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Old 11-27-2013, 03:37 PM   #1
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Default Rear end discussion, v. AIDS motor

I'm going ahead with my stupid motor swap. F2T truck/tractor/AIDS motor.

I'll be using an FD transmission.

Need a rear end setup. Leafy seemed somewhat offended at my casual answer of "Well i guess i'll just use a V8R setup of some sort" and hinted that there was probably other options.

I can't be snobby about a diff at the moment since i don't even know what the hell i'm going to use the car for, but let's say i'd rather not completely hamstring the car for lack of good diff options down the road.

My needs/wants in order:

1) Ratio that makes sense. This is a motor that's going to make midrange torque like very few 4 bangers do, and the delivery can be horrifying. It's unlikely that i will rev it higher than 7000rpms in the initial iteration. If my destroked long rod motor is a success, i will re-visit ratios. In the meantime, i'm looking somewhere in the 3.2-3.4ish area.

2) Strong as ****. Power delivery will be "lots of it and all at once."

3) Easy to source

4) Easy to install

5) Cheap


Cheap is the least important. I'm not worried about piecing something together for $500 or less. I like easy buttons more than i like pinching pennies on a build in which i have no real rules. $2000 or less would be awesome, but i'm also prepared to shell out for one of the V8R kits if it comes down to it, and i'm not 100% swayed towards the Getrag or the 8.8 yet if i go that route. Only thing to consider is that i'm going to need/want a BIG exhaust. Like.... 3.5-4". Potentially an issue if a PPF would be in play.
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Old 11-27-2013, 03:47 PM   #2
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You have two options. 7.5" CTS-V Getrag, or Ford aluminum 8.8". Both are in your price range. CTS-V guys upgrade to the 8.8 diff when they break their 7.5" at the drag strip. 8.8 gears are cheaper and more plentiful. The only downside to the 8.8 is exhaust clearance, but it's possible to get a 3" pipe snaked around it. If you need a 4" exhaust, twin 3" pipes around the diff would be doable.
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Old 11-27-2013, 03:51 PM   #3
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Let's say i'm going to be making north of 500ftlbs to the wheels. Is the Getrag pretty much a bad idea at that point?

I'm not against doing duals or routing the exhaust to exit the body in stupid places if i have to, but it'd be nifty if i had the option to not do that and clear a 3.5" straight pipe over the Getrag if it will hold up.


Which of those two setups have the better diff options if the "stock" differentials aren't satisfactory in their performance? If the destroked motor works out, i'd be able to move to a ring gear in the 3.7-4.0ish range down the road with either, yes?
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Old 11-27-2013, 03:59 PM   #4
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While the getrag is known to break, it came in a 400tq, 4000lb car. I'd be really impressed if you could break it in a miata. (Talking entirely out of my *** since I've got no experience with it)
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Old 11-27-2013, 04:00 PM   #5
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Quote:
Originally Posted by concealer404 View Post
Let's say i'm going to be making north of 500ftlbs to the wheels. Is the Getrag pretty much a bad idea at that point?

I'm not against doing duals or routing the exhaust to exit the body in stupid places if i have to, but it'd be nifty if i had the option to not do that and clear a 3.5" straight pipe over the Getrag if it will hold up.
The 8.8 is the stronger diff. You may not break the Getrag (I don't think anyone has), but Getrag guys upgrade to the 8.8, so I would just go with that.

Quote:
Which of those two setups have the better diff options if the "stock" differentials aren't satisfactory in their performance? If the destroked motor works out, i'd be able to move to a ring gear in the 3.7-4.0ish range down the road with either, yes?
Gear ratios are plentiful for both diffs. Google will help you with that.
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Old 11-27-2013, 04:04 PM   #6
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Quote:
Originally Posted by Savington View Post
The 8.8 is the stronger diff. You may not break the Getrag (I don't think anyone has), but Getrag guys upgrade to the 8.8, so I would just go with that.
Fair enough.



Quote:
Gear ratios are plentiful for both diffs. Google will help you with that.

Sorry, that was a two part question that i didn't separate well. The first part was the important-er part, that being: Are there aftermarket diffs worth a **** for both rear ends a la OS "The ***** Stimulator" Giken diffs for Miatas?

The second part was just a blatant cry for spoon feeding i threw in for good measure.
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