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Rear end ID?

EDL

New Member
So, my son and I are starting a project. It's his first build. It's 1980 Mercury Capri (I know, I know, it's not a Mustang, but it is a Fox body). He picked it up from a local guy who had it sitting in his garage for a number of years. It has a 302 v-8 in it already (but the plan is to swap in a stroked 351). Very little rust for a nearly 40 year old car.

Anyway, first up is body and chassis. We'd like to put a built 8 or 8.8 inch rear in it, but for now, we're just trying to identify the rear that's in it. I was always a Chevy guy growing up, so I'm not as knowledgeable on the older Ford stuff.

For the life of me, I can't find a picture of this rear end anywhere to ID it. I thought it was a 7.25, but every pic of that rear end it has octagonal angles on the diff cover. This one is square with round corners and 8 bolts holding the cover on. We don't know if this is the stock rear or it was ever swapped out at any point. The tag is too rusted to read it (even if we tried to sandpaper it) Attached is a pic, any ideas?

Thanks!
 

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broncojunkie

Active Member
So, my son and I are starting a project. It's his first build. It's 1980 Mercury Capri (I know, I know, it's not a Mustang, but it is a Fox body). He picked it up from a local guy who had it sitting in his garage for a number of years. It has a 302 v-8 in it already (but the plan is to swap in a stroked 351). Very little rust for a nearly 40 year old car.

Anyway, first up is body and chassis. We'd like to put a built 8 or 8.8 inch rear in it, but for now, we're just trying to identify the rear that's in it. I was always a Chevy guy growing up, so I'm not as knowledgeable on the older Ford stuff.

For the life of me, I can't find a picture of this rear end anywhere to ID it. I thought it was a 7.25, but every pic of that rear end it has octagonal angles on the diff cover. This one is square with round corners and 8 bolts holding the cover on. We don't know if this is the stock rear or it was ever swapped out at any point. The tag is too rusted to read it (even if we tried to sandpaper it) Attached is a pic, any ideas?

Thanks!
I believe what you're looking at is a 6.75 rear. If you thought the 7.5 was the bottom of the barrel, think again lol! No worries though. You'll want a good 8.8 behind a stroked 351w anyway and they'll swap over just the same! A well-built 8.8 rear is fairly simple to put together and not extremely expensive, depending on what you want to do. A 31 spline trac-lock carrier (3.73 gear can be found as oem) from an explorer, forged aftermarket axles, welded tubes (where they enter the center housing), and some new clutches/steels will handle just about anything you can throw at it.

And don't sell yourself short on it not being a mustang. It's a capri! And a pre-bubble back at that! Getting rare as hen's teeth these days and always cool to see one pop up!

Definitely start a build thread on it, if you can. We'd love to follow along!
 

EDL

New Member
Thanks!

Yes, we're going to document the build. He's out there right now stripping the interior out. We did find a small rust hole in the floor pan right behind the driver, but that'll be easy to fix.

That 302 is beat though. The guy that had it didn't know what he was doing with it. The timing was 180 off, vacuum hoses not sealed. We got it running, but one cylinder is missing.

He picked it up for $1,000 and that 302 already has an MSD distributor, Edelbrock intake, Edelbrock 4-bl carb and headers that are only a year old. We compression tested it and 2 of the cylinders are low. We decided against building up the 302 due to their nature of cracking (now, if it were a Dart block, that'd be a different story).

RIght now we're thinking a 351w, since aftermaket parts are so plentiful, either a 393 or 408 stroker kit, Promaxx heads, an Air Gap dual plane intake. Not sure on cam just yet, but either way, the engine will be last. He's on a bit of a budget :) We'll probably have to consider a tranny too as I'm not sure that T5 is gonna handle things too well.

Of course, along with the rear swap, the front will get 5-bolt spindle swaps too and probably a tube k-member.

Here's a pic of it on the trailer when I went down to is apartment to haul back to my house.
 

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broncojunkie

Active Member
Wow! You got a steal on that ol capri! I had a 79 when I was 17 and loved it. That was right around 1990 or 91. I had it repainted the same color as original (black) and it had perfect red interior. It was a 4-banger 4 speed with manual steering and brakes. It was a blast to drive, even being underpowered lol!

