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 Post subject: 904 Low Gear Sets
PostPosted: Sun Mar 01, 2009 8:03 am 
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Supercharged
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Location: IRWIN PA
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In which years / Engine combination of the 904 might I find a low 1st gear set?


Thanks! Greg

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PostPosted: Sun Mar 01, 2009 8:35 am 
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Location: Eugene, Oregon
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About '88 and up.

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 Post subject:
PostPosted: Sun Mar 01, 2009 9:22 am 
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Earlier than that, actually, the first year for the wide-ratio gearset was 1980 in the A904 (and its eventual derivative the A998).

Be sure to grab the governor assembly, too, which uses different weights to provide proper shift speeds with the wide ratios — otherwise no 2-3 shift under full throttle.

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 Post subject:
PostPosted: Sun Mar 01, 2009 10:16 am 
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Why do you want a low gearset? What car/combo?

Lou

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 Post subject:
PostPosted: Sun Mar 01, 2009 10:20 am 
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That's a good question. Me, I don't like the low-ratio gears so much; see here.

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 Post subject:
PostPosted: Sun Mar 01, 2009 3:05 pm 
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Supercharged
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Location: IRWIN PA
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Well I have a 904 out of an 81 Lebaron Wagon with a 318.. I am putting togther a "race" car and just weighing the options.

it's going to be a 68 Valiant Sedan.. Super short and Super light gutted interior Lots of rusty panels - Even more light weight.. I have raced the dart for a while and I just don't race enough to be consistent worth a crap with the 4 speed.

So this is my next project.

One question do the gear set care wether they come from lockup stuff (1981) going into non lockup stuff (1968)?

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Greg

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 Post subject:
PostPosted: Sun Mar 01, 2009 3:41 pm 
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Glad to hear you are starting a more dedicated racecar project. Sounds like a great starting point. I love your Dart, but very hard to bracket race a stick.

I would think twice about the low gearset in a racecar. If you want a racy NA motor with a high stall converter, the regular gearset is better due to less RPM drop on both shifts. You should run faster overall with the std gearset, but maybe 60 ft slightly faster with the low gearset.

There's not a huge difference overall, but hardly worth looking around for the low gearset for a racecar. If you already have it, fine to use it.

I would use the low gearset in an application where you could not use high stall (like best MPG), and still wanted to be quicker off the line. A lockup trans would be one such case where the low gearset is arguably better.

Lou

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 Post subject:
PostPosted: Sun Mar 01, 2009 3:47 pm 
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Turbo EFI
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Quote:
One question do the gear set care wether they come from lockup stuff (1981) going into non lockup stuff (1968)?
Does not matter. I have the low gearset in my car from a lock up trans.


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PostPosted: Sun Mar 01, 2009 4:00 pm 
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Location: Park Forest, Illinoisy
Car Model: 68 Valiant
The biggest problem with a low gear set is that what you gain in the 60' you give back at the wider shift spacing. It is harder for the motor to recover when it drops more RPM. :shock:

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 Post subject:
PostPosted: Sun Mar 01, 2009 5:51 pm 
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Supercharged
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Ok all good input.

I guess I was thinking about the low gearset due to the fact that I have one suposedley from my parted lebaron wagon and that I read the article in 6-2009 Mopar action about Doc's toad car and he has a low gear set there.


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Greg

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 Post subject:
PostPosted: Sun Mar 01, 2009 6:53 pm 
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Most of your time is made from the starting line. (NA motors)

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 Post subject:
PostPosted: Sun Mar 01, 2009 7:39 pm 
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Location: Park Forest, Illinoisy
Car Model: 68 Valiant
Quote:
Most of your time is made from the starting line. (NA motors)
Yes and no. If you're lugging the motor downtrack you will kill ET.

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 Post subject: low gears
PostPosted: Mon Mar 02, 2009 10:41 am 
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TBI Slant 6
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Location: Stryker OH
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I have a 3700# truck and it launches like a boat.my 60 ft times were embarrassing for a 13.5 second vehicle and i'm running the wide 904 gears with a 3.55 rear and no bog going into high gear.do you think I will gain et with close gears???I tend to think not.

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 Post subject:
PostPosted: Mon Mar 02, 2009 12:09 pm 
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Supercharged
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It's not really a bog so much as the engine lays down a little. I have the same problem with my 3-speed manual. The RPM drop is just too great to maintain pear or near-peak acceleration and the acceleration goes soft. A high stall torque converter won't help the gears being too far apart as the converter is slipping very little at the shift recovery point.

Most turbo vehicles leave soft. They just don't make their peak torque right out of the hole. A high stall torque converter will help a lot. If your truck pulls hard at the shift recovery RPM then the gears probably aren't doing your turbo combination much harm.

How much boost can you get at the starting line? What's the peak boost?

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