a good choice to go with in the event i go back to a irs.

once again tanks for all the info. my main reason for asking about gears is to gain knowledge and understanding. and the best set up for my previous driving prefrence.

 

[mj42]

once again i just want a good set up for how my car will be set up and with descent gas mileage. and i will be going back to a t-56 as soon as i have the funds to do so. Since we all know v8 engines plus descent hp gas is not very fuel efficient especially when we have that lead foot every now and then.

 

[tt335ci03cobra]

Rock on man, good luck!

 

[MysticDan]

4.56 man the first 3 gears must be fun!:burnout:

 

[mj42]

1st, 2nd i easily spin the tires but it feels notchy from a stop when i take off from a stop sometimes just when im driving normally. but as he stated 1st gear is very short and i can even take off in second.