I have a 408w stroker sitting on a stand right now. It has a set of promaxx cnc heads and rpm air gap intake. It will eventually go in my 86 coupe. I have a build thread on it, but it's slow going while I finish up the pace car and 88gt.
 

EDL

New Member
Oh, yeah, I forgot, it had the power steering removed and the rack was swapped to an aftermarket non-power rack (I have no idea on brand). According to the vin, this was a turbo RS model from the factory. I kind of hinted to my son we should do a 331 stroker and put a turbo on it. He just smirked at me. He wants what he calls a "canyon car" (I guess that's the new fangled term for road car these days). If you've ever seen Matt Farah's notch back fox, that's the look we're going for. I don't think we're going that crazy on suspension, so 245's or maybe 265's all around and mild flare work is it. I also floated the idea of getting it dipped, but he doesn't want to spend 2 grand for that. It's not going to be a show car, he wants to drive the piss out of it, so soda and media blasting, chassis saver (or some rust encapsulator) underneath and where ever we can squirt it. We will do sheet metal cut and replace though, no bondo unless it is absolutely needed. So, in the end, it'll be a somewhat budget build that looks nice. At least I get the chance to impart some of the "dad's hotrod" knowledge. He went to Wyotech and is working as a tech now at a dealership, but his goal is to get into a custom shop. He's a hell of a welder and fabricator. I told him if we build this well enough, this could be his resume and "business card." :)

Hehehe, I was 17 back in 1981. My very first car was a 56 Nomad (I rode motorcycles for main transportation, so cars were my hotrods). I sort of built it up and sold it. Next was a 73 Z-28. I fully rebuilt it and it became my first experience with blowers. After 3 transmissions and grenading the engine, I bought a 68 Camaro off a car lot for $1500. It had a 307 and 2-speed powerglide in it. I traded that 73 to a friend for a rusty 68 Camaro he had, but it had a 327 in it with 4-bolt mains (large journal block), basically it's a 350 with a shorter stroke as the large journal blocks were identical for the 327 and 350, and it had a Muncie 4-speed (rock crusher). I built that engine and swapped it and the Muncie into the other good 68. I also purchased brand new sheet metal from the firewall forward, and rear quarter panels from Chevrolet (they still sold those parts back then). I never completed the 68 as I went into the Military. I finally had to have my dad sell it. Wish to all hell I had any one of those cars today.

I'd be curious what sort of numbers you get out of your 408.
 

broncojunkie

Active Member
I'm looking forward to it as well. I'd be happy with 400 to the wheels. It's pushing 11:1 compression ratio and has a pretty rowdy cam. 210cc heads, iirc. It also has forged pistons, so a 200 shot could be an option.
 

EDL

New Member
Since engine will be last, we've got time to mull it over. Blue Print engines has a crate 408 stroker long block rated at 425 at the crank. They want $5499 for it. By the time we source a good 351 block, add a stroker kit, find some heads, port and polish them, or add some Promaxx heads, cam, intake, etc we'd be into it for nearly what that crate engine would cost. We'll see what happens though when we get to that point. Personally, I really am leaning to a cheaper build on the engine and adding a turbo. I think for the type of car he wants and the way he'll be driving it, the turbo would make a great choice, but, it's his car, we'll do it they way he wants it.

I think we could comfortably get 425-450 on less than 11:1. We'd like to be able to run pump gas and not have to run premium. I have a 2018 Chevy Silverado with the 6.2L in it and it requires premium because it's 11:1. Granted, the 420HP it makes is nice and for a truck it does get really good mileage with that displacement on demand stuff cutting off 4 cylinders, etc, but gas prices here in PA are outrageous (highest per gallon state tax of any state).

I know, you don't build a car like this to worry about fuel cost, but if you could get the desired HP range without having to run premium that just means more driving!
 

broncojunkie

Active Member
In my opinion, I'm running premium in anything more than about 10:1. Once it gets above 11:1, I'm weighing options on octane boosters or race fuel. I want to say the H.O. engine in the later fox Mustangs were around 9.5:1 and Ford recommended 89 or higher. It's been a long time since I've read up on it, but regardless, there are a lot of variables. Aluminum heads tend to reduce chance of detonation, as does backing off on the timing a little. But higher octane and somewhat higher compression (say, 9.5 or higher) will give you some leeway if your tune isn't just right. Newer engines utilize a knock sensor to retard timing when detonation is an issue.
 
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