Hofs01

I have a 500HP solid lift roller motor and an LS T56 installed in my 78. Currently I have a 3.08 rear gear. I knew going into this I would need to change but I never thought it would be this bad. Saturday I drove the car to town and could hardly keep it under 55 in fourth gear. It is fast but a dog off the line. I would like to hear from the guys who have a t56 and 4.11 or 4.56 gears do you like them? What would you do different? BTW, my tires are 29" tall. Thanks in advance

Hofs01

gkull

They also make 4.30 I was always a 4.11 person with my .064 OD, But I only had 26 inch tires

l88rocket

I would go with the 4.11's, I have had several 6 spds with 4.11's and like how they preform

bebezote

gto or g body t56?

subtlez28

I've had a couple T-56 cars, here is my $.02.

I had a 95 Caprice with an LT-1 and T-56 swapped in. It had 4.11s and was a fun street car. Plenty of gear, I see no reason to go higher. In fact the driveshaft speed was so high on the interstate I would suggest strongly agains 4.56s.

I had a 02 Z28 with a ~400 hp LS1 (reason for the screen name). It had factory 3.42s. It pulled great, and first gear was much more usable than. I am a road corse racer, so I actually considered going to a set of 3.23s just to get more use of 3rd on the track.

Sounds like you are looking for mainly a fun street car. 4.11s will be fun if you like spinning tires. 4.56s would be overkill IMHO. If it were me I would consider 3.45s or 3.73 ish gears. They will make quite a difference from 3.08s.

71454Chevelle

I'm running a T-56 Magnum with a 2.66 1st gear coupled with 4.56 rear gears and 30 inch tires, it works very well with my engine combo (see sig below). It launches hard and I have plenty of power in the upper rpms (7k rpm) to utilize the lower gears. The 5th and 6th gear ratios are .80 and .63, which translates to a 70 mph cruise rpm at a little over 2200 rpm. The best of both worlds.

Hofs01

G-body

Hofs01

Thanks, my Trans is a .75 5th and .50 4th. So I may have some different RPM's but not much. How is 1st? Is it unusable as so many people say it is? I also have the 2.66 1st gear

68Thunder427

I did a comparison on 3.73 and 4.11 and the rpm range was not that far apart at 70. 3.73 at 70 in 6th is 2110 rpm and 4.11 is 2325 rpm in 6th and 2600 or 2900 in 5th based on 27" tire. If you go with 3.73 you can use your original case etc. but if you go with 4.11 you will have to change it all. This is a great calculator to play around with the ratios: http://tri-5.chevyrides.com/rpm.php
After running numbers and looking at different set ups I am leaning towards the TKO-600 .64 final since at 70 in 5th is 2362 rpm which is almost the same as the T56 in 6th and 1/2 the cost. Mine will be a cruiser / street car but check out the site and see what suits your fancy.

MIKE80

I have a T56 out of a '94 Trans Am, stroker engine, 3.70 rear, and 25.55" tires. 5th at 60 mph is about 2250 rpm and 6th at 60 is about 1550 rpm. I don't get on the interstate that often, so I wouldn't mind a 3.90 or 4.11 rear.

Hofs01

Thanks Mike! I must say, I am not sure I could have had made my swap as easy without your writeup. It really helped!

71454Chevelle

Be careful when gear your car, with a .50 6th gear, not sure how usable it will be depending on your engine setup. My cam is pretty lumping (even with almost 500ci) and it does not like real low rpm's. You stated 500hp, I'm asuming a small block which I'm guessing is going to have some duration in your cam. You may have issues with surging at lower rpm's. With a .50 6th rpms will be fairly low until you get up to some decent interstate speeds (probably above 75mph). This is where a deeper gear is nice.

As far as 1st gear being too low, IMO, no its not. The lower 1st gear makes it drive easier on the street, IMO. Easier to get things moving, especially if you have a decent sized cam, larger heads, big intake and carb. Yes it will very easily overpower the tires, but pretty much any combo making decent power will lose traction "on the street". I've used regular street radials, M/T Drag radials and Hoosier QT Pros on the street and they all spin. You are not going to have real good traction until you get on a well prepped track.

Hofs01

Yes, I have very little power below 2500. All the calculators show that the 4.56 is the right gear-set to use.

Thanks for the info on 1st gear, that is really the info I am looking for. This cam kills me taking off with the 3.08. I feel like I am in a fully loaded tractor trailer!

One of the things I do worry about is the critical speed of the drive-shaft. My motor stops making power at 7800. However, I have a rev limiter set up for 7K now. In fourth with a 1:1 that sucker would be whirling at 7K but that would have me going 128MPH so that will most likely never happen. But 75 mph in 6th I would be about 2200 RPM which then translates to a drive shaft speed of about 4400 rpms. Seems ok to me. anyone have thoughts?

71454Chevelle

Critical speed for me was not an issue. When installing te transmission I had to shorten the driveshaft about 7 inches which increases your critical speed. If I remember correctly, my critical speed is around 9k rpm.

Hofs01

I bet your right, my drive shaft is only 25" long

gkull

I was concerned with drive shaft speed because I entered high speed road races and I drove at Bonneville once in my Vette.

I had 28 inch rear tires and 4.11 rear end. At the time a .70 OD. I installed a drive shaft safety hoop 1320 u-joints and a balanced chromemoly stock diameter drive shaft. over 6000 rpm the drive shaft is really doing some rpm.

Now with my present solid rollers they seem to like 2400 -2500 freeway and really purr at 3000. 80 -100 mph

Oh I have more than 500 hp and my present tko 600 is a 2.87 first with 26 inch street tires and with 4.11 is was easy to take off full blast with practice

cv67

with a 29 or 30 in tire definitely do the 4.56

Have a 26 in tire with rowdy solid roller and 4.11s...its "just" enough it almost wants more gear. I can cruise at 80,90 all day in 6th its awesome.
Or keep it at70 in 5th where the cam is happier and motor on. Hell, i love the sound.

Gear that sucker for your cam not your cruise rpm and youll be happy. See too many threads where posters get focused on cruise rpm in OD only to be dissapointed with the way it runs in the rest of the gears.

As said 2.66 is not low "feeling" at all, in fact its perfect. Not too short and accelerates well. When youre used to 2.20 low muncies at youd think it would feel short but it doesnt. When you get closer to the 3.00 1st, yeah a little short.

cv67

Wanted to add dont worry about critical speed/whipping...Ive had mine north of 140 and I have a lot longer driveshaft then the C3 (El Camino)
it acted just fine (but keep a loop on just in case!)

71454Chevelle

X2

When you run a cam with alot of overlap, you are not going to get away with those 1500 rpm interstate cruise rpm's.

Hofs01

Thanks guys, seems like With 30" tires and my cam 4.56 is the way to go.