HP Torque Converter?

[Cazman]

I have my '68 727 in the shop now for a rebuild. I have a 350hp 440. In the FSM they reference a regular torque converter and a HP version. I assume I have the regular. Does anyone know what the other one is and why I might want it. The FSM does not say much about it.

 

[Davea Lux]

I have my '68 727 in the shop now for a rebuild. I have a 350hp 440. In the FSM they reference a regular torque converter and a HP version. I assume I have the regular. Does anyone know what the other one is and why I might want it. The FSM does not say much about it.

The HP torque convertor is for the high performance or magnum engine. Many of the high performance engines in the road runners, chargers etc use a higher stall speed convertor to improve 'out of the hole' performance, this sacrifices some fuel economy for better acceleration from a standing stop. You probably will not gain much going to the high performance torque convertor if you are still running the stock 350 horse cam. Your '68 350 horse engine is also internally balanced and you do not want to go anywhere near a weighted convertor that was used on the later high performance engines unless you are going to the 6BBL style Crank and Rods with the appropriate harmonic balancer as these engines were externally balanced and the use of externally balanced components will cause severe vibration issues running a stock 350 horse crank.

Dave

 

[Cazman]

That’s good to know. Thanks

 

[1978 NYB]

I have a 2500 stall converter in my 78 NYB. I have a 400 with 450hp. It runs fine.

 

[Cazman]

What stall was the Hp?

 

[1978 NYB]

What stall was the Hp?

I'm not understanding your question.

I can take off from an idle, rpm's wind up a little or I can hold the brake pedal and wind her up to 2500 rpm's and let off the gas and roast the tires for a block. I don't have the axle and gearing that I want right now. Probably this summer I want to get and put in a 9.25" SG axle with 3.23's. My goal is just to have a bulletproof cruiser that I can take cross country any time I want to.

 

[Cazman]

I meant what stall speeds did the factory use? The regular was maybe 1800? The HP one 2500 like yours?

 

[Davea Lux]

I meant what stall speeds did the factory use? The regular was maybe 1800? The HP one 2500 like yours?

The 2500's are an after market unit. Factory stall speeds were quite a bit lower for economy reasons. I am working from memory but I think the 350 horse engine was somewhere around 1900 with the stock convertor and about 300 RPM's higher with the high performance option.

Dave

 

[1978 NYB]

The 2500's are an after market unit. Factory stall speeds were quite a bit lower for economy reasons. I am working from memory but I think the 350 horse engine was somewhere around 1300 with the stock convertor and about 300 RPM's higher with the high performance option.

Dave

Yep, Dave is correct.

My converter is an aftermarket B&M performance converter.

 

[PontiacJim]

I have my '68 727 in the shop now for a rebuild. I have a 350hp 440. In the FSM they reference a regular torque converter and a HP version. I assume I have the regular. Does anyone know what the other one is and why I might want it. The FSM does not say much about it.

There were 2 different sized torque converters having various stall speeds due in part to size of the converter and the HP/Torque of the engine and weight of the car.

The "Standard" TC for the 318 904 is shown as 10 3/4" while the 727 used the 11 3/4".

The "Standard" TC for the 400/440 is the 11 3/4". The "High Stall" TC is used on the 340/360/400/440 with the 727 is the 10 3/4." However, the larger 11 3/4" is shown used on the high-performance 440 cars as well (less slippage). From the 1973 Manual:

Any Model:
318 - 904 10 3/4" Stall RPM 2125-2425
Police & Taxi:
318 - 727 11 3/4 Stall RPM 1725-2025
CarLine VLBJRW:
340 4Bbl - 727 10 3/4" Stall RPM 2200-2500
CarLine PDC:
360 2Bbl - 727 10 3/4" Stall RPM 2300-2600
CarLine BJRWPDC:
400 2Bbl - 727 11 3/4" Stall RPM 1875-2175
CarLine BJRWPDC:
400 4Bbl - 727 10 3/4" Stall RPM 2400-2700 HiPerf
CarLine PDCY:
440 4Bbl - 727 11 3/4" Stall RPM 1975-2275
CarLine RW:
440 4Bbl - 727 10 3/4" Stall RPM 2600-2900 HiPerf
CarLine PDC:
440 4Bbl - 727 11 3/4" Stall RPM 2100-2400 HiPerf

I have the 360 2 Bbl and it has the high stall converter. It is a "loose" converter that has a noticeable amount of slip when easing into the gas, more so when it is cold and has sat for a while. BUT, when you nail the gas from a red light or stop, the converter allows the engine to jump right up to its maximum stall, putting the engine in its lower power band and it pulls away hard - very peppy.

