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Discussion Starter · #1 ·
Does anyone have actual test data displaying
the performance gained by switching from a 3.54 to a 3.90 rear end? ( e.g., 0-60 times, 1/4 mile etc.)
 

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Discussion Starter · #3 ·
Re: GEAR IT AND HAVE SOME FUN!!

> I never dragged with my old 3.36 rear end
> ,but when i installed my 3.9 it felt like I
> had added another 30 HP to the engine.The
> torque multiplication in the lower gears was
> INCREDIBLE.Also the nicest benefit is that
> you dont have to spin your tires to get good
> off the line performance! This much I can
> tell you.When I got my nitto drag tires I
> was not impressed with my 1/8 mile times
> with the stock 82 ZX 5 speed and 3.9 rear
> end in my 71 240Z.I had run BETTER times
> with my normal street tires,the lack of
> wheel spin was not allowing the engine to
> get in its powerband before the tires hooked
> up. So ,I installed a 79 transmission input
> shaft and front counter shaft gear on my 82
> zx 5 speed.This modification essentially
> changed my 3.9 reargear ratio on the first 3
> gears to an effective 4.356. This may be a
> little confusing but changing the shaft on
> the tranny increases the 1st,2nd,3rd,and 5th
> gear ratios 11.7%.4th is not affected
> because it is 1:1. The math 3.9 x
> 1.117=4.356 4.356-3.9=0.456 increase in gear
> ratio Anyway after doing this my 1/8 mile
> time went from an 8.85 to a best of 8.55! So
> you can see that by changing from a 3.54 to
> 3.9 gear should pick you up nearly 2-2.5
> tenths in the 1/8 mile!!! Going from 3.54 to
> 3.9 will give you about a 10% increase in
> torque in all 5 gears because you will
> actually be changing the rear gear ratio!!
> You should change your 3.54 to 3.9, it is
> the cheapest thing you can do to any Z car
> for a REAL noticable improvement in off the
> line acceleration and is mandatory when
> going to bigger cams which hurt off the line
> performance!! Later,norm

Thanks Norm, what about RPM's @ 60 MPH and the effect on top speed?

Rob
 

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Discussion Starter · #5 ·
Re: GEAR IT AND HAVE SOME FUN!!

> Rob, if you go from 3.54 to 3.9 you will
> turn about 10 % higher RPM. As far as top
> speed goes ,my car ran faster with the 3.9
> than 3.36 rear gear(the appropriate speedo
> gear for the 3.9 was installed).Twisting the
> engine at a higher rpm raised my top speed
> about 10 miles an hour by putting engine in
> more favorable part of the powerband.
> Later,norm P.S. if you go to 3.9 rear gear
> you WILL need a 5 speed if you don't already
> have one.

Thanks Norm, I appreciate the response. I do have a 5 speed on my '78 and will go find a 3.9!
 

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Discussion Starter · #9 ·
Re: I have Excel file with ratios

> Rob, I created an Excel file with the
> different transmissions and ratios. I also
> have calculated the gear spacing ratios for
> each transmission and have a [email protected]
> tablet to indicate new rpm with diff
> changes. Let me know if you could use this.

Dave,
Yes I would.
Thanks for the response.
Rob
 
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