When is a 904 too small?

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Valvebounce

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At what power level is a 904 no longer big enough?
Here's the story.
a couple of years Back My dad bought a drag free 904 w/full manual valve body from a reputable shop. The car is an Aussie Valiant hardtop. (Very similar to a 68 Dart) Runs a 340/418 stroker.
In the time it's been in there, the car has done around 1200 miles. and about 20 quarter mile passes. (best to date of 12.5@107 running a 2.92 rear end, and no rev counter yet)

thing it's doing is, under full power acceleration there's a flare on the 2-3 shift. So I messaged the shop who built/supplied it.
their reply was yeah, I'd say the High gear clutch is worn.
But after so little use??!! Then they said how much power you making? I dont know the actual numbers. but I told him what Times I've run.
Then they say yeah the 904 is limited in what high gear clutches it can take. And theyre considered a lighter duty transmission.

So are we dreaming to run a 904 in this car, or do you think he's downplaying that the trans they built isn't up to it?
20 passes, and 1200 miles.

What do you guys reckon?
 
Well there are 5 disc direct drums made for the 904, so I don't know what "limit" they're talkin about. Bucky Hess used to run a 904 in his SS/A Cuda.......with a Hemi. I think it went 8s and then he went to something else. Course, it was a build mojo. I would think you could build a 904 easily to withstand 600 HP on a pretty affordable budget.
 
Who installed it? What manual valve body? Did it need the throttle pressure/ kick down need to be set up on it? Have u checked the fluid in it? idling in neutral. Does it look dark or smelled burnt? Kim
 
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We installed the trans.
the whole transmission was bought complete from this trans shop.
currently running no kickdown at all because it's full manual. Should we be?
I told the shop we're not running one.
 
Depending on the kit or valve body u may or may not need it. U can try safety wiring the lever back if it has 1. U could also pull the pan and see what’s in there. Kim
 
Here's the deal on the 904 third gear clutch: The plates are thicker than the forward plates even tho they're the same size. Plus the thirds have grooves. The thickness and the grooves are to dissipate heat. And when you buy a Red Eagle overhaul pack they come with four thick grooved clutches for third. Grooves take up 20% of the surface. Thing is; reds in third can be thin and smooth because they can take the heat. You can run five frictions in the direct pack if you run the thin reds. SO-- if you run a 998 or 999 drum with 5 plates, you can actually put six in there. 4 smooths will be equal to 5 grooved. Grooves in a red eagle clutch are redundant. I buy reds ten at a time; all smooth thins. If your trans has a lot of end play and a worn third gear drum bushing, the rings will round off and leak. Set the end play at .010 with the trans ice cold. When it warms up, it will expand another .050. IF you follow the factory guidelines, your trans will have over .100 end play when hot. I want to try to run a 500 pump and direct drum in a 904 because it has two drum bushings; excessive end play won't cause it to wobble. Who's already dunnit?
 
I am wanting to say that the Bucky Hess/Herb McCandless type 904 drums in the heavily modified 727 case for the Hemi/BB bell are good for upwards of 800 plus horsepower wit the the 6 thin clutch discs. Of course the center support in the case helps control the already mentioned end play and wobble problems inherent in the 904 design so the realistic figures for a 904 drag trans is around 750 HP on a fully built trans brake unit is around 750 HP for a season on a set of clutches and seals. It seems like A&A's Rick Allison does a modified A500 front pump kit but it's been a while since I've looked at the site. Definitely worthwhile to get Tom Hands book on Torqueflite transmissions.
 
At what power level is a 904 no longer big enough?
Here's the story.
a couple of years Back My dad bought a drag free 904 w/full manual valve body from a reputable shop. The car is an Aussie Valiant hardtop. (Very similar to a 68 Dart) Runs a 340/418 stroker.
In the time it's been in there, the car has done around 1200 miles. and about 20 quarter mile passes. (best to date of 12.5@107 running a 2.92 rear end, and no rev counter yet)

thing it's doing is, under full power acceleration there's a flare on the 2-3 shift. So I messaged the shop who built/supplied it.
their reply was yeah, I'd say the High gear clutch is worn.
But after so little use??!! Then they said how much power you making? I dont know the actual numbers. but I told him what Times I've run.
Then they say yeah the 904 is limited in what high gear clutches it can take. And theyre considered a lighter duty transmission.

