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  #1  
Old 10-15-2007, 07:22 PM
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Z4-M: Some diff options



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Last edited by Ron Stygar; 10-15-2007 at 07:25 PM.
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  #2  
Old 10-15-2007, 09:48 PM
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Cool charts
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Old 10-15-2007, 09:52 PM
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Here's a spreadsheet that shows the same data but is in a bit more readable format IMO.
It's currently populated with 330i ZHP and ZHP w/ 3.46 diff info, obviously you'll want to populate it with the correct data for the Z4M .

http://www.linquist.net/temp/gearcalc-zhp.xls
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Old 10-15-2007, 10:20 PM
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Quote:
Originally Posted by KrisL View Post
Here's a spreadsheet that shows the same data but is in a bit more readable format IMO.
It's currently populated with 330i ZHP and ZHP w/ 3.46 diff info, obviously you'll want to populate it with the correct data for the Z4M .

http://www.linquist.net/temp/gearcalc-zhp.xls
Will do.
Thanks,
Ron
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Old 10-16-2007, 09:10 AM
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z4 diff assignment

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Old 10-16-2007, 05:46 PM
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How do you make those charts? You obviously don't run it at 12000 rpms...
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Old 10-16-2007, 06:09 PM
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How do you make those charts? You obviously don't run it at 12000 rpms...
I didn't make it.
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Old 10-16-2007, 09:28 PM
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Kris excel

Assuming the right numbers entered.

Stock -tires
3.62 at 75mph in sixth is 2980rpm
3.91 at 75mph in sixth is 3219rpm, 239rpm more than stock

3.62 at 75mph in fifth is 3506rpm
3.91 at 75mph in fifth is 3787rpm, 281rpm more than stock

Aftermarket larger -tires
3.91 at 75mph in sixth is 3286rpm, 306rpm more than stock
3.91 at 75mph in fifth is 3866rpm, 360rpm more than stock

4.10 at 75mph in sixth is 3446rpm, 466rpm more than stock
4.10 at 75rpm in fifth is 4054rpm, 548rpm more than stock



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  #9  
Old 10-17-2007, 06:24 PM
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I didn't make it.
Than how do you know they are correct?
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  #10  
Old 10-17-2007, 06:54 PM
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Originally Posted by Dammmittt View Post
Than how do you know they are correct?
I got it from Randy Forbes who got it from someone.
If you compare it with KrisL's one it matches.
It's just math.
Maybe Kris will explain.
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Old 10-17-2007, 07:23 PM
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Quote:
Originally Posted by Ron Stygar View Post
I got it from Randy Forbes who got it from someone.
If you compare it with KrisL's one it matches.
It's just math.
Maybe Kris will explain.


Yep, it's pretty easy math. You basically need to figure out how far the car travels for every revolution of the engine.

If the engine travels one revolution per minute, that single revolution is divided by the gear ratio then the final drive ratio.

So if your first gear is 1:4.35 and your final drive is 1:3.62, then the wheels travel (1/4.35/3.62) revolutions for every 1 revolution of the engine. That's .0635 revolutions.

So now you just need to figure out how far .0635 revolutions is.
A 255/35/18 rear wheel's circumference is (2(255*.35))+(18*25.4) multiplied by pi. That's 1997mm or 6.5518 feet per single revolution. Times .0635 revolutions = .416 feet.

So if the engine is going 1RPM, the car is traveling .416 feet per minute. .416fpm is equal to 0.004727mph.

So 3000rpm * .004727 = 14.181mph. Now, as you can see, my calc is slightly off of the spreadsheet - because I was rounding during each step - the spreadsheet is much more accurate.


Hope that helps.
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Old 10-17-2007, 07:34 PM
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Quote:
Originally Posted by Ron Stygar View Post
I got it from Randy Forbes who got it from Dan Masters.
If you compare it with KrisL's one it matches.
It's just math.
Maybe Kris will explain.
Fixed

He's the Ron Stygar of Triumphs and V8 engine swaps into British sportscars.
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  #13  
Old 12-23-2007, 08:33 PM
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Really dumb question.

Does anyone have the math to calculate 0-60 speeds with these ratios?
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Old 12-23-2007, 11:21 PM
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While it may be possible to calculate hhow long it takes for an engine to reach the rpms that equal 60 mph, there are too many variables for it to be realistic.

Though BMW quotes a 4.9sec 0-60 run, someone with a G-tech pro consistently got 4.6-4.7 times, which is in line with Greman car makers' tendency to fudge such things for legal reasons. The 3.91 diff should shave off a tenth, but the 4.10 will actually increase your time because you'll redline before you hit 60 and need to add a shift.

