I am gathering parts for my 54 F100 build. I have a 302 with a comp cam, Edlebrock 289 performer intake, holly 750 w/vacuum secondaries( I know that it is on the large side) and long tube headers and a c4 transmission. Is the Tbird and cougar irs rear end strong enough for this combo? I can get a cougar with a v6 for nothing.
Elmo

 

You'll want to get the IRS out of a V8 or SC (Super Coupe) or Lincoln Mark VIII as they had the 8.8" gear. The V6 car has the 7.5" gear which is weak. I'd recommend finding one from a 89-93 T-bird SC (or 89/90 Cougar XR7) as they were limited slip. Most of the 94-97 cars were 8.8", but not limited slip as they had electronic traction control.

 

Good info from BDYY...I would add, the wheel lug pattern on these rear ends are metric, not 4.5 inch as would be expected. I bought a MKIII IRS for a project and ended up spending some cash on a tracloc differential, hubs with 4.5 spacing, hub bearings, larger rotors, etc. I knew that I was going to put more cash into the IRS but there were some surprises that I had not anticipated.

 

Thanks for the information. I was thinking of the cougar because I could get it free. I am probably going with a 9" from a f100 because I want to eep to the
5 on 5 1/2 lug pattern.
Elmo

 

This.

Except that there WERE rears from 94-97 that were limited-slip. It was an option, just like the traction control. Trick was, you couldn't get BOTH.

 

I knew there was, but being so few, I didn't bother to mention the 94-97.

 

Another option to achieving the conversion from 4.25" to 4.5" bolt pattern is to have the stock hubs and rotors drilled to the 4.5" pattern.

 

That's true but it is so much simpler just to buy the "kit car" hubs and be done with it...most of these old IRS's need new bearings anyway.