Converter stall, launch rpm and shift points... ??

[HT413]

This question isnt really about finding the right converter for my application (yet).... I really just have questions regarding rpm strategies during a race and how the converter ties into that...

I hear a lot of guys with 4000-5000 stall converters are launching well below the stall, say 2800 rpm, 3500 rpm or whatever. I just dont understand this, wouldnt it be better for launch rpm to be at the stall?

Also, I *think* I've read where guys shift at a point where when it hits the next gear the motor drops below the converter stall.

Reason I'm asking is my car came w a 4000 stall converter but since I dont know whats in the motor (other than its a 413 with hydraulic cam and double springs), I've never taken it much above 5000 rpm. But if I shift at 5000 rpm it'll put me below the stall speed in the next gear. I plan on opening it up soon to see what I have, but not sure I'll be doing it before I hit the track this year.

Just tryin to learn here, so any help would be appreciated.

 

[Al K]

I'm following this thread! Some of the same questions I have,in picking what I want/need for my project.

 

[Budnicks]

this is a really complex question & answer

IMHFO your torque converter's effective {actual, not advertised} stall speed, is ultimately decided by many variables & engine torque out-put "at it's highest point" {especially for a drag race application}, your final gear ratio used, the camshaft size/type/design {especially the duration}, weight of the car {can & will effect stall speeds} & intended usage, type of rear suspension, shocks, front end lift {wear the weight is in the car can effect the stall speed too}, reciprocating weight, altitude also {can really effect the torque converter stall speed, a car generally can/will have a stall speed higher at a lower elevation}, if it's a all-out drag car with slicks or drag radials you can get away with more stall speed than a street/strip car or even taller tires can effect relative stall speed {generally the taller tire gives more stall speed than the same exact set-up with a shorter tire}, the steeper the gears "generally" the more torque converter stall speed, you will need... Example; with a true 3500rpm torque converter stall speed & a 3.91:1 gear will be very effective, but the same exact converter with a 4.56:1 gear won't stall up as far because of the torque multiplication of the rear gears, moves the car easier {unless you are using a Trans-Brake}, also if you have a heavy car, the stall speed will be effected differently {usually higher stall speeds}, than a lighter car with the same exact combo, also a bigger torquier engine, will stall at a higher RPM usually, than with the exact same converter, than a smaller sized less torqurier engine combo, that's if you understand what I'm saying... There is a great book "Torgueflite A-727 Transmission Handbook" by author Carl Monroe, published by HP-Books, very good explanation of how, why & what converter does & how it ultimately works... I hope I didn't just confuse the hell-out of everyone, my drag racing & engineering back ground kicks in, from time to time, I get a little **** retentive...LOL..at times & kind of sound like a "damn know it all" & I'm really not trying to be, I just don't want people to have to learn the hard way, like I always had too, when my piers/people, just wouldn't share their hard earned knowledge, with a fellow competitor...LOL...

 

[Al K]

Sir;that was well stated and very easy to understand. THANK YOU!

 

[Budnicks]

Sir;that was well stated and very easy to understand. THANK YOU!

Good... Glad I could help, I get a little crazy with my explanations at times...

 

[HT413]

Wow, that was great, Budnicks, that was great. So I've been reading a lot of guys saying they have a high stall converter but actually launch way lower than the stall. What's the deal with that? Thanks again.

 

[67 coronet]

Good... Glad I could help, I get a little crazy with my explanations at times...

first off i had to thank that post for one hell of an excellent explanation.remember ht413 each car will act way diff with the same stall and they could be leaving at a lower rpm to control consistancy.it can also"soften"the launch allowing for very agressive setups.

 

[dvw]

I will ad the shift point explanation. Look at a horsepower curve. Your shift point will generally be a horizontal line intersecting shift point RPM and the point where rpm drops after the shift. If the line tilts down towards the peak,the shift RPM is to high. if the line tilts down toward the shift fall off RPM, the shift point is to low. A flat high torque curve motor will be less sensitive to changes. Quickest way to figure it out? Use a G-Meter. Shift at peak G.

 

[383man]