This is the purpose of a higher stall converter - to raise and allow the engine's RPM to get to the point where HP/Torque begins to come on strong (usually determined by the camshaft selected) and then accelerate from there.

Down side of a "loose" converter is the slip at the lower RPM's (or under load like hills/mountains) which eat up gas mileage and may put excessive heat into the trans fluid. With today's technology, you can get what is called a "tight" converter, meaning it does not slip excessively at the lower RPM's or part throttle, but will snap right up to its maximum slip when HP/Torque is applied under full load.

Bought a "tight" 2500 RPM stall converter for my brother's 360 I built. Ease on the gas or let off, the tach will vary 200 RPM's. Nail the gas and it will zing right up to its max stall putting the engine in its power band and keep on pulling strong from there.

I have also used what is called an RV/Towing converter when I used to trailer cars. The converter is designed to lock up at a lower than stock RPM so you don't get excessive slip while pulling a load. Less slip also reduces heat which can destroy the trans over time.

With any high stall converter, muscle car, or for towing, I like to add an external trans cooler.

 

[Trace 300 Hurst]

See this thread, post 36 for pictures from the FSM discussing the converters in full size Chryslers in 1970.

Measuring the transmission fluid level (727)

I'll make it easy...here's the page from the 1970 Chrysler FSM:

 

[CBODY67]

Generally, the classic aluminum case (and possibly the cast iron case before it) were known for their "tight" torque converters. Put it in "1" or "2", get a little road speed, then back off the gas and the car immediately slows down. "Control", as they termed it, which came in very handy in the mountains rather than having to use the service brakes. That's why my uncle bought a '63 Polara V-8 rather than anything else. They liked to go to the horse races in Ruidosa and others had commented about driving their Chrysler products in "2" in the mountains and not having to use the brakes to keep their speed under control.

"Stall speed" was not something generally mentioned until the later '60s. If you wanted the engine to speed up quicker, you put a smaller torque converter behind it. Generally from another OEM application for a smaller engine with a smaller diameter torque converter. Each torque converter is tailored to its original application (4 cyl, 6 cyl, or 8 cyl). In the front of an old Chrysler parts catalog, in the reman parts section for torque converters, the Road Runner 383 converter was the same one used behind a Slant 6 225. That's how the higher stall speed was achieved. Having a torque converter with the guts to handle the higher horsepower, which would "over-ride" the original design stall speed with more power in front of the converter. Just as the '78 Camaro Z/28 THM350 used a converter originally spec'd for a V-6.

So, a converter that has a stall speed of 2000rpm behind a 350 horsepower engine would have a higher stall speed behind a 400 horsepower engine, for example. Although at those rpms, it's more about "torque" than "horsepower".

The surprising thing, as to factory spec stall speeds, is in the '78 Chrysler FSM. As "weak" as those 400s and 440s were supposed to be, they were still spec-ing stall speeds for the 440HO of nearly 3000spm. Quite surprising.

There are two general sizes of TF 727 torque converters. The 10.75" is the small one and 11.75 is the big one that's probably behind your 440/350 engine. The best way to tell is that when you do a trans fluid service, the smaller torque converter takes less fluid to get to the "FULL" mark on the trans dipstick. Which can also be determined by the fluid capacity specs in the FSM.

In the graphic above, the 383-4bbl obviously has the smaller converter behind it, whereas the 383-2bbl and 440-4bbl have the larger converter. The 383-2bbl and NY 440/350 would obviously have the 2.76 std axle ratio, but the 383-4bbl would have a 3.23. But a 300 440/350 would have a 3.23 std ratio. usually.

