Torque Converter? Where am I at? What is compromised?

[AJ/FormS]

Sorry, I must be lousy at expressing myself. I do understand that they can make good converters that have a higher stall but still be streetable. The logic goes like this. If I have a car that drives well on the street, the engine, transmission etc. What advantage do I gain by changing to a "better" TQ than what I have? Similarly, What do I give up, if anything, or nothing, by getting a better torque converter?

The cost is not a factor. 600-700$ is not going to sway my decision. Pulling the trans to do the job is more difficult to justify. If the benefit is not worth the effort to do so......

with 3.91 gears, braced in back. SS leaf springs. Competition engineering race shocks. Pypes exhaust 3" into 2.5 inch. RacePro mufflers. Mickey Thompson ET street SS Drag radials 255/60-15 27.3 inch) but going to 275/60-15 28.2 inch diameter

I think I get what yur asking;
With a Street car, IMO, you gotta think about things, in a different way.
A streeter, at WOT, is basically a one or a two gear car. For you, 60 mph will be about 6200 rpm, in FIRST gear, and it will take less than ~5 seconds to get there. So................. does stall make a difference? Well not on the shift because no shift has occurred. And at the other end, most horsing around starts at 25/30 mph; so does stall make a difference?
Not hardly.
For you; the only time stall can make a difference, is if you get NO tirespin from a dead stop, or if you just want to show off.
Like the guy above>>>> said; it might make a lil difference in your 60ft ............
Is .2 or .3 second, in the 60ft contest worth it to you?
Only you can answer that.
===============
Here's my thinking;
With 3.91s and 28.2s (88.6" roll-out); 3000rpm (at zero-slip), would get you 23mph in 2.45 first gear.
So any time that you are traveling at less than 23 mph, and you mash the gas, with a 3000TC, the Rpm will jump up to around 3000
But if you are already traveling at 35 mph, the rpm for zero-slip would be 4000.
So now, NO TC that flashes to less than 4000 will be of any use to you, after 35mph, in first gear, unless it happens to be more efficient.

Say you are tooling down the road in 1.45 Second gear at 35mph, doing 2365rpm plus say 3% slip =2435. Cuz with as much engine as you have, that's what I'd be doing.
Now when you mash the gas, the trans kicks down into First gear and the rpm pops up to say 4400@10% slip. The only way it can be any higher is to start with a higher Stall TC. So it's not likely you would ever choose that high a stall.
I chose 35mph in first gear because that 4400 is about where your peak torque will be happening, perhaps a a couple of hundred rpm sooner, it makes no difference, cuz your Scamp should be getting sideways with Street Tires.

So to make a long story short, your stall rpm in first gear, with your engine and combo, becomes less and less meaningful as the speed goes up. By 29/30ish mph, the road speed is high enough to lock up a 3000TC, so it ain't helping much any more.

But not true on the 1-2 shift. If you had a clutch the rpm drop from up-shifting First , into Second is a split of 59%; So shifting at 6000 would drop the Rs to 6000 x.59=3540.
If you had a 3540 stall TC that would get you the same 3540rpm, going into Second; so your engine would need a decent amount of torque at that rpm to continue accelerating briskly.
But if you had a 4540 stall, then at WOT the Rs would drop to only 4540, and you are 1000 rpm further up the power curve, and accelerating exponentially harder..
So ; on the 1-2 shift, the higher stall will make your car accelerate much harder.

Ok but, all of that above stuff is talking about WOT acceleration. Which with a Street car, you gotta think about, in a different way.
back to the Top.....

So then, what would a good number be for a stall?
IDK, I'm not a BB guy never mind a 512.

But; IMO, 1800 to 2400 is a lil too low.
However, the GVod turns your 3.91s into 3.05s and 65=2365rpm @zero-slip.
Your TC does Not have a lock-up so at 65 your Tc might want to slip say 3% so the Rs could be as high as 2440, and she'd be hydraulically coupled. Now, if you put a 2800TC on that; now reving 2440, she might be wanting to put some heat into the trans-oil.
However; coming out of overdrive at 60 would get you ~3100 in "Drive" for passing; not much rpm for a Small-block, but maybe lots enough for your engine. But notice that 3100 is higher than 2800, so again, any stall less than 3100 will not help you to pass.
I have always had small-blocks only (plus a few slantys), and I put 2800s on everything. Cuz I like how 2800s work. I like the feel of them. They drive decent all the time, but when I nail them with street gears like 3.23s or 3.55s, it kindof feels like a snow-mobile clutch. The engine winds up and then like a big ol' flywheel she unloads into the tires, and then here we go, hang the heck on!
But remember; I know nothing about BBs.........

