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Moving to 3.73 gears

KANE

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30+ years on the 82's rear end was a good run.

It was time to get some work done in the rear with shocks, bushings, and the differential. The rear end was coming out and so it was a good time to clean up the somewhat noisy rear end and go to a 3.73 ratio. I had thought about a 3.55 at one time- but decided against it.

I had the OEM 2.87... and with the modified motor, it leaves first gear at 5,450rpm on the 700r4. Along with packing 100+ more HP and almost 100 more lbs/ft of torque... the right gears would help me take advantage of the nearly 500 more rpm in gear and really leverage the motor's HP/TQ curve.

Here's how things fit together modified/stock...

  • 325hp @ 5,300rpm versus stock 200hp @ 4,200rpm- at 4,200rpm it is already pushing 260hp and still has another 63hp and almost 1,200 rpm to go before it leaves first gear
  • 373lbs-ft of torque @ 3,600rpm versus the stock 285hp @ 2,800rpm- at 2,800rpm it is already pushing 350lbs-ft of torque and still has 800 more rpm (before it falls off) and has another 23lbs-ft of torque left to go
  • The .465"/.488" cam starts to really come to life at 1,700rpm. That's when the VE starts to pick up (torque) and it holds through 4,400rpm (peak torque) and starts to fall off at 4,800rpm.


A 3.73 should increase the cruise rpm by about 500rpm. That's fine- at 45mph I am usually in 3rd anyways. :thumb

More than anything, the reason for going to the 3.73 was that I wanted to get 1.) quicker acceleration and 2.) to leverage the HP/TQ of the non-stock engine I have.

Since I have an EBL ECM... I have a lot of datalogs that show the acceleration with the 2.87 rear end. In fact, it routinely gets to 60mph on a 90+ degree day, in a hot summer, and even after running it hard for a while in a hair under 6 seconds from a dead stop. I don't drag the car- I just want it to be more responsive.

I should be able to compare pre/post pretty easily from my datalogs. :thumb

I'll post more when I get it back together...


:lou
 
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3.3 Rear Gears

You will love the 3.73's because they're perfectly suited for overdrive transmissions. With the big 255X60R15 tires you'll have 2040 rpm @ 60 mph which is ideal for most high performance camshafts.
 

Tom Bryant

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I agree that the 3.73 is about ideal for a 700R4 transmission. You get to take advantage of your modified engine during acceleration and passing and have acceptable rpm for highway cruising.

Tom
 

kpic

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More than anything, the reason for going to the 3.73 was that I wanted to get 1.) quicker acceleration and 2.) to leverage the HP/TQ of the non-stock engine I have.
:lou

Without any doubt, you will most certainly get #1 and 2.

Plus plenty of :lou:lou:louwhenever you please.

Buckle up and prepare to enjoy...
 

stevolwevol

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I agree, with a 700 you will enjoy the 3.73's. The only reason I am stuck with 3.55 gears is because I have a 350, and in 1.1 I rev about 3000 at 70, and that's enough revs for me. Just watch the blue suits, and ghost cars. Been there, done that.
 
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KANE

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I am happy so far!

It just rolls off the idle and moves effortlessly through the gears. It's a lot more responsive.

I am going to let it break in, but so far... it's a lot quicker through the gears and with less throttle. It just goes now!

I think I will need to adjust the tune a little. I had it optimized for the 2.87 and it may benefit from some tweaks perhaps in the lower KPAs around 2,000 to 2,500rpm (cruise and deceleration).

I had a friend do the work and he replaced the rear bushings with Energy Suspension Polyurethane and swapped out the shocks too.

So, all set. Just need to break it in before I datalog it for before and after numbers.



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Mac

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I think I will need to adjust the tune a little.

In other words, you're looking forward to squeezing a bit more oomph outta the old girl... ;LOL

Mac
 

Peer81

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Sounds great! As the first gear is very short is it still usable with the new gears? And a how many rpm torqueconverter are you running? :)

Greetings Peter
 
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KANE

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Sounds great! As the first gear is very short is it still usable with the new gears? And a how many rpm torqueconverter are you running? :)

Greetings Peter

Thanks Peter!

First isn't too terribly short.
I had already reset the governor to shift at 5450rpm, so it shifts about 500rpm higher than stock anyways.

Cruise tune looks great. :)

AE is spot on.

I think I might need to adjust the fueling in decel mode between 2k and 2,500 rpm. When I let abruptly off the throttle at 2,500rpm it goes a bit rich... then wanders leaner.... gets up to 18:1 after DE is complete and with NO throttle... and then wanders back down to 15:1 by about 2k rpm. This happens at the 30KPA areas. May be a touch lean... but the car doesn't stumble or anything during hard decel.







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KANE

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I completed a datalog yesterday.

It's the 2,000rpm area at 30-45 KPAs under decel / coast where it runs a little lean.

I'm going to add a little fuel in those areas and it should all be fine.

I'll post more once I get another session in.


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KANE

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I went out and logged the full throttle acceleration yesterday with a datalog. :D









0-60 mph.... in 5.2 seconds!

:eek :eek :eek :eek :eek







I am very happy with that old Vette!


I will need to adjust the governor. 5,800 rpm is a bit high for the 1-2 shift. So, not sure if I will go to a yellow spring or to the green.
 

Tom Bryant

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That's very quick.

Tom
 

Toms007

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Sounds like a fun car to drive, Johnney.
 

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