904 behind a big block.

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Doosterfy

Doosterfy

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I'm building a big block Duster. I removed the original slant 6/904 from the car. No one wanted the engine so I scrapped it. My question is; Is the 904 from the slant 6 a suitable core for a full race trans to go behind a big block? I know that no 904s will bolt to the big block without a different bell housing so what I'm getting at is, do I have to find a small block 904 or is this 6 cylinder core worth saving for this?
 
No go, bud. You'll have to find a big-block trans. No 904's ever came behind big blocks. Bellhousing is cast with trans case...no swapping bells. Never seen a small block to big block 904 adapter either.

Why not just sell the slanter trans and get a BB727?
 
the 904 slant sixes usually only have 3 disc and 3 steel in the front drum..and 3 disc in the rear drum..

those probably can be swapped out...but I dont think anyone makes a /6 to BB adapter...you will find a SB to BB adapter

I would find a small block 904....71 and newer...put 5 disc in the front drum using the thinner disc and steels.....
 
I still wouldn't put a 904 behind a bigblock, there good transmissions but I just don't trust them that much
 
Super stock racers used to put 904 guts into the 727 case to reduce the rotating mass. Only problem was the parking pawl would not reach the smaller drum so no park. The tech inspectors eventually got wise to it and started checking if the cars went into park.
 
mischiefdart said:
Super stock racers used to put 904 guts into the 727 case to reduce the rotating mass. Only problem was the parking pawl would not reach the smaller drum so no park. The tech inspectors eventually got wise to it and started checking if the cars went into park.
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Not quite, Ford stock and SS racers were using the TF guts in their C6's. They are the ones that didn't have a park. Stock and SS racers are still using 904 guts in their 727's albiet the stuff is all billet made by ProTrans and they are expensive. Over $5K. But you can use the JW bell to adapt the 904 to the BB, but unless this is an all out every thousanths of a second counts effort it's not worth the time or trouble. You aren't going to gain much with a big block at all.
 
I put a small block 904 behind my 383 in my Road Runner. The trans was sent to Protrans in Lancaster Ca (I highly recommend) for a rebuild and upgrade to low gear set. I machined the bell housing off and replaced it with a JW Ultra Bell (not cheap $300) and installed a 10 inch converter. The car picked up .5 and 5 mph in the quarter and had quite a few passes and no signs of any trouble. Worth every penny!! I know the internals of /6 904 are different but they can be converted.
 
Thanks to all for the info. The 440 going in now is somewhat mild and should be about 500 HP and I have two 727 cores and two A-518 cores. I was going A-518 but decided I don't want to butcher the floorboard so I'm using a 727 with a 10 inch verter with this motor. I have a 72 400 block for the next motor and I'll be aiming for alot more power. I have read that 904s are 3 to 4 tenths quicker than 727s so thats why I'm thinking about it for the next motor, and I'm aware that the stock internals will not hold up and I have to cut the bell housing off and go with a JW ultra bell so to sum it up; The only difference between a small block 904 case and a slant 6 904 case is the bell housing?
 
Doosterfy said:
Thanks to all for the info. The 440 going in now is somewhat mild and should be about 500 HP and I have two 727 cores and two A-518 cores. I was going A-518 but decided I don't want to butcher the floorboard so I'm using a 727 with a 10 inch verter with this motor. I have a 72 400 block for the next motor and I'll be aiming for alot more power. I have read that 904s are 3 to 4 tenths quicker than 727s so thats why I'm thinking about it for the next motor, and I'm aware that the stock internals will not hold up and I have to cut the bell housing off and go with a JW ultra bell so to sum it up; The only difference between a small block 904 case and a slant 6 904 case is the bell housing?
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guy on here did a nice post where only thing he had to cut was the transcross member that spot welds to the floor, floor is still factory
 
The 904 is no way, no how going to be 3 to 4 tenths quicker. I have two friends, one a C/SA 440 6 pack car and the other a SS/JA 6 pack car that spent the big bucks for the ProTrans and only picked up about .08. For just a bracket car or test n tune/street car it's not worth the money.
 
Guitar Jones said:
The 904 is no way, no how going to be 3 to 4 tenths quicker. I have two friends, one a C/SA 440 6 pack car and the other a SS/JA 6 pack car that spent the big bucks for the ProTrans and only picked up about .08. For just a bracket car or test n tune/street car it's not worth the money.
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I have done the swap on 3 cars now with back to back testing and the slowest one picked up 4 tenths. IDK what your buddies are doing to mess that one up.
 