Key thing for highway driving is that any resultant stall speed needs to be less than the rpm at about 55mph, for best results in the particular vehicle. This minimizes any slippage that's part of the non-lockup converter internal design. There might always be about 100rpm of "slip", but not much more. That means that the slightest throttle input gets a response in road speed increases.

Just some thoughts,
CBODY67

 

[Cazman]

Good things to consider. I like the idea of increasing the stall speed some to match the cam upgrade that I will be doing. I have the 2.76 gears (I would rather have the 3.23). I also like the idea of a “tight” TQ, as I indend to cruise mountain roads more than race.

 

[70bigblockdodge]

Good things to consider. I like the idea of increasing the stall speed some to match the cam upgrade that I will be doing. I have the 2.76 gears (I would rather have the 3.23). I also like the idea of a “tight” TQ, as I indend to cruise mountain roads more than race.

Stick with a near stock one.

 

[CBODY67]

What are the cam specs you've chosen? Reason is that some moderate grinds need a little more looseness at the very bottom end of things, for a better idle quality. As the converter puts a load on the engine at idle, less with a looser one, more with a tighter one. Which can affect how far open the idle plates need to be in the carb at hot curb idle. Then there's "creep", too.

Up until the later middle '60s, Chryslers products tended to have more "creep at idle, in gear", than GMs or Fords did. Due to their tighter and more responsive torque converter guts. CAR LIFE magazine put a '65 Belvedere 383 (3.23, 7.75-14 tires) on a drag strip and checked the trap speed of the car at hot base idle in "D". Something like 7mph at the end of the quarter. Others were more like 5-6mph. As a result, Chrysler products tended to "leap" off the line, off-idle more than similar Fords or GMs, by observation. That tighter feel made you smile when it happened. But the cams were closer the 256/260 specs than the later B/RB factory HP cams.

But choosing a cam with a LCL closer to the (generally) factory 114 degrees will have a better idle quality than one with 110 LCL, from my own experiences. A dual plane intake helps in the idle and lower rpm response, too, but can still have the same specs as the similar 110 LCA cam.

So, enjoy!
CBODY67

 

[PontiacJim]

Good things to consider. I like the idea of increasing the stall speed some to match the cam upgrade that I will be doing. I have the 2.76 gears (I would rather have the 3.23). I also like the idea of a “tight” TQ, as I indend to cruise mountain roads more than race.

The converter I put in my brother's 360 was from Edge. I used and built up the 904 transmission that came with the car. Also swapped the original 1st gear ratio for a lower 1st gear ratio which improves acceleration from a dead stop without changing rear gears. These guys are Mopar specialists. They seem to offer a lower first gear which would allow you to keep the gas economy rear gear and add a little more acceleration. Might be worth a call or email just to inquire. Home - A&A Transmissions

Here is an offering for the 727 converter: 727 : Edge Racing Converters, More Horsepower with More Torque Guaranteed!

The 1977 360 was built with a SixPack and I used a Competition Cam brand 280H cam with .480" lift and 280 degrees duration.

You don't necessarily need a higher stall converter with a mild street/strip cam if you choose not to run one. To create a smooth stock idle, I used Rhodes lifters in the 360. The engine idles like a stock engine at 750 RPM and has excellent vacuum to operate the power brakes. The Rhodes lifters will make a bigger cam act smaller under 3500 RPM. The lifters "pump" up about 3500 RPM's to give you the full punch of a hi-perf cam, so it works perfect with the 2500 RPM stall converter and the 3.55 gearing. Original Flat Tappets

The key is to match all your engine parts along with the drive train components. It is important to take into account your Cruising MPH, Tire Size, Rear Gear, and the RPM the engine will be turning at cruise. Read this spec sheet and you will get an idea of what is really required to match a torque converter to your car/application. Don't listen to what your buddy says you need. Do it right and do it once. Mild Street Edge Converter for Chrysler 727 Transmissions [MSE727] - $345.00 : Edge Racing Converters, More Horsepower with More Torque Guaranteed!

 

[Cazman]

Never considered a different 1st gear. Thanks.