» Site Navigation | | » Recent Threads | | My 318ti build 05-21-2024 04:48 PM 05-21-2024 04:48 PM 0 Replies, 1,168 Views | | | | | 02-28-2008, 01:20 AM | #1 | Senior Member Join Date: Nov 2004 Location: Minneapolis Posts: 1,587 | Project 318ti eta So I've had a brand new 318ti 3.45 open differential laying around for a number of years. The other day I got to thinking if putting the 3.45 diff into my automatic 318ti (4.44 diff) would help my freeway fuel economy significantly without killing acceleration. Yesterday I ran the numbers in a gearing calculator and found out the 3.45 would drop my cruising RPM at 70mph from 3000 to 2350. Sounds good as my all time high MPG figure (38.1 mpg) was done at 60mph which is about 2550 RPM. My big concern with swapping in the diff was with acceleration. I'm not too concerned about quick acceleration, but more was worried about lugging the engine. Today I thought I'd give it a try. My results..... Acceleration: Not nearly as bad as I thought it would be! Before the swap I did numerous starts in 2nd gear so I could get the feel of it. I was really hoping it wouldn't be like starting in 2nd gear every time. The 3.45 is slower off the line than the 4.44 diff, but the car doesn't lug at all. It still feels fairly quick if I push it. I think 1st is short enough in this car that the difference isn't too large. Crusing: 70 mph does sit right at 2350 in 4th (top gear) Hopefully that's not too low and I'm on the back side of the "efficiency curve" (if that exists). Only a good road trip will tell. Another plus is the noise level. My old diff always had a little whine, and this new one is silent as can be. The freeway noise of the 318ti has been bothering me lately. Essentially I'm getting old I want this thing quiet, comfortable and efficient. | | | 02-28-2008, 04:13 PM | #2 | Senior Member Join Date: Oct 2007 Location: Eugene Oregon Posts: 6,182 | very nice i swapped from a 3.45 to a 2.79 and it was such an improvement for the highway cruising! __________________ -Josh Sold-1995 318ti, Club Sport, Hellrot Sold-1996 318ti, Active Model, Boston Green Current- 1995 318ti, sport model, schwartz | | | 02-28-2008, 04:18 PM | #3 | Senior Member Join Date: Jan 2005 Location: Fort Collins, CO Posts: 1,305 | nice swap and great gas mileage | | | 03-27-2008, 04:34 AM | #4 | Junior Member Join Date: Nov 2006 Location: northboro Posts: 11 | any update on the mpg? | | | 03-27-2008, 04:52 AM | #5 | Senior Member Join Date: Nov 2003 Location: Walnut Creek, CA Posts: 642 | Quote: Originally Posted by thesk8nmidget very nice i swapped from a 3.45 to a 2.79 and it was such an improvement for the highway cruising! | Josh, Do you still have your 3.45 lying around and if so, do you want to sell it? __________________ '95 330ti CS w/sr delete, S50USB30, cams, 24# inj, Conforti SW, Euro HFM, Samco Silicone Intake Boot, BBTB, Euro Oil Cooler, JTD CAI Duct, RE DMS exhaust, RE Tranny mounts, CF Valve Cover, LTW flywheel/Kevlar sprung hub clutch, RE SSK, 3.46 Finned LSD (M6) , M3 tranny, Brembos, RE Wheel Studs, SS brake/clutch lines, CF interior, Rear Headrest retrofit, Tilt Steering retrofit, 13.5 lb DynaBatt in rear, LED interior/footwell lights, ZKW HID, Headlight Aim Control, Rear fog light w/cluster indicator, CF 3 Aux gauge pod, BMW Traffic Pro/Alpine MP3-CD Changer, Staggered LTW wheels, '95 M3 steering rack, VIS CF Hood, M3 LTW Strut Bar, TCK SA coilovers, Red LTW Motorsport Seatbelts, OEM Fire Extinguisher, Z8 Starter button, Auto dim rear view mirror w/ Homelink/Compass, PDC, Rear Sun Shade, Euro Gauge Cluster w/oil temp/shift light , Headlight Washers, "Motorsport" Door Handles, CF Grills, French ZKW Fogs, Euro dash bins, Power Lumbar Support is next, Coming e39 M5 interior light, Bimmer Magazine 8/2007 | | | 03-27-2008, 02:19 PM | #6 | Senior Member Join Date: Oct 2007 Location: Eugene Oregon Posts: 6,182 | Quote: Originally Posted by clex2 Josh, Do you still have your 3.45 lying around and if so, do you want to sell it? | yeah i do but i did the swap on my last ti. so i only have an open diff sitting around. my club sport still has the stock lsd in it __________________ -Josh Sold-1995 318ti, Club Sport, Hellrot Sold-1996 318ti, Active Model, Boston Green Current- 1995 318ti, sport model, schwartz | | | | Currently Active Users Viewing This Thread: 1 (0 members and 1 guests) | | 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 | | | |