New rear end, gearing question

[brent1976]

I bought a 67 Camaro last year. The suspension was still completely stock from 1967 and shot. I bought full ridetech front with truturn and rear 4 link, front and rear sway bars. I have done a mini tub in the rear and the front suspension is completely done.
I’m getting ready to install the four link and am thinking I’d rather buy a new rear end with the correct brackets on it instead of hacking up the stock rear end and then needing a new stronger rear end next winter when I do an ls swap and having to do it anyways.

I’m planning on a TKX 5 speed and am wondering how high I can go with the rear gear to be livable with now and not be too high for the TKX. It looks like 3.25 will put the TKX at 75mph at around 2300rpm. The Saginaw that’s in the car now will be at 75mph at around 3200rpm. That sounds ok to me, but want opinions from people with experience. I don’t want to go too high geared now and be too low in the rpms later. If I have to I’ll just regear it later but would prefer to not.

[mikedc]

A few thoughts on this:


-- When calculating RPMs, remember that the tire diameter will be shortened by sidewall compression when it's on the car. I once read a figure in an article about (street) tires that the functional rolling diameter is down to about 97% of the stated size. That typically subtracts a good 3/4" from the stated diameter, maybe more. This goes for street radials (not bias plys). And I'm guessing that taller-profile sidewalls will compress more than low-profile tires.


-- I dunno about the TKX, but with the old TKO you could get the overdrive ratio swapped out for different one. Some of the trans modifying shops like Liberty Gears would do it. The TKX gear charts include overdrives of 0.68, 0.72, and 0.81.

A guy at Liberty once told me that they have custom-made a few overdrive gear ratios for TKO customers. Cost about $1000. Again, I don't know if the TKX situation is different or not.


-- Yes, plan around cruising at 75 mph. A lot of the muscle car hobby is behind the times on this. Traffic speeds have been creeping up as modern vehicles get bigger & safer. 75 mph is not the new fast, it's the new average.


-- IMO low gears (like the 1st, 2nd, 3rd) are overrated on street cars. If you aren't using the car in some kind of competition then I don't see the point. It's more fun to cruise a car when you don't have to shift into 2nd almost immediately after you start rolling. And at the high end, you can run a super-tall overdrive 5th ratio to keep the revs down, but it means a huge clumsy RPM drop from 4th-to-5th. That's much more annoying on the street than on the racetrack.

IMO there is something to be said for avoiding low axle gears and widely-spaced overdrives.

[Kenova]

Here is a calculator that I use when deciding on gears and transmissions.

https://weddleindustries.com/gear-calculator

Once you have your transmission ratios and tire diameter entered it is just a matter of changing the rear end ratios untill you find something you like.

Ken

[Motobrewmaster]

I suggest you down load the Tremec App for your phone. It is pre-loaded with the gear ratio's of the transmissions and you can enter the tire size to get the correct tire diameter. https://www.tremec.com/menu/tremec-toolbox-app/

[brent1976]

Both of those look handy. I’ll probably use a couple of the ones from tremec after I start putting things back together.

I’m looking at the ridetech subframe connectors with rear spring shackles built into them. Do you think I would still need to reinforce the pocket with those built into them.

[TheJDMan]

Honestly ask yourself how much time you will actually spend at 75mph. I suspect not that much. Percentage wise the bulk of normal driving is done around town. Personally a 3.50 or even a 3.73 would be a much better choice.

[brent1976]

Most of the highways out here are 75 mph so I plan on going 75-85 a lot. I bought the car to replace my DD that I recently sold. The car is very nice with zero rust and no wrecks but it’s nothing special yet so I plan on putting some miles on it. It’s not going to be a garage queen. I’ve been driving my truck I bought for off-roading but the snow is starting to melt in the mountains so if I break something on it...

3.73 would put me at 4000 at 80mph. That seems a bit excessive.

[65 drop top]

Assuming a .72 5th gear, and 26” tall tire, approximately

3.25 rear, 80 mph, at 2400 rpm

3.73 rear 80 mph at 2800 rpm

[brent1976]

For this year it will have the Saginaw 4 speed with a 1.00 1st with a 315/30-18

[Hotwire]

Just want to add that LS motors are not some fabled creature that eat rearends and spit out pinion gears? Unless you're going with a +$20k engine build your stock rear will hold. I'm running a cammed 6.0 with my stock 64 8.2" rear/axles with just a stud girdle.

Here's the calculator I use, you can input tire size, trans gear ratios, and rear gear. It will give you full spectrum of what to expect out of your gear ratio decision. You can even compare different gear ratios or tire sizes to see what affect each has.

This site does have ads so be careful of where you click, but it is a great page. I printed out my setup and it's helped me visualize where I'll be when downshifting/upshifting.

https://www.blocklayer.com/rpm-gear.aspx

[brent1976]

I’m planning on an LS2 with heads cam and super charger. I figure that I’m going to be making 500+ whp with room to grow with a pulley change. I think that would probably end up making me nervous every time I run it hard. Plus I would have to hack up my 10 bolt then I would end up doing the 9” anyway so I might as well just do it now.

I’ve been using the calculators for a couple days over thinking it like I always do. I think the 3.25 sounds best. I can always pick the 5th gear I want.

[Kuhlhaus]

Just want to add that LS motors are not some fabled creature that eat rearends and spit out pinion gears? Unless you're going with a +$20k engine build your stock rear will hold. I'm running a cammed 6.0 with my stock 64 8.2" rear/axles with just a stud girdle.

Here's the calculator I use, you can input tire size, trans gear ratios, and rear gear. It will give you full spectrum of what to expect out of your gear ratio decision. You can even compare different gear ratios or tire sizes to see what affect each has.

This site does have ads so be careful of where you click, but it is a great page. I printed out my setup and it's helped me visualize where I'll be when downshifting/upshifting.

https://www.blocklayer.com/rpm-gear.aspx


Great calculator! Like it! Thanks.

[Hotwire]

I’m planning on an LS2 with heads cam and super charger. I figure that I’m going to be making 500+ whp with room to grow with a pulley change. I think that would probably end up making me nervous every time I run it hard. Plus I would have to hack up my 10 bolt then I would end up doing the 9” anyway so I might as well just do it now.

I’ve been using the calculators for a couple days over thinking it like I always do. I think the 3.25 sounds best. I can always pick the 5th gear I want.

Completely understood, should have realized what you were going for with your setup so far, thanks for going easy on me and best of luck on it!


Great calculator! Like it! Thanks.

You're welcome, I use that page more than I'd like to admit. He's got some other pretty cool calculators at the top of the page too.

[brent1976]

Completely understood, should have realized what you were going for with your setup so far, thanks for going easy on me and best of luck on it!


That is a good calculator.

This car is similar to me as your Malibu is to you. I’ve done a 400 whp h/c 6.0 Silverado, and a 650 whp h/c turbo 6.0 4wd Silverado. Bought a new STi but didn’t like it at all. Everyone said get an old car like a mustang or chevelle and found this. Now I’m going overboard after driving it 3 times with clapped out original suspension.

[brent1976]

Is there a certain u-joint that fits the 9” rear end and my driveshaft. Also does the driveshaft need shortened at all.

[chpr1972]

Napa carriers a u-joint that fits Ford rear end to Chevy. Old Fords I believe have 1310, 1330, 1350 series. As far a gear ratio, I have a TKO600 and it has a .64 OD. 3:70 25.5 " tall tires and at 60 I'm turning 1800 and at 70 2200. 75 should be 2400. Try to get solid, no grease u-joints as they are stronger.