Anyone actually running a late model automatic behind a flat six?

[papajohn]

I know a lot of you are against running a late model transmission and most seem to favor a t5 if they do upgrade. I have also seen comments posted that a late model automatic "would probably" take too much horse power...etc.

 

So what I am looking for is real world input from someone who has done it. Was it worth it? Does it really steal all the power? What trans are you running, what adapter, rear gear ratio etc?

 

thanks

 

 

[Young Ed]

I know a lot of you are against running a late model transmission and most seem to favor a t5 if they do upgrade. I have also seen comments posted that a late model automatic "would probably" take too much horse power...etc.

 

So what I am looking for is real world input from someone who has done it. Was it worth it? Does it really steal all the power? What trans are you running, what adapter, rear gear ratio etc?

 

thanks

 

We had a forum member running an auto behind his flatty with no issues. It was John Burke and he's sadly passed away. Try searching for some of his old posts.  

[Don Coatney]

What is the logic of an auto transmission taking too much horse power? Where did you hear this? I dont understand?

[Plymouthy Adams]

without doing an actual dyno reading on your given vehicle utilizing both setup for comparison...figuring any loss is a guess at most.  Avg rule of thumb for power loss is calculated roughly at 10-15% utilizing a manual shift and 15-20% utilizing an automatic...the differences is not that great...however considering some of the advantages....no clutching, no up-down arm slinging shifts,  torque multiplication of the converter for actual smoother applied power and such...better towing capacity....the power trade off is not that significant..the gain of smooth acceleration is unsurpassed....on my 54 powerflite 230 Plymouth the take off is very smooth and quicker than one would think...

[greg g]

Check your local municipal air port for Clark tractor airplane tugs and other ground support equipment.  Many of the later ones made int he 60' and 70's had torqueflite transmissions behind Mopar flathead 6's.  A lot of them have been consigned to surplus status and a re just sitting around.  And like Tims says the torque converter easily makes up for any horses the automatic might let escape.

[papajohn]

Thanks for the info guys.

 

Don- I was reading some forum posts (not sure if it was this forum or a different one) and a couple guys commented that having only 100 HP, putting an A/T on it would not be good.

[hkestes41]

Get with 73RR over on the HAMB. He has a lot of info on transmission swaps for the flathead Mopars. His company is Quality Engineered Components and linked below.

 

http://www.qualityengineeredcomponents.com/

[hendo0601]

The chrysler 904 automatic transmission was used behind countless slant 6s which didnt make gobs of power either. Testing on these has proven that they are in fact one of the most efficient automatic transmissions ever made. The loss of power through an A-904 is nearly as low as most manual transmissions. The 727 is about as bullet proof as they come, but seems to be a bit overkill behind a flathead but by all means will work. The modern A508 is basically a 727 but with overdrive. As was stated before, 73RR on the HAMB makes adapters to fit these automatics to the back of the flatties. He is a wealth of information on this topic and will set you up the right way.

[Frank Elder]

73RR is wayfarer on here..................

[Don Coatney]

I can understand a slight slippage resulting in loss of efficency but with a lockup converter there is no slippage nor loss of efficency.

[wayfarer]

The information that I have gleaned from some of the old trans gurus is that the planetary gear set in the 727 consumes about 50hp just to drive the gears and the 904 is a bit less, in the 25hp range.

All automatics will have some parasitic losses, depending on the internal designs. (I don't know (or care) how bad/good the gm and fords are so cannot opine.)

I do not recommend the 727 for use on any inliner for this reason alone and have designed my adapter accordingly. As mentioned, the 904 served the /6 famously and is readily available in v-8 form for swapping....no, the /6 trans cannot be used due to the starter location.

[Don Coatney]

I am trying to understand this. Where does that lost horse power go? Is it consumed as heat generated by friction? Is it consumed by attempting to get an object at a standstill in motion? And if this is the case would a vehicle with a standard transmission also consume 50 or so horses to set it in motion? I hope I am not over thinking this but I really do not understand why a 727 would consume 50 HP just to drive the gears?

