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

[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.

[Sharroll Celby]

I have a 351W, alum heads and manifold, lumpy cam, and 3.23 gears, and the T5 with the .64 OD. At 80 in 5th, I am turning 1900 RPM. At 80 in 4th, I am turning 3000 RPM. The Cobra still accelerates in 5th gear from 80 MPH, but at quite a leisurely pace!

I am thinking about a gear change to 3.55s, to get more OOMPH thru the gears, and keeping the .64 OD.

I think the .64 OD would let you get by with a shorter gear ratio and still be able to drive on the freeway, without rattling the fillings out of your head. I have about 30,000 miles with this combo, and 80,000 miles (almost) with the .64 OD.

[RodKnock]

Originally Posted by timsullivan

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

If I remember correctly, then I'm running the 275-50-15 Yoko Avids. At some point, I'll be getting the 295's from Avon.

[DAVID GAGNARD]

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

Very simple, you know your tire size and rear end gear ratio, you need to "plug in" these numbers into anyone one of the many gear calculators and see what your rpms will be at any given speed......

You also need to know what your engine torque range will be, as stated, don't worry about your peak hp #'s, worry about your engines torque band and try to get your rpms into the torque band..........

I'm running an older Tremec 5 speed in my 65 fastback with the .64 5th gear, 3.25 rear gear and 25.5 inch tall tires, 350hp, 351-W.......I do a lot of highway cruising and a lot of interstate driving in this car... 2000 rpms comes out to right at 75 mph in 5th gear and it's perfect for my motor, I can cruise all day at this level and get 23 mpg........

My cam is a mild camshaft and will run nicely down to about 1500rpms in any gear, so my cruising rpm is perfect for my set-up. If I want to pass someone, I don't have to downshift, just give it more gas and it will accelerate nicely from 2000 rpms.....

With the .64 OD, when shifting from 4th to 5th gear, my rpms drop approx. 900 rpms.......

Your tire/rear gear is known, now you need to determine what rpm level your motor will like to run at and the rpm level your comfortable with at cruising speed........
Just a wild guess, but with a 351-W based stroker, you should have tons of torque and I would think (depending on your camshaft) you could have your cruising rpm level in the 2000 to 2200 rpm range and be fine and still get some decent fuel mileage..........

The only time you'll need 5th gear is on the open road, so don't worry about city driving......

David

[Brian F.]

I have had two T5 transmissions in my roadster. One had approximately a .8 5th gear, the other slightly less, .6 about. With my setup, 351w, 400 hp/tq, 3.55 rear, I like the .6 a lot better. I didn't like the high rmps with the .8. At 75 mph, the .8 was around 2,700 and the .6 is about 2,100 rpm. It doesn't lug, though.

[Got the Bug]

Originally Posted by DAVID GAGNARD

Very simple, you know your tire size and rear end gear ratio, you need to "plug in" these numbers into anyone one of the many gear calculators and see what your rpms will be at any given speed......

You also need to know what your engine torque range will be, as stated, don't worry about your peak hp #'s, worry about your engines torque band and try to get your rpms into the torque band..........

David

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

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