Ive got a 68 cougar stock 302.
Stock c4 trans
Stock 8"
Thinking on getting a 347
10:1 compression.
Lift 595
Dur 230
Wanting to do a pro charger
600 hp range.
The question is I’m wanting something with overdrive more steerable .
Thought of the AOD
After reading i found the 4r70
Is a lot stronger
What’s the price built to handle 600 hp
500 + torque.
Then thought of the tremec tkx 5 speed.
Having to set everything up by tremec guidelines to
Get the warranty .
Just not sure what the better choice is between the two if any other than personal preference.
I like the tkx 5 speed idea because of not having to shift all the time and like the aod because of the pain
Of figuring converter size.
I know i need a 9" rear . Ive put a post looking for one.
( N ) case
31 spline .
Around 355 gear im guessing.
Thanks for the input everyone.
There is a lot to unpack here, and more things to consider.
TKX 5 speed is a manual transmission. You will need to ‘shift’, regularly. Meaning ‘most of the time’.
Gearing needs to be selected optimally on many things. Driving use, RPM range, tire size, etc.
You should contact Currie Enterprises, or someone similar, for your rear end needs.
If this is a ‘cars and coffee’ type of build? or is it going to see track time?
You don’t mention suspension upgrades/changes or body stiffening.
Brakes?
Something to keep in mind, 4R70W is typically only good up to 500HP unless you have them specifically built and will require a ECU to operate it… Something like US Shift - Quick 4…
Depending on tire height, you might want to go with deeper gears with an overdrive, depending on what your final ratio is. Tremec has a neat app that can calculate engine rpm, tire height, gear ratio in trans and rearend and speed. Manuals are more fun but it depends on the driver and what kind of driving you plan on doing.
If your going to run a carb , youll need around 2000 rpm at cruse speed to make it happy . Id try a leaf spring explorer 8.8 rear
Most were posi 3.73 gear with disc. Currie has the brake assy complete along with the spring saddle for the bastard size axle tube. And…if ya want to narrow it , you only have to cut the long side…that means you only need 1 new axle
You’ve chosen a lot of cam for regular street driving. Blowers are great torque adders - meaning if you are looking for a lot of torque AND good idle and street drivability, I’d dial down the cam a good bit. With the blower you’ll have huge torque available.
My Jag F type R in factory trim had 550 HP and 503 ft. lbs. of torque - all out of a 5.0 motor with a mild, smooth idle (and wonderful exhaust note). In current trim with 15 lbs. of boost (vs. factory 10 lbs.) I’m likely at 630+HP and ~600 ft. lbs. of torque. The published torque curve shape has near full torque by 2000 RPM; I had same results each time I put it on a chassis dyno. It pulls like a diesel yet idles and drives like any street car.
Engine Masters did a piece on blower cams (busting a lot of myths). I don’t know which one but you may wish to peruse through them on Motor Trend.
I faced very similar questions but had a different starting point. I started with a N/A stroker 390 that should be in the 600hp+ range. Yet to be built.
I looked at the cost to build an AOD or 4R70 but went with a stock 6R80 as they can handle that HP/TQ as is. The 6R80 could be had for a very reasonable price back then. My cost was 1,000 per gear all said and done. Not a budget build but that’s the price for wading into new territory. Check out my build and you will get an idea of all the little things that are needed to get and electronic transmission fully functional in a 68 Cougar.
Id run an aod. Simply because it can be controlled without an ECU. Now the one drawback being it won’t have a lock up converter. The aod can be upgraded easily to 4r70 internals.
If you run a smaller tire on the back I personally would just run a 3.50 gear if you run anything over a 27" tire I’d go with a 4.10.