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Thread: 3000rpm @ 70mph...what can be done to lower that first figure?

  1. #1
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    3000rpm @ 70mph...what can be done to lower that first figure?

    I'll admit--I know nothing about gearing, final drive ratios, etc.
    Can anyone tell me what can be done to leave gearing 1-4 alone but lower the strain on the motor at highway speeds? I was driving my A4 last night between Philly and DC. It was running 2100rpm at 70mph (6th gear). So much nicer for the long haul (and better fuel consumption).

    Any recommendations? It doesn't seem, in normal backroads driving, that there is much difference between 4th and 5th. I would sacrifice some torque/acceleration in 5th to have a mellower highway drone.
    Thanks in advance,
    Brad
    Last edited by Watch Carefully; 11-14-2017 at 11:59 AM.

  2. #2
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    Quote Originally Posted by Watch Carefully View Post
    Can anyone tell me what can be done to leave gearing 1-4 alone but lower the strain on the motor at highway speeds?
    There really is no way to lower gearing in just SOME gears without changing the gearbox itself. You have options though:

    Swap in a 6 speed transmission, many of which maintain a very-close-to-stock ratio on gears 1-5. Possible but expensive and not really worth it on non-M's sorry to say

    Custom build a 5 speed transmission so gears 1-4 are the same but 5 is a long overdrive (not really possible)

    The easiest solution is to swap in a taller diff, say moving from a 3.64 to a 3.46, but this will affect all gears not just 1-4. Cost is also a small fraction of swapping in a 6 speed, but you gain lower highway cruising speeds at the expense of acceleration.

    Best advice imo, unless your car is used for highway cruising, enjoy it as it is for what it is

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    Quote Originally Posted by Watch Carefully View Post
    I'll admit--I know nothing about gearing, final drive ratios, etc.
    Can anyone tell me what can be done to leave gearing 1-4 alone but lower the strain on the motor at highway speeds? I was driving my A4 last night between Philly and DC. It was running 2100rpm at 70mph (6th gear). So much nicer for the long haul (and better fuel consumption).

    Any recommendations? It doesn't seem, in normal backroads driving, that there is much difference between 4th and 5th. I would sacrifice some torque/acceleration in 5th to have a mellower highway drone.
    Thanks in advance,
    Brad
    A lower gear differential than what you have currently and/or a 6 speed transmission (out of E46 -using their clutch or a euro 6 speed).

    I've used this calculator in the past
    http://www.bokchoys.com/differential...calculator.htm

    - - - Updated - - -

    Quote Originally Posted by Watch Carefully View Post
    I'll admit--I know nothing about gearing, final drive ratios, etc.
    Can anyone tell me what can be done to leave gearing 1-4 alone but lower the strain on the motor at highway speeds? I was driving my A4 last night between Philly and DC. It was running 2100rpm at 70mph (6th gear). So much nicer for the long haul (and better fuel consumption).

    Any recommendations? It doesn't seem, in normal backroads driving, that there is much difference between 4th and 5th. I would sacrifice some torque/acceleration in 5th to have a mellower highway drone.
    Thanks in advance,
    Brad
    A lower gear differential than what you have currently and/or a 6 speed transmission (out of E46 -using their clutch or a euro 6 speed).

    I've used this calculator in the past
    http://www.bokchoys.com/differential...calculator.htm

  4. #4
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    Beat ya there Tony

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    If you want to leave 1-4 alone, there is only one answer. 6speed.


    /.randy

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    Quote Originally Posted by Watch Carefully View Post
    ... what can be done to leave gearing 1-4 alone but lower the strain on the motor at highway speeds? I was driving my A4... It was running 2100rpm at 70mph (6th gear). So much nicer for the long haul (and better fuel consumption).
    Any recommendations? It doesn't seem, in normal backroads driving, that there is much difference between 4th and 5th. I would sacrifice some torque/acceleration in 5th to have a mellower highway drone...
    BMW optimized the gear ratios and the final drive ratio for general use like yours, and the engine is not straining at its cruising rpms in 5th gear. You can change the final drive rather inexpensively to drop the rpms in all the gears. What exhaust system are you using that drones?
    BMW MOA 696, BMW CCA 1405

  7. #7
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    Just realized OP asked how to lower the first figure. Never said second figure had to be the same

    Try 60mph and your cruising rpm will go down too

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    Cheapest/easiest alternative is taller rear tires, worked on my 95 M3 with a 3.90 rear, brought revs down maybe 10/15 %, but still screamed on the interstate.