[wayfarer]

Good questions. It has been long awhile since I sat in my ME classes so I cannot effectively communicate the details, but, in very basic terms, anything that requires movement will require hp (or torque) to make it move. If you walk up a flight of stairs, folks will refer to burning calories but that is easily converted to hp, lifting your beer stein, same deal. The auto trans has a vast array of gears that require movement, driven by the converter. The front and rear pumps(where equipped) require some motive force to operate.

Pumping enough viscous fluid to make it all happen does indeed generate heat as well and all of this eats up power.

Manual transmissions are more efficient simply because you have direct transfer of motion from gear to gear, although some power is lost in overcoming the friction of the gear interface as well as the gear lube. There is a reason why a manual trans get warm/hot when driving but nothing like the atf if you attempt to drain it without a cool-down period.

[Plymouthy Adams]

there is always HP loss to the wheel through any tranny and differential....cannot be helped..however the concerns of the 727 behind a flattie is not that big of an issue as the very transmission was used successfully behind the /6 in truck and vans for many years and having said truck and tranny set up in factory camper special short bed..let me assure you it was very much up to the task of about any job you put toward it and would do highway speed with no problems whatsoever..  While an automatic will be more spinning mass...do not forget the very application of torque multiplication that is in effect here...it is torque that does the work...no the HP..little guide for those that may be interested..I cannot in any manner vouch for any of the stated figures..just a little quide as posted by a famous hot rod mag...

 

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

[greg g]

friction, heat, pumping losses, clutch slippage, fluid inefficiency, HP don't get lost they get used..

[hendo0601]

It is much the same way as using a supercharger actually requires HP for it to operate vs a turbo which has no parasitic loss of power because it is driven off of the exhaust. The supercharger is a big rotating mass that requires power to move, the same as the internals of your transmission. All of those gears and pumps take power to operate, and that power is taken from somewhere. This is why you will see someone advertise their car as having a "450 HP engine at the crank, 365 at the rear wheels." Measured at the crankshaft there is no transmission, driveshaft, differential etc there to rob power from....sending that power down there to the rear wheels costs you. As wayfarer (73RR) stated the 727 is definitely not recommended but a small block 904 will work like a champ. I have owned many 904s behind both /6s and v8s and they have been absolutely bulletproof. They can be built to withstand massive amounts of power as well, but I doubt a flat 6 will be doing much of that. If you do decide to go with a 904, I recommend going to a deeper pan and running a nice trans cooler with plenty of air flow. The killer of any automatic transmission is heat. The extra fluid and a functional trans cooler will keep your fluid from getting too hot and keep the insides of your trans happy. 

[martybose]

It is much the same way as using a supercharger actually requires HP for it to operate vs a turbo which has no parasitic loss of power because it is driven off of the exhaust. (snip)

Actually there is a parasitic loss due to the added restriction in the exhaust prior to the turbo, as well as the general lack of tuning length in a turbo header.  It's just impossible to quantify the way that the horsepower needed to drive the supercharger is, and is relatively insignificant compared to the massive HP boost a turbo can deliver.

 

interestingly, the prevailing horsepower number for top fuel superchargers is in excess of 500 HP, so if the engine is putting out 9000 HP, the crankshaft is delivering over 9500 HP .......

 

Marty

[Robert Horne]

there is always HP loss to the wheel through any tranny and differential....cannot be helped..however the concerns of the 727 behind a flattie is not that big of an issue as the very transmission was used successfully behind the /6 in truck and vans for many years and having said truck and tranny set up in factory camper special short bed..let me assure you it was very much up to the task of about any job you put toward it and would do highway speed with no problems whatsoever..  While an automatic will be more spinning mass...do not forget the very application of torque multiplication that is in effect here...it is torque that does the work...no the HP..little guide for those that may be interested..I cannot in any manner vouch for any of the stated figures..just a little quide as posted by a famous hot rod mag...

 

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

With this kind of HP loss, I will have to stay with my little 5 speed Ranger setup, in my 80HP Coupe...

 

Yesterday I was doing 55mph at around 1600 to 1800 rpm on mostly level roads in 5th gear.

 

Slowed down to 50mph on a slight upgrade, but did not have to shift to 4th.