So are we dreaming to run a 904 in this car, or do you think he's downplaying that the trans they built isn't up to it?
20 passes, and 1200 miles.

What do you guys reckon?
12.5 is really good considering a 2.92 rear end. What stall do you run? Is the rear a 7 1/4?
I ask because I have the 2.92 rear, and a 450 hp 340 sitting in the corner of the garage. The car has a 273 in it, which is stock, but pairs with the 2.92 fine. I am hesitant to put the 340 in it because it seems like such a mismatch.
But, sounds like you did it, and it works well..
I have a built 904 like yours too, sitting on the garage floor. It has a 4k stall and manual valve body. All that just seems like to much for a 2.92 to me, but maybe not? Yes, a 8 3/4 is on my list..
 
Just got back from the A&A website. They have mostly high dollar race components; except for their 999 direct drum for $75 and their red clutch overhaul kits that contain five thins for the direct drum for $130. Course you'd need an extra one if you go for the 999 drum. I forgot to look for thin top pressure plates.
 
12.5 is really good considering a 2.92 rear end. What stall do you run? Is the rear a 7 1/4?
I ask because I have the 2.92 rear, and a 450 hp 340 sitting in the corner of the garage. The car has a 273 in it, which is stock, but pairs with the 2.92 fine. I am hesitant to put the 340 in it because it seems like such a mismatch.
But, sounds like you did it, and it works well..
I have a built 904 like yours too, sitting on the garage floor. It has a 4k stall and manual valve body. All that just seems like to much for a 2.92 to me, but maybe not? Yes, a 8 3/4 is on my list..

A 340 is just a big-bore 273......
What can make a 340 ugly is the cam and cylinder pressure.
The tendency for the majority of guys is to stuff a big cam into a 340 and rev it. But with 2.92s, 6000rpm makes a one gear run to 65 mph. To do that well, requires a 5600rpm cam which is about a 240@.050, and that is gonna want a 10.4 Scr. So far so good. Except for one little detail, the bottom end is now as soft as a 318LA 2bbl.
But no problem for you, you have a 4000TC; no bottom end to worry about.
Taking off HARD from zero mph is the big deal.
Say your 273 maxes out at 180 ftlbs at 2000 stall, and has a 904, and that 2.92, and say 27" tall tires Ok this conspires to put
180x2.45x2.92x24/27=1145 ftlbs to the pavement....... and you are ok with that. Remember that number;1145 ftlbs.
Now,say at 4000rpm your 340 maxes out at 380 ftlbs, and yur gonna keep all the rest as it is. Ok then
380x2.45x2.92x24/27=2416................... that's over double 1145....... where's the problem?
A footpound is a footpound.
Or say you had a TC that dragged your 340s rpm down to 284 ftlbs, and you had 3.91s. Now
284x2.45x3.91x24/27=2418 ftlbs .
Or say the TC dragged the torque down to 258ftlbs and you had 4.30s, you guessed it
258x2.45x4.30x24/27=2416 ftlbs.
Now if you had left that same 2000TC in there and your monster 340 maxed out at the same 180 ftlbs, 180x2.45x2.92x24/27=1145 ftlbs to the pavement ; and then I can see that being somewhat disappointing..... because if it doesn't spin the tires, it's gonna be a bit of a wait until the engine gets up on the cam.
All of these apply at zero mph. How they blam thru the rpm band is a whole nuther story.

Sure it seems like a mismatch, and it is..... for drag-racing;
but you might have the street-combo of combos right there.... Well except for one thing; I can't say how a 4000TC is gonna like traffic. I've seen it on U-tube and it was kindof cool, but I bet it sure sucks gas.It reminded me a lot of my daughters CVT equipped Forrester.
Hope this helps
 
