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Discussion Starter #1
I have been reading many threads on this swap, but am wondering about freeway RPM's with my auto trans. Has anyone here done that swap from a 3.73 or 3.91 to a 4.30, auto only. I have read one positive thread by OutofStep that said he enjoyed it, and I think another by Nashman, but not sure if he is auto.

DrJones and Bishops names have came across in most of the differential threads I searched, but niether are Auto.



Thanks,
Dominic

PS I am aware of LSD only in sport package N/As
 

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I dabble with that cartest program now and then. I don't know how far off it is, but I assume the gearing/speed calcs would be accurate, as opposed to their drag time simulation.

Here is what I got from it using auto gears and 4.3
 

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I've had it for 2 weeks now. Switched from a 3:91 to the 4:30 LSD unit. I'm happy with it, the car seems to pull harder off the line and it revs way harder/higher on the freeway. By the way, I have the auto. Couldn't wait to take her to the track and see how it goes. I didn't switch the speed sensor unit, so I know that my speed accuracy is suspect but that is the least of my worries for now.

Cheers,
Ti
 

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Well, I havent done the swap, but I own cars with both ratios. I can surely say the 4.30s will make your car alot more fun to drive, and it will be a bit more responsive. I would say go for it if you dont venture out of town much. The downside of this will be higher cruising RPMs and lower fuel economy. My n/a is 5spd, so your auto would make it a bit lower, but at around 70 Mph in 5th Im at 3150 RPM. Now switch to my turbo auto it rolls 70 at about 2300. Somewhere around there, cant remember exactly, but its a big drop. It just makes it so much more comforterable for highway or high speed driving. I always wondered why the n/a version had worse gas mileage. Now I know, its because of the gearing.

Basically I think you should consider this. If you just drive your car around your town and it doesnt reach freeway speeds, then by all means go for the swap. Youll probably enjoy the extra little kick youll get. However, if you take your car onto the interstate or you live in a big town like san diego or something where the normal roads reach 60 and 70 MPH, I would stay away from this swap. For me anyways it makes it pretty uncomforterable cruising at high rpm down the freeway. Hopefully this helps you some, and more people should be able to help you out who have done it first hand.
 
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Discussion Starter #6
if you are getting an upgraded ct-26 or anything larger you will be bouncing off the rev limiter if you run the car at the drag strip with OD off and a 4.30.
 

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4.3 + turbo = 90% suck

I was having troubles keeping up with traffic in texas... just cruising, if I were to let of the gas I would get a little BOV flutter... it was revving that hard.

I put on 225/60R16's just to bring the revs down.
 

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I'm happy with it, the car seems to pull harder off the line and it revs way harder/higher on the freeway
werd^2

4.3 + turbo = best thing ever.

Faster off the line, faster from a roll (though lower top end. Who goes 180 mph anyways?)), faster to spool from a roll (rpms already up).

My mileage in town only dropped .5 - 1 mpg.

heh, all the local MK3 guys are swapping to 4.3 rears after they saw the diffrence in my ride.
 
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Discussion Starter #9
outofstep said:
werd^2

4.3 + turbo = best thing ever.

Faster off the line, faster from a roll (though lower top end. Who goes 180 mph anyways?)), faster to spool from a roll (rpms already up).

My mileage in town only dropped .5 - 1 mpg.

heh, all the local MK3 guys are swapping to 4.3 rears after they saw the diffrence in my ride.
Your auto?? Does the freeway suck?
 

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Wow! for a second, I thought it seems like nobody likes the turbo + 4:30 + auto but me. The first thing I dislike about my auto was that it doesn't rev too easily like the manual tranny does but now with the 4:30 gears the revs is music to my ears. Tomorrow, I'm going to find out if it's true that if I switch off the O/D, I will be bouncing off the rev limiter, as said above??? I highly doubt it, unless you have tranny issues.

Yea, twice it happened to me that if I let go off the gas too quickly while initiating boosting, the car behaves strangely?? So, I try to control that -- no problems. I have 255/40/17 in the rear and they break loose easily. You've gotto love that in an auto!!

As for high revs and poor gas mileage -- eh! that's among the least of my worries, man, after all it's a Supra and I don't know about you guys but as for me -- I love to drive mine hard and ruff!!!

Cheers,
Ti
 

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Your auto?? Does the freeway suck?
I'm auto right now, but soon to by 5speed.

What aspect of freeway? It's most def. faster and full boost is sooner as compaired to a 3.x car at the same speed. However you are cruising at a higher RPM and your topend will be lower.


The only way you could get me back to the 3.X series of diffs would be if I'm going to go dyno for bragging rights. Other than that the 4.30 rules!
 
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Discussion Starter #12
So would it be better to swap in the 4.30's with a 5-speed or stick with the 3.73's?? I'm looking to drag and auto-X, and maybe a lil street racing/freeway racing. I dont give a damn about fuel ecomomy. I also have an upgraded CT.
 

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Some numbers I calced out awhile ago for the 5 speed and various rear ends.

Turbo supra (r154) with 4.30 rear end. Tires are 245 45 16. The speeds are measured at 6500rpm
1:34
2:65
3:85
4:111
5:148

R154 w/3.9 (forgot the exact, so i just plugged in 3.90). Same rims/tires @6500rpm
1:38
2:72
3:94
4:122
5:163

R154 3.73 245/45/16 @6500
1:39
2:75
3:99
4:128
5:171

Because tons of folks use the mk4 rims with a 275 45 combo, here are the numbers for that.

R154 4.30 275/45/17 @6500
1:37
2:71
3:92
4:120
5:160

r154 3.9 275/45/17 @6500
1:41
2:78
3:102
4:132
5:177

r154 3.73 275/45/17 @6500
1:43
2:81
3:106
4:138
5:185
 
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