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 Post subject: Converter stall??
 Post Posted: Thu Oct 28, 2010 3:29 pm 
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With all the talk over on John's post how do you know if the stall is correct
and efficiency is right at the other end??? Now ken is going to race 1/4 mile next year so will he need a stall change or something??

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 Post subject: Re: Converter stall??
 Post Posted: Thu Oct 28, 2010 5:04 pm 
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To measure efficiency you have to have engine RPM divided by driveshaft RPM .


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 Post subject: Re: Converter stall??
 Post Posted: Thu Oct 28, 2010 7:09 pm 
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Beretta wrote:
With all the talk over on John's post how do you know if the stall is correct
and efficiency is right at the other end??? Now ken is going to race 1/4 mile next year so will he need a stall change or something??


From what I have learned from others and experimenting, there are more than one way to gain stall and they can have opposite effects in different areas. The stator is the biggest factor in controlling these. If you have a stator that has high torque multiplication it will slip more on the big end and vise-versa. So a big high torque engine doesn't need the tq multiplication (depending on the car) and can use the top end efficiency. Some things probably increase stall and decrease efficiency like internal spacing and fin angle.

My converter in the dragster is a bolt together that I have 2 different stators for. The one in the car now has much thicker wing shaped fins. The other stator has much flatter fins. Next Spring I plan to have data aquisition on the car and will do a stator swap to see how they affect G's, 60', fall back rpm, top end lock-up etc. I think the stator in the car now is the one that multiplies torque better. I only ran the other stator in the roadster and it seemed to stall nearly the same (when it was still 4-barrels), but then switched the carb to 2 barrels so I could race w/o certifying the car.

My friend with a heavy car w/355 engine bought an ATI converter and it seemed to be really efficient and had lower than expected finish line rpm. but seemed slow in 60' which makes me think it is a low TQ mult and good effiiciency type. A recent swap to a bolt together of Randy's produced 60's equal to the best mine shaft air times he had in 2500' DA.

There are things in the valve body that affect fluid flow to/from the converter and can move stall speed a few hundred rpm also. Lots to it and I plan to learn more in the Spring. stay tuned... my work schedule is about to drop back to ~40hrs a week for the first time in 2-1/2 yrs so I will have more time this Winter to prepare for racing in the Spring.

Rick


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 Post subject: Re: Converter stall??
 Post Posted: Thu Oct 28, 2010 7:25 pm 
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There is a mechanical diode in mine....

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 Post subject: Re: Converter stall??
 Post Posted: Thu Oct 28, 2010 8:39 pm 
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Beretta wrote:
There is a mechanical diode in mine....

That is another type of one way device like a sprag. Doesn't affect the way it works. The sprag/mech diode allows the stator to only rotate in one direction.

Rick


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 Post subject: Re: Converter stall??
 Post Posted: Thu Oct 28, 2010 8:46 pm 
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Barry I'm not going to change either the gear or the verter. Right now I'm running through around 7400 so quarter mile will likely be up around 8200 or so, which this engine can handle. I've turned it 8600 before so I know it can.

Racing at Dinwiddie is normally eight mile just like everywhere else now a days. The guy did tell me that I could make some q mile passes during their Saturday test and tune sessions, which is what I plan to do so it's not like I'll be doing q miles every week. ;-)

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 Post subject: Re: Converter stall??
 Post Posted: Fri Oct 29, 2010 3:53 pm 
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Beretta wrote:
With all the talk over on John's post how do you know if the stall is correct?


Looking at your dyno sheets again it looks like I'd want ~6500 stall, maybe higher its hard to tell since you didn't pull the engine past what we can only assume is peak hp rpm of 7500. I always like to pull it on up 500 rpm past peak hp on at least one pull to see how quick the power falls off since that can change where you want the stall rpm to be. If you look at your TQ numbers at 7400-7500 they were not dropping much so lets say the TQ dropped 5ft-lbs to 657 which would be 950hp, a new peak hp. I can't say if it would have, but we'll never know. Your shift rpm is harder to determine also w/o the numbers on up.

Rick


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 Post subject: Re: Converter stall??
 Post Posted: Fri Oct 29, 2010 4:04 pm 
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I know theres is lots of different opinion on the subject of where to put the stall. My opinion is a torque converter is a torque multiplier so you want it to multiply the maximum torque so stick it there. Then get the number of gear ratios and the split and the rpm shift points to keep the most area under the curve of driveshaft torque. To do that you have to log the acceleration rate (G's) or work out the rate from driveshaft speed curvature. Doing it that way accounts for all physical factors of the cars actual performance, (wind, tire, friction losses,inertia losses, tune etc). I find the point on the high rpm side where a shift will bring the driveshaft torque to equal so that before and after the shift the applied torque is the same.
To me thats the real world way of doing it.


