727 or 904?

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Magster65

Magster65

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Saanichton BC Canada eh.
It's behind a 408 in a Dart. I'm gonna race a couple times but mainly street use on some sticky tires (I'll be hard on it). Advice says to use a 904 for less parasitic drag. I agree.
Question is what do I need to do to the 904 so it will survive?
2800-ish converter.
Thanks
 
Race.....youl be hard on it....... and a 2800 converter? Seriously? Put 4500 or 5000 stall speed converter behind it. Sheesh. Save yourself the $ and put the stock one back in. Nothing wrong with a 5000 stall in a hot street car. Yes, I have personally done it and would again.
 
Thanks for the converter advice but I'm asking about the transmission.
d55dave said:
Race.....youl be hard on it....... and a 2800 converter? Seriously? Put 4500 or 5000 stall speed converter behind it. Sheesh. Save yourself the $ and put the stock one back in. Nothing wrong with a 5000 stall in a hot street car. Yes, I have personally done it and would again.
Click to expand...
 
Yes I have a couple of both.
The info I'm after is what mods need to be done to reliably hold a 904 together with probably double the power they were designed for. I don't mind spending some money on it it's a doable thing.

d55dave said:
Do you have a core to start with?
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Cool, this one is easy- the 904 hands down. Now I myself can't be givin an exact $ number, but I'm to understand it to be around 6 hundred or so in extra heavy duty parts.
 
Ok cool. Do we know which parts we need to upgrade?
I have a trans guy but he doesn't build that much race / high hp stuff. I mentioned this site and he said to ask and see what we learn.
Appreciate everyones input ty

j par said:
Cool, this one is easy- the 904 hands down. Now I myself can't be givin an exact $ number, but I'm to understand it to be around 6 hundred or so in extra heavy duty parts.
Click to expand...
 
Magster65 said:
It's behind a 408 in a Dart. I'm gonna race a couple times but mainly street use on some sticky tires (I'll be hard on it). Advice says to use a 904 for less parasitic drag. I agree.
Question is what do I need to do to the 904 so it will survive?
2800-ish converter.
Thanks
Click to expand...
You can contact Chris Andrews here in Colorado. He specializes in 904s.
https://www.facebook.com/duster346
 
55 custom royal lancer. Same car as a regent, different trim level.

Many things to consider, for the question of 727 / 904. What driveshaft do you have ( 904 is longer), what is your hp level, what cores do you have, what year are they from, what condition are they in........?
 
The mid 70s 904 I had was for lack of better terms beefier than the 68 one I have.
Also If you can rebuild a carburetor you have twice the skill needed to rebuild a 904. Almost absolutely no special tools required at all. no special skills needed, just take it apart and put it back together with the new beefier parts. Remember I'm not sure if they'll be machine work needed but I think something about a removable sprag in the back to make it easier and serviceable or last longer I'm not sure. But like said people who really know will chime in soon. If 70aarcuda chimes in listen closely would be my advice.
 
Now I say all this about rebuilding it because I have one 904 rebuilt under my belt this last summer. It was just behind a 318 but it was completely rebuilt with a stock rebuild kit and stock clutches with the stage 3 shift kit and man that thing worked well. I was tempted to try it behind my Stroker and think it would have lasted for quite some time but I'm sure that motor it's broke everything else in front and behind it and would have broke that transmission had it not been beefed up after some good abuse.
 
Love the car.
I'll make a driveshaft and our converter guy has a drive shaft balancer. Good there.
The engine hasn't hit the dyno yet but it's similar engine to the 465 hp and 500 tq. crate motors (with some porting).
I don't know what the cores are but my bro has a wrecker, I have access to most anything.
Looking for info on specific parts that might fail.
Thanks

d55dave said:
55 custom royal lancer. Same car as a regent, different trim level.

Many things to consider, for the question of 727 / 904. What driveshaft do you have ( 904 is longer), what is your hp level, what cores do you have, what year are they from, what condition are they in........?
Click to expand...
 
