Help me pick a rear gear for my 68 camaro.

[rp0029]

So I am deep into a rebuild in my 1968 Camaro. I have the body tub off the subframe and we're doing the sheetmetal work and getting every last square inch of rust blasted, cut, or sanded off, including up in the cowls.


I have decided on doing an aluminum GEN IV 5.3L block with Darton sleeves and a 454 rotating assembly and some CNC LS7 heads. I want to run this motor through a T56 magnum tranzilla. This car is for the street. I am not a drag racer, or autocrosser, but I do enjoy whipping my 2014 Z51 C7 around corners. So I just want an all around fun car with serious grunt. I imagine the combo I pick for this engine will make similar HP/Torque as a 2016 Z06, probably with the torque curve shifted up a bit. I will probably go with either CA 4 link rear or a torque arm for traction out back. I thought the final drive ratios of the Z06 might be an appropriate place to pick gears, because I don't want first gear to be useless:


Z06:
2.29
1.61
1.21
1.00
0.82
0.68
0.45
3.42 Rear.


Final drives for each gear:
7.8318
5.5062
4.1382
3.42
2.8044
2.3256
1.539





The tranzilla I want to go with has the following gears:

2.66
1.78
1.3
1
0.74
0.5


So here are the final drives for the following rear gears:


3.42 rear:
9.0972
6.0876
4.446
3.42
2.5308
1.71


3.23 rear:
8.5918
5.7494
4.199
3.23
2.3902
1.615


3.08 rear:
8.1928
5.4824
4.004
3.08
2.2792
1.54


2.73 rear:
7.2618
4.8594
3.549
2.73
2.0202
1.365

So I was thinking either a 3.08 or 3.23 rear gear. Am I off my rocker on this? I don't intend to do full drag race launches at 4K rpm, just want to be able to gun it off the line and have it pull hard without going completely sideways with the slightest tap in first.

[CliffsBlueCamaro]

I've currently got 3.08 rear gears in my 67 Camaro and a Viper T56 with 2.66 first gear. My SBC is right at 300 HP and 300 Lb./Ft. to the rear wheels. It sounds like you are aiming for a whole lot more power than I've got, but I will say that I am completely underwhelmed by the straight-line acceleration my car now has. A few years back I had the same engine with a 4-speed and 4.11 rear gears. I really miss the acceleration the car had back then. I do love the ability to actually cruise on the highway I have now even more though.

Another consideration would be your cruise RPM. Again, my little 300 HP SBC has a pretty big cam in it. It isn't very happy lugging along at only 1,200 RPM at 70 MPH like I have it doing now with the 3.08 gears. I would imagine that a build of your caliber would also use a pretty lumpy cam and would like a little more RPM.

I wouldn't recommend going with a 3.08 or a 3.23 even if you do have Z06-type power. I would go at least 3.42 or 3.55. Vipers also have a 3.42, and I've read that one of the first mods guys like to make is going to a 3.55 for better all around performance. Just some food for thought. :-)

[sam 74]

in my car i have 3.90 with a a518 auto, but i'm running 29 inch tall tires, what is your tire height going to be, that will play a big role in your gear selection as well as the ratios. i'm running about 1900 rpms at 70 mph, i'm probably going to step up to 4.11 with the tall tires.

[TheJDMan]

I really think you need to do some more research. A 3.23 is nowhere remotely close to where you want to be with any OD trans. I'm running a 1st Gen SBC 383 with a T56 Magnum model# TUET11009 close ratio equipped with a 2.66 1st and .80 5th .63 6th OD. I'm running a 3.89 rear gear with 26" tall tires and it is, IMO, near perfect. Great acceleration and I can still cruse 70mph at 2500rpm. Tremec has a very nice gear ratio calculator located at the following link. I recommend you spend some time playing with rear gears and tire sizes.

http://tremec.com/calculadora.php

Also, here a the link to the official Tremec T56 Magnum page(BTW, I have no idea what a "tranzilla" is). Check the "Technical Specs" link.

http://tremec.com/menu.php?m=104

Also on a side note, make sure you do some research on the CA G-Link triangulated 4 link rear suspension. The suspension it's self is not specifically problematic but the shocks that are supplied with the suspension kit do not work for a low ride height. Many here, myself included, are less than impressed with CA customer support. You might want to read some of the feedback section comments about CA. Now for the record, ridetech sells a very nice triangulated 4 link that shares a common origin with the CA 4 link and is supplied with a choice of shocks tailored for your application.

[andrewb70]

The missing piece of this puzzle is your intended tire height. So what size tires will you be running?

Andrew

[rp0029]

Thanks for the response.

70mph at 2500rpm? I live in a city with a lot of highways. Half of my driving is at 70, 2500 to me is crazy. My C7 is at about 1500 RPM at 70. I've been spoiled. I shift 1-4 usually, and then skip 5-6 and land in 7th. Rear in that is 3.42 with a .48 7th gear. 1st gear is 2.97. With 3.42 (10.1574 FD ratio) it shreds pavement with just 450/ft lbs without TC turned on. Might as well start in second gear. With the bigger engine/more torque and no traction control I figured first gear closer to the Z06 is better, which is actually a 3.08, but you guys are steering me to the 3.23 (hell I can always drop the rear and swap gears).

