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The great rear end debate
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Dewey316
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Joined: 08 Jan 2004
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Location: Bringing the tech

1990 Chevrolet Camaro RS

PostPosted: Wed Apr 06, 2016 7:07 am    Post subject: The great rear end debate Reply with quote

No, I'm not talking J-Lo or Beyonce.

Bring the tech from experience to pure theory and gut feel, I want lots of peoples thoughts and debate on the subject. I have a good feel for almost everything that my car will eventually be getting, this is one of the things that I can't really decide what direction I want to go.

Living behind a manual trans, expect a good amount of power, weight matters to me, since unsprung weight kills handling.

Here we go... the contenders:

Ford 8.8 -- Hawks sells housings and full kits. 31 Spline is the norm, 33 would be an option if I spent some big coin, but very limited diff options at 33 spline. Being the smallest upgrade option, it should be the most efficient for power.

GM 12 Bolt -- Moser builds them with either 33 or 35 spline axles -- Wavelock is only 35 spline diff option, which is cool, but $$$$. The 12 bolt is a pretty expensive option, but is GM, hard to find real efficiency numbers compared to other options. Any info here would be great.

Ford 9" -- The standard. Big, tough, heavy? With real diff options, comes in either 31 or 35 spline. In looking, this may actually be the cheapest option available. Potential to offset the cheapness with an alum center section, might be as light as 12 bolt. We know they are not the most efficient design.

Dana S60 -- Several companies build these. 35 spline axles only. Most expensive options, strongest option, and likely the heaviest. My thoughts are this is overkill... however, I think this also has the most efficient power transmission of the group, is that worth all the other trade off's potentially?

Those cover most of the options I can think of, until you go crazy talk and lots of custom fab work.

Thoughts, feedback, experience and idea's of what way to go?
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aaron_sK
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1987 Chevrolet Camaro IROC-Z

PostPosted: Wed Apr 06, 2016 9:34 am    Post subject: Reply with quote

And people say I'm a cocktease with my secret builds. Razz How much power? What tires?

If you're not against some fab work how about an Explorer 8.8? It needs to be narrowed asymmetrically to fix the pinion position and SUV width but they grow on trees and you've got an easy factory disk brake option.

9" is big and dumb and just eats power. Unless you're looking to really hook up with a strip car it's not worth it IMHO.
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Dewey316
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Joined: 08 Jan 2004
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1990 Chevrolet Camaro RS

PostPosted: Wed Apr 06, 2016 9:44 am    Post subject: Reply with quote

aaron_sK wrote:
And people say I'm a cocktease with my secret builds. Razz How much power? What tires?


You just want to find out what my plans are! hahah


mostly street, who knows it might see a few drag launches though, probably some track days. Lets just for arguments sake, lets pick a round number and say 500hp at the wheels, but don't limit that, I do have a nitrous kit laying around after all, and we all know I am waiting to see Ian's turbo dyno numbers before I set a power goal. Razz

Build myself, at this point, I might be better off just dropping the money to get one ready to roll. Take that in or out of the equation as you like, its more a merit of which flavor rear to go with, and why.
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aaron_sK
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1987 Chevrolet Camaro IROC-Z

PostPosted: Wed Apr 06, 2016 10:24 am    Post subject: Reply with quote

Dewey316 wrote:
You just want to find out what my plans are! hahah


That is true, actually. My current money would be on a gen-3 V8 swap with some sort of homebrew forced induction, possibly twin M90's... Any comments on this theory?

To the topic at hand: Hawk$ wants around $2200~2500 plus freight shipping for an 8.8 that still has c-clips in it. For the same money you could have a real axle shop build an Exploder 8.8 to your specs, not limit yourself to LT1 brakes, and have a whole pile of beer money left over.

But I'm biased towards fabrication and I really dislike Hawks for many reasons, so grains of salt and all that. Smile
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Dewey316
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1990 Chevrolet Camaro RS

PostPosted: Wed Apr 06, 2016 10:45 am    Post subject: Reply with quote

The point isn't so much the vendor or anything, just the concept and ideas of what is good and bad about the various options, and why.

