How much power does a 727 consume?

I ask because I have a D150 with a slant 6 and a 727. The /6 guys are all saying that the 727 saps too much power to run vs a 904.
My problem is that I have had many of both a 904seems quite weak, I don't have much luck with them.
Being that I have the 727 already it seems like a bonus to me, many are saying it is really a curse.
I have heard 15% to 25% I have heard "about 100 hp" which can't be because that is about All my stock slant makes. If that were true the truck would not be able to pull itself at any speed above a crawl.

I am going a different direction with this one, previously on past-owned vehicles, I did the typical "yank the slant 6 and put a V8 in its place" but I am experimenting with building up another slant 6 for this one, to see what I can get from it.

Via a google search I came upon a discussion on trans power consumption on a Dodge charger forum of which I am not yet a member.
I did recognize some names in that thread over there that I see here also. John Kunkel among others. Hopefully he sees this question posted here.
While I definitely realize that I will most likely have to overhaul this trans just because of it being 35 years old if nothing else. I know they used ALOT of 904s in half ton trucks as well but I'm not looking at going that direction. If I swap to a different trans it will be something with an OD so being as how I have never seen a 500 or 518 cast with a slant bell housing, it will probably be converted to a manual.
But for now the 727 stays. I may look into some other torque converter to slide in when I put my fresh engine in, and possibly some sort of a shift kit to hopefully improve on (cut down on) the amount of power that the trans robs, but definitely not looking to do anything as crazy as putting 904 guts inside as many racers do, this is a truck, and 90% of the time it will just be a daily driver, but I do occasionally want to pull my pop-up with it or maybe my utility trailer with a garden tractor on it.
Any ideas?

Playing devil's advocate here......with all else being equal how much more zip would I gain and/or mileage (which is not my #1 goal here btw, but had to ask) what would I gain by going to the weaker trans?

How much does converter choice have to with the amount of power lost/consumed by the tranny?

Another thought; (and was brought up in the thread in the Dodge charger forum)
Can I assume that a given trans will absorb the same amount of engine power if the engine ahead of it makes 100 hp or if it makes 300 hp? (For that last part let's assume for a minute that I could directly bolt up a bigger engine to this same trans)
I have heard that it takes 40-50hp to maintain a steady speed going down the road. Most HP above that that isn't eaten up by the drivetrain, is most useful in getting up to that speed at a reasonable rate.
But if my trans takes "100hp" to run and 40-50hp to maintain speed, I don't see how it is possible to even get the truck moving,and up to speed as there's 150hp right there, and supposedly stock (current) slant 6 is only good for 100hp at best "it don't compute"
150 is a common hp rating I see on even a 318 after they went to"net" ratings. So that being said, even a 318 wouldn't have enough to get the truck moving and keep it there. So those power consumption numbers can't be true.

Isn't the excepted loss hp number 20% from flywheel to rear wheel?

Many, many years ago I read the 727's were pulling ~ 45 hp, and the 904's ~ 25 hp. In my '82 Ramcharger 318 I had A998 w/o troubles. Later I went to a '91 360 with the A998, later I went with an A500 due to swapping in a 9.1/4 diff w/ 4.10 gears. Never broke any of them.

Short of a dyno there is no steadfast answer here. It varies with HP in and RPM run. Steady state versus accelerating.

Lots of variables for a one size fits all answer.

727 is much heavier than a 904 so, there is that

Chrysler did some testing in the '70's between a 727 and 904 transmissions in drag racing. With everything else being equal, including converter specs, a 904 was about .15 seconds faster in the 1/4 mile than a 727.

Nice thing about a 904 is that you can get a 2.74 low gear from a later 904/988/999 even if it's a lock-up trans.

And that is constant whether behind a weak, stock 318, or a Race Hemi? still 20%? an engine (using stock published specs as I can remember from over the years, but the variation given youll get my drift) a 150hp 318 takes 20%..... a 425hp 426 Hemi also takes 20% of its power to run the 727... so a 318 would use 30 hp and the Hemi would take around 85 hp to run the same transmission? somehow that doesn't seem right.
and mr "300".... I never really "broke" anything with a 904, they just seemed to "burn up the frictions" at what seems premature usage, to me. and definitely more often than any 727 I have ever had.....