How much HP/Torque does your 383 make? I'm talking an aluminum block 454. It's not going to be a high RPM cam. This car is being built for the street. I still anticipate it will make 550-600 hp with probably 550 TQ out back. Long legs are more important than peak numbers. So the concern is if I put 4.10s out there first gear will be completely useless.

I looked at Ride Tech. I have many of their products on my front end already. The rear suspension seemed great but they told me you could not really adjust ride height, it just lowers the car substantially, and I have had severe problems with my car scraping with the 2" drop GW springs on there before. My city has a lot of hi hats and construction. Alston's kit allows you to set ride hide more IIRC. So it's that or a torque arm.

Thanks for your thoughts again.

I really think you need to do some more research. A 3.23 is nowhere remotely close to where you want to be with any OD trans. I'm running a 1st Gen SBC 383 with a T56 Magnum model# TUET11009 close ratio equipped with a 2.66 1st and .80 5th .63 6th OD. I'm running a 3.89 rear gear with 26" tall tires and it is, IMO, near perfect. Great acceleration and I can still cruse 70mph at 2500rpm. Tremec has a very nice gear ratio calculator located at the following link. I recommend you spend some time playing with rear gears and tire sizes.

http://tremec.com/calculadora.php

Also, here a the link to the official Tremec T56 Magnum page(BTW, I have no idea what a "tranzilla" is). Check the "Technical Specs" link.

http://tremec.com/menu.php?m=104

Also on a side note, make sure you do some research on the CA G-Link triangulated 4 link rear suspension. The suspension it's self is not specifically problematic but the shocks that are supplied with the suspension kit do not work for a low ride height. Many here, myself included, are less than impressed with CA customer support. You might want to read some of the feedback section comments about CA. Now for the record, ridetech sells a very nice triangulated 4 link that shares a common origin with the CA 4 link and is supplied with a choice of shocks tailored for your application.

[rp0029]

Also, the rims will be the forgelines, I want to sort of copy the vengeance Camaro's rim/tire size, but with like ZXR3s or something: 19x11s in the front, 19x14s in the rear. He actually stretches 275 and 345s on them, I think it looks pretty mean. But I am not sure it is the best idea to stretch them out. Still looks cool though.

http://www.thestreetfighters.com/201...aro-vengeance/

[andrewb70]

Also, the rims will be the forgelines, I want to sort of copy the vengeance Camaro's rim/tire size, but with like ZXR3s or something: 19x11s in the front, 19x14s in the rear. He actually stretches 275 and 345s on them, I think it looks pretty mean. But I am not sure it is the best idea to stretch them out. Still looks cool though.

http://www.thestreetfighters.com/201...aro-vengeance/

Sooooo....how tall is the planned rear tire?

Andrew

[rp0029]

Seems like the tire I will likely go with is 27.36 inches. NT05R P345/30R19 LL tires - height = 27.36.

[andrewb70]

With that tire I would do a 3.73 gear. That will put you at about 1730 RPM in 6th gear @ 75 MPH. Provided the cam you pick doesn't have a lot of overlap, it'll be happy there all day long.

Andrew

[TheJDMan]

Thanks for the response.

70mph at 2500rpm? I live in a city with a lot of highways. Half of my driving is at 70, 2500 to me is crazy. My C7 is at about 1500 RPM at 70. I've been spoiled. I shift 1-4 usually, and then skip 5-6 and land in 7th. Rear in that is 3.42 with a .48 7th gear. 1st gear is 2.97. With 3.42 (10.1574 FD ratio) it shreds pavement with just 450/ft lbs without TC turned on. Might as well start in second gear. With the bigger engine/more torque and no traction control I figured first gear closer to the Z06 is better, which is actually a 3.08, but you guys are steering me to the 3.23 (hell I can always drop the rear and swap gears).

How much HP/Torque does your 383 make? I'm talking an aluminum block 454. It's not going to be a high RPM cam. This car is being built for the street. I still anticipate it will make 550-600 hp with probably 550 TQ out back. Long legs are more important than peak numbers. So the concern is if I put 4.10s out there first gear will be completely useless.

I looked at Ride Tech. I have many of their products on my front end already. The rear suspension seemed great but they told me you could not really adjust ride height, it just lowers the car substantially, and I have had severe problems with my car scraping with the 2" drop GW springs on there before. My city has a lot of hi hats and construction. Alston's kit allows you to set ride hide more IIRC. So it's that or a torque arm.

Thanks for your thoughts again.

I'm old school where an engine was allowed to breath, and 2500 is just a nice cruse rpm. To me a 1500/1700 cruse rpm is what a diesel truck engine runs. My 383 was dynoed at 518 hp as I recall.

Given your intended use and tire diameter I would agree with Andrew, a 3.73 would be a good choice.

[Z06vet]

If it helps you for highway specs, I'm running the same ratios in my F-body T56 with 4.10 gears & 335/30/18 rear tires. At 80 mph it turns 2100rpm. I think 4.10 is perfect, but 3.90 would work. The more duration with the cam choice, the more gear the motor will like. Look at the operating range of the cam you select, and choose the gears accordingly.