 

[Kent mosby]

I think I get what yur asking;
With a Street car, IMO, you gotta think about things, in a different way.
A streeter, at WOT, is basically a one or a two gear car. For you, 60 mph will be about 6200 rpm, in FIRST gear, and it will take less than ~5 seconds to get there. So................. does stall make a difference? Well not on the shift because no shift has occurred. And at the other end, most horsing around starts at 25/30 mph; so does stall make a difference?
Not hardly.
For you; the only time stall can make a difference, is if you get NO tirespin from a dead stop, or if you just want to show off.
Like the guy above>>>> said; it might make a lil difference in your 60ft ............
Is .2 or .3 second, in the 60ft contest worth it to you?
Only you can answer that.
===============
Here's my thinking;
With 3.91s and 28.2s (88.6" roll-out); 3000rpm (at zero-slip), would get you 23mph in 2.45 first gear.
So any time that you are traveling at less than 23 mph, and you mash the gas, with a 3000TC, the Rpm will jump up to around 3000
But if you are already traveling at 35 mph, the rpm for zero-slip would be 4000.
So now, NO TC that flashes to less than 4000 will be of any use to you, after 35mph, in first gear, unless it happens to be more efficient.

Say you are tooling down the road in 1.45 Second gear at 35mph, doing 2365rpm plus say 3% slip =2435. Cuz with as much engine as you have, that's what I'd be doing.
Now when you mash the gas, the trans kicks down into First gear and the rpm pops up to say 4400@10% slip. The only way it can be any higher is to start with a higher Stall TC. So it's not likely you would ever choose that high a stall.
I chose 35mph in first gear because that 4400 is about where your peak torque will be happening, perhaps a a couple of hundred rpm sooner, it makes no difference, cuz your Scamp should be getting sideways with Street Tires.

So to make a long story short, your stall rpm in first gear, with your engine and combo, becomes less and less meaningful as the speed goes up. By 29/30ish mph, the road speed is high enough to lock up a 3000TC, so it ain't helping much any more.

But not true on the 1-2 shift. If you had a clutch the rpm drop from up-shifting First , into Second is a split of 59%; So shifting at 6000 would drop the Rs to 6000 x.59=3540.
If you had a 3540 stall TC that would get you the same 3540rpm, going into Second; so your engine would need a decent amount of torque at that rpm to continue accelerating briskly.
But if you had a 4540 stall, then at WOT the Rs would drop to only 4540, and you are 1000 rpm further up the power curve, and accelerating exponentially harder..
So ; on the 1-2 shift, the higher stall will make your car accelerate much harder.

Ok but, all of that above stuff is talking about WOT acceleration. Which with a Street car, you gotta think about, in a different way.
back to the Top.....

So then, what would a good number be for a stall?
IDK, I'm not a BB guy never mind a 512.

But; IMO, 1800 to 2400 is a lil too low.
However, the GVod turns your 3.91s into 3.05s and 65=2365rpm @zero-slip.
Your TC does Not have a lock-up so at 65 your Tc might want to slip say 3% so the Rs could be as high as 2440, and she'd be hydraulically coupled. Now, if you put a 2800TC on that; now reving 2440, she might be wanting to put some heat into the trans-oil.
However; coming out of overdrive at 60 would get you ~3100 in "Drive" for passing; not much rpm for a Small-block, but maybe lots enough for your engine. But notice that 3100 is higher than 2800, so again, any stall less than 3100 will not help you to pass.
I have always had small-blocks only (plus a few slantys), and I put 2800s on everything. Cuz I like how 2800s work. I like the feel of them. They drive decent all the time, but when I nail them with street gears like 3.23s or 3.55s, it kindof feels like a snow-mobile clutch. The engine winds up and then like a big ol' flywheel she unloads into the tires, and then here we go, hang the heck on!
But remember; I know nothing about BBs.........