From what I've read on the M3 forums, the 3.91 is more for someone that prowls the interstates a lot as you're not much off the stock diff's fuel economy while getting more grunt for on-ramp assaults, but you still might find yourself downshifting to pass.

The 4.10 is for folks that want passing power to be an ankle-flex away, no matter the gear, no matter the (fuel) cost.
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Old 12-23-2007, 11:48 PM
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Great charts, thx. How much is a 3.91 swap?
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Old 12-24-2007, 01:14 AM
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Great charts, thx. How much is a 3.91 swap?
Annoyingly, it's the same as a 4.10 swap. Typically about $2500 plus a core charge for your gears, then add installation.
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Old 12-24-2007, 06:31 AM
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Annoyingly, it's the same as a 4.10 swap. Typically about $2500 plus a core charge for your gears, then add installation.
Actually i have seen it done for $1200 including the core charge and then labour on top of that...
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Old 12-24-2007, 09:43 AM
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Originally Posted by KrisL View Post
Yep, it's pretty easy math. You basically need to figure out how far the car travels for every revolution of the engine.

If the engine travels one revolution per minute, that single revolution is divided by the gear ratio then the final drive ratio.

So if your first gear is 1:4.35 and your final drive is 1:3.62, then the wheels travel (1/4.35/3.62) revolutions for every 1 revolution of the engine. That's .0635 revolutions.

So now you just need to figure out how far .0635 revolutions is.
A 255/35/18 rear wheel's circumference is (2(255*.35))+(18*25.4) multiplied by pi. That's 1997mm or 6.5518 feet per single revolution. Times .0635 revolutions = .416 feet.

So if the engine is going 1RPM, the car is traveling .416 feet per minute. .416fpm is equal to 0.004727mph.

So 3000rpm * .004727 = 14.181mph. Now, as you can see, my calc is slightly off of the spreadsheet - because I was rounding during each step - the spreadsheet is much more accurate.


Hope that helps.


I feel ya. Thanks
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Old 12-24-2007, 10:02 AM
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Originally Posted by Bammered View Post
Actually i have seen it done for $1200 including the core charge and then labour on top of that...
Turner Motorsport has a complete e46 m3 diff in either 3.91 or 4.10 for $2095 and that includes the $1000 core charge which you get back once you send them your diff.
Diff changes are not that difficult at all and can be done in the garage as long as the person has some half decent mechanic skills.
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Old 12-24-2007, 12:58 PM
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Turner Motorsport has a complete e46 m3 diff in either 3.91 or 4.10 for $2095 and that includes the $1000 core charge which you get back once you send them your diff.
Diff changes are not that difficult at all and can be done in the garage as long as the person has some half decent mechanic skills.
So your net cost is $1,095 plus all applicable shipping charges?
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Old 12-24-2007, 04:45 PM
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So your net cost is $1,095 plus all applicable shipping charges?
That would be outstanding.
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Old 12-24-2007, 06:50 PM
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So your net cost is $1,095 plus all applicable shipping charges?
That is what I understand from reading their website. It makes sense too because the ring and pinnon is $500 so the rest of the cost would cover the installation in the diff. email turner to comfirm this.
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Old 12-24-2007, 08:40 PM
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That is what I understand from reading their website. It makes sense too because the ring and pinnon is $500 so the rest of the cost would cover the installation in the diff. email turner to comfirm this.
Did you check diffsonline.com do see what they want to do it?
They are in MA too.
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Old 12-24-2007, 08:47 PM
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Did you check diffsonline.com do see what they want to do it?
They are in MA too.
Yeah I have email them a couple years back when I was thinking of picking up an m3. I think they wanted some where in the neighborhood of 3k including the core charge. Turner seems to be about half that....
here is the link to the Turner one..... you guys tell me if I am reading this wrong.
http://http://www.turnermotorsport.com/html/detail.asp?PRODUCT_ID=E46-M3-LIMITED-SLIP-3.91-4.10
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Old 12-24-2007, 08:54 PM
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Yeah I have email them a couple years back when I was thinking of picking up an m3. I think they wanted some where in the neighborhood of 3k including the core charge. Turner seems to be about half that....
here is the link to the Turner one..... you guys tell me if I am reading this wrong.
http://http://www.turnermotorsport.com/html/detail.asp?PRODUCT_ID=E46-M3-LIMITED-SLIP-3.91-4.10
I look at it as $2095 plus $1000 core.
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