Picking a New Full Race Stall Speed

[Alky V6]

My tuning adventure of the car is reaching completion. The last major hurdle is to pick a new torque converter stall speed.

The TC I'm presently using is stalling at 2440 rpm, no nitrous, no boost. With the nitrous shot, it is stalling at 3900 rpm.

The boost rise curve is tightly tied to the rpm of the engine and the use of the nitrous shot I use to help spool the turbo.
I'm thinking that I need at least 4-8 psi boost at the launch to reach my goal of a 1.2x 60 foot.
The latest datalogs show that I'm reaching 130 kPa by 5200 rpm and 145 kPa by 5600-5700 rpm. 5700 rpm is the point of peak torque for the motor, determined by the fuel table.
Fuel delivery peaks at 5700 rpm.

I'm thinking that a launch stall speed of 5600-5900 rpm would get me to my target.

I'm also hoping for a shift rpm drop of 300-400 rpm, instead of the 1,000 rpm drops with the present TC. The large drop is having a lot to do with the tires blowing away on the shift.

The last target for the new TC is minimum slippage on the top end. 2-4 percent.

 

[charlief1]

Didn't you just get a new converter last year Donnie?

 

[Alky V6]

Didn't you just get a new converter last year Donnie?

I tried a different stator for this TC that I've been using since around 2001.
I've thrown in the towel on this TC. It's allowed me to develop the midrange rpm of the fuel table, and worked very well with the T76, but the larger turbo is needing much more help than the nitrous alone can provide.

 

[Alky V6]

This is the latest fuel map revision.
With a fuel table that is well dialed in, you can use it as a good indicator of the engine's torque curve. This view shows where the present launch stall speed is at.

 

[Alky V6]

This view shows where the proposed new stall speed will be.

This sucker is going to YANK HARD!

 

[bison]

Its about time. I agree on the launch speed. It will depend on how much you chassis can take. Id want more than 300-400 drop though. I dont think your truly overpowering the tires and something else may need adjustment. Your flash stall should be around your peak torque rpm or slightly higher so you will likely still see 1000+ rpm drops. With the current tech the PTC converters have ive seen them drop considerably on the shift and continue dropping slightly for a second or so after the shift and almost flat line the engine for a couple seconds. This leads to some incredible g forces and the best e.t.'s. The launch stall speed you are looking at at 4-8psi will be hard to couple with the internals needed to get the high stall at low boost on your engine.You will probably have 7-9% slip when everything is optimally dialed in up top.

 

[Nick Micale]

My advise in one word - Dusty/PTC!

I doubt that there is anyone more qualified to provide you with a converter that will be right for you, generally the first time.

After spending a few days with him at the Turbobuick.com event last week, he shared his knowledge and experience with us and has supplied some of the fastest turbo converters to many happy racers.

My customers have great success with his converters from 11 sec. to 7 sec. builds.

 

[Alky V6]

Its about time. I agree on the launch speed. It will depend on how much you chassis can take. Id want more than 300-400 drop though. I dont think your truly overpowering the tires and something else may need adjustment. Your flash stall should be around your peak torque rpm or slightly higher so you will likely still see 1000+ rpm drops. With the current tech the PTC converters have ive seen them drop considerably on the shift and continue dropping slightly for a second or so after the shift and almost flat line the engine for a couple seconds. This leads to some incredible g forces and the best e.t.'s. The launch stall speed you are looking at at 4-8psi will be hard to couple with the internals needed to get the high stall at low boost on your engine.You will probably have 7-9% slip when everything is optimally dialed in up top.

Don't forget that the 4-8 psi launch target is on top of the nitrous shot. That's going to add a little bit to the mix.

 

[Dusty Bradford]

I'm also hoping for a shift rpm drop of 300-400 rpm, instead of the 1,000 rpm drops with the present TC. The large drop is having a lot to do with the tires blowing away on the shift.

The last target for the new TC is minimum slippage on the top end. 2-4 percent.