A 340 is just a big-bore 273......
What can make a 340 ugly is the cam and cylinder pressure.
The tendency for the majority of guys is to stuff a big cam into a 340 and rev it. But with 2.92s, 6000rpm makes a one gear run to 65 mph. To do that well, requires a 5600rpm cam which is about a 240@.050, and that is gonna want a 10.4 Scr. So far so good. Except for one little detail, the bottom end is now as soft as a 318LA 2bbl.
But no problem for you, you have a 4000TC; no bottom end to worry about.
Taking off HARD from zero mph is the big deal.
Say your 273 maxes out at 180 ftlbs at 2000 stall, and has a 904, and that 2.92, and say 27" tall tires Ok this conspires to put
180x2.45x2.92x24/27=1145 ftlbs to the pavement....... and you are ok with that. Remember that number;1145 ftlbs.
Now,say at 4000rpm your 340 maxes out at 380 ftlbs, and yur gonna keep all the rest as it is. Ok then
380x2.45x2.92x24/27=2416................... that's over double 1145....... where's the problem?
A footpound is a footpound.
Or say you had a TC that dragged your 340s rpm down to 284 ftlbs, and you had 3.91s. Now
284x2.45x3.91x24/27=2418 ftlbs .
Or say the TC dragged the torque down to 258ftlbs and you had 4.30s, you guessed it
258x2.45x4.30x24/27=2416 ftlbs.
Now if you had left that same 2000TC in there and your monster 340 maxed out at the same 180 ftlbs, 180x2.45x2.92x24/27=1145 ftlbs to the pavement ; and then I can see that being somewhat disappointing..... because if it doesn't spin the tires, it's gonna be a bit of a wait until the engine gets up on the cam.
All of these apply at zero mph. How they blam thru the rpm band is a whole nuther story.

Sure it seems like a mismatch, and it is..... for drag-racing;
but you might have the street-combo of combos right there.... Well except for one thing; I can't say how a 4000TC is gonna like traffic. I've seen it on U-tube and it was kindof cool, but I bet it sure sucks gas.It reminded me a lot of my daughters CVT equipped Forrester.
Hope this helps
Good info for sure, thanks!
When I bought my 340, it was already built. It has roller everything, .589 lift cam, crazy compression, Miloden gear drive, on and on, so its not really set up as a low rpm engine. I'd really have to de-tune it to run that 2.92.
I also feel like the motor would just break that old 7.25 rear as well with some hard bangs to it.
The thing is, I don't want a race car, lol..but something I'd like to have better performance than the 273 gets me.
 
Well yeah a 450hp 340 with crazy compression, has the ability to explode that 7.25 at a moments notice..... if you choose to. But the operator is in charge of that, right.
It sounds like that 340 is fully optimized and detuning it is likely gonna cost some coin. Three or Four cam sizes is well beyond a gasket swap.

Gears are the 2.73s friend
 
At what power level is a 904 no longer big enough?
Here's the story.
a couple of years Back My dad bought a drag free 904 w/full manual valve body from a reputable shop. The car is an Aussie Valiant hardtop. (Very similar to a 68 Dart) Runs a 340/418 stroker.
In the time it's been in there, the car has done around 1200 miles. and about 20 quarter mile passes. (best to date of 12.5@107 running a 2.92 rear end, and no rev counter yet)

thing it's doing is, under full power acceleration there's a flare on the 2-3 shift. So I messaged the shop who built/supplied it.
their reply was yeah, I'd say the High gear clutch is worn.
But after so little use??!! Then they said how much power you making? I dont know the actual numbers. but I told him what Times I've run.
Then they say yeah the 904 is limited in what high gear clutches it can take. And theyre considered a lighter duty transmission.

So are we dreaming to run a 904 in this car, or do you think he's downplaying that the trans they built isn't up to it?
20 passes, and 1200 miles.

What do you guys reckon?
My ex-employer ran a 904 behind a 500 cubic inch Steve Schmidt pro-stock engine. As I recall the engine was in the 1200-1300 HP range. There is a photo of the car on their web page: www.tcsproducts.com, and you can see what high performance products they manufacture for the TF series of transmissions.
 
Like others said, Alto's PowerPak is the hot tip for the 904-998-999. I too have played with the 904 guts in the 727 and it is amazing how well the multiple small thin frictions hold up when set up correctly.
 
I rebuilt a 904 6 yrs. and approx 12,000 hard miles ago using the Alto thin red's for my 3450 lb Cuda and it's holding up fine behind my 408 that's a torque monster and makes about 475 hp. I'm not even using a manual VB which provides more clutch pressure to reduce the chance of slippage. Just a stock VB with a TF-2 kit. The biggest problem I have is keeping back tires on it, lol... I can't say the exact limits to them but if you build them right they'll for sure take a whole lot of power
 
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