Thread: Stall converter

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What do they do and when do you need one? Just got my truck back on the road with more HP(425) turo 400 from a 78 suburban. My wife is grinning ear to ear I am a blessed man!

Originally Posted by sfort

What do they do and when do you need one? Just got my truck back on the road with more HP(425) turo 400 from a 78 suburban. My wife is grinning ear to ear I am a blessed man!

Many factors determine the need for a looser converter, among them rear tire size, rear gear ratio, vehicle weight, induction system, camshaft timing and so forth.

Let's say that you have a stock vehicle with the stock converter. It is matched by the engineers at the factory to be just loose enough to allow the motor to idle at a stoplight without pulling too hard against the brakes in gear and just tight enough to prevent allowing over-revving the motor on acceleration and wasting fuel. The stock camshaft is designed to make power from idle to 4000 rpm's or maybe just a tad higher.

Now, you swap the cam for one with longer timing. This new cam makes power in the motor from 2500 to 6000 rpm's, so there will be a dead zone from idle to 2500. With a stock converter that hooks up at maybe 1200 rpm's, the motor must pull through this dead zone, making little power and resulting in a slower car than you had with the stock cam in place. Also, the new cam wants to idle the motor at 1000 rpm's instead of 750 like the stock cam, so the motor is tugging at the brakes at every stoplight because the converter is up near its stall rpm.

At this point, a looser converter, one that stalls at around 2500 rpm's will be needed to deal with the longer cam. This new converter will allow the motor to idle higher without tugging on the brakes at stoplights and will also allow the motor to rev through the dead zone before the converter begins to stall at the higher rpm's. So, from a standstill, when you wood the loud pedal, the motor rpm's will flash up to about 2500, allowing the motor to be in the power-making zone and applying some real grunt to the drive rubber.

Converters are available in a wide range of stall speeds. A stall of around 3000 is generally considered by many to be perfectly acceptable behind a street motor, but much more than that is considered unfriendly on the street. Of course, a looser converter will make more heat, so that issue must be addressed with a cooler mounted in front of the radiator.

Thanks Tech! I need to get all the details about the engine rebuild and the truck. So far I am super happy with the way it performs. We have had the truck for a year and have just got it on the road (engine was sick when we got it). Worth the wait!

if you can put it in drive can its idles with you foot on the brake with out pulling then you do not need a stall .if you need one call coan and they will go thru you build gear etc and pick one out for you. for a mild build if you can get away with less stall the better . i wish i had all the money i have spent on stalls

Pat I really appreciate everyones help. What brought the question up is when shifting in and out of gear at idle there is really not a lot of noticeable rpm change (don't know for sure tach is not working yet) but there is a noticeable lurch, both forward and reverse.

sounds like it has some stall a stock 400 stall with some cam would be pulling hard if you put your foot on the brake they try to hop abit with a stock stall. were the cam dur at .050 ?

A number the builder gave me was 280 at .050. Does this make sense. Supposedly an RV cam. Some of the dyno numbers are below.
RPM TQ HP
2700 519 266.9
3600 534 366.1
4600 481 421.9
4900 456 425.3
5000 442 420

Originally Posted by sfort

A number the builder gave me was 280 at .050. Does this make sense. Supposedly an RV cam. Some of the dyno numbers are below.
RPM TQ HP
2700 519 266.9
3600 534 366.1
4600 481 421.9
4900 456 425.3
5000 442 420

no that number is not rigth at 050 a RV cam would be low 200 mild 200s and you will not need a stall the a RV cam

The dyno numbers were run while I was there. Common sense tells me you could not run those numbers with an RV cam. I bet you guys that know this stuff are surprised how little some of us really know about our rods. Since they were in the engine business I just gave them my HP goal and expected them to get as close as possible. I do not like not having answers to questions someone is asking while trying to help me. I will do better! Thanks guys!!

yep i have a 280 @ 050 cam on the street it anit no RV cam and needs a 4000 stall now your wife would smile when she step in to it. but its not a every day car more like point and shoot , very stock 454 with a RV cam should make good power and EZ to tune in and will move that truck very good

Since your engine builder is familiar with your motor, the cam they put in it and your vehicle, I would ask them for a recommendation. You could get second and third opinions from a couple of the converter builders.