Also, no, i will not c-clip anything, not matter what option I go, that is getting solved.

So why are you partial to the 8.8? strength vs weight ratio? cost? parts availability? other?

It also limits me in going crazy if I wanted, since the largest axle options are really 31 spline. No chance of going 35 spline and getting them gun drilled for weight.

AND, that in mind, mustang boys have issues with their road racing cars bending the axle tubes and tweaking the housing. Would that be a consideration I should worry about?
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Dewey316
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Joined: 08 Jan 2004
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Location: Bringing the tech

1990 Chevrolet Camaro RS

PostPosted: Wed Apr 06, 2016 10:47 am    Post subject: Reply with quote

aaron_sK wrote:
That is true, actually. My current money would be on a gen-3 V8 swap with some sort of homebrew forced induction, possibly twin M90's... Any comments on this theory?


Think of my car use... think something that is highly over square, and get me to the power levels I'm talking.

Other than that, no comment.
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QwkTrip
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1989 Pontiac Firebird

PostPosted: Wed Apr 06, 2016 2:46 pm    Post subject: Reply with quote

Midwest Chassis (in the town next door to me) claims their fabricated rear is less weight than a stock 10 bolt. Get used to waiting for it though.... they work on their own time, not yours.
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QwkTrip
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PostPosted: Wed Apr 06, 2016 3:05 pm    Post subject: Reply with quote

Dewey316 wrote:
Think of my car use... think something that is highly over square, and get me to the power levels I'm talking.


A Ford Triton V10
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aaron_sK
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1987 Chevrolet Camaro IROC-Z

PostPosted: Wed Apr 06, 2016 6:46 pm    Post subject: Reply with quote

QwkTrip wrote:
Dewey316 wrote:
Think of my car use... think something that is highly over square, and get me to the power levels I'm talking.


A Ford Triton V10


Benz 3.5L M116!

Dewey316 wrote:
why are you partial to the 8.8? strength vs weight ratio? cost? parts availability? other?


I'm not dead set on it. It has it's advantages for sure: dirt cheap, grows on trees, factory disc brakes, strong for it's weight. Stock diff is trash, stock cover is trash (not a problem for you) tubes are pressed and spin as you say, need to be welded into the housing for long-term strength.

The other issue is that we don't know your budget. I suspect it's extremely high when I hear things like "500 whp" and "M6" and "no comment" Laughing
If your budget is in the 2-3K range then the 8.8 becomes less appealing.

Honestly, not to beat a dead horse but I would still consider finding a Borg Warner to toss in there, if nothing else just to see how long it would hold up.

Remember, I bought Mike's backup axle because he never needed it. Laughing
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Twilightoptics
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1987 Chevrolet Camaro IROC-Z

PostPosted: Wed Apr 06, 2016 9:01 pm    Post subject: Reply with quote

I lost no power putting in the 9" going from 373 to 433 gearing. Which I on paper would have lost twice; numerically higher gears, 9".

Thay said it wasn't much heavier than the 10 and 33 spline axles twisted. I would look at the M9.

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Dewey316
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1990 Chevrolet Camaro RS

PostPosted: Thu Apr 07, 2016 6:52 am    Post subject: Reply with quote

aaron_sK wrote:
The other issue is that we don't know your budget. I suspect it's extremely high when I hear things like "500 whp" and "M6" and "no comment" Laughing
If your budget is in the 2-3K range then the 8.8 becomes less appealing.


I was trying to not put a budget constraint on the discussion, I am more interested in the technical reasoning for going different routes. At this point, we all know my car has been in sitting mode for a while, and will still be for while I get stuff together, and buy parts, etc. I will budget how I need to do it right, even if that means the project goes on for another 6 months while I save some extra coin.

