Why swap stall when swapping cam?

[kool-aide]

Ok, I have noticed in a couple of cam swap threads people stating you need a different stall for an auto on a cam swap. What am I missing here? Doesn't the stall converter just act like a disengaged clutch so the engine can spin and the trans sits relatively still with little break pressure?

Is every one saying you need a new stall because you may begin idling higher? I guess I just don't see the connection between a higher stall and a bigger cam. Would a bigger cam really idle so high that the stock unit won't do?

I'm not very familiar with autos and why you would go w/ a higher stall for any reason.

thanks

kool-aide

[bills98ta]

It's not really a higher idle, but the cam loping at the idle means that it has no power at idle causing it to stall when you put it in gear. A higher stall will slip to let the cam take hold at a higher rpm. ( something like that !!! )

[kool-aide]

hmm....ok so no its time for the really dumb question. Are stall and torque converter synonymous terms?

[kool-aide]

It's not really a higher idle, but the cam loping at the idle means that it has no power at idle causing it to stall when you put it in gear. A higher stall will slip to let the cam take hold at a higher rpm. ( something like that !!! )

is that kind of like getting a stall that matches the power band of the cam?

it just seems so weird i guess, to say your enigine won't mate up with the trans until a high RPM. I would think you would always want a lower stall vs higher.

I guess maybe if i think about it and the fact it is a rotating assembly of things then maybe it makes sense. it doesn't come alive until it is rotating at a good speed.

[bills98ta]

hmm....ok so no its time for the really dumb question. Are stall and torque converter synonymous terms?

Uhhmmm.... The stall is the rating of the torque convertor. If you want a good street convertor, stay around 2800 to 3600... I'm on the track more than the street, so I now run a 4600 stall convertor. Then you also want it rated as a locker, so it will still lock in at lower rpm's while cruising !!!
Hope this helps !!!

[bills98ta]

My cam is rated at 3000 - 7200 rpm, so I need a higher stall speed. At 2200 rpm, my car will start bucking, untill I hit a lower gear...

[kool-aide]

Uhhmmm.... The stall is the rating of the torque convertor. If you want a good street convertor, stay around 2800 to 3600... I'm on the track more than the street, so I now run a 4600 stall convertor. Then you also want it rated as a locker, so it will still lock in at lower rpm's while cruising !!!
Hope this helps !!!

right when you say rating, are you refering to the RPM at which the two don't fully mate up or lock together? Doesn't stall refer to the RPM range at which the converter will just spin the fluid and not engage the trans mission, well not fully?

too bad we couldn't break out the crayons for this kindergardner and draw some pictures.

thanks

[bills98ta]

Yea, you're gettin it !!! I think the stock stall rating is around 1600 rpm. So, while idling in gear, it's slipping. Don't know about the crayons, but I'm one of those who talk with their hands !!! LOL !!!

[kool-aide]

lol...thanks.

[shiftless]

Yes, the "stall speed" is the speed at which the turbine (output) of the converter begins turning at (roughly) the same speed as the engine (input). I say roughly because there is always a small percentage of slippage. The better the converter, the less slippage. Now with a lockup converter, there is a clutch inside that locks up under cruise to ensure that there is no slippage.

[kool-aide]

thanks. that's how i was trying to interpret the how things work web site, or how stuff works, whatever.

I never liked Auto Trans. I guess maybe because I have a tough time visualizing all of the parts, lol...