IMHFO your torque converter's effective {actual, not advertised} stall speed, is ultimately decided by many variables & engine torque out-put "at it's highest point" {especially for a drag race application}, your final gear ratio used, the camshaft size/type/design {especially the duration}, weight of the car {can & will effect stall speeds} & intended usage, type of rear suspension, shocks, front end lift {wear the weight is in the car can effect the stall speed too}, reciprocating weight, altitude also {can really effect the torque converter stall speed, a car generally can/will have a stall speed higher at a lower elevation}, if it's a all-out drag car with slicks or drag radials you can get away with more stall speed than a street/strip car or even taller tires can effect relative stall speed {generally the taller tire gives more stall speed than the same exact set-up with a shorter tire}, the steeper the gears "generally" the more torque converter stall speed, you will need... Example; with a true 3500rpm torque converter stall speed & a 3.91:1 gear will be very effective, but the same exact converter with a 4.56:1 gear won't stall up as far because of the torque multiplication of the rear gears, moves the car easier {unless you are using a Trans-Brake}, also if you have a heavy car, the stall speed will be effected differently {usually higher stall speeds}, than a lighter car with the same exact combo, also a bigger torquier engine, will stall at a higher RPM usually, than with the exact same converter, than a smaller sized less torqurier engine combo, that's if you understand what I'm saying... There is a great book "Torgueflite A-727 Transmission Handbook" by author Carl Monroe, published by HP-Books, very good explanation of how, why & what converter does & how it ultimately works... I hope I didn't just confuse the hell-out of everyone, my drag racing & engineering back ground kicks in, from time to time, I get a little **** retentive...LOL..at times & kind of sound like a "damn know it all" & I'm really not trying to be, I just don't want people to have to learn the hard way, like I always had too, when my piers/people, just wouldn't share their hard earned knowledge, with a fellow competitor...LOL...

Well said Budnicks.
One thing that I can tell you is that when I am foot braking my 63 (which is the only way I race it) I will come up on the converter at the line. It wont go up to the stall speed sitting still as I usually power brake mine to about 2000 at the line. Then when I launch I just release the brake and floor it. Then the converter will flash the rpm up where it should be around the stall speed where the car has the least amount of converter slippage. Thats why you might hear guys say "I come up on the converter to 2000 rpm at the line" and it may be a 4200 stall converter that should flash to about 4200 when floored and you put the full eng power to it. My Dynamic 9.5 converter will flash about 4200 rpm when I nail it at the line but it will cruise the streets all day long at 3000 rpm and have no problems at all. Thats the good thing about todays converters as many are like mine which is considered a street/strip converter that will drive normal but will flash about 4200 when floored with full eng power. Ron

 

[oldbee]

I concur with budnicks & 383man..Although way back when; I did it a little different. Idle at the lights and then just 'nail it',,But you have to have the carb set up good for no hesitation at all when nailed.

 

[Budnicks]

oldbee yeah the off high idle deal, then just nailing it, can get a near full flash & can work well, if you can tune the car well enough, get enough of a shot of fuel {good fuel pump Ignition & 50cc acel. pumps & jet extensions, much easier with Fuel Injetion} & not fall on it's face or be able to handle it & have the suspension set up properly, with some pre-load, so you don't blow drive-shafts or axles out of it, with slicks & a good track or hard hook... My step father Bob, use to do that style launch, back in the late 60'searly 70's, with his 64 GTO Pontiac S/S... Long before any decent quality Tires, TQ converters & Trans-Brakes were being used..

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383man yeah with out a Trans-Brake, usually you cant get to full stall speed, until it flashes, I use to do somewhat the same thing, with a reworked to flash at 4200 rpm, 11" 175k Mopar J converter {reworked for N20}, bring it up-to about 3200rpm {that's when it would drive thru the brakes, if you went any farther}, then nail it when I see yellow, on a pro-tree, it would flash at sea level to about 4500rpm... With the trans-brake & slicks, {instead of Drag radials & just foot braking, it would blow the tires off w/trans-brake & Drag radials, the way the car was set-up, w/CalTracs} it was worth about almost a full a 0.10 {or more} better in 60ft & 0.25 in the full 1/4 mile, at sea level, on a good prepped track, even better with alittle cloud cover, with that 479ci 6bbl combo, a little less as the altitude rises or relative air density worsens/changes...

 

[Cranky]

I concur with budnicks & 383man..Although way back when; I did it a little different. Idle at the lights and then just 'nail it',,But you have to have the carb set up good for no hesitation at all when nailed.

That's the way I used to run my old car. It had a 4500 stall and 2 750 DP's on a Weiand TR. Using the stall it would run a 10.68 and off idle, it ran a .69 so idle it was unless I needed the .01....

 

[Budnicks]

Wow, that was great, Budnicks, that was great. So I've been reading a lot of guys saying they have a high stall converter but actually launch way lower than the stall. What's the deal with that? Thanks again.

IMHFO with out a trans-brake you won't be able to probably hold it, with just the brakes long enough to get it to full stall speed... But it should flash to the proper stall speed {at least near it}, if the converter was set-up/built properly, for your specific engine, trans, gears, suspension, tires, weight, combo etc...

 

[arizona satellite]

I concur with budnicks & 383man..Although way back when; I did it a little different. Idle at the lights and then just 'nail it',,But you have to have the carb set up good for no hesitation at all when nailed.

that how I use to run my 66 coronet it had a 3500 rpm stall and I would set in the "lights" at idle and then just mash it! it would flash to 4000 and just go like hell(use to drive the guys in the other lanes nuts) and if my decrepit memory serves I think I only lost a couple hundred rpm between shifts. the tach would just "dip". I mean it was not a rocket but a solid 12.0 daily driver.