Not likely to happen. Some of the 10" cores can have less rpm drop and great efficiency but they are also very tight down low.....basically a nitrous converter. You've got a variant of this type converter in your car now.

I do not agree that the rpm drop is causing traction issues. Fiscus, Gomes and many of the 7 second V8 cars running these converters all drop 1000 and in some cases 1200 and none have a traction issue because of it. You've got suspension issues somewhere causing this upset or a bump in the track your racing at.

Why don't you post a picture of yours taken apart so I can possibly tell you what I would change about it:biggrin: I betting you have a very tight stator with little fin angle.

 

[baadgn]

My tuning adventure of the car is reaching completion. The last major hurdle is to pick a new torque converter stall speed.

The TC I'm presently using is stalling at 2440 rpm, no nitrous, no boost. With the nitrous shot, it is stalling at 3900 rpm.

The boost rise curve is tightly tied to the rpm of the engine and the use of the nitrous shot I use to help spool the turbo.
I'm thinking that I need at least 4-8 psi boost at the launch to reach my goal of a 1.2x 60 foot.
The latest datalogs show that I'm reaching 130 kPa by 5200 rpm and 145 kPa by 5600-5700 rpm. 5700 rpm is the point of peak torque for the motor, determined by the fuel table.
Fuel delivery peaks at 5700 rpm.

I'm thinking that a launch stall speed of 5600-5900 rpm would get me to my target.

I'm also hoping for a shift rpm drop of 300-400 rpm, instead of the 1,000 rpm drops with the present TC. The large drop is having a lot to do with the tires blowing away on the shift.

The last target for the new TC is minimum slippage on the top end. 2-4 percent.

So if I am reading this right what you are implying is that with your combo you can not get it to work with the nitrous. I thought this whole journey was to show that it CAN be done, shurley a new convertor is going to cost money. Which has been a hinderence of yours in the past and an excuse to not do what MANY knowledable people have recommended you to do.

 

[baadgn]

Not likely to happen. Some of the 10" cores can have less rpm drop and great efficiency but they are also very tight down low.....basically a nitrous converter. You've got a variant of this type converter in your car now.

I do not agree that the rpm drop is causing traction issues. Fiscus, Gomes and many of the 7 second V8 cars running these converters all drop 1000 and in some cases 1200 and none have a traction issue because of it. You've got suspension issues somewhere causing this upset or a bump in the track your racing at.

Exactly !!!!!!!

 

[Alky V6]

Not likely to happen. Some of the 10" cores can have less rpm drop and great efficiency but they are also very tight down low.....basically a nitrous converter. You've got a variant of this type converter in your car now.

I do not agree that the rpm drop is causing traction issues. Fiscus, Gomes and many of the 7 second V8 cars running these converters all drop 1000 and in some cases 1200 and none have a traction issue because of it. You've got suspension issues somewhere causing this upset or a bump in the track your racing at.

Why don't you post a picture of yours taken apart so I can possibly tell you what I would change about it:biggrin: I betting you have a very tight stator with little fin angle.

Then I guess the bumps in the track are all in a place right at the finish of a shift.
Maybe we should just keep it at it being a problem with my suspension.

 

[Alky V6]

So if I am reading this right what you are implying is that with your combo you can not get it to work with the nitrous. I thought this whole journey was to show that it CAN be done, shurley a new convertor is going to cost money. Which has been a hinderence of yours in the past and an excuse to not do what MANY knowledable people have recommended you to do.

How much experience do you have with using nitrous to help with different turbo and converter combinations? How many people do you know that do?

If you've paid just a tiny bit of attention to what I've been doing, you'll know that I never ruled out a converter change. Just when to do it. It is now time.

When I was using this same torque converter with the T76 turbo and doing 1.28 60 foots, I don't recall you declaring then that I should be changing the torque converter. Hmmm, why do you suppose that was?

 

[Dusty Bradford]

Then I guess the bumps in the track are all in a place right at the finish of a shift.
Maybe we should just keep it at it being a problem with my suspension.