Were you putting low gear set 904's in compared to the standard low gear in the 727? Because that could be the big difference especially with a heavier car and a small engine. If you compare them with the same ratios you won't get that kind of improvement.
 
Guitar Jones said:
Were you putting low gear set 904's in compared to the standard low gear in the 727? Because that could be the big difference especially with a heavier car and a small engine. If you compare them with the same ratios you won't get that kind of improvement.
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Yeah it was with low gear sets. Why would you run anything else? My cars were right at 3000 pounds if you call that heavy. I would bet that you would still see .3 tenths without the gear sets but I haven't done that yet. Thats part of the allure of the 904 too is that you can get factory low gear sets in the junk yard.
 
66plyValiant said:
guy on here did a nice post where only thing he had to cut was the transcross member that spot welds to the floor, floor is still factory
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Yea, I mulled over the A-518 for awhile and looked at alot of pics of the swap but the cons out way the pros for me. I noticed while moving the transmissions around my garage that the A-518s are quite a bit heavyer than the 727s. I also have a friend who knows 727s really well and he's going to walk me through a rebuild and the only labor cost is a case of beer, and I'll be learning how to tear it down and rebuild it. The cheapest rebuild price I was able to get on the A-518 is $1000 and on top of that theres not many converters available for it. Then there is the added time of the install and my wife is already making life hard cuz of all the time I'm putting into the car so the 727 became a no brainer. Any 904 install is years away so I'm simply going to save the 904 and maybe use it eventually. Thanks again.
 
Guitar Jones said:
The 904 is no way, no how going to be 3 to 4 tenths quicker. I have two friends, one a C/SA 440 6 pack car and the other a SS/JA 6 pack car that spent the big bucks for the ProTrans and only picked up about .08. For just a bracket car or test n tune/street car it's not worth the money.
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Not that everything you read is true but, I remember seeing a Challenger in a magazine. It had a full race stroker small block and was running 10.os with a 727. The guy made the swap to a 904 and it put the car into the 9.70s. I don't remember if he went with a low gear set, but remember , a low gear set will also mean a bigger RPM drop on the 1-2 shift so one would need to consider that as far as the cam and engine.
 
After I had my converter fixed I took the low gear out of my 904, it lost nothing. With my 340 in a 3000 pound car yeah it woke it up, but now with the stroker and at 2700 pounds it's just a wash, if the converter is right the low gear set just isn't needed.
 
I agree "Angry Johnny",them big blocks don't really care what there pulling.Swap outs from one to another are hard to compare when you can't even get two torque converters built to be identical! I hate to say it,but both of our bracket/1/8 mile cars are quicker and faster with glides.One is 3300 pounds with a 414" small block,the other is a fairly mild 440,it weighs 3200.I once added 300lbs. to the big block and it only lost 0.06 (trying to slow it for an index)while the small block has proven to pick up .1 per 100 pounds.
 
There is a difference when comparing 3 spd trans to 2 spd trans.... there is less drag with a 2pd vs 3spd, which gets more power free, i forget the formula for each gear but it's a fairly substantial difference.

The 904 didn't have the low 1st gear we all use in the 727, the 999 did, and the 904 and 998 didn't get the 2.7 1st until after 1980, so his trans if it is a 04 isn't the one to want to dick around with for the BB, which then it'll need an adapter anyway.


The reason that you went faster if you used the 999 gearing over the 727 was that the 999 had the 2.7 1st and 1.5 2nd and the 727 had the 2.4 and 1.4

So if you have the factory 727 and the same car has everything you do but it has the 999, you lose. If you have the 727 with the 2.7 1st and the same car has the 999 it becomes closer but it'll be close.

Going from the factory 727 gear to the 999 gear, you'll get a few tenths, going from the 2.7 1st 727 to the 999 you'll get close to a tenth probably, if he has a stl shaft you get the AL shaft and then you're faster till he gets the AL shaft....
 
Guitar Jones said:
After I had my converter fixed I took the low gear out of my 904, it lost nothing. With my 340 in a 3000 pound car yeah it woke it up, but now with the stroker and at 2700 pounds it's just a wash, if the converter is right the low gear set just isn't needed.
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This supports what I was saying, but your car is so fast and light that it probably wont have the typical results to expect from a 904/999. At some point a 727 is necessary, my turbo car has a small block 727 because of the torque capability. My point is that in my opinion the 904/999 has advanced quite a bit with new part available for it. This makes it a good choice for the hp challenged and in my experience will yield some imrovement in ET your results will vary just like anything.
 
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