Which is better for my Cobra: Tremec .62 or .82 OD?

[twobjshelbys]

Mine is a 3.54 rear end with a .82 5th. It works very well on the freeway - 2500-3000 RPM at 75-85MPH. The engine starts to lug down at about 2200 RPM at these speeds.

[patrickt]

... with the .64 OD. But, I do like the fact that I redline 5th at 225MPH for those quick trips to the Salt Flats.

[twobjshelbys]

Originally Posted by patrickt

... with the .64 OD. But, I do like the fact that I redline 5th at 225MPH for those quick trips to the Salt Flats.

I never thought of it that way. Hmmm...

Heck I haven't even hit the red line at 4th gear yet. Working.... I did in 3rd though. I think it was about 95 but I wasn't watching speedo only the tach.

[jwd]

You'll find there are 2 types of people. Ones that have the .82 5th gear and those that regret not having it. I have it with a 3.27 rear and it is PERFECT.

Jim

[patrickt]

Originally Posted by jwd

You'll find there are 2 types of people. Ones that have the .82 5th gear and those that regret not having it. I have it with a 3.27 rear and it is PERFECT.

Jim, cruising at 80 mph with your set up is 2700RPM. That's kind of high, but maybe doable (probably not, though). Move your rear down to a 3.54 though and the revs climb to 3000RPM. That's just too high for pleasant cruising and chatting.

[jhv48]

It all boils down to your engine. Will it be comfortable cruising in fifth gear at 2000-2200 RPM?

If not, go with the .82 ratio.

Mine is.

[Ralphy]

I am new to the Cobra World and I am considering the same thing. Looked at the T 56 Magnum. After getting familiar with my car I agree with most posts here. The .62 would be fun. however the .82 will be used more often in my opinion. I am running a 428 plus 03. 4 speed top loader with 3.36 gears. Someone mentioned going with the same gears as the top loader, yes to that also. If you want the .62's go with the T 56 Magnum if you can.

[jwd]

Originally Posted by patrickt

Jim, cruising at 80 mph with your set up is 2700RPM. That's kind of high, but maybe doable (probably not, though). Move your rear down to a 3.54 though and the revs climb to 3000RPM. That's just too high for pleasant cruising and chatting.

I suppose if you live in "Moose Butt, Wyoming", you're correct. There is no place you can cruise at 80 MPH in my area.

My Corvette has 4.11's and 60 MPH is 3000RPM. I avoid driving on the freeways.

[eschaider]

Originally Posted by timsullivan

I'm building a Superformance with most likely a 351W stroker of around 418 or 420 CI that I'm shooting for 450 to 500HP. I will be running 15 inch BFG's or Goodyear GT2's. My rear end ratio is 3.46:1 I am unable to afford changes to the wheel size or tires and don't want to change the rear end ratio. I will be doing occasional freeway driving here in SoCal and occasional longer trips on the freeway but the vast majority of my driving being simply around town.

Which TKO 600 should I get .62 or .82 OD and why in your judgment? Thank you in advance for any input you can give me on this.

-Tim

Tim,

You ought to do some searches on here and other places about TKO shifting problems going into third gear. Another good search is TKOs that have locked up in gear forcing you to drive home in whatever gear you parked it in.

Both are real problems and take a lot of the driving fun and turn it into maintenance fun. Driving fun is preferable.

Tremec has a very good transmission in the T56 that does none of the above and if you are after brute strength then check out their new T56 Magnum that they rate at 700 ft/lbs of TQ.

Although you can change once the trans is in, if it is not in yet the T56 might just be the better choice ...

Ed

[Rwillia4]

CA highway crusing is at 80. Go with the T56 and don't worry about it. It cost more but it comes with a bellhousing which will cover the cost and has a great feel.

I got mine for $2100 and love it. I just moved from CA and cruised comfortably in 6th most of the time.

[patrickt]

Originally Posted by jwd

I suppose if you live in "Moose Butt, Wyoming", you're correct. There is no place you can cruise at 80 MPH in my area.

