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Discussion Starter · #1 ·
I will just be driving My Valiant around town and to car shows. I have a storck 727 tranny and I was woundering if it can handle 500 HP?
 

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KOG
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That depends on how it's used and what speed/torque is put through it. But most of the time, no way. It can be modified rather easily.
 

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A shift kit will heip improve that amount of power if on the street, racing at the track is another thing, some actual better components are needed. A shift kit increases the line pressure so that much power doesn't slip the clutches and bands as easily.
 

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My dad (and his dad) were big fans of the 318 w/ same (or similar) transmission, and my initial reaction on reading the question was, "No way!" But I'm not a mechanic, like they were.

I was reading some threads here, about which I had no clue, so I thought it amusing that I think I know something about this :)

What do you have in it that makes that much power?

Just for reference, Dad did take the 318 out of a '61 Plymouth station wagon, and put a 440 in there for the purpose of hauling a travel trailer. May have installed a transmission cooler, but I don't know for sure. This was in the early '70's, IIRC.
 

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I will just be driving My Valiant around town and to car shows. I have a storck 727 tranny and I was woundering if it can handle 500 HP?
I suppose it wouldn't matter if you had even 800hp. if you only plan to use car as a 'daily driver'. I doubt you would be utilizing anything close to your anticipated hp rating just by putting around town and to the occasional cruises. Of course there would be many internal concerns should you decide to take it to the track and initiate a 'brake stand'. Yes, please tell us more of what you have under the hood (and between the rear wheels). :stirthepot:
 

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KOG
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If you have street tires on a Valiant you won't be able to hurt a 727 very much. Slicks and traction compound on a drag strip and you'll grenade it instantly.
 

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And besides, that 500hp isn't off the line, it isn't until you most likely hit 4500rpm or above. Use an 11 inch torque converter, gives you about a 2000rpm stall and will help run on the street a little better.
 

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Back in the sixties I went with a friend to pick up his brand new Plymouth 413 club coupe. A true from the factory stripped-down muscle car. When riding in it the transmission shifted harshly BANG! I always remember the California Highway Patrol 426 2X4 barrel cross-ram patrol cars. They had lots and lots of power. One cop who we nick-maned "bullet-head" was always bragging how tough this car was and that "it will do 140, easy".
 

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As long as it isn't an old and tired 727, but freshened and shift kitted it will be fine. There have been many a time I have built even stock engines and dropped them back into a car behind a transmission with the equal miles of the engine, just to pull the transmission out of the car to rebuild it within a year. In short, a fresh engine of any power level and a fresh transmission is the best insurance, even if you have to save for a transmission rebuild and shift kit (Mopar kit is the quickest and easiest out there and works just fine), and the 11 inch torque converter is the heavy duty stock converter which is usually cheaper than an aftermarket unit, very happy with them myself.
 

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Discussion Starter · #11 ·
I have a 360 engine being turned into a 408 stroker. This entire project is new to me. Having found this site and being able to have access to all of the combined knowledge is very helpful. I have realized that certain parts of this project i will have to leave up to the professionals. Like the entire motor build.

After reading the advise that all of you have given. I Think I will have the tranny rebuilt and add a shift kit. I do not want any problems down the road.

This brings me to my next question. Do you think it would be a good idea for me to try to rebuild the trannsmission on my own? I have good mechanical skills but no knowledge.
 

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Depends. The 727 is one of the easiest transmissions to rebuild and assemble, the shift kit is the easiest on the market because the transmission is built to be strong to start with. I find with a manual the 727 and 904 to be easier to rebuild than a manual transmission. They do take a little finesse at times, but it is minimal, and not that many special tools needed. Best way to get the guts assembled is to stand the transmission on its tail, so an old yoke and plate welded to it works well, clearances are tight but they fit together very smoothly when assembling. The clutch pack seals are the most fun, so care has to be done to assemble them, then the spring packs and snap rings need to be compressed (a jack screw works well or a small press). I would actually think if you have the engine rebuilt you may think twice on the transmission though, a 727 is about one step up from complexity to the engine. If you had a stock 727 rebuilt at a shop, you could install a shift kit in it in about an hour out of the car, only the valve body needs to be removed, a slot drilled, a spring removed from the kickdown and the line pressure cage readjusted.
 

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KOG
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If you decide to rebuild it yourself post back. There are a couple of tricks the manual won't tell you.
 

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My dad (and his dad) were big fans of the 318 w/ same (or similar) transmission, and my initial reaction on reading the question was, "No way!" But I'm not a mechanic, like they were.

I was reading some threads here, about which I had no clue, so I thought it amusing that I think I know something about this :)

What do you have in it that makes that much power?

Just for reference, Dad did take the 318 out of a '61 Plymouth station wagon, and put a 440 in there for the purpose of hauling a travel trailer. May have installed a transmission cooler, but I don't know for sure. This was in the early '70's, IIRC.
At the time the 727 was THE transmission for H.D. towing GM & Ford had weak transmissions.
 

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It kind of depends..
Behinda a tuned cummin diesel - no
Behind a high revver 318 - yes
Its not the peak horsepower that breaks it, its the amount of torque you put in.
And as long as you doesent start to charge the engine it would basically withstand any chrysler gas engine but its always possible to break things for some people.
 

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Agree torque is the limiting factor on transmission - torque determines the force exerted on various components - torque and force related directly through radius of the element only. HP is a function of RPM as well - RPM does not matter ... to a reasonable point.
In addition to shift kits, there are also different specs of 727's in any given year and different modifications you can easily do if you rebuild it. More clutch plates and more planetary gears can handle more torque and power. Not sure if yours is original to the car or if you know what kind of engine it was originally delivered with.
I've been working on my '74 727 - original numbers matching to the 360 car - per the FSM in 1974 SB engines were delivered with 3 front and 4 rear clutch plates where BB esp 400 and 440 HP engines came with 4 front and 4 rear. I think there are some (Hemi?) versions with 5 clutch plates in the front - 1971 Hemi and 440-6. There are different thicknesses of clutch plates that can accommodate this or you can spend money on modified drums. Then there is planetaries - I believe standard on SB was 3 gear planetaries front and rear. BB HP I think had 4 gears on the front and 3 on the rear. A previous owner had nicely replaced the front planetary with a 4 gear set but I have left the clutches at stock 3 front and 4 rear. I am targeting something like 400HP / 400 Ft Lbs. There is a ton of how to videos and material / references on the 727 on line.
Also if you rebuild it an easy add is HP clutches and bands which I went with. Ordered my kit from Transwarehouse in California.
 

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Part of the equation is traction. If you’re spinning wheels at launch, a transmission can hold up longer than if you get a good, strong hookup at launch.
 
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