[Plymouthy Adams]

is it really a loss..that is the question..remember...a TQ amplifies the torgue available at 2.3 times on the average..it is the torque that does the work...I do not really know the source of this data...whether it was a rule of theumb or based on dyno, I just posted the data as found on the internet..the small 2.5 4 cylinders of later years was actually some 105 horse through a FWD 727 set up...they suffered no significant lack of power or ability to get to speed..right torque and correct mixture of ratio and you can spin the earth backwards...lol    (looks good on paper)

[murfman1967]

Don't forget the A500 or 44RH transmission is an OD version of the 904.

[murfman1967]

And I'd look for one with a lock up torque converter as you then have a solid direct link in 3rd or OD if you go that way for economy and lower RPMs on the highway.

[B-Watson]

I am trying to understand this. Where does that lost horse power go? Is it consumed as heat generated by friction? Is it consumed by attempting to get an object at a standstill in motion? And if this is the case would a vehicle with a standard transmission also consume 50 or so horses to set it in motion? I hope I am not over thinking this but I really do not understand why a 727 would consume 50 HP just to drive the gears?

 

Both fluid coupling and a torque converter have two vanes in a housing with fluid.  The vane attached to the engine turns and uses the fluid to move the second vane, which is attached to the transmission.  Torque converters also have fluid under pressure by a pump which is used to move the second vane.  The first automatics had a front and rear pump, with the rear pump supplying the fluid to the torque converter.  Which is why you can push start an early automatic and not the later ones.  The rear pump was eliminated in 1965-66 for Torqueflite.  But it is that fluid which is used to move the second vane that causes the loss of power in getting the car off the line.

 

The fluid coupling with no pump-supplied fluid pressure aiding the movement of the second vane is very sluggish off the line.  GM's Hydramatic which appeared for the 1940 model year (one year before Chrysler's 4-speed semi-automatic), had fluid coupling and 4 speeds with 1st gear lower than normal to compensate.

 

Torque converter lockup gives a straight through flow of power from the engine to the transmission.   The 1949 Packard was the first with a torque converter lockup.   Studebaker followed in 1950 with a converter lock up on its automatic, built for Studebaker by the Detroit Gear Division of Borg-Warner.   Ultramatic died with Packard in 1956 and Studebaker replaced its automatic for Ford's B-W built unit in 1957.  The next manufacturer to have a torque converter lock up was Chrysler in 1978. 

[Ed Louie]

HI all, I am running a 700r4 behind my flat 6. Its a 47 Plymouth business coupe. I used the Wilcap converter and have been driving it for about 1000 miles or so now. I also put an Explorer rear axle with disc brakes and 3.56 ratio. It tachs about 2200 at 65mph. It definitely doesnt have the torque it used to with the 3sp but i can drive on the freeway easily now. I have no regrets other than the fact that i could have put in a v8 w auto trans easier. I havent installed the lockup kit yet but i have the TCi kit to put in.

[blucarsdn]

It is a fact of life that with the common application of automatic transmissions in the late '40's by the majority of the auto manufctures, resulted in drastic improvements in horse power and stouter rotating assemblies, i.e. crank shafts and bearing...

Case in point the Chevy 216 babbit bearing engines vs 235 full pressure/incert bearing. Ford also had to step up to the plate with 239/255 CID engines..

Probably one of the dumbest applications was the 1953 Plymouth Hi-Drive behind a flathead engine...

Of course it is also a fact of life that AT's improved significantly by the mid 60's. therefore engines with 225/ 230 CID, slant six and Chevy 6, with their respective horse power improvements preformed very well with AT's...

I don't think a small CID/horse power engine like the Plymouth/Dodge flatheads could/would work very well with an automatic trans..

Of course it could be argued that modern engines with less than 3 litres pull automaic transmissions very well while delivering significant fuel economy.. Of course, many of the small modern engines put out over 150 HP... A far cry from the 85/95 HP of the '40'50's...

Edited November 28, 2013 by blucarsdn

[Ed Louie]

  I dont notice any significant power loss, it drives like a normal car.  I drive almost daily around town and on the freeway up to 80mph.  Im not going to win a drag races but thats not what i set this up for.  Ive made a rod from the original shift selecter to the transmission and left the clutch pedal in. Anyone looking in the car would never suspect it was automatic. The gears shift nice and smooth, i can hold my coffee cup while driving, and the overdrive is awesome.