A flat % as noted is misleading, as noted: the same trans shouldn't require more power to run with different engines.
I think it's a set HP/TQ level, but I can't recall a trans-dyno test to establish precise data.
There's no doubt some power required to drive a manual trans as well.
Seems pretty well established that a 904 consumes less power than a 727, and that the 727's beefier nature makes it more bulletproof.
As my drag car went from under 600HP to about 640 or so, its basically-stock 904 went through clutches & bands more quickly.
But to be fair the idiot driver (me) left in 2nd gear a few times.
Upgrading to a CRT 904 and keeping my hand off the shifter at launch has fixed those issues.

Just a couple comments, first about cruising horsepower. If you have a vehicle that is getting 20 mpg at 60 mph, you are burning 3 gallons/hour. A gallon of gasoline weighs about 6.3 pounds so you are burning about 18.9 lbs/hr. A reasonable estimate for BSFC is 0.5 lb/hp-hr so you end up with about 38 hp. As to a TF "consuming" power, where would that due to? Hydraulic losses due to the pump and thermal losses due to the converter. What are those? I haven't a clue but I can't believe figures in the 50-100 hp range. Even the old Fluid Drives weren't that bad!

You may get different results based on which Wallace calculator you use. But on one of them, I was getting 20-25 HP difference will make about a .15 second ET difference in the 1/4 mile in an 11.- second car.

I don't think different converters use different amounts of power. They determine how efficiently the power is being used based on their stall/flash/slippage configuration in relationship to the engine's power curve and the application it's being used in.

Check his response here:

JK Response linky

These numbers are from an article in Car Craft Magazine.

Powerglide_____18 hp
TH-350________36 hp
TH-400________44 hp
Ford_C-6______55-60 hp
Ford_C-4______28 hp
Ford_FMX______25 hp
Chrysler_A904__25 hp
Chrysler_727___45 hp

Sniper above mentioned steady state vs accelerating. Changing the rate of acceleration on an engine dyno will effect the measured power output. The quicker the RPMs come up, the more power is lost. On the strip, the greater rotating mass of the 727 may cost 30 hp, but at a steady 2500 rpm the difference may be minimal.

Car Craft isn't know to be overly scientific in it's procedures.

I can pretty much guarantee a 727 isn't sucking 45 HP out of a 100HP slant six.

Don, put the 727 in it and tell people it's a 904. That way everybody happy!

If your concerned about how much power a 727 may take away from your slant 6, after you install the 727, add more power to the slant 6. Problem solved!

If you had both transmissions in the same vehicle, I suspect the 904 would feel faster, the lower 1st gear and the smaller rotating assembly would both be something you could feel, if both were in the same vehicle. To compare the two while in different vehicles, it would be pretty hard to pin any difference on the trans alone. While riding in a vehicle, I doubt there is anyone that could tell you which transmission was in the vehicle by the ride alone, without looking at it.

As far as breakage, I've broke them both. from my perspective, the weakest point on a 904 seems to be the front pump/torque converter hub. Every failed 904 I've had, had a cracked converter hub and a damaged pump. Gene

I don't have to put the 727 in.... the factory did that for me on the assembly line already!

More curious I guess, than "concerned". just because of what I'm seeing on a couple of other forums I am on.....

Back in the 80s/90s, I replaced more dead 904s with 727s than I care to try to think back and count. Most of the dead 904s were just "burnt up" clutches, steels and seals..... , not "hard part" carnage//// though I do remember a few cracked converter hubs.
Back then, one of them that I 727 swapped, was in a 318 powered '81 B-150 short wheelbase vans. It belonged to a friend's dad and he pulled a pretty big camper with. He burnt up the 904, had it rebuilt. (by who I don't remember.) I did the R&R and he took it for a "bench rebuild" somewhere. We added a pretty big aux fluid cooler along with the rebuild. A couple years later, it blew again. This time I talked him into a 727. That trans never blew again. My buddy's dad had bought this van brand new, and it was his daily driver for work in between camp trips. As I remember, I believe he said at one point he "lost" a MPG or maybe 2, since the 727 went in on daily driver duty.

among others that I had done 904-to-727 in, were a 76 Charger, a 75 Cordoba, an 85 Diplomat, and then some. I did do a few 904-904 swaps back then too.... I did notice that stock converters in 904s seemed "whinier" than 727s did, especially when driving slow as you would going up+down rows at a store looking for a parking spot where you would hold 1st for a while..... I did notice the difference in take off power between 904s between ones with and ones without the lower 1st.....

and Gene..... I have another slant 6 in the works, that is getting that "Tim Taylor" "more power" treatment for that truck, as we speak.

