High stall converter

[72dart]

I have a 71 dodge demon 340 that I got recently and have been trying to sort out some of its drivability characteristics. The car had been traded in at a dealership for a new vehicle so I had limited information about how the car was built. It has a 340 that is basically stock except for the Comp cam 268 which I have learned is just a little more than stock. It has a 727 auto trans that has a shift kit and and a high stall converter. I was told it has a 323 rear non sure grip. It has the 71 thermoquad carb along with stock intake and stock exhaust manifolds.

The car seems to stall out until it gets really warm and seems to bog somewhat when I accelerate from a dead stop. At speeds of 60 or 70 the car runs great but when I floor it I do not feel the passing gear kick in but do feel the secondaries of the carb. I was thinking I might have carb issues with the thermoquad and was looking at what could be done.

When I come to my driveway and come to a stop with the front wheels resting against the curb it takes a lot of RPM to just get the car going and get it in the driveway. I researched on the internet what a high stall converter does and learned that it is used to be able to brake the car and then bring RPM up to the point where the engine reaches its peak torque for racing purposes. If this high stall converter is the culprit I will have it replaced for a more stock one because I am not a racer and just want good streetable qualities. Your thoughts appreciated.

 

[wjajr]

It has a 340 that is basically stock except for the Comp cam 268 which I have learned is just a little more than stock. It has a 727 auto trans that has a shift kit and a high stall converter. I was told it has a 323 rear non sure grip.

We need more information about carburetor: make; vacuum or mechanical secondaries; size/cfm; jetting; and choke type to start.

Your current cam/rear gear configuration appears to incompatible particularly if its stall speed is near or above your highway cruise rpm making it fuel hungry, and probably causing a lot of excess heat in transmission. Converters have to be matched to tire size, cam profile, engine, transmission, and use of car (race, street strip, grocery getter).

The car seems to stall out until it gets really warm and seems to bog somewhat when I accelerate from a dead stop.

Need more info on carburetor size, brand, type (vacuum or mechanical secondaries), jetting, choke, and if any factory carburetor heating devices are in place. Stalling at low rpm when cold indicates choke problems, and or mixture problem. A bog during acceleration can indicate: too lean or rich condition; secondaries opening too soon at too low rpm if mechanical; poorly timed or sized accelerator pump shot; wrong power valve if equipped, and other reasons.

At speeds of 60 or 70 the car runs great but when I floor it I do not feel the passing gear kick in but do feel the secondaries of the carb.

Governor of transmission may not allow down shift while in “D” at that highway rpm, or throttle position rod and or cable is maladjusted. Feeling secondaries is a bog where mixture is off of ideal… see above.

When I come to my driveway and come to a stop with the front wheels resting against the curb it takes a lot of RPM to just get the car going and get it in the driveway.

This is the sloppy high stall converter’s contribution. Engine has to spin the converter fast enough to approach lock-up before it will turn the transmission. Next time you crawl over a curb, make a note at which rpm the car decides move, and that is approximately the converter’s stall speed. While driving at any rpm under converter’s stall speed, it is slipping to some degree wasting fuel, and generating heat in transmission fluid needlessly.

I researched on the internet what a high stall converter does and learned that it is used to be able to brake the car and then bring RPM up to the point where the engine reaches its peak torque for racing purposes

Basically yes; torque converter is a torque multiplier. Generally a loose or high stall converter is used behind an engine with a lumpy cam and poor loping idle, and with a low geared rear (3.7x, 4.11, etc.) allowing engine to stay happy at its higher rpm design parameters, but still be streetable. Dose you engine idle smooth with good vacuum in gear with brakes applied, or is it lumpy with low vacuum? We need that idle vacuum & rpm info.

Your set-up is in need of carburetor adjustment perhaps more, and probably a stock converter or one real close to stock, based on an almost stock engine, and stock rear gearing.

 

[72dart]

The carburetor is a 71 thermoquad and appears stock to me in that the choke is connected to the manifold and works off of heat I would guess. However, the choke does not work as far as I can determine. The engine idles fine once it gets warmed sufficiently. I do notice bad gas mileage and guess that can be attributed to the converter. The car does not have a tach so I do not know what RPM it takes to get the car going over the curb. The more I learn about this the more I think I need to have a more stock converter installed.

 

[fanofpetty]

PM sent

 

[crackedback]

Some of your issues are likely rooted in ignition timing.

 

[fishy68]

Sounds like you may have a few issues. Like Rob mentioned above some of the problem may be ignition related. Anytime a larger cam is installed the distributor centrifugal advance will usually re-curved and the initial timing bumped up. Also, the secondary air valve on the carb may be too loose causing the stall when you mash it fast. It is adjustable and the adjustment is on the drivers side. It's easy to do but not real easy to explain but I just rebuilt a Thermoquad and have the papers that came with the rebuild kit that shows how to do it. If you'd like I can scan them and e-mail them to you. Just PM me with your e-mail address if your interested. It could also be it's just running lean which means the carb needs bigger jets. I'd try the adjustment 1st.

As for it taking a lot of rpm to climb the curb that could be a few things. First off how steep is this curb? Second it's hard to really blame the converter not knowing how many rpm it's actually taking to climb that curb. Saying you have a high stall converter tells very little because if it's even a 2200 stall it's considered a high stall converter and in reality that's not much over stock. Without knowing what it really is stalling to (rpm)anyone would just be guessing in saying it's too loose. By your description of how the engine is running the converter is at the bottom of my list of suspects.

 

[green1]

Agree with the above. tuning and carb, first. Listen to Rob on the timing, throw away they factory book. "can feel the secondaries come in" that is a bog. "bad milage" doubt that is the converter. "curb- no tach" You can't tell what the assembly is doing without a tach.

An example; I helped a bud restore a 69 440 car; talked to Forte, had a 3000 stall converter come with it. First time buddy tried to back out of the shop" the trans is slipping" Not. The front pump doesn't run in park; only neutral and gears. Start it in neatral, fill the converter.

New verter tech; actually no slippage at cruise, aside from normal.

 

[green1]

Oh, no kickdown invovles linkage and or governor.