| Boost_me |
Posted
Thursday, Mar 22nd 5:44am [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 151
Victoria, Australia
1981 BMW 323i |
I was jus thinking and had a couple of question's....
How strong is the 323i diff??? At what sort of power level's does it start to fail?? 350hp(260KWATW)?? And what sort of diff's can we change them with?? Here in Australia we have different car's to the world that I would use (Namely :Holden Commodore IRS V8 Diff) Has anyone done a conversion?? I'm just playing with idea's.......... |
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| davethedog |
Posted
Thursday, Mar 22nd 3:09pm [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 165
Northants, England
E21 320 |
The E21 standard diff is supposed to be good up to 220bhp. My dad used a standard Diff in his race car putting out 230bhp and never had a problem.
I am looking at putting at least double this amount of power through mine, so I am using an E12 M535 diff. This is supposed to be good for 1000bhp. But I am not holding my breath.
I sourced the diff from a very nice man on this forum and brought a conversion kit from Fritz’s Bits here in the UK.
The kit comprises of a modified rear cross member.
I will be fitting this all in the next few weeks so I’ll keep you posted on how it goes.
Hope this helps. 
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| imaradiostar |
Posted
Thursday, Mar 22nd 4:46pm [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 1034
Nashville, TN
81 323i, 82 525i, 85 524td, 90 535i |
Your mileage may vary but this is what I was told:
If you have a stock old diff it can't be expected to take much over 200hp; more important is the torque. Pete blew up a rebuilt diff in his M30 engined E21 accelerating out of a corner. I'd imagine the well over 200 foot pounds of torque did it.
I talked to Jim at Metric Mechanic about this one time- he suggested that lower ratio diffs generally have higher torque handling because the relationship between the size of the pinion/ring teeth and the amount of tooth contact goes up as the ratio goes down. Jim felt pretty strongly that one of his E21 3.45 rebuilds would take almost anything a 300hp turbo M20 could dish out. Failing that he said an E30 323i 3.23 ring and pinion (small case diff, very rare in the states) in the E21 diff case would take even more abuse and would be very tough to kill! The other advantage is that the lower ratio would make a better match for a high power engine.
Personally, I'm leaning toward a modified rear diff carrier that will accept an E30 diff with an E36 rear cover. This will allow dual rear mounts ala Alpina and a wide variety of ratios and replacements if you break one. I'd like to use a 2.93 limited slip diff in combination with an E36 328i transmission. This would yield a 1:1 5th gear for economy and pretty decent ratios across the board. This same rear diff should also work nicely with the factory E21 dogleg. The factory E21 overdrive box would probably be better with a 3.25 diff from an E28 533i.
jamie |
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| Boost_me |
Posted
Friday, Mar 23rd 1:51am [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 153
Victoria, Australia
1981 BMW 323i |
When you say a smaller gear/ratio what side of the scale is smaller 3.08 or 4.11?? It may sound like a stupid question but I don't know which one has more or less teeth......I was thinking of around 350HP at the wheels, and around 400NM of torqe....(Engine Transplant my apology's to the purist's)
davethedog, e12 M535(diff)=1000HP Rating DAAMMNNN!!!!!!!! Please do keep us posted, If you can, is there any way you could take photo's and document the conversion?? Just as future refrence for everyone, this seem's like a really good conversion and would be awsome to see it in a 320..... |
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