Feeling of 4.30s vs 3.73s

[rtrdpenguin]

I've recently swapped my drivetrain into a new shell and went from an open 4.30 diff to a 3.73 LSD. The whole drivetrain is exactly the same as it was before except for the change from a MBC to an EBC, and I've run both setups at ~8 psi.

Thing is, my car feels a whole lot slower now. The old one (which even had upgraded suspension vs. old worn out stock suspension on the new car) used to squat down and push me back in my seat pretty hard when I got on it, but this new one pulls a lot less. Like I can put stuff on the dash and it stays there during WOT less... Before it took effort to even push my head forward!

I know going to a lower diff gear will do this, but I was wondering if anyone else has used both with the same/similar drivetrain and if it's normal to feel such a huge difference.

If it's not supposed to be this different, I may have some engine issues :nono: The wiring in this chassis is really messed up and I'm not about to pull the harness out and go over it like I did the other car... I'm afraid I might have ignition issues :aigo:

 

[need new tires]

turn the boost up and get into 3rd gear then tell us what you think.

 

[RazoE]

the NA diff has shorter gears so it'll accelerate decently..

the turbos had longer gears to take advantage of boost...

 

[IJ.]

There's a line with our fat pig cars where the mechanical advantage of lower diff gears (4 series) intersects with load on the Turbo building boost and power.

4.3 will get things happening off boost and get it out of the hole harder but there's less load on the Turbo so they will rarely reach full boost in 1st.

3.9's would be a good compromise gear to run.

 

[rtrdpenguin]

I did notice first gear went by extremely fast with the 4.30s... it was pretty much useless. What I think I'm missing is the lower end torque. Out of boost with 3.73s 7Ms are pretty slow aren't they?

 

[IJ.]

Yep you're trying to accelerate a HUGE mass with very little power/torque as the engine isn't into it's happy zone, 4.30's make up for this with mechanical advantage (it's why NA's have them).

As I said 3.9 is a good compromise gear as you get some advantage and less rpm on the highway.

 

[empera]

hmmm which will be best for drag?

im sure this topic has been talked about before but since we're on this topic.

 

[Rennat]

my n/a wiht a 4.3LSD felt a lot 'quicker' but my turbo supra with the 3.73LSD feels overall MUCH faster (duh!)

im much happier with the 3.73 though, i wouldnt mind the 3.9 though... defintaley a good compromise.

 

[IJ.]

hmmm which will be best for drag?

im sure this topic has been talked about before but since we're on this topic.

Sorry NFI I'm not a drag raacer but I'd imagine numerically higher ie: 4.30 would be quicker out of the hole so would give a better ET?
(I'm sure one of the racer types will have a better answer on this)

 

[dumbo]

i got the 4.3lsd, NA, goin turbo, a little worried about how short 1st is going to be, espicially with W58.(think 1st is even shorter) but man top speed is ridiculous, like when do you need to go 200km??
120mph for y'all, eh:biglaugh:

 

[suprabad]

Sorry NFI I'm not a drag raacer but I'd imagine numerically higher ie: 4.30 would be quicker out of the hole so would give a better ET?
(I'm sure one of the racer types will have a better answer on this)

I am a drag racer, and 4.30's with an auto is definitely quicker out of the hole, and also going to net a lower et than a 3.anything gear ratio.

If I could (practically) go lower, I would. There is definitly a point when low rear end gears would limit your trap speeds to the point it would hurt your et, but I would say it's going to be in the high 4.'s or early 5.'s before that would be a consideration.

 

[rtrdpenguin]

I mostly wanted to change to 3.73s because I'm going to be doing a lot of highway driving going to college and the 4.30s were at something like 3k rpm at 80 mph! I suppose I just have to live with the lessened acceleration as part of the compromise =( Oh well, another excuse to up the power!

 

[figgie]

I mostly wanted to change to 3.73s because I'm going to be doing a lot of highway driving going to college and the 4.30s were at something like 3k rpm at 80 mph! I suppose I just have to live with the lessened acceleration as part of the compromise =( Oh well, another excuse to up the power!

doubt it was that low.

r154 + 3.9 = 2950 rpm @ 70 mph. @ 80 = 3400 rpm. on 4.3 you are looking at closer to 4k.

 

[RazoE]

my w58/4.3 does 80mph @ 3k in 5th...

 

[1-2clutch-u]

yea 3600 at or so dep on ur tire size

 

[rtrdpenguin]

Oops, forgot to say I was on a W58. I never actually went on the highway with the R154/4.30 combo =\ 4k rpm is insane though!

 

[xsjado]

Going from a 4.56 to 3.73 felt a lot quicker overall to me. Was a huge help not having as many traction issues and seeing barely any boost in first gear though. But I think I will be going back to the 4.56 because I'm only interested in going in a straight line .

 

[mk34life]

hey guys,
ironicaly I've just tested out a 4.3 LSD diff. yesterday. I thought it would be faster then my original 3.7 LSD, but it feels slower. It doesn't make sense, but maybe like some of you said, due to the turbo load being reduce with the higer LSD (4.3), slower. 1st gear feels slower, 2nd/3rd feels good, and on the freeway at about 70+ feels slow. I have a single 2jzgte w/open wastgate, makes alot of noise but slow, i'm changing it back today.

4 years ago I had a 1.5jz everything stock w/4.3 non-LSD, man it haul ass!
3.0 liter stock 1j turbo = no turbo lack If anyone have ever driven an STI, that's how it accelerates. Makes our supra feel light.

Anyways I thought that changing my current 3.7 to 4.3 would be something like back then, it's not. how weird.

 

[s383mmber1]

i got the 4.3lsd, NA, goin turbo, a little worried about how short 1st is going to be, espicially with W58.(think 1st is even shorter) but man top speed is ridiculous, like when do you need to go 200km??
120mph for y'all, eh:biglaugh:

Putting a turbo on will not change the gears, or make 1st gear shorter.

 

[dumbo]

Putting a turbo on will not change the gears, or make 1st gear shorter.

ahhh.... yah i konw

but if the gear is TOO short you wont fully boost and take advantage of the turbo, pretty sure.