Differentials, gear ratios, RPMS

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Mar 20, 2002 | 05:32 AM

Giedrius

Thread Starter

Registered User

Joined: Mar 2002

Posts: 21

From: MD

Differentials, gear ratios, RPMS

I've heard and read few things stating that if you have 3.90 or 4.11 rear, car would become quicker, but the top speed would be lower, RPMS higher at higher speeds causing higher fuel consumption. I was trying to figure it out, but I can't. It seems that 4.11 rear would make the top speed higher, since the final drive ratio is higher, and the speed at the same RPMS will be higher with 4.11 diff than with the 3.70. Am I missing something? Please explain or tell me where I can find answers. Thanks.

'74 260Z

Mar 20, 2002 | 06:04 AM

1tuffz

Registered User

Joined: Dec 2000

Posts: 128

From: Rochester, NY

Re: Differentials, gear ratios, RPMS

check this link, it should help.

http://www.geocities.com/z_design_studio/

David
1TuffZ
zccr.net

Mar 20, 2002 | 08:44 AM

Giedrius

Thread Starter

Registered User

Joined: Mar 2002

Posts: 21

From: MD

Re: Differentials, gear ratios, RPMS

Great Info! I have right now what I believe is 77-79 5-speed tranny in my Z with original R180 differential (3.364) Using the charts it seemed that I could achieve higher spead in each gear than using any higher ratio differential. I know from reading that higher gear differential would make the car quicker, but according to the graphs it isn't so. I guess I am still a little confused.

'74 260Z

Mar 20, 2002 | 04:21 PM

Skaitan

Guest

Posts: n/a

Re: Differentials, gear ratios, RPMS

The higher the number for the ratio, the lower the gearing, I know it sounds backwards, but this is the case. So if you're running a 4.11 rear end, your car will hit redline quicker, make power quicker, but be going slower. Ummmm, I'm terrible at math, and I'm having problems trying to explain how it is that that works mathematically, but I know this to be true, because I swapped my diff from a 3.5 to a 3.7 and now it reads the same speed at the same RPM (didn't change the drive gear) but is actually going slower.

The Beast is back and badder than ever!

Mar 20, 2002 | 05:31 PM

Giedrius

Thread Starter

Registered User

Joined: Mar 2002

Posts: 21

From: MD

Re: Differentials, gear ratios, RPMS

OK, now all things are clear. So what do you guys think of Detroit Locker 4.5 differential in Z?

'74 260Z

Mar 20, 2002 | 10:52 PM

krtowner

RHD Datsun Dude

Joined: Feb 2001

Posts: 13

From: Pasadena, Maryland

Z-CCR

David Palermo,

I was not aware that Rochester had a Z Car Club. I was born in Rochester, lived in Honeoye, but was rasied in Arizona and Florida. I still have family in Rochester and visit regularly, can you provide me with a point of contact for the club. When I am in town with my Fairlady Z I will get in touch with the club.

Cheers, Kirk Towner
Victoria, BC, Canada

Kirk (81 FairladyZ)