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 Post subject: Re: Converter stall??
 Post Posted: Fri Oct 29, 2010 4:47 pm 
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The way it was explained to me by a Comp eliminator racer was you look at the highest average HP in the range you run, usually a 1200 RPM or so range, The bottom point, usually somewhere over the peak torque, is the stall point. The top end, somewhere just over the peak HP, is the shift point. As long as it does not effect the efficiency of the converter, a little higher on the stall will not usually hurt and may soften the hit a little for bad tracks, and makes it a little more consistent.


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 Post subject: Re: Converter stall??
 Post Posted: Fri Oct 29, 2010 6:12 pm 
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Beretta wrote:
With all the talk over on John's post how do you know if the stall is correct
and efficiency is right at the other end??? Now ken is going to race 1/4 mile next year so will he need a stall change or something??


Way to go on draggin me into this Barry :- =;

See, this is where I go blurred with all this info and talk about stall also! The info jmarkaudio mention's could be very clean info as the Comp. Elimn. guys spend BIG bucks to fine the right converter for there engine whether it being a 331cuin from Patterson, or a large inch engine. I understand what you are saying too jmarkaudio, or what the comp. elimn. guy was telling you that is, but these guys make hundreds of passes in there hotrods and know them well unlike a lot of us bracketeer's #-o but a lot can be learned from them for sure.

Shrinker, I haven't forgotten about your info either, your info reads true as much as I can understand it and it is very useful provided the racer has access to the G meter, and data logging equipment to read drive shaft speed vs engine speed, my Ultimate II tach has this function of data retrieving too, but I have misplaced my download cable, so I will jump in the car this weekend and see if I can get the tach to showback the run I recorded.

I understand what you are saying also shrinker on having the stall be right at the max of torque power. So, once I get my engine dyno'd, and find out where max torque is, whoever I select to build my converter (SHOULD) be able to get it right the first time out, right?, or you would think? :-k

You know, I wish these torque converter companies would work closer with the racer and take the credit card number, and then build the converter and send it to the racer to try it out, at THAT point, that is when the driver car owner or whoever, will know it works for there combo, then charge that card and be done with it, otherwise send it back and try again, but we all know that won't right? :- If my converter isn't right when I get it and put a HUGH smile on my face, it is going back A.S.A.P. and a phone call is right after it ships. ;-) I don't know what else to do if it is wrong, or not matched properly! :-k

This is great info too guys, thanks for posting it. \:D/ \:D/

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 Post subject: Re: Converter stall??
 Post Posted: Sat Oct 30, 2010 10:08 am 
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Hummm, so use to be that if the stall wasn't where you wanted it, they would rework it for shipping charges only? Is that not the case anymore? :-k

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 Post subject: Re: Converter stall??
 Post Posted: Sat Oct 30, 2010 6:48 pm 
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I would assume that is the case Ken, it just starts to get expensinve if it goes back more than once! ](*,)

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 Post subject: Re: Converter stall??
 Post Posted: Sun Oct 31, 2010 4:30 pm 
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shrinker wrote:
I know theres is lots of different opinion on the subject of where to put the stall. My opinion is a torque converter is a torque multiplier so you want it to multiply the maximum torque so stick it there.

The engine stays on the converter for a while on the launch and then again after the shift so the stall needs to be at a higher rpm that is higher in HP to accelerate the quickest. On larger engines with longer strokes and heavier rotating inertia the stall should probably be closer to peak HP, and on small ci, short stroke high rpm engines it should be 500-600 below peak hp. A broad range depending on the application, but I don't think a drag race car would ever run quickest with the stall at or below peak TQ rpm.

shrinker wrote:
Then get the number of gear ratios and the split and the rpm shift points to keep the most area under the curve of driveshaft torque. To do that you have to log the acceleration rate (G's) or work out the rate from driveshaft speed curvature. Doing it that way accounts for all physical factors of the cars actual performance, (wind, tire, friction losses,inertia losses, tune etc). I find the point on the high rpm side where a shift will bring the driveshaft torque to equal so that before and after the shift the applied torque is the same.
To me thats the real world way of doing it.


Yes, driveshaft torque or axle torque is what accelerates the car. Most area under the curve should be close, but since the engine is at stall speed earlier in the run makes it more important to your ET. There will always be some trial and error with converter selection because the torque multiplication is an unknown (at least to most of us). It would be great if they had converter dyno's that they could actually show the input rpm and torque and output rpm and torque. Maybe they have them but if they do we don't get to see any info for our converter we are buying.

