Plz Help with Trans Gearing

[patrickt]

Tommy is right on everything he wrote. Now, with that said, let me tell you why I went with a .64 OD with my 3.54 rear. That TKO 5th gear ratio gives me 34 miles per hour per 1000 RPM. I use 5th gear for nothing other than pleasant highway cruising and there is nothing I enjoy more than easing along at 2200 RPM, which is 75 MPH, out in the countryside, and the engine is at its quietest and is smooth as glass. You can actually hold a conversation with your passenger. That is the only thing my fifth gear is good for, but that's why I chose it. Now, it would also come in handy if I made a run to see what my top speed was, which I've never done. I think she'd top out somewhere in the 160's, but I don't know. But, that little item is on my bucket list... probably the last item, especially if the ol' girl blew a tire at that speed.

[jhv48]

I had the .64 overdrive in my TKO600 and absolutely hated it. 3.54 rear gears. I’ve got a street friendly 550 horse engine that pulls just fine from 1800 rpm in top gear. I found myself rowing back and forth from 5th to 4th during freeway driving. There was such a big jump from the fourth to fifth gear. Almost 1000 rpm.
Swapped out the tranny for one with a .81 fifth gear and couldn’t be happier. Now I actually have a usable fifth gear. I’m turning about 2500 rpm at freeway speeds and can accelerate smoothly if needed without dropping a gear.
I highly recommend the .81 fifth gear. Based on 35,000 miles of all kinds of conditions.

[Davidless]

Originally Posted by jhv48

I had the .64 overdrive in my TKO600 and absolutely hated it. 3.54 rear gears. I’ve got a street friendly 550 horse engine that pulls just fine from 1800 rpm in top gear. I found myself rowing back and forth from 5th to 4th during freeway driving. There was such a big jump from the fourth to fifth gear. Almost 1000 rpm.
Swapped out the tranny for one with a .81 fifth gear and couldn’t be happier. Now I actually have a usable fifth gear. I’m turning about 2500 rpm at freeway speeds and can accelerate smoothly if needed without dropping a gear.
I highly recommend the .81 fifth gear. Based on 35,000 miles of all kinds of conditions.

Great info, I'm now leaning back towards the .81 OD

Even Prestige Motors spec'd the same OD (.81), its just the the guy at MDL through me off when he said the 0.68 would be better for mostly street driving.

I agree too large of a jump between 4th and 5th!

Thanks loads

[Davidless]

Originally Posted by patrickt

Tommy is right on everything he wrote. Now, with that said, let me tell you why I went with a .64 OD with my 3.54 rear. That TKO 5th gear ratio gives me 34 miles per hour per 1000 RPM. I use 5th gear for nothing other than pleasant highway cruising and there is nothing I enjoy more than easing along at 2200 RPM, which is 75 MPH, out in the countryside, and the engine is at its quietest and is smooth as glass. You can actually hold a conversation with your passenger. That is the only thing my fifth gear is good for, but that's why I chose it. Now, it would also come in handy if I made a run to see what my top speed was, which I've never done. I think she'd top out somewhere in the 160's, but I don't know. But, that little item is on my bucket list... probably the last item, especially if the ol' girl blew a tire at that speed.

Good to know what RPM is nice for conversation at cruising highway spd. What is you cam LSA ? mine is 110, I'm calling tom at ford performance and see what the lowest cruising RPM the engine will handle, hopefully its 2200 also and not 2500.

With a 0.81 @ 2200 cruising in 5th would be 70 MPH
0.68 83 MPH
I made up a spreadsheet so I can message the numbers but I'm leaning towards the 0.81 OD

Thanks

[patrickt]

Originally Posted by Davidless

Good to know what RPM is nice for conversation at cruising highway spd. What is you cam LSA ?

Here is my cam -- it's an old school cam that has a wonderful sound and idle when tuned perfectly along with decent manners down low. Remember is a solid flat tappet. Now jhv48's comments on the RPM drop are valid. Unless you're really sure how you're going to drive the car, the .81 ratio is the safer choice. But you should ask your builder what's the lowest sweet spot in your rpm curve just so you can do your math. Remember though, regardless of what you choose it will be better than an original Cobra with a four speed.