FBM 8.8 IRS Rear Diff Conversion - Page 4 - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

XPR Small Block · 03-20-2013, 03:09 PM

Quote:

Originally Posted by FullBlown

we have tons of these kits on 2.0L-2.2L making 800-1000hp+ without any issues. These cars are going anywhere from 10's - 8.50's in the quarter.

I'm sure a lot of big block domestic guys are breaking these , but this has been tested and proven for what we are doing.

well whats the difference big power is big power no matter where you go??? launch 800-1000 hp on a drag strip is gonna do the same damage to the diff, i have a corvette with 500+ hp to the wheels with a small block chevy motor i have blown 1 ring an pinion on 15 hard launches i would love to see a 8.8 keep up with a dana 44

FullBlown · 03-20-2013, 03:21 PM

Well, torque + a heavy car breaks things. I don't want to get in a whole big debate on which is better. This has been working for us for years, that is the reason we stuck with with it.

XPR Small Block · 03-20-2013, 03:23 PM

my vett only weighs 200 lbs more than a frs..

FullBlown · 03-20-2013, 03:33 PM

we'll let you know when we break it

XPR Small Block · 03-20-2013, 03:35 PM

haha good deal shouldnt be too long with your 607 hp mark

Tunagoat · 03-20-2013, 04:22 PM

The 04-06 GTO gys are switching to these.. a couple of themm are into the 8s at 3800+lbs.

Tansey86 · 03-20-2013, 04:30 PM

This setup may be a 8.8 IRS but will be built with stronger parts than a factory mustang IRS. This rear in a 2700lb car will handle whatever you throw at it.

EZWood · 03-20-2013, 05:07 PM

Quote:

Originally Posted by XPR Small Block

well whats the difference big power is big power no matter where you go??? launch 800-1000 hp on a drag strip is gonna do the same damage to the diff, i have a corvette with 500+ hp to the wheels with a small block chevy motor i have blown 1 ring an pinion on 15 hard launches i would love to see a 8.8 keep up with a dana 44

In the jeep world the 8.8's are stronger than the 44's, but the 44a with the aluminum housing for IRS are stronger than the ones with tubes attached. With the tubes connected it stresses the housing and it flexes breaking the r&p. So I'm not sure how the irs 8.8 compares to the IRS 44, but I've been told by reputable sources that the internals for the 8.8 are sturdier, so in the end it depends on the weight, power and application and sometimes a little trial and error are necessary for these kinds of things. Instead of saying this is better than that, let's get some numbers for weight power and tire info for where these break instead of saying I wouldn't buy this, or that is better. Pics or it didn't happen!

XPR Small Block · 03-20-2013, 06:04 PM

Quote:

Originally Posted by EZWood

In the jeep world the 8.8's are stronger than the 44's, but the 44a with the aluminum housing for IRS are stronger than the ones with tubes attached. With the tubes connected it stresses the housing and it flexes breaking the r&p. So I'm not sure how the irs 8.8 compares to the IRS 44, but I've been told by reputable sources that the internals for the 8.8 are sturdier, so in the end it depends on the weight, power and application and sometimes a little trial and error are necessary for these kinds of things. Instead of saying this is better than that, let's get some numbers for weight power and tire info for where these break instead of saying I wouldn't buy this, or that is better. Pics or it didn't happen!

ok so tell me why toyota guys go dana 44 with chromoly shafts?? thats all i see in nor-cal same for jeeps either dana 44 or 60's.. never see ford running gear under any rig but a ford..." except the 9 inch" im just repeating what ive been seen and told for years from hundreds of people, ive never seen anyone get excited about putting a for 8.8 in there car or truck i even have ford guys saying they wouldnt do that swap

silverlegacy · 03-20-2013, 06:40 PM

Comparing solid axle versions of Dana 44 and Ford 8.8 isn't relevant to this, not in the least. There are different variables at play there.

The Dana44 ICA or Dana 44 IRS used in Corvettes and Vipers are a little bit weaker in overall design than the Ford 8.8 IRS. The Corvettes and Vipers have stronger axle shafts, but that is not included in the argument here. Most of the 44 IRS units you will find are from Corvettes which use the 8.5" ring gear which is slightly (very slightly) weaker than the Ford 8.8" ring gear (I've seen some with the Chrysler 8.75" as well, there may have been years where those were used as well). Now the Vipers use a 8.9" ring gear which can be retrofitted into the Corvette housing if you know what you are doing. It might be stronger than Ford, but it will be very, very slight. You can also get a 8.75" ring gear for the Dana 44. When it really comes down to it the strength difference between the 8.5" and 8.9" ring gear are not going to be apparent until you are well into the 9's.

Where the Dana 44 is weaker is the case design. In general they have a lot more flex in them. The case will actually twist on hard launches and crack. The cast iron ones will even do it, and that is assuming you can find one of those easily. The aluminum ones will flex even worse (most all semi-modern Vettes and all Vipers have aluminum cases). Still this isn't a problem until you get in the high 800s in RWTQ on a heavy car. There is also a weak casting where the ring gear attaches to the housing, I have seen this break before, but was on a way more powerful car than any of these will be.

The Ford's biggest weakness isn't the case or gears, it is the differential itself. Most are 28 spline and will simply break axle shafts or spider gears. Those can easily be upgraded to 31 or 33 spline and there shouldn't be a problem until big power.

So in the end, without getting technical, the ford 8.8 axle is a better, stronger design you just need to get rid of the stock diff. Though the difference is very very minor. Then, it also has the availability advantage. I could go a junkyard today and pull 3-4 aluminum version and 10+ iron versions for $25. I probably couldn't even find a dana 44 for under $6-700.

