2020-B2-5

Author Topic: Overdrive with a 403  (Read 147 times)

General Mopars

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Overdrive with a 403
« on: September 13, 2020, 10:32:40 AM »
So, I was driving a very nice IROC yesterday, and of course began comparing it with a Second Gen. The most noticeable difference is the fourth gear the automatic transmission has.

I'm currently having a Holley Sniper EFI system installed and of course the next logical upgrade would be an overdrive. I had toyed with the idea years ago, but ultimately dismissed it because my transmission is fine, so why mess with it and open up a can of worms?

I searched a bit, and it seems like a 200 4R is preferred over a 700 R4. Is there a general consensus here? Is it better to just to an (expensive) Gear Vendors unit? Obviously it would need to bolt up to a 403. Does the EFI conversion play into it either way? FWIW, this is not a race car, I'd just like to drop the RPM on the highway.



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Wallington

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Re: Overdrive with a 403
« Reply #1 on: September 13, 2020, 10:38:40 AM »
Your existing rear gear will also depend if suitable or not, select something better.

General Mopars

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Re: Overdrive with a 403
« Reply #2 on: September 13, 2020, 10:59:05 AM »
I think I have a 3.08 or 3.23.



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tribute

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Re: Overdrive with a 403
« Reply #3 on: September 13, 2020, 12:25:21 PM »
your rpms will be extremely low with that rear gear.  I switched to 3.73s with my 2004r and while much quicker off the line still pulls pretty low rpms on the highway.  I wouldn't go less then 3.42 with the overdrive.  Many will tell you the 700s are stronger but you will have to get an adaptor and get a shorter driveshaft or shorten yours.  The gearvendors are amazing but really expensive.  I wanted simplicity so I went with the 2004r but it does have some troubles with the extra power I am putting down (425hp/496torque) with my 403.  Most shops work with the 700s and will steer you towards them but there are builders that can make your 200 stout.  Is your engine stock?

FormTA

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Re: Overdrive with a 403
« Reply #4 on: September 13, 2020, 02:28:02 PM »
It may not matter but my car has 2.73s with a 4L60E (LS swap). The car I pulled the engine and trans from (98TA) also had the 2.73s.  It does have low rpms, at 55 I'm putting at 1500 rpms. J have plenty of power and I'm sure 3.73s would make it even quicker but the 2.73s work.
79 Trans am low buck LS swapped
79 Formula 301 (Work in progress)
67 RS Camaro (This one is next)


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General Mopars

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Re: Overdrive with a 403
« Reply #5 on: September 13, 2020, 02:51:06 PM »
your rpms will be extremely low with that rear gear.  I switched to 3.73s with my 2004r and while much quicker off the line still pulls pretty low rpms on the highway.  I wouldn't go less then 3.42 with the overdrive.  Many will tell you the 700s are stronger but you will have to get an adaptor and get a shorter driveshaft or shorten yours.  The gearvendors are amazing but really expensive.  I wanted simplicity so I went with the 2004r but it does have some troubles with the extra power I am putting down (425hp/496torque) with my 403.  Most shops work with the 700s and will steer you towards them but there are builders that can make your 200 stout.  Is your engine stock?

Other than the sniper EFI that it will soon have and dual exhaust sans cats, it is stock. My other '79 (the Mayan Red car) has a 2.41 rear and honestly, I love it.



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Fbird

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Re: Overdrive with a 403
« Reply #6 on: September 16, 2020, 07:21:01 AM »
its just $$$$$
obviously several ways to get there...each with it's own issues.
2004r BOLT IN ...ish MUST be built to handle POWER = $$$ because stock...it will die.
700r4 ..adapter plate, driveshaft,...stock will live...just not great. The 3.00 first gear is DEEP
Vebdors OD.... $$$$ driveshaft VIBRATION concerns due to excessive shortening of d-shaft ..makes the u-joints ..unhappy

all work...pick your pioson.
67 Firebird
1981 Turbo TA (injected 400 now :) )

Re: Overdrive with a 403
« Reply #6 on: September 16, 2020, 07:21:01 AM »
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