Should I Bother With 7at Gear Ratio's when FI?

JenovaI

I currently have a pretty aggressively tuned Stillen SC'd 370z 7at with a base open diff. Next step is LSD. Everyone says 3.69 or 4.08 gears are amazing, but since I'm at 479hp on a dyno, should I bother gear swapping? Am I going to put unnecessary load on my 7at by going to the closer gears?

Wonka2581

I say NO, sense your boosted... But ill let everyone else chime in...

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Chuck33079

No, but get a LSD in there.

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2011 MB Touring-Sport-6sp-Nav/GTM TT/FI TT TDX/JTran/Kosmic/Eibach/Hotchkis/SPC/CSF/RPS/SoThatsWhereAllMyMoneyWent

JenovaI

Great, thanks guys. Ya I definitely need the LSD.. I lose traction at the very slightest wheel traction imbalance haha

blueranger

I will soon see firsthand how the 3.69 gear swap I currently have on my 7AT works.

Fast Intentions is wrapping up my Twin Turbo install and I already have MT ET Street SS radials waiting.

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F.I. Stage 1 Twin Turbo #48 | E85 FlexFuel | Built 7AT | F.I. 34 Row Oil Cooler | F.I. Flex Plate | F.I. 19 row Trans Cooler | MT ET Street S/S | ECUTEK Tuned by Seb | RPM Roll Bar

blueranger

My map #1 (9lb) is 500+whp on E85 and it does launch strong with the 3.69 VLSD pumpkin swap I did. I have not tried the other maps (boost levels) yet but it pulls hard on my first map.

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F.I. Stage 1 Twin Turbo #48 | E85 FlexFuel | Built 7AT | F.I. 34 Row Oil Cooler | F.I. Flex Plate | F.I. 19 row Trans Cooler | MT ET Street S/S | ECUTEK Tuned by Seb | RPM Roll Bar

jchammond

I Love my Quaife & retained Factory gearing (3.357:1) & will peg Speedo @7800 in 5th (1:1)

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jchammond

Quaife made a HUGE difference in traction,,,not boosted yet-but Completely Satisfied with traction!

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solidus

Changing the ratios is a bad idea traction wise. I went 3.69 and the traction was scarce. The money would be better spent on a new diff. If you can't use the traction availible with stock gearing it makes better sense/cents to fix the traction problem first. If I had'nt experienced it N/A I would'nt have anything to say but having been there and being freshly boosted with a 6MT I'd say don't do it. Personally my next mod will be an OS Geiken or Wavetrac rear diff as soon as possible. I've heard at least one scary story about boost and VLSD going off into insurance adjuster land.

Shin Beats

JenovaI do you have any other work done to the transmission?

RadioFlyer

I'll be the voice on the other side of the coin... I just ordered 3.9 gears for my MT, that's up from 3.69. I suspect it will make little difference, but while I'm in there installing an LSD, I figured I'd give the marginally shorter ratio a try. I have a Stillen supercharger on the car, and I dyno a bit over 400 at the wheels. I chose to do this for a few reasons:

1) When people are saying that they have no traction with the stock ratios, it's because of the open/viscus stock diff. Address the wheelspin, and you'll want more gear.

2) The stock ratios (with the stock ring/pinion) are geared really long and wide in my opinion. 2nd gear runs out to like, 70mph - that's too long for a sports car! And the gearing tops out at over 200, that's too long in my opinion. Dropping the FD ratio puts that more inline with other sports cars, and keeps you active on the gearbox, which I prefer.

3) It's not that much power. 400-450 isn't too much power as long as you're hooking up. It's about as much power as a modern Camaro/Mustang is putting down stock, and they're gearing down too. It would be a different story if I had more power though. With more power, I'd want to stick with the stock ratios, but 400-450 isn't THAT much. The BMW 550i does that stock, and it's a luxo sedan. And I believe they change the gear ratio for the M-Sport package. That's not even talking about the M5.

But in the end, it all might be moot because the difference is minimal between 3.69 and 3.91. Consider that for G37's, they use a 3.69 for the 6MT coupe, and a 3.9 for the 6MT convertible just to offset the weight. So it doesn't sound like there will be a whole slew of downsides to trying it out, and if you're already in there changing out the diff (and addressing my first point), then you may as well give it a try. Just my 2C.

jchammond

RadioFlyer,
I've been eyeballing the 3.90's myself,,,on a 1:1 trans ratio;can still hit 150 (if so desired)
Also would enlighten the meaning of a Hole-Shot w/4.924 1st gear.
A very large difference for me,from a 3.357diff.
I would lose about 10mph@2500 in OD,but still netting over 25mpg after mods.
Also,where i live/The speed limit don't allow 180mph runs,,,not to mention the Chitty Roads.

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MazWorx built long block | FI-TT-100 Stage 2.75 | IPT built 7A/T

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