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View Full Version : 12 bolt or 9" 68 camaro



justasquid
05-10-2010, 10:19 AM
The car is a 68 camaro. Currently has a 10-bolt, with what I think is an 8.2. I am planning on installing a slightly worked ls-1 with a 6 speed. My hp goals are 450 or so at the crank, nothing too radical, but enough to warrant an upgrade in the rear of the weak stock one. Plus, the rear there now makes some odd clunking, and will be getting replaced regardless.

My qestion is, do I go with a 9", or should find a 12 bolt. Im not sure of the final gear I will be using just yet, but probably 3.42, or in that area, or maybe even as high as 3.08. I plan on going new, so Im wondering what the pro's and cons of each are for price and durability. The car will be seen mostly road use, power tours, cruise nights, daily driving, and probably not too much in the way of road courses. So the rear won't be seeing extreme abuse, but I'd rather be safe than sorry.

I've heard the 10-bolt 8.5 is a strong rearend, but just for the sake of saving money later on if I decide to go more power, I want a strong rearend.

Also, I was wondering if anyone knows the hp limit of the 6 speed trans? I'm sure I am safe at 450 hp, but in case I decide to go further, it would be nice to know what the limits are. I haven't aquired one yet, but I'm assuming it will be early 2000 LS1 and 6 speed.

thanks,

John Wright
05-10-2010, 10:48 AM
3.08 with a 6 speed?....5th and 6th won't get used much except on a track. I'd stay with the 3.42 or lower.
.....just my two cents.

TT302Z28
05-10-2010, 02:00 PM
I have 3:73 gears in the back of my Camaro now with the 6 speed. If I wasn't using my old Z/28 rear end until I quadralink I would go down to 4:10. This makes 6th much more usable.

6'9"Witha69
05-10-2010, 02:04 PM
I would stick to a 12 bolt. The 9" is tougher, but eats more power. For under ~600 crank HP and ~550lb. ft. TQ I would run the 12 bolt. Of course, that is in general. If you call Currie or Strange or other crate rear end companies they will tell you what their 12 bnolts are really good until and when they would suggest a 9".

wmhjr
05-10-2010, 02:33 PM
For higher than those numbers, Moser was quite comfortable with their 12 bolt and Truetrak. Just an FYI.

justasquid
05-10-2010, 04:22 PM
Thanks for the reply's everyone. I wasn't sure about the gear ratio, so thanks for the heads up on that JohnWright, I will definately stay away from higher than 3.42. Honestly, Im not sure what the best ratio is to run for my situation. I know most here are performance for the track, but this car will see quite a bit of highway use. I thought 3.42 would be a good ratio, but maybe even lower.

TT302z28, What rpms are you turning at highway speeds in 6th now with the 3.73? Also, are you running larger that stock dia' tires? I am planning on running 255/40-17's at 25 inch dia, if I can fit them, which come out to about a quarter inch taller than the stock 195-70-14's currently on the car. Of course, this will all depend on how the car looks after I drop it a few inches. 4.10 just sounds awful low, but that might just be my own aprehension as I had a 4.10 geared car years ago and I couldn't comfortably take it on the highway. But that was a 4 speed. I gotta get past that.

so it looks like a 12 bolt should be plenty for my needs. Thanks everyone. I truly appreciate it. this forum never ceases to amaze me at the wealth of information. Its going to make my build a lot less headaches and save some money from mistakes....

thanks again.

ProdigyCustoms
05-10-2010, 05:27 PM
We sell more Moser's to the Pro Touring crowd then anyone, and 2/3 of those are 12 bolts.

I would put a 12 bolt in anything I could put one in.

86Cutlass383SR
05-10-2010, 06:45 PM
The 6th gear ratio in an LT1 (94 & up) and LS1 6 speeds, is a .50. That .50 will make a 4.10 rear gear the same as a 2.05 rear gear with a non-overdrive trans. a 3.73 with .50 6th gear will act like a 1.865 rear gear and a 3.42 will be like a 1.71 rear gear. That's why most people recommend a 4.10 rear gear. Even a 4.56 would be like a 2.28 gear.