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    Quote Originally Posted by BimmerBreaker View Post
    Beat ya there Tony
    Yes but I double posted so I'm sure that accounted for the minute delay.. haha.

    3k @ 70mph ain't bad. It's been awhile but my my 318is was way worse and obnoxious at 70 mph.

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    While it's customary to think that 4th gear is 1:1 and 5th is an overdrive ratio, that's not the case with the 5-speed in the 2.8, 3.0 & 3.2 Z3/Ms; 5th gear is 1:1__or direct drive (so I'm still puzzled that most dyno operators insist on using 4th...).

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    I've done back to back in 4th and 5th, the difference is negligible. I use 4th on the dyno because 5th pushes the speed too close to the tire limit

    But yes. In both the Getrag and ZF, 5th gear isn't really gears. IT is merely locking the input shaft to the output for a 1:1 ratio.


    A few years back while in a caravan to Zfest, a group on Co-dependency Central were comparing cruising RPMS. So I snapped a pic of my dash and had the wife post it. 70MPH @ 2350 rpm. 6sp, 2.93 and 315/35-17 FTW.
    Last edited by rf900rkw; 11-14-2017 at 03:38 PM.


    /.randy

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    Quote Originally Posted by Vintage42 View Post
    BMW optimized the gear ratios and the final drive ratio for general use like yours, and the engine is not straining at its cruising rpms in 5th gear. You can change the final drive rather inexpensively to drop the rpms in all the gears. What exhaust system are you using that drones?
    It's not an exhaust drone that bothers me--I probably should have described it differently--nor am I concerned about stressing the motor.
    Rather, I'm at the point (age 50, a veteran of 1000s of loud musical performances, although many with ear plugs) where a long highway drive is such a strain on my senses that my head hums and or my ears ring afterward, if I don't stuff them with cotton. Surprisingly, this practice sees me arrive at my destination feeling less worn out.

    Driving my nicely insulated A4 Avant at 2100 rpm for 100+ miles is lovely. Driving the Z3 at 3000 rpm for so long is an assault on my senses, by comparison. I'm willing to endure the noise during open driving (even the residual noise in my cranium). Unfortunately, I drive ~300 highway miles from PA to MD to PA most weeks, with a few nights in MD. When the weather is suitable, I really enjoy having the Z3 on such trips. Driving much less than 70 on I-95 isn't any fun. It's an imbalanced equation...

    I was hoping someone would say "replace 5th gear, it's easy."
    Thanks for the realistic comments. I doubt I'll spend the $ necessary to install a 6-speed and/or change the diff. Either would probably cost as much as I paid for the car, and other upgrades (cooling system) should take preference. I'll just add extra cotton and deal with it!
    Brad
    Last edited by Watch Carefully; 11-14-2017 at 03:34 PM.

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    Quote Originally Posted by Watch Carefully View Post

    Driving my nicely insulated A4 Avant at 2100 rpm for 100+ miles is lovely. Driving the Z3 at 3000 rpm for so long is an assault on my senses, by comparison.
    I hear you loud (I know you'd like a bit quieter) and clear. I came from a double-paned acoustic glass optioned D2 S8. I could whisper at 100mph into my cell phone and the other end wouldn't know I wasn't sitting in a library. Long drives were a complete joy as well; I actually felt rested on occasion. I did have to pay attention quite a bit more for emergency vehicles though; they really would sneak right up on me.

    I love the way my Coupe performs (3.46 diff) but it does get up there when on the highway. I think I recall around 3850rpm at 80mph. if I ever drive 70 I'll take note of that too . It's probably around 3400rpm. The only saving graces are the fixed roof and the tires I chose. My Z3M on the other hand is always dialed up to 11. Supercharger, extremely loud exhaust (actually planning cutouts next year for a bit more volume) but I bought it to be an assault on my senses. It's the fun car. I don't think I could handle it as a DD. I'd go insane. But, canyon road with the top down and all the parts working together: I'm in heaven.

