On another site there is on going debate on stall and fall back. I seem to be on wrong side of it,hd to happen sometime .

Cpl are saying no matter where you shift its going to fallback to converters stall. Others me included where of the thinking the two where totally separate. If you shift a lot higher it would fall back more but nor to same point.

Opinions. Or maybe just facts you choose.

Mine falls back to roughly 300 above flash,which is the same point I have lockup.i have another converter that is really loose and flash and drop back are close to the same

No matter what RPM you shift it at it will fall back to the converters stall. At least, within the 7200-7600 range that I've tried in my car.

Just like no matter what RPM you launch at the converter flash is the same.

All converters do one thing and one thing only, sense load! and respond by stall or slip! Typically load will be higher just after the gear change vs at the hit and therefore stall/slip therefore will higher be too. It just measures load... change the load and the slip/stall will change too.

example I used for question. Was if you shift at 7500 and falls back to 6600(my flash stall) and then you go out next run and hang it out and shift at 8500. Is car going to drop back to 6660 or more like 7300,figuring stall and about 10% slippage at gear change?

Mine stalls at 6400, shift at 7600 and it falls back to approx 6800 (IIRC) then comes across finish line at 7400 1/8 and 7800 1/4.

quote:

Originally posted by wideopen231:
example I used for question. Was if you shift at 7500 and falls back to 6600(my flash stall) and then you go out next run and hang it out and shift at 8500. Is car going to drop back to 6660 or more like 7300,figuring stall and about 10% slippage at gear change?

More like 7300 or a little higher.

quote:

Originally posted by wideopen231:
example I used for question. Was if you shift at 7500 and falls back to 6600(my flash stall) and then you go out next run and hang it out and shift at 8500. Is car going to drop back to 6660 or more like 7300,figuring stall and about 10% slippage at gear change?

I believe you are thinking correct. It only falls back depending on the difference in ratios. Most of us are dipping down into the converter on the shift, so the fall back is more or less the stall. But as you said, if you wing it up there, you still only fall back so far regazrdless of the stall.

Mine is rated at 6000 stall. I shift at 7400 and it falls back to 6400. Not sure if it's best for the car but seems to be set up nicely.

I do know that simply changing gears in the diff means the converter stall will react differently. I have 4.86 gears in the diff. When I switched to 4.57 for a weekend, the stall speed sucked. Engine just couldn't get me down the track the same. Went back to 4.86 and performance picked right back up again. I don't know if a different stall converter with the 4.57 gears could have brought performance back up but that's the assumption I got from the gear change.

quote:

Originally posted by Bucky:

quote:

Originally posted by wideopen231:
example I used for question. Was if you shift at 7500 and falls back to 6600(my flash stall) and then you go out next run and hang it out and shift at 8500. Is car going to drop back to 6660 or more like 7300,figuring stall and about 10% slippage at gear change?

I believe you are thinking correct. It only falls back depending on the difference in ratios. Most of us are dipping down into the converter on the shift, so the fall back is more or less the stall. But as you said, if you wing it up there, you still only fall back so far regazrdless of the stall.

Huh???

Fallback is fallback. I can shift at 7500 or 8200, it's still going to fall back to 7000 give or take a 100. I'm assuming we're talking glides. If it's a 5 speed with a Bruno and a tight converter you might be going fast enough to not fall back on the converter, but I don't think that's what we're talking about here.

sorry just take for granite everyone is looking at glide. Funny I use to think everyone was talking about a blown Hemi with a lenco or the where talking about Top fuel. All in what your into at time I guess.

quote:

Originally posted by BJs Wild Ride:

quote:

Originally posted by Bucky:

quote:

Originally posted by wideopen231:
example I used for question. Was if you shift at 7500 and falls back to 6600(my flash stall) and then you go out next run and hang it out and shift at 8500. Is car going to drop back to 6660 or more like 7300,figuring stall and about 10% slippage at gear change?

I believe you are thinking correct. It only falls back depending on the difference in ratios. Most of us are dipping down into the converter on the shift, so the fall back is more or less the stall. But as you said, if you wing it up there, you still only fall back so far regazrdless of the stall.

Huh???

