Rear Gear Choice w/ TKO

rr454 · #1 (**permalink**) 05-25-2004, 11:48 PM

Just looking to see what's popular in gear ratios with a TKO w/.68 OD. Its behind a 460/550hp w/ a 9" carrier.

Thanks
dave

Excaliber · #2 (**permalink**) 05-26-2004, 01:53 AM

This question does NOT have an easy answer. But you insist? OK. heres what a LOT of people are running.

4 speed top loader with Jag IRS: 3.31 rear gear. 2800 rpm at 70 mph with 26.5" tires. 140+ top speed at around 6000 rpm.

Live axle (8.8 or 9") with 5 speed: 3.5 is pretty common.

Critical question: Are people HAPPY with these gear combos? A LOT of them are not! MOST folks wind up running whatever "rear gear" they got and whatever trans O.D. gear they got. Rarely do they consider their CAMSHAFT profile and THINK about the optimum "cruising rpm" and the CRITICAL 1st gear ratio.

5 speed with a 3.5 rear gear? Figure 25 to 30 mph TOP SPEED and tires going up in SMOKE in first gear. With a 460 you will quickly find 1st gear is not only "useless" it's downright dangerous! It will result in wheel spin when you LEAST expect it. Your 1/4 mile times will actually be FASTER using 2nd gear to launch (because 1st gear is a joke).

But with that high 5th gear O.D. (.68) your cruising rpm at 70 mph will be around 2000 (maybe less). Will your MOTOR like that ultra low rpm with that "radical" cam you got? Maybe not! You could drive faster! OR not use 5th at all?

HERE IS WHAT I WOULD DO:
I'd find me a 5 speed with a FIRST gear ratio between 2.32 and 2.78. 2.32 being a CLOSE ratio top loader gear and 2.78 being the WIDE ratio top loader gear. I'd find me a 5 speed with a .86 5th gear (just a little over drive, not NEAR as much as .68). Then I'd run a 3.31 rear gear. THEN I'd make sure my CAMSHAFT profile would "like" to cruise at about 2200-2300 rpm at 70 mph.

What you most likely WILL do:
Run the trans you got, wether it matches your camshaft profile or not. Pick a rear gear by looking at "top speed" and "cruising" rpm and pretty much ignore the 1st gear problem. Buy LOTS of tires looking for more "traction" and lots of "underwear" because the back end broke loose "again" when you least expected it!

,,,,choose wisely and good luck.

Roxie_427 · #3 (**permalink**) 05-26-2004, 05:39 AM

Dave,
Send me your email and I'll send you an Excel file, where you can plug in your gearbox and rear gear ratios and see the results, by gear and by mph.

As long as I'm here, I just purchased a new TKO-500 with the .68 gear. In my completed car, I'm planning to run somewhere in the neighborhood of a 3.00 to 3.25 gear behind an aluminum 427. I'm still evaluating. The good news for me is that my kit currently has a used "open" rear gear and I can drive the car for a bit and then decide on a posi unit.

Excaliber brings up some really good points. At least you can play with the spreadsheet and see what are the redlines and cruising rpm.

Tim

DonC · #4 (**permalink**) 05-26-2004, 07:54 AM

Dave:
Here is a gear ratio calculator that does a pretty good job http://www.368s.com/tools_rpm.phtml, just plug in the numbers and go. Even calculates tire diameter for you.
I agree with Ernie about some people not looking at the whole picture when they should be.
In my case I'm holding out as long as possible for the new TKO600 with the .82 or .83 (depending on who you talk to) 5th and a 3.07 rear. The TKO600 has a higher 1st gear than the TKO, TKOII and Richmond and comes close to the toploader wide ratio numbers with the addition of an overdrive 5th.
If you go with the standard TKO or TKOII you can bring the rear end up to 2.88 since the first gear is so low but as Ernie mentioned your 5th at .68 is going to turn some really low rpm's and may well be pretty useless. The TKO .82/.83 5th would probably work out to be a bit more streetable.
Just my $0.02.
DonC

Excaliber · #5 (**permalink**) 05-26-2004, 09:36 AM

http://www.368s.com/tools_rpm.phtml

,,,corrected link by removing the " , " at the end.

DonC · #6 (**permalink**) 05-26-2004, 10:37 AM

Oops, missed that, thanks Ernie
DonC

MidOHasp · #7 (**permalink**) 05-26-2004, 10:40 AM

I have 3.7 rear gear w/ that transmission and it's not a good combo. 1st gear is a joke, OD is a bit too tall. I'd like to run around 3.3 gears, maybe lower with the TKO II. That would make me happier.

rr454 · #8 (**permalink**) 05-26-2004, 01:15 PM

I have bought the trans yet but was kinda stuck on a 5 speed, just because it's more modern(?), but a toploader is still an option as I don't need to travel 140 mph plus. I'll give it more thought and maybe 4 gears is enough.
dave

Junket · #9 (**permalink**) 05-26-2004, 01:38 PM

Dave I would stay with 1000 RPM =10 MPH in 1st gear that works good for me and cruise at 2200-2300 in 5th and every thing is just fun in between. Works good for a street car.One thing about a 9"you can get every # from 2.00-6.00 used for about $100 on some of the Nascar sites.
Ken

CJ428CJ · #10 (**permalink**) 05-26-2004, 02:07 PM

There's a bunch of useful information regarding transmission/rearend combinations in the ERA assembly manual. Go here: http://erareplicas.com/freeman/427.pdf

Scroll down to page 13.

