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**cooljess76** · 07-18-2010, 11:08 PM

Well you posted in the proper section, did you happen to read any of the threads?

Here's a little help, 5th gear is 1 to 1 on both Getrag and ZF transmissions, so swapping the tranny is usless as far as RPMs are concerned. US 318ti's with manual transmissions came with 3.45 diffs while models equipped with automatic transmissions came with 4.44 ratio diffs. You can google "BMW final drive calculator" and find out which ratio best suits your needs. Most of us with 6cyl swaps are running either 3.46 or 3.25 ratios in the rear end because it keeps the rpm's at a tollerable level at highway speeds. 318ti's came stock with small case diffs. It's recommended to replace it with a medium case diff and shorter halfshafts to handle the added torque of the 6cyl engines. Before you go out and purchase a medium case diff, it's important to know which ones are compatible with the Ti. E36 coupe and sedan diffs WILL NOT FIT on the Ti as they have different mounting points. The Ti shares a similar design as the e30 and Z3, however those diffs do not come with 3.46 or 3.25 ratios. Manual transmission e30's came with 3.73 final drives while automatics came with 4.10. Both are significantly higher than the Ti's stock ratio, which means increased rpm's. Most people want to lower the rpms or keep them near stock. E24's came with 3.46 diffs and e28's came with 3.25. The cases themselves have the same mounting points, however the rear cover will not bolt up to the Ti and the output flanges won't bolt up to e30 halfshafts. I used an e24 3.46LSD with an e30 rear cover, e30 output flanges and e30 halfshafts. It fit perfectly and the RPMs will be very close to stock. Since the medium case diff is wider than the small case diff, you'll need shorter halfshafts. E30 halfshafts are the perfect length and are slightly larger in diameter. Ti halfshafts can be forced to fit, but I strongly recommend against it because it puts excessive strain on your CV joints. Since the e30 halfshafts are larger in diameter, the ABS tone rings are also larger. This means that you will need to shim your ABS sensors so they don't contact the tone rings and become damged.

So you need to figure out which diff you want. You might as well upgrade to a limited slip diff(LSD). Medium case to handle the torque of the 6cyl. Remember that BMW 4cyl models came with small case diffs and 6 cyl models came with medium case diffs. European models came with all sorts of wacky final drive ratios, so you'll need to figure out what's available and which model cars they came on. Remember the Ti shares the same mounting points as Z3's and e30's. E24 and e28's have the same mounting points except for the rear cover and output flanges, they can be made to fit by using e30 parts. The higher the ratio, the higher the RPMs will be. 3.45=3800rpm @ 80mph, 4.10=4500rpm @ 80mph. 3.73 will be somewhere between that and 2.93 will be way less.

I feel like a broken record repeating this information, please search this section as I'm certain that any question you might have has already been answered.

07-18-2010, 11:08 PM	#3
cooljess76 NOBODY F's with the Jesus Join Date: Oct 2006 Location: Ventura California Posts: 7,824 iTrader: (6) Photo Gallery	Well you posted in the proper section, did you happen to read any of the threads? Here's a little help, 5th gear is 1 to 1 on both Getrag and ZF transmissions, so swapping the tranny is usless as far as RPMs are concerned. US 318ti's with manual transmissions came with 3.45 diffs while models equipped with automatic transmissions came with 4.44 ratio diffs. You can google "BMW final drive calculator" and find out which ratio best suits your needs. Most of us with 6cyl swaps are running either 3.46 or 3.25 ratios in the rear end because it keeps the rpm's at a tollerable level at highway speeds. 318ti's came stock with small case diffs. It's recommended to replace it with a medium case diff and shorter halfshafts to handle the added torque of the 6cyl engines. Before you go out and purchase a medium case diff, it's important to know which ones are compatible with the Ti. E36 coupe and sedan diffs WILL NOT FIT on the Ti as they have different mounting points. The Ti shares a similar design as the e30 and Z3, however those diffs do not come with 3.46 or 3.25 ratios. Manual transmission e30's came with 3.73 final drives while automatics came with 4.10. Both are significantly higher than the Ti's stock ratio, which means increased rpm's. Most people want to lower the rpms or keep them near stock. E24's came with 3.46 diffs and e28's came with 3.25. The cases themselves have the same mounting points, however the rear cover will not bolt up to the Ti and the output flanges won't bolt up to e30 halfshafts. I used an e24 3.46LSD with an e30 rear cover, e30 output flanges and e30 halfshafts. It fit perfectly and the RPMs will be very close to stock. Since the medium case diff is wider than the small case diff, you'll need shorter halfshafts. E30 halfshafts are the perfect length and are slightly larger in diameter. Ti halfshafts can be forced to fit, but I strongly recommend against it because it puts excessive strain on your CV joints. Since the e30 halfshafts are larger in diameter, the ABS tone rings are also larger. This means that you will need to shim your ABS sensors so they don't contact the tone rings and become damged. So you need to figure out which diff you want. You might as well upgrade to a limited slip diff(LSD). Medium case to handle the torque of the 6cyl. Remember that BMW 4cyl models came with small case diffs and 6 cyl models came with medium case diffs. European models came with all sorts of wacky final drive ratios, so you'll need to figure out what's available and which model cars they came on. Remember the Ti shares the same mounting points as Z3's and e30's. E24 and e28's have the same mounting points except for the rear cover and output flanges, they can be made to fit by using e30 parts. The higher the ratio, the higher the RPMs will be. 3.45=3800rpm @ 80mph, 4.10=4500rpm @ 80mph. 3.73 will be somewhere between that and 2.93 will be way less. I feel like a broken record repeating this information, please search this section as I'm certain that any question you might have has already been answered.