My Corvette has 4.11's and 60 MPH is 3000RPM. I avoid driving on the freeways.

I live in a very urban area and, this morning, will head in to my office via a 4 lane highway (8 lanes total). The far right lane will be doing low 70s. State troopers will pass you on the left doing well in to the 80s. The posted limit is 55, btw. A 30 minute drive will take you away from the urban area to beautiful rolling country side where you can cruise peacefully in the low 80s and not even worry about local sheriffs bothering you. Those posted limits are 65. Jim, if you can't get your car out of the 60s then you definitely have your car geared properly, but you're missing a lot of nice relaxation. 80MPH is a "sweet spot" for calm cruising in a Cobra and, when geared properly, the wind noise is actually louder than the pipes.

[Jim Norris]

Originally Posted by mikeforte

Hi Jim,
I sold a guy a TKO years ago to install in his 428 Shelby Mustang. It had 3.89 gears, 2 4 bbl Holleys & a nice Crower cam. The problem was the cam wanted to go 80-90 mph to run clean and not buck. We installed a much more docile camshaft and he then loved to drive his car at normal speeds. The cam we used lost a tiny at redline and gained total driveability....

Mike,
Thanks for the suggestions. I'll take a look at a cam profile change. I don't relish the thought of cruising at 3000 or more rpm.

[Mister]

I have the .64 5th and have very mixed emotions about it.

In Western Pa, where we live, it is too long. The speed limits are too low, traffic is too slow and the hills are too steep.

This summer we drove out to Colorado, up through the Rockies and then back home. It was great where traffic was light and the speed limits higher.
The longer 5th is great out on the road but it is too long around town.
Compromises, compromises.................
Mike

[snakebitekit]

Originally Posted by jwd

I suppose if you live in "Moose Butt, Wyoming", you're correct. There is no place you can cruise at 80 MPH in my area.

My Corvette has 4.11's and 60 MPH is 3000RPM. I avoid driving on the freeways.

Your living in the wrong state.
In Arizona you get run over at 80.
snakebitekit

[patrickt]

Do we have any states where there is effectively no speed limit? Somebody was telling me that they were out west somewhere and some sort of highway sign said something to the effect of "this highway is not patrolled for speeders, but if you run off this road you might not be found for days" or something like that. Now mind you, that could have been a COS story (crock o' shi_).

[SPF2245]

The .82 will allow you to drive fine on the highway, you don't have to worry about the engine being off cam at lower speeds in 5th, it still usable at the track and in town you can throw it into 5th and enjoy a conversation. The few times I wished I had the taller gear was on long road trips (over 300 miles), but then again, those were the far and few between times the car actually went out. The majority of the time these cars go for short hops, and a usable 5th for fun makes more sense IMO.

[twobjshelbys]

Originally Posted by patrickt

Do we have any states where there is effectively no speed limit? Somebody was telling me that they were out west somewhere and some sort of highway sign said something to the effect of "this highway is not patrolled for speeders, but if you run off this road you might not be found for days" or something like that. Now mind you, that could have been a COS story (crock o' shi_).

Montana used to have a "reasonable and prudent" with no posted numeric limit, but they took it away in the late 90's.

Almost all states have a "reasonable and prudent" clause that would be triggered, for example, going 75 on the freeway during a blizzard and causing a 50 care pileup.

[RodKnock]

Originally Posted by jwd

I suppose if you live in "Moose Butt, Wyoming", you're correct. There is no place you can cruise at 80 MPH in my area.

Hey, I grew up Moose Butt, Wyoming, and I find that very insulting.

I have the 0.82 5th gear and a 3.42 rear end it's perfect. 70-75 MPH is about all you can do in the SF Bay Area w/o alerting the CHP. Although there are definitely some spots where...

[timsullivan]

Rodknock: What size tires are you running with that combination?

[Got the Bug]

Tim,

I'm running 295/50/15 with a .082 Tremec and it's perfect for freeway cruising in CA.