Thanks for the incredible wisdom and response. You are much more experienced and learned than I am. It will take some time to completely digest it all. I even have to evaluate if my transmission even kicks down to 1st automatically when I punch it. Not another factor to consider!!! Again Thanks for the info. FWIW, with the GVOD, I am at 2700 or so at 70 mph. Would that be slipping?

 

[AJ/FormS]

With 3.91s, 28.2s , a TF automatic, and the GVod, the math is
(70 x1056 x3.91 x .78) divided by
( 28.2 x 3.1416)=2545rpm@ zero-slip
If your tach is accurate then (2700/2545) =1.061 so 6.1% slip; seems a lil excessive for a Scamp. More typical is 2/3%
What is your cruise timing? I bet not enough,lol. Ima thinking your combo will like 50 to 56 degrees. If, with your vacuum advance, you are only running say 40*, then 50/55 will greatly increase your cruise torque, and that should show up as a lower cruise rpm, which would translate to less slip.
3% up from the calculated 2545, is 2620. I use a digital tach for this kind of work, cuz the width of my tach needle is like a hundred rpm.

 

[Rmoore]

I sorta agree....but there are some really crappy converters out there. If he has one of those, he could gain a lot even on the street. He DID ask.

Totally agree !! I have 4 buddies that have all out drag cars !! Not street cars . My point being that 3 of them have 8 inch 5500 conv. 1 has 9.5 5500 conv. All 4 can put the pedal on the wood they flash stall approx 3500... All 4 cars leave off the trans brake at 4400.. Let the brake go all 4 cars will jump to 6500 to 6800 shift at 7200 to 7400... After shift drop back to that 6500 to 6800 and cross the traps around 7000 to 7200.. All 4 of these cars are 5.30 to 5.50 1/8 cars ... With all that said, I think it possible for OP to have a high stall conv and it still be very street friendly.. Custom conv in the last 10 yrs have come along way ! IMO you can have the best of both worlds with a good custom conv....

 

[Kent mosby]

With 3.91s, 28.2s , a TF automatic, and the GVod, the mathy is
(70 x1056 x3.91 x .78) divided by
( 28.2 x 3.1416)=2545rpm
If your tach is accurate then (2700/2545) =1.061 so 6.1% slip; seems a lil excessive for a Scamp. More typical is 2/3%

Currently the tires are 255s. So 27.3 when new going to be 28.2 with the next set of tires. My math got me 2.7% thanks. Closer to norm?

 

[Rmoore]

With 3.91s, 28.2s , a TF automatic, and the GVod, the math is
(70 x1056 x3.91 x .78) divided by
( 28.2 x 3.1416)=2545rpm@ zero-slip
If your tach is accurate then (2700/2545) =1.061 so 6.1% slip; seems a lil excessive for a Scamp. More typical is 2/3%
What is your cruise timing? I bet not enough,lol. Ima thinking your combo will like 50 to 56 degrees. If, with your vacuum advance, you are only running say 40*, then 50/55 will greatly increase your cruise torque, and that should show up as a lower cruise rpm, which would translate to less slip.
3% up from the calculated 2545, is 2620. I use a digital tach for this kind of work, cuz the width of my tach needle is like a hundred rpm.

Man i wish i wasnt a math retard !! My wife said she wishes i was not a retard period !!! AJ that actually makes sense !!

 

[AJ/FormS]

yes; 27.3" tires math to 2628rpm@ zero slip, and 2700/2628=1.027= 2.7% slip, which is right where I would expect it to be. I forgot your current tires were shorter.

I included the math so you guys can figure stuff out for yourselves, and not think that more highly of me than you ought to; I just plug the numbers into the appropriate places and let the formula be the wizard.
Here it is in shorthand
MPH = (rpm x Tire roll-out)/ 1056x R1 xR2 xR3
where
>Tire roll-out is in inches & can be tire circumference, or diameter x Pi
> Pi is 3.1416
>R1 is the trans gear
>R2 is the rear gear
>R3 can be any other torque multiplier you might have such as;
an overdrive/ transfer case/ gear splitter/or Torque Convertor/ etc.
>1056 is a constant that converts everything to the same units