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Hello to all. I am a newbie to this site, so let me start out explaining what I am building. I am building a 1976 F100 Street Rod. I have the truck down to the bare frame and have installed a 2008 Crown Vic front end and am now working on the rear. I plan on running a 460 big block putting out around 550HP. I just bought a 1989 MN12 IRS with an 8.8 ring gear out of a SC T-bird. (I believe this was a 6 cylnd. turbo car). I am planning on running some very wide rear tires on this once complete. This will be a street car with little to no racing done with it. So with this information I have a few questions for the experts here:
1. Will this rear take this set up or will it tear up as soon as I put the power to it?
2. What recommendation do you have to beef it up. (I have been reading the tech articles on the forum and have gotten some really good info)
3. I plan on replacing all of the bushings everywhere on the rear before I install and see there are several options so I would love some recommendations given the set up I have.
4.What are the key things I need to be aware of as I take on this install.
5. Are there other parts I should plan on replacing ? Bearings, seals, hubs......

Thanks so much in advance for your help and advise!:smile2:
 

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Well, the 89 SC's were 6 cylinder supercharged from the factory, but you're close. :)

I would be more worried about your transmission than the rear end personally, and I assume you're using the entire rear subframe? If that's the case, get the good delrin bushings all over it. If it's a tracklock (not sure if all SC's were or not) and it's from an 89, it's probably a 2.73:1 rear end if it was a manual car, 3.08 I think if it was an automatic, not really sure on that.

Most of the standard "tricks" for the 8.8 rear end work in the IRS 8.8. The rear end in mine for example is using a 3.73:1 gear with the TrackLoc, a F-150 S spring for more preload, and it's nice and tight, but very easily street driven.

It's essentially the same rear end as the 99-04 Cobras, and while they never put out 550hp stock, there are plenty out there in that rage. Should make for a very nice riding truck! Show us some pics!
 

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1) The 8.8 is a sound rear end; it fits behind even beefier Mustangs today, so it's got the possibility. I WOULD ...

2) Recommend a complete rebuild, using the carbon fiber pack out of a IRS Cobra 8.8 rebuild kit for the traclok differential. Also, all new bushings. Plus look at the gear ratio; if it was a standard, the gear is a stock 2.73 (!!) due to the rock crusher 1st gear in the M5R2 5 speed used on the manual SCs.

3) With a truck chassis, I'd look hard at Delrin bushings around; Jay Richmond (98mark8lsc here, Jay Richmond on Facebook) makes Delrin bushings for the spindles to the control arms and the subframe to the body/chassis; SuperCoupePerformance amongst others has a nice beefy poly rear diff mount for the IRS differential; also a LPW rear cover that's a bit beefier.

4) Stuff as I listed above; also, the wheel pattern on a stock hub for a MN12 is rather sucky for wheel choices and won't match the hubs on the Crown Vic front. I don't know off hand what you can do on the Crown Vic end, but for this end, you can also consider converting to the Mustang bolt pattern (Cobra hubs, a set of relocation brackets for the calipers, and even a set of Cobra calipers to go with the Cobra rotor); I don't know how that will match the front, however. *googles* Oh, the Crown Vic and the turn of the century Mustang uses the same bolt pattern; that's nice, a Mustang/Cobra hub swap on the back will make the wheels matchable.

5) Hub bearings should be redone; see #4's notes on the Mustang/Cobra hub pattern (you can redrill the MN12 hubs, or use Cobra hubs, kind of your pick; to use the MN12 brakes, you'll have to have the rotors redrilled, and to use the Cobra brakes, you'll have to pick up a caliper relocation bracket set. STILL cheaper than trying to find a Cobra IRS from what Googling I can do ... ) Also, see note about getting that diff rebuilt to be rock solid. It should be good for > 1,000 HP with an automatic; if you're really serious about planting it, though, you might want to consider some custom made half-shafts since a firmly planted manual launch can pop the half-shafts on these (the automatic kind of "spools up" through the torque converter, so it's just enough softer to let the IRS launch; dumping the clutch on the manual can shock load it and bust them.)

Enjoy!

There's actually a guy over on SCCoA.COM that did a 3.8SC and the IRS in his F100 (IIRC); might want to check over there also.

ALSO. If you're transplanting the entire rear subframe, there's a gotcha on the UCA/subframe bushing; check the posts over in the suspension subforum to help make sure you get the RIGHT one instead of the non-adjustable Piece of Stuff that most folks sell nowadays.

Delrin bushings on the knuckle, delrin LCA/subframe bushings, and you'll take care of most of the "wheel hop" some folks complain about.

RwP
 

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Crown Vics are same bolt pattern as Mustang, so a Cobra rear hub swap would work beautifully for his situation.
 

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Just curious, what are you doing to the 460 to get 550 hp?

I have one.
 

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Discussion Starter #6
I have not started on my motor yet but it is not that hard to get 550 HP out of a 460. There is a good post on the Big Block Ford site that spells out what to buy for certain HP. This came from that post:

550-575HP 460ci

Intake System:

950cfm Holley DP Carb professionally calibrated for your application
Weiand Stealth Standard Port Intake Manifold

Cylinder Heads:

TFS street heads with mild clean-up and chambers polished
Roller rockers.

Short Block:

Comp Cam 34-652-5 solid flat tappet cam or equivalent
(Specs:294/304 adv., 256/[email protected], .589/.615, 108 LSA)
Compression around 10.5:1
Stock crank
Scat H-beam rods
Block oiling mods
High volume oil pump
Deepened oil pan with windage tray

Exhaust:

1 7/8" headers to dual 3" pipes with H-pipe. Good flowing 3" Magnaflow mufflers or equivalent.

Summary:

91-octane. Keep redline to 7000 rpm.

Hope that helps!
 
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