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

[patrickt]

I still think with the OP's 3.46 rear that the .82 is probably better for him. BUT, if his engine builder says his engine will run smoothly, without hiccupping, at 2000RPM -- forget about accelerating, it doesn't matter -- and 2000RPM translates to a speed that he believes he will be cruising at on his state's highways, then go with the .64 gear. With my 3.54 rear, 2000RPM is 68MPH, and it's almost like coasting with the engine off -- very pleasant.

[DAVID GAGNARD]

Originally Posted by Got the Bug

Here's a link to the calculator on Second Strike.

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

That one works great, according to it at 2000rpms I should be doing 74 mph, my speedometer shows right at 75 mph, so it's all correct........

I've used a few of the other calcualtors, but I like this one the best.........

David

[jhv48]

Here in So. Cal. if you are on the freeway and not going 75-80 MPH, you will be rear ended (unless there is rush hour traffic).

My car runs 2200-2400 RPM at those speeds and provides a nice quiet cruise. If I want to accellerate quickly, I downshift. If mild accelleration is needed, fifth is fine. Don't want to be turning 3000 RPM on the freeway. My engine drives just fine at 2200.

To each his own. Do what suits your driving habits, road conditions and engine setup.

[timsullivan]

Jim: I like the sound of that. What rear end ratio, tire size and 5th gear OD are you running? I'm assuming your running a moderate cam as opposed to some high RPM nasty stick?

[jhv48]

I have a Roush 427 SRTW with the dual plane intake for low end torque. My fifth gear is the .64 in my TKO 600 5 speed.
My rear end is the stock 3.46 and the tires are 315X35X17's. My engine purrs at 2000 rpm and hiway cruising is very comfortable at 75-80 MPH (turning 2200-2400 rpm).

Around town in fourth gear at 60 MPH, I'm turning about 2900 RPM. Comfortable for short times and if you need to pass someone, just floor it and be gone.

If your engine is a torker, get the .64. If it's a revver, get the .82.

[WarrenG]

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

Sorry, three types. I have the 0.64 and don't regret it a bit! Also no problems or issues with shifting or getting stuck in 3rd or any other gear.

[patrickt]

Originally Posted by WarrenG

Sorry, three types.

Jim's brilliant analysis is close, but needs a tweak... there are indeed only two types of people -- those who categorize all people in to two categories, and those who do not.

[RodKnock]

According to Clint Eastwood in The Good, The Bad and The Ugly, there were only two types of people. Those with guns and those who dig. I think the ones with the guns had the 0.82 5th gear.

[jhv48]

Originally Posted by RodKnock

According to Clint Eastwood in The Good, The Bad and The Ugly, there were only two types of people. Those with guns and those who dig. I think the ones with the guns had the 0.82 5th gear.

That means that the ones who dig (.64) get to bury the ones with guns (.82)!

[BeasleyRB]

351W .82 3.25 rearend. 5 great gears.

[Mooch]

I was having the same decision making trouble and made some rpm calculations for the ERA 3.54 and 3.31 rear ends. See pages 2 and 3 of this thread:

http://www.clubcobra.com/forums/showthread.php?t=99751

I've decided to go with the 3.31 rear and the 0.82 5th for the better shift and balance, and I'll deal with the higher rpms and noise at higher speeds - which can be frequent on Florida freeways.

I'll let you know how it turns out.

[mdross1]

I did the rear gear change 3.54 to 3.70,with the .62 od behind a 550hp 460 suggested by Mike Forte.It is the perfect combo for me.Like you have read it is all about getting it right.My first combination was Okay for a while 3.54 rear,with a TopLoader.

[Boostedsnake]

Thank you very much. My plan whas the 0.64. I hate when it rews to much on the highway. But after reading this i have been comfused?

I have 3.54 in the back and driving a kind chevy 350 turbo engine. Do you know how much different its in on the fourth gear in tremec against the munice?
Its perfect in any places but not on the highway.
My idea whas a pure overdrivegear for highways. Not a performencegear.

What do you tryout experts think?

[Slick61]

I've got an aluminum 427W with a fairly snotty cam... aluminum flywheel too. I'm running a 3.73 rear end & the TKO-600 with the 0.82 overdrive. When I first got it, I thought I wanted the 0.64 as well- but as I drove it more, I discovered it was set up perfectly. My engine doesn't come on-cam til about 2400 rpm, so the 0.82 is ideal- especially for freeway cruising. 2700-3000 rpm is an uncomfortable cruising range??? For my engine, it's the sweet spot... sounds amazing without being too loud. My engine could never handle cruising a 1900-2200 rpm... it would buck like crazy. As others have said... it's the combination of engine setup/cam profile and rear end that will dictate the best overdrive for you. Good luck with your build!

[Boostedsnake]

My engine runs very smothly even at very low rpm. And probobly capable to produce around 1000nm+.

Sounds like 0.64 would be good? Or? Its a hard choise!?