I have the 1978 Ghia.It has the 4 bolt lug pattern.
I was wonderring about how much HP can these stock axels handle before I will have to upgrade?

If your car has the 8" rear end, roughly 300hp if you're not brutally abusive with it. If it has the 6.25" rear end? Not much more than a stock 2.3 or 2.8 puts out.

Thats pretty dissapointing to here.
How do I go about finding out which rearend and gears I have?

If it has a removable cover on the rear of the axle, too bad. If it is solid in the rear and the carrier drops out of the front, you have an 8". The gear ratio should be on a tag on one of the carrier bolts. If not, roll the car forwards slowly one tire revolution and count the number of times the pinion goes around. (helps to mark it with chalk)

If you've got an 8", it'll look like a mini 9" pumpkin. I'd say that chances are that yours is a 6 3/4 with the 3:18 gear. I ran my 78 for a few years at the strip with a 6 3/4 and a modified 302 and had no troubles at all. i later upgraded to the 8" unit for a differant gear ratio [3:40] and still ran it till I sold out. I wasn't pushing any major power but had alot of fun. Friends of mine ran and still run these small rears in their minisport circle track race cars and run em up to 8500 rpm with no modifications to the rears although most of the trouble you'd see would be from a takeoff at the strip and snapping wheel studs if any.

Just for my own information, when did the 8" come with a 4 lug axle?
Dave

The 74-78 Mustang II came with the 8" with the 4 lug and the 3rd member interchanges with that of the old Mustangs. I had put a 3:55 in my 65 when I first built it out of a II.

Thats what I got then-
So I can deliver a bit more power to it then.right?

I have a 1978 ghia coupe and I am wanting to put a 302 or a 305 in so will I need to change the axles if I put the of them in there ?

Mine was able to handle 308hp but I went with hardned studs but I just went ahead and changed over to a ford 9 inche lincoln versilles rear end with disc brakes.

the 8'' rear end, came also in the 1974 mustang II, my car have a 2.3 engine, so don't know which rear end came in the first 74 stangs. I'll check if i have luck enough to have a 8'' rear end, but any of you knows will make it more easy

If yours has the 2.3 then it has the 6 3/4 rear... only the V-6 came with the 8inch diff..... my 74 was a v-6 and it had a 3.55 gears open 8 inch diff

What kind of fabricating did you do to be able to bolt that in?

Not all 2.3 cars had the 6.75 rear, my old '74 had a factory 2.3/4spd with an 8"

The first-gen six cylinder cars had 4-lug 8" rear ends too, but it was on the larger bolt pattern shared with the Falcon instead of on the bolt patter shared with the Pinto and fox-chassis cars.

This is in regards to the question about the 9" Lincoln. I installed a 9" complete rearend from a 1980 Granada in my 78 II. It is the same rearend except it has drum brakes instead of disc. Mine was a direct bolt in except you'll need longer and wider U bolts. If you have the factory rear sway bar for the II, it won't fit around the hump in the back of the housing. The width of the Granada and factory II rearend are the same. The difference in braking was unbelievable. The Granada rearend also connected with the factory parking brake. I know for the Lincoln it is different and that could be something that needs fabricated.