If you are serious about racing and safety, here is what I've been using. If you cannot afford a dedicated race car and want to do street/strip with the same vehicle, then this might be overkill:
I've been racing a 727 behind about 750 hp for 4 years now.
1. Ultimate bolt in sprag from A&A. Sprag is Weakest part of tranny. Approx $200
2. Hardened steel or billet aluminum drum from A&A. 2nd weakest part. Known to grenade if you break u-joint and overrev motor. About $700 for steel
3. Reverse pattern manual shift valve body, with or without low band apply. This also allows you to safely raise pump pressure a little for firmer shifts $250 ($1,000 with transbrake)
4. Don't run transmission fluid. Use #303 hydraulic fluid. Again firmer shift, less slippage. It's cheap at Tractor Supply. $25 for 5 gallon bucket.
5. A good SFI rated flexplate. ATI is a good brand. use ARP converter bolts and ARP crank to flexplate bolts. $125 for flexplate
6. 5500 stall 8" converter. Performance Torque Converters is the one I use. $700-900.
7. Transmission blanket or shield. $125-400.
8. A good transmission cooler with it's own fan. $150-750.
I have a small block case with as many big block internals as possible. 4 gear planetary, big pump. Don't know if you can do that with a 904.
As I said it's been raced about twice a month 9 months out of the year for 4 years. Had it taken apart 2 years ago and it didn't even need new clutches!
 
search 904 recipe here. There is a list of parts that will make a 904 run.

904 race tranny Recipe

For a kit to start with transtar 12008C from northern auto for about $100. Buy the other stuff in the recipe.

I don't run anything but the stock clutches. Put 5 in the front drum using thin rear frictions/steels. It won't be $200 cheap to rebuild it, but with the right parts, it will hold up fine. Plenty of stroker SB's running transbraked 904's out there.

There is a reverse wound spring so the 24 spring kit may not be required. Probably a bunch less $

No expensive front drum required using a 904, that's a 727 issue!

Just say no to low stall converters :)
 
Thanks for sharing this. You have a lot more power than I'll have. I'm not a trans guy myself but any info I get here on either I'll pass on to my trans guy.
Cheers

RockinRobin said:
If you are serious about racing and safety, here is what I've been using. If you cannot afford a dedicated race car and want to do street/strip with the same vehicle, then this might be overkill:
I've been racing a 727 behind about 750 hp for 4 years now.
1. Ultimate bolt in sprag from A&A. Sprag is Weakest part of tranny. Approx $200
2. Hardened steel or billet aluminum drum from A&A. 2nd weakest part. Known to grenade if you break u-joint and overrev motor. About $700 for steel
3. Reverse pattern manual shift valve body, with or without low band apply. This also allows you to safely raise pump pressure a little for firmer shifts $250 ($1,000 with transbrake)
4. Don't run transmission fluid. Use #303 hydraulic fluid. Again firmer shift, less slippage. It's cheap at Tractor Supply. $25 for 5 gallon bucket.
5. A good SFI rated flexplate. ATI is a good brand. use ARP converter bolts and ARP crank to flexplate bolts. $125 for flexplate
6. 5500 stall 8" converter. Performance Torque Converters is the one I use. $700-900.
7. Transmission blanket or shield. $125-400.
8. A good transmission cooler with it's own fan. $150-750.
I have a small block case with as many big block internals as possible. 4 gear planetary, big pump. Don't know if you can do that with a 904.
As I said it's been raced about twice a month 9 months out of the year for 4 years. Had it taken apart 2 years ago and it didn't even need new clutches!
Click to expand...
 
Perfect.
Not worried about the budget so much... that was blown building the 408. haha
One failure and it negates anything you saved on the build.
Thanks

crackedback said:
search 904 recipe here. There is a list of parts that will make a 904 run.

904 race tranny Recipe

For a kit to start with transtar 12008C from northern auto for about $100. Buy the other stuff in the recipe.

I don't run anything but the stock clutches. Put 5 in the front drum using thin rear frictions/steels. It won't be $200 cheap to rebuild it, but with the right parts, it will hold up fine. Plenty of stroker SB's running transbraked 904's out there.

There is a reverse wound spring so the 24 spring kit may not be required. Probably a bunch less $

No expensive front drum required using a 904, that's a 727 issue!

Just say no to low stall converters :)
Click to expand...
 
I'm also doing a 904 for a 408 stroker.

20170904_163942.jpg
 
The old parasitic drag notion has been around ever since some joker put a 727 from a new Yorker into a Duster. Problem was, he used the New Yorker converter. A lot lower stall than a 904, hence the 'parasitic drag'. Racers run the 904 so they can get every tenth available, but for the street, it isn't worth it. You can actually drop a 904 clutch THROUGH a 727 clutch; there's that much difference in strength. Just a bone stock three clutch direct 727 is twice as strong as a 904. In my 37 years rebuilding them I've only seen one blown sprag; and it was in an old New Yorker being driven by a senior citizen who got stuck in the snow. Hopped up 904's are good for making a ton of money for rebuilders off people who are afraid to cut their driveshaft.
 
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