I'm running the Richmond 5 speed with 2.88 gears. I think 1st gear is very usable (approximately 50 mph at 6000 rpms) and at 70 mph in 5th I'm turning 2700 rpms (just hitting 2500-6200 rpm window for my cam).

Chris

ChrisL · #11 (**permalink**) 06-08-2004, 05:43 PM

what do you guys think of a TKO with a HiPO 302 about 400 HP and a 3.55 rear

Roxie_427 · #12 (**permalink**) 06-08-2004, 06:19 PM

Which TKO?

decooney · #13 (**permalink**) 06-08-2004, 06:34 PM

A torque monster 460 or FE coupled with a TKO-I, a moderate cam, and a low rear axle ratio makes for a very unusable 1st gear. Spacing between 1st/2nd/3rd is too short as well for the standard TKO in comparison to a Top Loader 4speed with the 3.08/3.31 axle combination. I run with two friends side by side with SPFs; both have TKOs, with 3.73 rear axle ratio, and they both want to drop down to axle ratios around 3.25/3.08/2.88 OR switch to the newer TKO transmissions with taller first/second gears and lower overdrives for more even gear spacing from 1-5. If you don't have a super radical cam, it might be worth doing what CJ428CJ went with if you can get the newer .8 type 5th overdrive setup. With the Big Block stump puller motors, the taller first/second gear seems to really make all the difference and its more fun to drive vs. short shifting the low 1st/2nd gears all the time. Good Luck.

NeedAntiVenom · #14 (**permalink**) 06-09-2004, 06:11 AM

ChrisL,

I have a 320 HP 302 w/ TKO and 3.54 gears. Nice combo overall, but the jump from 4th to 5th is a little big. The TKO II has the same ratios as the TKO except for 5th. TKO 5th is .68, TKO-II 5th is .82. If I did it over I would get the TKO-II.

Tony Aprile · #15 (**permalink**) 06-09-2004, 07:04 AM

Dave

I take it you have the TKO II with the 3.27 first and .068 fifth.

The Superformance standard gear is 3.73 and I have the same TKO II transmission. In 5th at 65 it's about 2000 rpms which is great for just crusing on the highway. There is a gear/ tire calculator on the Superperformance/Second Strike website to help with your question. What's right is personal preference.

http://www.secondstrike.com/Technical/GearCalc.asp

With my 460 I don't feel the factory gearing is correct and I agree with MidOHasp. With 3.73's in the rear first gear is useless and 5th gear is almost a 1500 rpm drop from 4th. Next time around I will change transmissions to the new TKO 600 with a 2.87 first and 0.83 fifth with 3.27 gears. Big Blocks don't need all the gear, let the torque do the work.

Tony

ChrisL · #16 (**permalink**) 06-09-2004, 02:34 PM

Roxie.
It is the TKO with the .68 5th gear .it was a good buy So I am trying to see if it will work well the the gearing I have . I also have a World Class T-5 (2.95 1st gear and a .63 5th gear) but I am under the impression that the TKO is a better way to go .Which way do you guys think I should go .I am looking for the best of both worlds fun to play with and good highway cruising tooThanks Chris

rr454 · #17 (**permalink**) 06-12-2004, 04:29 PM

wrong button
dave

rr454 · #18 (**permalink**) 06-12-2004, 04:38 PM

In my earlier post I stated that "I have bought the trans", but it should have been "have not bought the trans yet" (typo) . I am mulling over what was discussed and will apply this to my selection of gear and trans units.

Thanks
dave

CC5S · #19 (**permalink**) 06-23-2004, 12:13 PM

Here's a quick breakdown of the gears for the new Tremec TKO's:

TKO 500: 1st (3.27), 2nd (1.97), 3rd (1.34), 4th (1.0), 5th (.68)

TKO 600 (road race): 1st (2.87), 2nd (1.89), 3rd (1.28), 4th (1.0), 5th (.82)

TKO 600 (street): 1st (2.87), 2nd (1.89), 3rd (1.28), 4th (1.0), 5th (.64)

Best sellers have been the TKO 600's (600 ft/lb torque)

TerrysSPF · #20 (**permalink**) 06-23-2004, 01:45 PM

I have the TKO now (.68 5th) with a 3.73. First gear is totally useless and 5th is a pain unless you're on the highway. I always start out in 2nd if I'm messing with a friend (or rice burner!). I Thought about changing to a 3.08, but now I'm considering staying with the 3.73.....or maybe going to a 3.54, and holding out for a new TKO600. Looks to be the best gearing available, and you gotta love the 600lb tq rating.