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IMHFO with out a trans-brake you won't be able to probably hold it, with just the brakes long enough to get it to full stall speed... But it should flash to the proper stall speed {at least near it}, if the converter was set-up/built properly, for your specific engine, trans, gears, suspension, tires, weight, combo etc...

budnicks, what about using a 2 step rev limiter like the MSD 6al-2 and setting the 1st stage on the brake switch at a certain rpm and then wamo! you let off the brake? flash the converter.

 

[383man]

I concur with budnicks & 383man..Although way back when; I did it a little different. Idle at the lights and then just 'nail it',,But you have to have the carb set up good for no hesitation at all when nailed.

I tried my car a few different ways. I have left from and idle and from 1500 rpm to 2000. It seems to 60 ft the best launching from about 2000 rpm against the converter. It is amazing how hard and auto car will launch with these modern converters. Ron

 

[Budnicks]

budnicks, what about using a 2 step rev limiter like the MSD 6al-2 and setting the 1st stage on the brake switch at a certain rpm and then wamo! you let off the brake? flash the converter.

Good idea, yeah with some added electronics, I'm sure you could do wonderful things... I had MSD 7 w/multi step chips, & retard stuff, back in 2007ish {I think} & progressive application of N20, because I had 3 kits, a plate kit/under carbs, a spray-bar kit/plumbed in the manifold plenum & port Nozzles/at the base of the intake manifold, pointing at the top of the intake ports/valve, on one of my old fast race cars {with Top Gun & Jacobs Electronics, I don't even know if they are still in business}, you can have a bunch of timing/rpm/N20 or what ever at the line & drop it off/or ramp it up, at the big end, so you get the best of both/all worlds, what fits your specific application/combo/ignition/launch & needs... IMHFO if the rules allow it, then by all means, use what ever is at your disposal, to make the car work best... Now after saying all that... But I have none of that electronic aided stuff currently now, on my current 68 RR, just old school foot braking & a manual valve-body type deal, I haven't been to the track in a couple years now either {taking care of old Pops, the property & an old dog, not much work, it's dipping into my race funds & have I allot milder street/strip car too}... I'm not trying to set the world on fire anymore, well at least not for now anyway...LOL... but soon maybe I hope, I'm just trying to help/pass on some of my experience/knowledge, what I did & how I run my stuff, may not be the best thing for all cases/people... good luck

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I tried my car a few different ways. I have left from and idle and from 1500 rpm to 2000. It seems to 60 ft the best launching from about 2000 rpm against the converter. It is amazing how hard and auto car will launch with these modern converters. Ron

383man That's the perfect example trial & error, to help to figure out, what works the best, for your specific combo, they are all different... I was kind of a die-hard test & tuner, lots of time spent at the track & wouldn't really actually race, until I got everything sorted out 1st & could be really consistant at doing it.... my $0.02 cents

 

[womanator]

Ok I'll start off by saying this stuff worked for me.
Not a marble left in this brain.
Had my engine dyno'd.
My tq converter flashed 200 rpm over that.
I Leave off the trans brake.

Tip on reaction time's.
Use a rotory wheel rev limiter.
If you are red lighting lower your launch rpm's and it will make you car react slower.
if you are late raise your rpm limiter and your car reacts faster.
Leave your adjustable trans brake button alone it doesn't know 1/4 or 5/8ths of a turn differance.
Not consitant enough.

Now shift points.
90% of the racers out here 1-2 2-3 at the same rpm.
I did this for years.
Then I wanted to go faster and not spend a ton more money.
I spent a day at the chassis dyno and ran all gear dyno pulls.
This is very hard on the car.
No flex for the chassis because of the way they have to tie the car down.
What I learned from this is where my peak tq was in each gear.
Now I can set my shift points where my peak tq is at instead of using my engine dyno numbers.
What I also learned from the chassis pulls from video the runs was that I was not shifting where I thought I was.
I learned that by the time I shifted I was 200 rpm's over where I wanted to be at.
It also helped having a shift light that you can set each shift to.
This info gained me a .10 in the 1/4 mile.

Ramblings of an old man.

 

[HT413]

WOW. Thank you, fellas, for sharing some wisdom. You already put this rookie gearhead years ahead of where I'd be otherwise. As a payback to the racing gods, I plan on going a couple of times just to watch the staging and pre-race procedures before I bring the car just so I don't piss anyone off behind me.

 

[Budnicks]

HT413 Good luck & it never hurts to be familiar with what's going on... I like that saying, rookie gearhead years ahead...LOL...

 

[67 coronet]

WOW. Thank you, fellas, for sharing some wisdom. You already put this rookie gearhead years ahead of where I'd be otherwise. As a payback to the racing gods, I plan on going a couple of times just to watch the staging and pre-race procedures before I bring the car just so I don't piss anyone off behind me.

you shouldnt ever piss anyone off,but you could get laughed at.my fav are the rookies that line up at the tree and not at the lights.