A literal explanation of what stall speed is: The RPM the engine will rise to when you apply the brake and throttle at the same time. A strong engine like yours will over power the brakes at some point and begin to spin the tires or slide the car forward. A transmission brake in a race application will enable you to give more throttle without this happening. A "high stall" converter will be looser as techinspector said, that will allow the converter to slip at lower RPM and not push the vehicle forward and will finally "Catch" at a higher RPM and give you a better launch. Compare it to a stick shift car, a stock converter is like dumping the clutch and flooring it at 1100 RPM. A 3000 stall converter is like dumping the clutch and flooring it at 3000 RPM. Of course there will be a little more slippage with the automatic, but that illustrates the point. Given your motor, I would think 4000 Stall would be too much for anything that you plan to drive very much on the street. Again, ask your engine builder what they recommend, and if you must error, I would suggest you do so on the low side.

Good luck with it, sounds like they built you a nice street fighter. Be careful!

Pat

Thanks for the reply! I emailed the builder this morning with questions about the cam. The builder is not familiar with the truck. I pulled the engine delivered it to them and picked it up 14 days later. I wanted around a 400hp no hassle engine so my wife could get in it and have no problems getting it started. I will get back when I get some data. Thanks again guys!

if it works good like i said you do not need a stall as for it pulling with your foot on the brake at a light your wife would of said some thing about that.as for a 4000 stall i never said you need one of them and if a RV cam you do not need a stall .i have two cars with 4500 and a hi 3800 there both driven on the street they work find for what i do .like i said talk to the engine builder get the cam sheet you should of had one with the engine when you pick it up? engine builds i do less i do not want the guy to know if its one of my cams but i still will tell him about were it is. fun thing is this is about the first thing that rolls out of my mouth when taking to a customer about engine build that and the CR and rear gear so I know how much cam i can put in to the engine for the street.... he may know about how much stall you will need.... BUT.... less he builds them to you need to talk to Coan or someone like that. i have had them build custom stall at $1300.+ and they will know how much one of there stall is going to stall at in back of your engine with the rear gear you have. size of carb heads cam and weight if you think you need a stall

Originally Posted by techinspector1

Converters are available in a wide range of stall speeds. A stall of around 3000 is generally considered by many to be perfectly acceptable behind a street motor, but much more than that is considered unfriendly on the street. Of course, a looser converter will make more heat, so that issue must be addressed with a cooler mounted in front of the radiator.

You bring up many issues I am dealing with at this point with a TCI SSF 700R4 and, originally a 2600 or 2800 TC , now, a 1800. The more I research the more I understand what is happening to this tranny.

How do I know if the TC has Locked-Up and or Unlocked? I think the Switch is hooked to my Brake Peddle, the Brake light on the Dash comes on and goes off occassionally, but remains on mostly. I think I would like to have more control of the Lock-up, so does a manual switch make sense?

I think the fluid might be boiling in the tranny and causing my leaks, don't have a temp gauge hooked to it to find out temp of cooling going in and out of tranny, lines hooked into radiator, no external cooler (How much of a diff does it make?) Shouldn't the vehicles radiator keep the new Tranny at Operating Temp?

So many more questions,

Your knowledge on this subject seems to be ummmm, pretty good, I think you know what you are talking about more so than most Technicians I have spoken with on this Install, Thanks for any info you are able to provide.

Originally Posted by pat mccarthy

if it works good like i said you do not need a stall as for it pulling with your foot on the brake at a light your wife would of said some thing about that.as for a 4000 stall i never said you need one of them and if a RV cam you do not need a stall .i have two cars with 4500 and a hi 3800 there both driven on the street they work find for what i do .like i said talk to the engine builder get the cam sheet you should of had one with the engine when you pick it up? engine builds i do less i do not want the guy to know if its one of my cams but i still will tell him about were it is. fun thing is this is about the first thing that rolls out of my mouth when taking to a customer about engine build that and the CR and rear gear so I know how much cam i can put in to the engine for the street.... he may know about how much stall you will need.... BUT.... less he builds them to you need to talk to Coan or someone like that. i have had them build custom stall at $1300.+ and they will know how much one of there stall is going to stall at in back of your engine with the rear gear you have. size of carb heads cam and weight if you think you need a stall

I am guessing that the next best performance improvement I can do is throw a cam in. or even a TC? I originally had a 2800, now a 1800, is this the right choice?

I originally purchased a ZZ4 350 and a SSF 700R4 and had the rear changed to 4.10 or .11 not sure, This went into a 1976 GMC 1/2 Ton Pick-Up Truck that weights 6200 lbs and has 16" wheels stock.

Other than taking out the Old Engine/Tranny and replacing with the New, what kind of set up should I be looking at for a Truck like this , Rear Gears?, Special Cooling? What size TC should be in the truck? What kind of Cam can I put into the ZZ4 Engine? Someone Suggested Voodoo Cams, any thoughts?