Rick


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 Post subject: Re: Converter stall??
 Post Posted: Sun Oct 31, 2010 6:32 pm 
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rick360 wrote:
The engine stays on the converter for a while on the launch and then again after the shift so the stall needs to be at a higher rpm that is higher in HP to accelerate the quickest. On larger engines with longer strokes and heavier rotating inertia the stall should probably be closer to peak HP, and on small ci, short stroke high rpm engines it should be 500-600 below peak hp. A broad range depending on the application, but I don't think a drag race car would ever run quickest with the stall at or below peak TQ rpm.Rick

Interesting; This is how I think about it.
From what I know a torque converter doesn't increase its multiplication ratio if you make it hold the engine at higher RPM. Unless your changing the design of the stator vanes (primarily) your not altering its multiplication. So if you swap out a converter that's holding at say max torque with a given multiplication for one that's at max HP you don't gain multiplication factor to compensate for the lower torque value of the maximum HP point. So to me that means you get the most drive-shaft torque if the hold is on the max torque.
Because a torque converter isolates the engine RPM from the input shaft RPM during the periods where it is in slip the input shaft/drive-shaft will provide the most HP when the converter is in slip, thats because the engine is outputting the maximum torque into a slower rotating input shaft. So the input shaft HP is highest when the converter holds the engine on maximum torque not at an RPM above that point.
Whats more important to me is to know what the multiplication factor response curve looks like and you can get that from a data logger. Provided your car cannot spin the wheels you get good information on the converter by doing incremental calculations or using a front wheel speed sensor or fifth wheel.
If you analyze the torque necessary to move the car in increments as measured on a data logger (especially easy with a fifth wheel) you can correlate that information with an engine dyno sheet and figure out if moving the hold point higher will benefit you with whatever gear ratios you have. If you have close gearing steps your engine may not drop down enough RPM to unlock the converter for long enough or even at all. So in that situation it possibly would be better to set the hold (stall) above the gear shift drop RPM.

Torque converters are very interesting but its expensive to play with them.


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 Post subject: Re: Converter stall??
 Post Posted: Sun Oct 31, 2010 8:58 pm 
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shrinker wrote:
Interesting; This is how I think about it.
From what I know a torque converter doesn't increase its multiplication ratio if you make it hold the engine at higher RPM. Unless your changing the design of the stator vanes (primarily) your not altering its multiplication. So if you swap out a converter that's holding at say max torque with a given multiplication for one that's at max HP you don't gain multiplication factor to compensate for the lower torque value of the maximum HP point. So to me that means you get the most drive-shaft torque if the hold is on the max torque.
Because a torque converter isolates the engine RPM from the input shaft RPM during the periods where it is in slip the input shaft/drive-shaft will provide the most HP when the converter is in slip, thats because the engine is outputting the maximum torque into a slower rotating input shaft. So the input shaft HP is highest when the converter holds the engine on maximum torque not at an RPM above that point.
Whats more important to me is to know what the multiplication factor response curve looks like and you can get that from a data logger. Provided your car cannot spin the wheels you get good information on the converter by doing incremental calculations or using a front wheel speed sensor or fifth wheel.
If you analyze the torque necessary to move the car in increments as measured on a data logger (especially easy with a fifth wheel) you can correlate that information with an engine dyno sheet and figure out if moving the hold point higher will benefit you with whatever gear ratios you have. If you have close gearing steps your engine may not drop down enough RPM to unlock the converter for long enough or even at all. So in that situation it possibly would be better to set the hold (stall) above the gear shift drop RPM.


You make some good points and all I have are possible theories as to why higher stall works better. It might be because the stator would start spinning earlier on a lower stalling converter stopping/reducing the TQ multiplication earlier in the run. I can assure you the cars where I have seen converter changes work better when stalling well past peak TQ rpm. I had a Coan behind a engine that stalled ~ 7000-7100 and after dynoing the engine found peak TQ was at 7000rpm peak HP at 8000 and sent that dyno sheet to Coan to rebuild and adjust stall as needed. They said it needed loosened and it stalled 7500 when I got it back. My dragster converter stalls 5700 and peak TQ is 5200-5300 and I think it needs a couple hundred more stall.

shrinker wrote:
Torque converters are very interesting but its expensive to play with them.

Yes, having a bolt-together makes experimenting easier. We are lucky here to have a local guy who builds bolt-together race converters and has been for many years. They have always worked well. I plan to do converter stator testing in the Spring with data acquisition on the dragster.

Rick


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