It takes a lot of torque to pull a 3.42 with .50 6th gear. Depending on your rear tire size, you could be cruising upwards of 80+ mph at under 2000 rpm...

smhigh
05-10-2010, 06:49 PM
I really like my 9" as if I need to change gears it's easy. I also like the fact that I'm not relying on c clips to retain my axles.

justasquid
05-10-2010, 07:56 PM
thanks cutless for the information. It really helps me understand why the lower gears are wanted.

I guess my other concern was the 1st gear. I didnt want it to run out to quickly. I would hate to have a basically useless 1st gear. I don't mind a very low 6th gear, as I would probably only use it on the highway, and use 4th or 5th for normal driving. But I hate the thought of having to shift out of first right away, as this car will see mostly pretty relaxed driving. I guess Im trying to make the best comprimise for decent performance and good driveability.

I guess I also need to figure out where my car is most efficient once Its built. If its very efficient at 2000 rpms, is that where I need to shoot for the 6th gear at freeway speeds? I would think there is a sweet spot for the engine to be making enough power to pull the car, but not too many rpms to drink too much fuel. too low or too high on the rpms, and Im sacrificing the whole point of a 6 speed.

again, thanks everyone for the input. I'm getting a better understanding of what I will need..:)

John Wright
05-11-2010, 03:31 AM
I'm using a 3.73 with my 6 speed...but the reasoning was I have a TPI 350, so I wanted to take advantage of the torque, since these TPI motors run out of steam pretty early and don't rev very high without some extensive work. If I thought the motor would scream, I would have gone with the 4.10 or 4.56.....but then you really have to watch the driveshaft speeds and choose a drive shaft that will handle the high rpms. With a .500 ratio 6th gear and a 4.56 rear ratio, the drive shaft will really be zinging.

ProdigyCustoms
05-11-2010, 04:10 AM
I really like my 9" as if I need to change gears it's easy. I also like the fact that I'm not relying on c clips to retain my axles.

We usually build our 12 bolts with new style big Ford Ends because of the better axle retaining design.

wmhjr
05-11-2010, 06:25 AM
I guess I also need to figure out where my car is most efficient once Its built. If its very efficient at 2000 rpms, is that where I need to shoot for the 6th gear at freeway speeds? I would think there is a sweet spot for the engine to be making enough power to pull the car, but not too many rpms to drink too much fuel. too low or too high on the rpms, and Im sacrificing the whole point of a 6 speed.


There are a bunch of calculators out there. I spend a great deal of time with them just for the reasons you mention. I'm running a TKO600, but needed to make sure that 1st gear wasn't too low, but 5th gear wasn't too high that I'd never use it. The calculator that helped me the most was at

http://www.5speedtransmissions.com/gear_calculator.html

I thought about the bottom and top of my "driving" torque range and plugged in those numbers to determine my speed ranges and shift points.

TT302Z28
05-11-2010, 06:34 AM
Right now I have a 275/35/17 on the back. I'm not sure exactly what the RPM's are but I can tell you I need to be above 75 to really use 6th. With a carbed 496 I worry about detonation if I lug it down too far.

I have ridden in a 2002 Camaro that had the gears changed to 4:10 and what a difference.

justasquid
05-11-2010, 06:10 PM
thanks a ton wmhjr!!!. that calculator really puts in perspective what I need to do. Im definately going to go lower gears than I originally thought. For right now, it looks like 4.10 is probably going to be the best of both worlds. I never thought of going that low.

thanks TT302z28. that also puts my mind at ease for going lower yet. If i was a betting man, I'd have lots some money cause I never would have dreamed going that low in the rear. Your tire size is pretty close to what I will end up with on dia, so its good to know your 3.73 is not quite low enough.

thanks JW, I know I will upgrade my driveshaft too, but its good to know about the rpms and what it will have to handle..

thanks again everyone for taking the time to share your information. A lot of light has been shed on this for me. I now have a solid direction to go with. I avoided a pretty big mistake for sure on this one thanks to you guys..