Wes B. · 03-20-2013, 06:56 PM

Totally pumped about this! Ford 8.8 diffs (including the IRS ones) are fantastic.

bpracer · 03-20-2013, 07:00 PM

I would think this kit will now make the transmission the weak link in the driveline so the rest of the discussion is a bit academic.

Wes B. · 03-20-2013, 07:01 PM

Quote:

Originally Posted by bpracer

I would think this kit will now make the transmission the weak link in the driveline so the rest of the discussion is a bit academic.

But hasn't the transmission been shown to withhold somewhere around 450hp under forced induction?

Tansey86 · 03-20-2013, 07:34 PM

Just because a piece of the car has withstood 450hp for X amount of time doesn't mean its reliable.

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03-20-2013, 03:21 PM	#44
FullBlown Senior Member Join Date: Sep 2012 Drives: Scion FRS Location: MN Posts: 1,171 Thanks: 242 Thanked 2,026 Times in 548 Posts Mentioned: 298 Post(s)	Well, torque + a heavy car breaks things. I don't want to get in a whole big debate on which is better. This has been working for us for years, that is the reason we stuck with with it.

03-20-2013, 03:23 PM	#45
XPR Small Block Member Join Date: Feb 2013 Drives: Scion Frs Location: Santa Rosa, Ca Posts: 70 Thanks: 21 Thanked 9 Times in 8 Posts Mentioned: 0 Post(s)	my vett only weighs 200 lbs more than a frs..

03-20-2013, 03:33 PM	#46
FullBlown Senior Member Join Date: Sep 2012 Drives: Scion FRS Location: MN Posts: 1,171 Thanks: 242 Thanked 2,026 Times in 548 Posts Mentioned: 298 Post(s)	we'll let you know when we break it

03-20-2013, 03:35 PM	#47
XPR Small Block Member Join Date: Feb 2013 Drives: Scion Frs Location: Santa Rosa, Ca Posts: 70 Thanks: 21 Thanked 9 Times in 8 Posts Mentioned: 0 Post(s)	haha good deal shouldnt be too long with your 607 hp mark

03-20-2013, 04:22 PM	#48
Tunagoat Junior Member Join Date: Jun 2012 Drives: 2004 GTO Location: CT Posts: 8 Thanks: 0 Thanked 2 Times in 2 Posts Mentioned: 0 Post(s)	The 04-06 GTO gys are switching to these.. a couple of themm are into the 8s at 3800+lbs.

03-20-2013, 04:30 PM	#49
Tansey86 Senior Member Join Date: Sep 2012 Drives: 2003 Subaru Outback Location: Long Island, NY Posts: 1,318 Thanks: 154 Thanked 529 Times in 300 Posts Mentioned: 3 Post(s)	This setup may be a 8.8 IRS but will be built with stronger parts than a factory mustang IRS. This rear in a 2700lb car will handle whatever you throw at it.

03-20-2013, 06:40 PM	#52
silverlegacy Member Join Date: Dec 2012 Drives: Turbo Miata-Fairmont drag project Location: Where it is windy and cold Posts: 11 Thanks: 0 Thanked 3 Times in 3 Posts Mentioned: 0 Post(s)	Comparing solid axle versions of Dana 44 and Ford 8.8 isn't relevant to this, not in the least. There are different variables at play there. The Dana44 ICA or Dana 44 IRS used in Corvettes and Vipers are a little bit weaker in overall design than the Ford 8.8 IRS. The Corvettes and Vipers have stronger axle shafts, but that is not included in the argument here. Most of the 44 IRS units you will find are from Corvettes which use the 8.5" ring gear which is slightly (very slightly) weaker than the Ford 8.8" ring gear (I've seen some with the Chrysler 8.75" as well, there may have been years where those were used as well). Now the Vipers use a 8.9" ring gear which can be retrofitted into the Corvette housing if you know what you are doing. It might be stronger than Ford, but it will be very, very slight. You can also get a 8.75" ring gear for the Dana 44. When it really comes down to it the strength difference between the 8.5" and 8.9" ring gear are not going to be apparent until you are well into the 9's. Where the Dana 44 is weaker is the case design. In general they have a lot more flex in them. The case will actually twist on hard launches and crack. The cast iron ones will even do it, and that is assuming you can find one of those easily. The aluminum ones will flex even worse (most all semi-modern Vettes and all Vipers have aluminum cases). Still this isn't a problem until you get in the high 800s in RWTQ on a heavy car. There is also a weak casting where the ring gear attaches to the housing, I have seen this break before, but was on a way more powerful car than any of these will be. The Ford's biggest weakness isn't the case or gears, it is the differential itself. Most are 28 spline and will simply break axle shafts or spider gears. Those can easily be upgraded to 31 or 33 spline and there shouldn't be a problem until big power. So in the end, without getting technical, the ford 8.8 axle is a better, stronger design you just need to get rid of the stock diff. Though the difference is very very minor. Then, it also has the availability advantage. I could go a junkyard today and pull 3-4 aluminum version and 10+ iron versions for $25. I probably couldn't even find a dana 44 for under $6-700.

03-20-2013, 06:56 PM	#53
Wes B. Automotive Enthusiast Join Date: Sep 2012 Drives: 2013 Scion FR-S Location: United States Posts: 458 Thanks: 166 Thanked 125 Times in 87 Posts Mentioned: 0 Post(s)	Totally pumped about this! Ford 8.8 diffs (including the IRS ones) are fantastic.

03-20-2013, 07:34 PM	#56
Tansey86 Senior Member Join Date: Sep 2012 Drives: 2003 Subaru Outback Location: Long Island, NY Posts: 1,318 Thanks: 154 Thanked 529 Times in 300 Posts Mentioned: 3 Post(s)	Just because a piece of the car has withstood 450hp for X amount of time doesn't mean its reliable.

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