    I do have a hardtop and that helps a lot for the assaulted feeling; perhaps that's a possibility for you? It really quiets things down. But, then you can't enjoy the weather you bought the car for. It's an unbalanced equation for sure.
    Last edited by s8ilver; 11-14-2017 at 03:59 PM.
    Nathan in Denver

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  14. #14
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    Quote Originally Posted by s8ilver View Post
    I hear you loud (I know you'd like a bit quieter) and clear. I came from a double-paned acoustic glass optioned D2 S8. I could whisper at 100mph into my cell phone and the other end wouldn't know I wasn't sitting in a library. Long drives were a complete joy as well; I actually felt rested on occasion. I did have to pay attention quite a bit more for emergency vehicles though; they really would sneak right up on me.

    I love the way my Coupe performs (3.46 diff) but it does get up there when on the highway. I think I recall around 3850rpm at 80mph. if I ever drive 70 I'll take note of that too . It's probably around 3400rpm. The only saving graces are the fixed roof and the tires I chose. My Z3M on the other hand is always dialed up to 11. Supercharger, extremely loud exhaust (actually planning cutouts next year for a bit more volume) but I bought it to be an assault on my senses. It's the fun car. I don't think I could handle it as a DD. I'd go insane. But, canyon road with the top down and all the parts working together: I'm in heaven.

    I do have a hardtop and that helps a lot for the assaulted feeling; perhaps that's a possibility for you? It really quiets things down. But, then you can't enjoy the weather you bought the car for. It's an unbalanced equation for sure.
    Thanks for the well-considered reply, Nathan. I would love to use the Z3 as a DD...in general I take it everywhere that doesn't require more than 2 seats.
    Therefore, getting better highway fuel economy and having less noise would be welcome. Regarding the hardtop, it does help on the highway (aside from an annoying squeak/rattle tendency I need to diagnose), but I have no place to store it while I am in MD.

    The S8 has a double-pane glass option? Wow...talk about pampering!

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    I really liked the lower RPM's at 70MPH I got when I bought my Z3 years ago. Of course, I came from a Miata, which pushed 4000RPM at 70MPH. THAT was loud...
    I did go up one size on my tires, and it dropped the RPM's by maybe 50-100RPM at the most. Diameter is only 1" larger. That wasn't the primary reason for doing the increase (mostly liked how the larger tires filled the rear wheel wells) but it did help a little bit. Straight line acceleration is not my top priority.

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    Quote Originally Posted by Watch Carefully View Post
    The S8 has a double-pane glass option? Wow...talk about pampering!
    20160822_164304.jpg20160822_170504.jpg

    Windows so thick there's even a post type mechanism built into the glass and a guide rail on each side of the b-pillar to ease the up or down operation. My 2nd photo was supposed to be a video of the windows working with the key fob...neat feature I reprogrammed with the VCDS software.
    Last edited by s8ilver; 11-14-2017 at 06:45 PM.

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    Quote Originally Posted by Watch Carefully View Post
    Therefore, getting better highway fuel economy and having less noise would be welcome. Regarding the hardtop, it does help on the highway (aside from an annoying squeak/rattle tendency I need to diagnose), but I have no place to store it while I am in MD.
    I would also suggest the hardtop, having driven my car from where I purchased it in Florida back to New Jersey. Not only did it make the car quieter, the heater didn't have to work as hard. (It was early January.) Lower revs will help with noise but not necessarily with fuel economy. Each engine has its sweet spot in RPM where economy is maximized. I'm not familiar enough with the S52 to know that. I think most of the noise from the Z comes through the convertible top.
    Wayne

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    Quote Originally Posted by Watch Carefully View Post
    ... It's not an exhaust drone that bothers me... long highway drive is such a strain on my senses that my head hums and or my ears ring afterward, if I don't stuff them with cotton... I'll just add extra cotton and deal with it!...
    Quote Originally Posted by rasmuw View Post
    ... I think most of the noise from the Z comes through the convertible top.
    I ran a Supersprint exhaust for 15,000 miles and now have returned to the original exhaust. At 70 mph, whatever sound the two exhausts make is gone and faded into the background, where it is overpowered by the the road noise, the wind noise and the hum of the engine coming back into the cabin. I have tinnitus and hyperacuity, so I sometimes wear earplugs in movies and bars, and might do it in the Z3 if I had to make a long trip.

