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904 vs 727

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Category: Competition
Forum Name: Drag Racing
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URL: https://theamcforum.com/forum/forum_posts.asp?TID=93846
Printed Date: Mar/28/2024 at 4:00am
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Topic: 904 vs 727
Posted By: speed_is_addictive
Subject: 904 vs 727
Date Posted: Apr/27/2018 at 5:26pm
My hornet came with a 904.

i will be running a stout 360.

is this trans able to handle the power built properly or should i just invest in a 727. . .

im new to amc but not to power or drag racing. . .

thanks



Replies:
Posted By: gremlin1945
Date Posted: Apr/27/2018 at 6:07pm
 A well built 904 will handle anything you'll throw at it, and it's lighter and smaller than a 727, a consideration installing it in a hornet/gremlin.

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former NHRA #1945

former IHRA #1945

T/SA


Posted By: matty 401
Date Posted: Apr/27/2018 at 8:08pm
was it from a 6 cylinder or a 304 

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72 matador 401 the beast
79 concord 2 door
72 matador 304 grasshopper
68 Rogue 406
93 Cherokee 4.0 5 speed



Posted By: speed_is_addictive
Date Posted: Apr/27/2018 at 8:57pm
hmmm, how do i tell the difference. . . 


Posted By: gremlin1945
Date Posted: Apr/27/2018 at 9:07pm
If you're putting it in without doing any rebuild I wouldn't do it you will have to have it rebuilt to the specs for high performance use a lot of guys run them and they don't have a problem with them it's not cheap though

-------------
former NHRA #1945

former IHRA #1945

T/SA


Posted By: purple72Gremlin
Date Posted: Apr/28/2018 at 6:09am
a 304 runs a 998. which is a beefier 904.  


Posted By: jpnjim
Date Posted: Apr/29/2018 at 10:25am
They put small case 9xx series transmissions behind race Hemi's so they can be built to take the heat.
Racers even run 9xx series internals in 727 cases to cut down on weight/drag,
so the small case parts can be made to live.

If your Hornet is a 1970, the 9xx case would have been swapped from a 72 or later AMC (assuming it's an AMC case),
so you'd want to identify it to be sure what you have.

9xx series transmissions are also easier to get with the 2.75 low first gear,
if you want to run a little taller rear gear,
 the deeper first can help compansate, while still giving you a good gear to launch from.
The 2.75 first for a 727 is much more difficult to get, and expensive.

An AMC 360 with a 904/998/999 is a good combination.

IIRC, the 999 was actually originally introduced when the Chrysler 360 came out,
to handle the extra torque without going to a 727.


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71 P-code 4spd Javelin/AMX
some Jeeps and some Fords


Posted By: BassBoat
Date Posted: Apr/30/2018 at 10:01am
I used to argue that the cost to beef up a 904 or 998 to take the kind of power that even a mediocre 727 will handle wasn't worth it.  I still think so today but less strongly.  If durability is your number one concern, then the 727 is still the best choice.  But the rotational inertia of the smaller transmission is much less and frees up a lot of power.  When I switched to a 998 from a 727 in a 360 American I picked up a couple of tenths just due to the rotational inertia improvement.  One thing that isn't obvious when comparing the bigger clutches of the 727 to the puny clutches of the 998 is the quantity.  Typical 727 has 3, maybe 4, and it takes some work or the right drum to get 5.  Basic 998 has 5 already.  Smaller clutches, but more of them so I would call it a wash.  A second advantage to the 998 is that Chrysler made a lot of low gear planetary 998 transmissions and you have a decent chance of finding a low gear ratio where the 727 low gear planetary seems rare and/or expensive.  That same 998 is now behind a 401 and we will see how long it lasts.  Went 5 years without maintenance behind a 360.
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