I've killed at least 2 904s more then just clutch wear and also end up going to 727. These were always behind 360s. I never had much problems with 318s.
For a slant 6 if you already have the parts to switch to a 904 that's the route I would go because you probably would notice a bit of a difference with it.

I run 904's in my junk. The only one I've wounded was a pump gear, and it cracked the snout on my PTC converter. 4000 on the chip on the brake could have something to do with it.

I don't agree with those Clowns' numbers either, but it is something to go on. A percentage is what needs to be determined:

The generally accepted number for transmission AND differential power loss to the tires is 20% for a manual and 25 to 30% with an auto.

I did a bit of math based on their numbers and I come up with roughly 7% hp difference by dumping the 727 and switching to a 904.

I have switched from a 727 to an A833 and the 727-based 46RE to NV3500 with identical engines and the seat-of-the-pants difference was night and day. If anything happens to my 46RE it's getting replaced with a 904-based 44RE.

Everywhere: from idle to redline.

You give it 10% throttle at 1500 rpm in a manual and the vehicle moves forward. Do the same thing in a 727 or 46RE and almost nothing happens. The lower the horsepower (318 for example) the more obvious the power loss is. That, and the real proof is seen at the fuel pumps.

Understood - let me rephrase the question.

In high gear in any manual with 1 to 1 ratio, or 727 in high gear - the only real difference is the converter and loss from running the pump.
Yes a small weight difference in internal parts but that’s it.

The real test would be to take both the 833 and a 727 lockup and do an acceleration test between the two keeping the 727 locked up.
I doubt you would feel the difference.

All the chatter about differences between the two - depends on thru gear acceleration - the manual has a extra gear, lower first gear, etc., can’t compare the two this way.

I don’t have any records of parasitic loss on the autos, at Chrysler we had a test stand that measured that.
But some guys have gotten close here in their observations, by using on track performance. Assuming stall speed and converter efficiency remain close in their tests.

Yes, and I had "when my 46re is locked up in 4th gear you get a sniff of how much power you are losing" typed up, but, I deleted it because the predicted responses would have misunderstood what I was talking about

I know you get it, but others have a pedal to the metal mentality and don't have the patience to drive an auto in top gear lockup without getting the big downshift to third or passing gear.

Isn’t there also the torque multiplication of a converter that comes into play? Lot of variables if you think about it!

Ive had 904s die behind /6, 318 and 360's. All 3. common denominator.. 904. and I have never owned a race car.

truck already has the 727 in it, that's how it came when I got it. seems to be working fine. All I have done to it was a pan drop/fluid and filter swap, as the old pan gasket was leaking. Had not planned on pulling the 727. as long as it continues to work as is it aint coming out.
And no, I don't have a 904 sitting around collecting dust whether for /6 or V8.
I bring this up for a couple of reasons.... I can't be the only one that has ever wondered teh answer to my original Q, and a couple of certain guys on various forums seem to think there is something "wrong" with having a 727, that anyone would be crazy for wanting one, it "must" come out, it needs to be scrapped, you "have to" have a 904 "only" behind a slant 6 or small block, a 727 is a waste, etc......
When I build something I tend to the side of "overkill" which a 727 behind a slant certainly is. While I have had trouble over the years with both types of transmissions in various vehicles I have owned, by far more headaches and breakdowns from 904's than 727s...
In my experience a 904 does not seem worth the hassle and is more likely to burn up in any given vehicle. It has never seemed "worth it" to build up a 904/ when all I usually have had to do for better durability was a 6" shorter driveshaft, a fatter yoke, a different dipstick and tube, and bolt in the 727. no more effort to put in either trans over the other, since all these parts all have to be "handled" in the swap process anyway

A properly built 904/998/999 should not fail behind a small block street motor.

Does it have less clutch capacity than a 727, yes.
Does it handle more torque than a 727, no.

