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Thread: New rear end, gearing question
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04-03-2021 #1Registered User
- Join Date
- Jun 2020
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- Denver
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New rear end, gearing question
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.
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04-04-2021 #2Registered User
- Join Date
- Sep 2007
- Posts
- 424
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.
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04-07-2021 #3