Paul, So, you twisted 33 spline axles when you launched it on sticky tires? I take it, you are suggesting no matter what I do, I look for 35 spline axles? Should I also not consider gun drilled, or do you think a drilled 35 spline would twist/break like your 33 splines?
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Twilightoptics
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PostPosted: Thu Apr 07, 2016 1:33 pm    Post subject: Reply with quote

They didn't break, just twisted. Moser told me that as long as it doesn't twist to one full spline difference, it's okay. Axles came from Moser. So it was 3/4 of the way there and I ran it. Yes that was with sticky tires, 3950lb race weight 330tq on the ground. When you get into 35spline plus stuff, your spider gear carrier selection shrinks and the price goes up dramatically.

Not sure how normal this is, but thought I'd share my experience.

The m9 looks to be a very stout yet lighter weight housing for the 9". Then look into say a strange carrier. IIRC they make strong as hell aluminum ones.

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Dewey316
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1990 Chevrolet Camaro RS

PostPosted: Thu Apr 07, 2016 2:05 pm    Post subject: Reply with quote

Sure, the diffs at 35 vs 33 spline really aren't that different in cost once you start pricing a whole center section from the start.

Just another random though. Coleman sells full floating assemblies in a 62" track width. Would take brackets and such to work, but full floating would be very advantageous for strength and brake options.

They largest they sell is 31 spline floating axles, but makes you wonder, if NASCAR can run 31 spline floaters, I think it would be enough to hold me.

Would look pretty slick running around with full on floater hubs. Also saw a place that builds the brackets to attach a ZR1 Vette hub and brakes to a 9" housing end for floating set ups. That is way interesting.
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QwkTrip
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PostPosted: Thu Apr 07, 2016 3:04 pm    Post subject: Reply with quote

Just saw that Heidts makes an independent rear suspension for our cars.
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Dewey316
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1990 Chevrolet Camaro RS

PostPosted: Thu Apr 07, 2016 3:57 pm    Post subject: Reply with quote

QwkTrip wrote:
Just saw that Heidts makes an independent rear suspension for our cars.


For the sake of discussion. $10k for that, is out of my budget. HA

looks trick as all get out though.
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Twilightoptics
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PostPosted: Thu Apr 07, 2016 5:42 pm    Post subject: Reply with quote

I don't know what you mean by full floating axles....
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QwkTrip
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PostPosted: Thu Apr 07, 2016 5:53 pm    Post subject: Reply with quote

A full floating axle only transmits drive torque, meaning the axle shaft does not carry the weight of the vehicle. It greatly increases load capacity and has other advantages too. Cars usually have a semi-floating axle where the wheel is bolted to the axle shaft and the shaft carries the weight of the vehicle.

I have now exhausted my full knowledge of rear axles. But it was a glorious 5 seconds though.
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Twilightoptics
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PostPosted: Thu Apr 07, 2016 7:03 pm    Post subject: Reply with quote

Ahh. So like a truck. Got it. Thanks. :0)
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Dewey316
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1990 Chevrolet Camaro RS

PostPosted: Mon Apr 11, 2016 11:13 am    Post subject: Reply with quote

Did some checking into floater options. Parts to support the type of weight and horsepower a street car makes, become pretty limited. So, that idea is probably out the window, as it really adds another $1200+ just to make that happen.

I'm starting to lean towards 9" for cost vs strength vs weight at this point. For the cost difference you can go with an alum. center section in a 9" and some other lighter weight housing options and still end up costing at or below what a 12 bolt runs.

unless I find a place to fab up an 8.8, I don't see getting the bang from the buck and weight down any lower than I can just spending the money for a 9".
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aaron_sK
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PostPosted: Mon Apr 11, 2016 9:59 pm    Post subject: Reply with quote

As I understand it the reason Nascar runs them is so that they can dial rear camber. They also have the issue of axle and brake deflection while turning left at a couple hundred miles per hour. I doubt you'll be very worried about either issue. Laughing
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