Fallback is fallback. I can shift at 7500 or 8200, it's still going to fall back to 7000 give or take a 100. I'm assuming we're talking glides. If it's a 5 speed with a Bruno and a tight converter you might be going fast enough to not fall back on the converter, but I don't think that's what we're talking about here.

There are limits to it.
For instance, if you have a 3000 stall, and 1.72 first gear, and you shift at 8500, your driveshaft speed ought to be 4941 before the shift. After the shift, what is the driveshaft speed? 4941 right?
What does the engine speed drop back to in second gear? 3000 rpm? No.
Is my math off here?

Sure, but that's the same as the 5 speed with the Bruno example I gave (meaning, yes, you can possibly run it past the converter). For a typical bracket race glide setup like Chris's, you are going to have to go north of 10,000 in low gear to stay above the converter after the shift. I guess he could probably do that since he has a hemi but I don't think that's what he was after.

been there broke that! No 10 k now unless something breaks and rev limiter does not kick in. I don't plan n seeing 8500 unless its 1/4 mile.Let it live is new rule and damn what a change.

This motor had been north of 10,000 but had 52# of boost (blowers don't quite pulling then either),plus Chris was making lot more money then,hence Chris has none now. LMAO because CMAO wouldn't change that.

quote:

Originally posted by TOP38:
Typically load will be higher just after the gear change vs at the hit and therefore stall/slip therefore will higher be too.

You're telling me that the load is higher trying to accelerate a car that is already going near 100 mph, than it was to get the car moving from a dead stop? I don't think so.

The RPM is higher at the gear change because there is less resistance, not because the load is greater.

This can get long so stay with me!!

Typically a spragless converter will fall back within 200 of the flash stall of the converter if the car is geared correctly.. Gear ratio will affect this as well because vehicle weight to a converter is altered by gear ratio.

On Sprague type converters with curved blades they will typically fall to 400 -500 over te flash point of the converter. If you use a flat blade stator with a diode it will act more like a spragless but recover better on the gear change in a low hp application.

Understand that the converter only multiplies torque when the stator is held still. This happens on the starting line until the turbine meats 40% of impeller speed and a split second at the gear change.

Please remember to take into effect the the transmission gear ratio will affect converter fall back as well. When a pg equipped car with a 1.80 ratio low gear shifts to high you have a .80 ratio change. when a th400 equipped car shifts with a 2.48 gear set shifts it looses 1.0 on the 1-2 change and .48 on the 2-3 change therefore making the fallback different as well. Please take this into consideration.

Summary. We use different fall back ratios per different applications. Such as but not limited to bracket racing, nitrous applications,boosted applications,small tire applications,etc.

Greg

quote:

Originally posted by Lenny5160:

quote:

Originally posted by TOP38:
Typically load will be higher just after the gear change vs at the hit and therefore stall/slip therefore will higher be too.

You're telling me that the load is higher trying to accelerate a car that is already going near 100 mph, than it was to get the car moving from a dead stop? I don't think so.

The RPM is higher at the gear change because there is less resistance, not because the load is greater.

Yes, The load is higher trying to accelerate a car that is going 100 mph. Mass is the same, gear ratio is lower, and aero drag force is higher. There is no velocity term in F=ma

quote:

Originally posted by BJs Wild Ride:
Yes, The load is higher trying to accelerate a car that is going 100 mph. Mass is the same, gear ratio is lower, and aero drag force is higher. There is no velocity term in F=ma

There is no velocity term, but what is the 'a' element in your equation at the gear change compared to what it was at the starting line? Acceleration is highest at launch and drops continually during the run.

A static stall test is the greatest load you can put on a converter. It is trying to move something that cannot be moved. A higher "stall" at the gear change only shows the lack of resistance by comparison.

I really don't have a dog in this fight,yet. I plan to shift 7500 and with 6600 stall(flash) I figure to fall back to that. Now if I put 25% load in it which according to Greg at FTI should raise my stall to about 7300 I guess I will have to move shift up or call it a high gear run. In all honesty will need second converter then,but that's down the road away.

Thanks for replys especially Greg. Was hoping you would chime in.

This message has been edited. Last edited by: wideopen231,