Don’t take this wrong, but given the engines you mention, sounds like there are issues with the build, cooler capacity, something.

In answer to your original question, I think you would be well served by building a good lockup 999 using the later 2.77 low gear planetary package.
Good mileage, good scoots off the line with plenty of durability for your application.

Has the ear tear off the sheet metal band in an a998 twice behind a 360. Finally got the earlier style forged band and that fixed that.

Seen flex bands rip the welds before in both small and large box trans. Not dependent on which engine it’s behind.
It’s all a matter of quality control at the band manufacturer.

Improper design developed for a certain purpose usually results in a design change later because of frequent failures.
We used flex bands for years and years with no issues in production. A bad design wouldn’t have lasted that long.

that may be it.... never "built" a 904/998, most were either stock and never having been into (no farther into than needed for fluid/filter swap) or rebuilt to "stock" specs. never really had to build up a 727 as I have rarely had anything very "Hi-Po".... a manifold and carb swap here and there..... back in the late 80s I had a 75 Cordoba. originally a 360, I swapped a 318 into it, and I kid you not, I had the trans out (and after the first few, apart, as well) about once a month. That was also my 1st exp with a shift kit, I put a "B&M" in it.. '80s "Super Shops special". and the particular trans that I had that shift kit in would bark 2nd gear without even trying, but I could never get it to "turn a tire" off the line, to save my life,.even with wet pavement. It was a peg leg 2.76, 8-1/4. I probably had 5-6 trannys for that car, the last year I had it, I'd pull one, put the other one in, rebuild the one I pulled... next month wash, rinse, repeat. Got sick n tired of it. the car "sounded mean," but was probably the worst turd I have ever owned.... I still like the looks of those cars though.


I was around 19 or 20 when I had that car. I junked it when I bought my Ramcharger, because I was tired of spending my paychecks on ATF for the Cordoba. .... now that Ramcharger, I had all sorts of "fun" with that thing in the local farm fields and over into Indiana's sand dunes near Lake Michigan and I never had to touch that trans.....

they were factory bands. First time was shortly after I replaced the original 318 with a mild 360. Pulled the trans, found the issue, put another factory band out of a spare trans in. Same thing happened. So I pulled the forged band from a 68 trans and no more issues. Maybe I am just unlucky, but that 360 wasn't all that warm. Just a Performer intake, 600 cfm Performer carb and a 340 4bbl cam, it was originally a 2bbl.

[quote=slantzilla]I run 904's in my junk. The only one I've wounded was a pump gear, and it cracked the snout on my PTC converter. 4000 on the chip on the brake could have something to do with it. [quote]

I have three four speed cars with big blocks, I guess I have 135 free horse power.

If you're looking for efficiency you should be looking for something with a stick. Anyone who's driven the same gutless vehicle in an auto vs a stick will be able to tell you that!



I've heard that saying peddled my whole life and I still don't understand how a slipping converter is any different from slipping the clutch at launch on a stick.

Because a torque converter (when the output shaft is stationary e.g. at the moment of launch) multiplies the input shaft (engine) torque by an amount that varies with converter design, generally around 1.8 to 2 times. This multiplication quickly drops off as the rest of the driveline starts turning and reaches essentially 1:1 at high driveline speed.

Converter slip when operating above stall speed is a different animal. Then it's just wasted power.

The manual transmission's clutch transmits no torque to the output (transmission input shaft) when completely disengaged, and as the pedal comes up, passes more and more engine torque to the input shaft. But it never exceeds 1.0 (no multiplication) and that's when fully engaged with no slip.

I believe its because in a torque converter the input and output are fluid coupled together so it kinda acts like a gearbox - a gearbox is a torque multiplier. In a slipping clutch, you aren't coupled - just burning it off as heat.

See I don't know if that's right though. When you slip a clutch you create a variable ratio between the crankshaft and the transmission input shaft. With any sort of gearbox an increase in ratio creates a corresponding increase in torque. Yes clutch slips does burn off some energy as heat but so does a torque converter or any hydraulic pump for that matter.

In my opinion a properly adjusted "soft clutch" can have many benefits on a high horsepower manual shift car. It can help with traction and is easier on parts.

However it does not create any additional torque, any energy not passed to the rear wheels is turned into heat.