» Site Navigation | | » Recent Threads | | | | | | | | 09-28-2009, 03:20 PM | #1 | Member Join Date: Sep 2009 Location: Bowling Green, OH Posts: 75 | 3.15 too high? Ok Im not about crazy acceleration, more about good gas mileage. I can pickup a z3 3.15 lsd right now online. Just wondering if this is high? Like will my car be a wicked dog? | | | 09-28-2009, 03:52 PM | #2 | Senior Member Join Date: Aug 2008 Location: Raleigh/Charlotte, NC Posts: 1,233 | will kill your acceleration, but its not too tall. My 6cyl ti had a 2.93... __________________ -Jeff | | | 09-28-2009, 04:18 PM | #3 | Senior Member Join Date: Apr 2007 Location: Elizabeth City, NC Posts: 3,877 | Stock manual diff is 3.46, automatic is 4.44 (I think...) If you do a lot of highway driving it will drop your cruising RPMs and help mpg a little. But like Xeno said, you'll lose a bit of acceleration as the trade off. __________________ ~Dave~ 98 328ti Morea Grun slicktop 11 128i space gray slicktop 13 JGC WK2 Deep Cherry Search | RealOEM | | | 09-28-2009, 06:37 PM | #4 | Senior Member Join Date: Nov 2006 Location: Land of the Vikings Posts: 2,700 | get it, you can hold insanely long second gear drifts __________________ Vin Number decode and Retrofit Pdfs Available Free ! Just PM | | | 09-28-2009, 06:49 PM | #5 | Senior Member Join Date: Feb 2009 Location: Charlotte / Thomasville NC Posts: 240 | You most likely wont see any MPG improvement. It will drop the revs low enough to were your engine will be working harder (using more fuel) to maintain highway speed. I know at 55mph I get better mileage in 4th gear then in fifth; however, once I reach about ~63 It changes over to being better MPG in 5th. | | | 09-28-2009, 07:13 PM | #6 | Member Join Date: Sep 2009 Location: Bowling Green, OH Posts: 75 | Ok well speaking of for now I am swapping in my standard's LSD into my automatic. That should be ok right? | | | 09-28-2009, 10:47 PM | #7 | Senior Member Join Date: Apr 2007 Location: Elizabeth City, NC Posts: 3,877 | Yeah, it should work, but that will be a huge drop in accel. __________________ ~Dave~ 98 328ti Morea Grun slicktop 11 128i space gray slicktop 13 JGC WK2 Deep Cherry Search | RealOEM | | | 09-29-2009, 03:15 PM | #8 | Member Join Date: Sep 2009 Location: Bowling Green, OH Posts: 75 | Its ok. I have a Ninja for going fast. | | | 09-29-2009, 07:45 PM | #9 | Senior Member Join Date: Jun 2003 Location: Saint Paul, MN Posts: 3,244 | I have a Ninja for killing people. He lives in my garage. __________________ My Former Rides 1999 318ti Alpine White, Cali Roof, Dinan goodies 1996 318ti Hellrot California Edition | | | 09-30-2009, 01:27 AM | #10 | Senior Member Join Date: Feb 2009 Location: Charlotte / Thomasville NC Posts: 240 | not really sure why you want an LSD so bad. With the ratio of the LSD mated to the auto you're not going to be able to break tires loose in anything but snow/gravel anyways. | | | 09-30-2009, 02:16 AM | #11 | Senior Member Join Date: Sep 2007 Location: asdfasdf Posts: 10,002 | it improves traction in snow, and in New England, that's a good thing | | | 09-30-2009, 02:56 AM | #12 | Senior Member Join Date: May 2006 Location: 43609 Posts: 3,425 | Id go for a 3.25lsd rather than a 3.15. I have a 2.5L non-vanos with 4.10lsd and it gets the same mileage as my old 3.25LSD on the highway and it revs at about 5k @75-80mph. I also have proof from a trip i took to New Hampshire, well over 40 hours of driving alone at that RPM and gas mileage was about 28-30mpg. As far as an auto equipped ti goes, 4.10lsd is about as high as id go, for a manual, the 3.45 is the best but would prefer a 3.73 over that. __________________ 1995 Hellrot Clubsport 318ti -Gone 1996 Schwartz II Sport 357ti - 5.7L V8 LS1/6 1997 Moregrun Metallic 318ti - Gone 1998 Schwartz II sport 318ti - M50TUB25/5 | | | 10-12-2009, 10:13 PM | #13 | Senior Member Join Date: Aug 2009 Location: Novi, MI Posts: 115 | To OP: I would expect a slight increase in mileage if the numerical ratio is lowered slightly, but switching from a 4.4X:1 to 3.15 or even 3.45:1 might not help mileage. There a are a few factors going on...engine friction typically scales with the square of engine speed, so slowing the engine down does help engine efficiency. Also, at a lower rpm you will need more throttle, reducing the pumping losses across the throttle, which is a good thing. However, at too low of speeds the engine begins to fall off the range where it has good volumetric efficiency. Without having a fueling map of the engine, it's not possible to say for certain - only experiments with good repeatability can decide. | | | | Currently Active Users Viewing This Thread: 1 (0 members and 1 guests) | | Thread Tools | | Display Modes | Linear Mode | Posting Rules | You may not post new threads You may not post replies You may not post attachments You may not edit your posts HTML code is Off | | | |