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Discussion Starter #1
i own a 1969 cougar. currently i have a 351c (cracked block) and a 9" rear end and what i believe has a 3.00 ring and pinion gear set. my transmission is a fmx. the reason i believe they are 3.00 gears because it always felt like it had no power output to the rear wheels. my question is how do i identify my rear end.

second: i have not decided fully yet on the motor but i have been told the 400m is a great motor to build for power, i originally had decided on a 460, but my question is i want to have 500-600 hp to the rear wheel. i want to utilize a c6 transmission. i believe they are 28 spline axles in the rear end. what kind of ring and pinion gear set would you recommend and how easy would it be to swap my existing third member for a complete third member i buy.

I was thinking of going to 4.11 gears but i have been told that may be unwise, the car will not be an everyday driver, trips to the strip and a sunday car. will i need to look for anything special in the 3rd member i buy, do i need a nodular case, etc? any info please help.
 

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There should be a tag on your rear end. Can you post the information on it? We can help you decode it.

"There is no replacement for displacement". 500 to 600rwhp naturally aspirated?

A pumpkin swap is pretty easy.

Here are my recommendations for ratios
For mostly cruising & daily drivers: 2.79 to 3.00
For street and a little strip: 3.00 to 3.25
For street and a strip (good all around): 3.25 to 3.5
For little street and more strip: 3.5 to 3.89
For almost no street: 4.11 and up (depending on desired top speed and maximum engine RPM)

Without an overdrive and a 4.11, your engine will be running at about 4000 RPM at 70 MPH (depending on transmission losses and tire size of course). That can be a little bit hard to take even on short trips.
 

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The 351M/400 and 429/460 are very tall and very wide. The engine bay was widened in '71 specifically for the 429 engine option, so shoehorning one into an earlier cat is an exercise in contortionism... The 351M/400 is just as wide as the 429/460, but is about an inch and a half shorter front to back. Remember also that the 351M/400 and 429/460 use a tall bellhousing bolt pattern. Ford did use the FMX behind the 351M so you can still do that if you want to. BTW, I know you've probably seen me post it before, but this car has an FMX behind a 484-inch stroked 460 by using the 351M/fmx bellhousing from my previous '78 LTD wagon...



BUT - you can also get big block power and torque from a smaller package with one of today's 351W-based stroker kits. Much easier to fit in your early Cat engine bay, too! My very mild 9.4:1 393W is pumping out over 370hp to the rear wheels (460 crank horsepower) on 89-octane regular unleaded!



Now, as for your rear gears... what sort of purpose are you building this car for? If it is just for cruising around town, stick with 3.25s or less. For a dual-purpose car , 3.50-3.70s are perfect. For all-out racing, 3.91-4.30s.
 

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Discussion Starter #4
I can get the tag info tonight i am at work now, i am building the car probably more for strip and sunday driving, it wont be used for highways much if any at all. I actually found a website i forgot at the moment that pretty much walks you through step by step on how to put a 460 in a 69 so i feel confident (now lol) on doing that motor. Will that much power require a nodular case, they are big bucks.
 

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I think 500 to 600rwhp is on the edge of what a normal 9 inch can take, but it is more about traction. You can get away with a lot if you let the tires slip and don't launch really hard.
 

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Discussion Starter #6
i owned a 2001 corvette and although it was a very performance based vehicle it was running 350hp or something like that and it was pretty nasty so anything above 450 i am sure will be pretty aggressive. my dad has a 9" rear end that is sitting at the side of the house i hope that it may have like a 3.50 3rd member in it i think that would be a pretty comfortable swap for what i am doing.
 

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Discussion Starter #7
haha, 2.75 ratio in my 9 inch that would explain alot. go figure i never thought to look.
 

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You are building a 500-600hp motor but don't want to spring $200 for a N case??
 

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If you gonna do any amount of freeway driving I would not go any deeper than 3.50 gears.
 

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Discussion Starter #11
yeah i know lol, to do it right i probably should go for the n case, i was thinking 3.50 aswell.
 
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