    But I don't think the RPMs alone are the source of the strain on the senses, so changing the transmission or final drive would not make much difference.
    Last edited by Vintage42; 11-14-2017 at 08:58 PM.
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    Quote Originally Posted by Vintage42 View Post
    ... I sometimes wear earplugs in movies and bars, and might do it in the Z3 if I had to make a long trip.

    But I don't think the RPMs alone are the source of the strain on the senses, so changing the transmission or final drive would not make much difference.
    I'm with you on the first count, and appreciate the comment at the end. My Z is running stock exhaust configuration, I believe, and I sometimes use the hardtop for quieter long trips.

    Funny, I am just now listening to Page & Plant and recall in 1997 or so seeing their show at the hockey-arena-of-many-names in Philly. There were perhaps 7 rows of seats farther from the stage than mine--and I still needed earplugs as much as when I was near the stage. That was hundreds of performances (mine, not necessarily theirs) ago and my hearing is much murkier now, though oddly sensitive.
    Last edited by Watch Carefully; 11-14-2017 at 09:08 PM.

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    Insulate! In both my Z3 and Z3M I have done some good insulation, and it helped tremendously. I also have no place for a hardtop, so I insulated the convertible top. It was really a lot of work, but well worth it. I took the doors apart, the kick panels out, and put insulation everywhere I could. A sheet laid flat in the area where the top lays really helps a lot. My wife has a 325i, and it's still much quieter, but mine is far better than it was.

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    Quote Originally Posted by zellamay View Post
    Insulate! In both my Z3 and Z3M I have done some good insulation, and it helped tremendously. I also have no place for a hardtop, so I insulated the convertible top. It was really a lot of work, but well worth it. I took the doors apart, the kick panels out, and put insulation everywhere I could. A sheet laid flat in the area where the top lays really helps a lot. My wife has a 325i, and it's still much quieter, but mine is far better than it was.
    What sort of insulation do you recommend? I've not done this before. Any advice is much appreciated. (Duh, I suppose I can go check the FAQ). Thanks for the advice!

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    I just turn up the stereo

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    I used padded insulation, (like carpet padding), with foil on both sides. It's cheap and convenient to buy near my home. There are better materials, which cost a lot more. I think I did the whole car for about $100, including black stretch cloth to line the insulation in the top. Advice: be generous with the insulation, but careful in the doors to avoid window mechanism. If you want to do the top, I'll offer some pics and help, but be warned: it takes patience and savvy.

  24. #24
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    Quote Originally Posted by Randy Forbes View Post
    While it's customary to think that 4th gear is 1:1 and 5th is an overdrive ratio, that's not the case with the 5-speed in the 2.8, 3.0 & 3.2 Z3/Ms; 5th gear is 1:1__or direct drive (so I'm still puzzled that most dyno operators insist on using 4th...).
    Brad,

    Just want to make sure this didn't slip by from Randy. Fifth is one-to-one, there is no overdrive, ever with a stock box. Consider a 2.91:1 diff. Pretty sure that is the ratio. A bit slower, better economy since lower revs. Should be quieter too. Affordable.

    Terry
    Last edited by Terry F.; 11-15-2017 at 01:23 AM.

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    Quote Originally Posted by Terry F. View Post
    Brad,

    Just want to make sure this didn't slip by from Randy. Fifth is one-to-one, there is no overdrive, ever with a stock box. Consider a 2.91:1 diff. Pretty sure that is the ratio. A bit slower, better economy since lower revs. Should be quieter too. Affordable.

    Terry
    Thanks, Terry. I really appreciate all the good replies (and their variety) from the gang here.
    I might look into better insulation to start with. Sacrificing some revs doesn't scare me too much (I don't need this to be a rocket); I think I will be happy with a nice balance between seat-of-the-pants driving excitement and casual cruising comfort.

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