If you run at the same track everytime, it's a good possibility. One particular track I race at I will pull out a good bit of timing right after the gear change because of a dip in the track that unloads the suspension. If I don't, it won't make a full pass.

 

[BadAssGN]

Then I guess the bumps in the track are all in a place right at the finish of a shift.
Maybe we should just keep it at it being a problem with my suspension.

Do you usually run at a well prepped Track Don?

Are there many fast cars making it down without problems?


Can you not "Soften the shifts " with Motec?

 

[Alky V6]

I have run at this track for years. Since 2001. I have only had problems lately with traction. I seem to be the only person at the track having this problem. There are a handful of low 5 cars and a few in the 4s. Not with 10.5" tires, though.
When I was using the T76 and running 5.80s, 5.90s at around 122 pretty regularly, I don't recall having traction difficulties, unless I got carried away with the launch boost level. Even then, the problem wasn't really traction. I tried a few 16 psi launches, and with the chassis the way it was, that didn't work out very well. Back then, with the T76, I could leave the line at 16 psi if I wanted with only .4 of a second of lead time. No sitting at the line burning my converter and transmission down. That was with the same converter I have in the car now, and it worked with that combination very, very well. After changing the turbo, you have to understand that I didn't want to give up on this TC, that had worked so well for me, until I had exhausted all other tuning avenues.

I'm using the Motec software only for graphing of my fuel and timing tables. The WinTEC software graphing is lacking.

The tires breaking traction at the shift has a lot to do with the boost control. I've been working on the boost control pressure curve. That, I'm not really worried about. That will come around with more work with the boost controller.
The 60 foot is the main focus for the converter change at this point.

 

[Alky V6]

Its about time. I agree on the launch speed. It will depend on how much you chassis can take. Id want more than 300-400 drop though. I dont think your truly overpowering the tires and something else may need adjustment. Your flash stall should be around your peak torque rpm or slightly higher so you will likely still see 1000+ rpm drops. With the current tech the PTC converters have ive seen them drop considerably on the shift and continue dropping slightly for a second or so after the shift and almost flat line the engine for a couple seconds. This leads to some incredible g forces and the best e.t.'s. The launch stall speed you are looking at at 4-8psi will be hard to couple with the internals needed to get the high stall at low boost on your engine.You will probably have 7-9% slip when everything is optimally dialed in up top.

I agree with you on the top end slippage, but why not throw in some wishful thinking into the target requirements.

 

[S2V6RACER]

Don, my advise here is to just make a phone call to Dusty and send a check out and just turn your brain off until you get the converter in your car. I think you will end up with a lot more time to work on your chassis and other things when you are not fighting the converter anymore. I respect your drive to figure everything out, but at some point everybody should realize their limitations (we don't build converters) and let the pro's do their job.


I predict you will look back and be very disappointed on how many brain cells you burned up fighting a converter that just plain won't work.

 

[Alky V6]

Don, my advise here is to just make a phone call to Dusty and send a check out and just turn your brain off until you get the converter in your car. I think you will end up with a lot more time to work on your chassis and other things when you are not fighting the converter anymore. I respect your drive to figure everything out, but at some point everybody should realize their limitations (we don't build converters) and let the pro's do their job.


I predict you will look back and be very disappointed on how many brain cells you burned up fighting a converter that just plain won't work.

I'm really curious. How many people fight their torque converter with a tuneup on an engine that is not optimized first? With all these stabs and jabs, I'm getting the impression that either you all really haven't been following what I've been doing, or, there are no true tuners among you.
Let me make it clear. All this time has been spent optimizing the engine fuel table, the nitrous system, and the general engine tune. I wanted to see what an optimized engine tune would do with this torque converter. You can't find that out until first, you optimize the engine tune. I hope you all are following me here. Are some of you actually changing torque converters before you get the engine tune straightened out? Maybe my thinking is wrong here, but I always learned that you can't judge the performance of a torque converter until the engine performance potential is well understood. Maybe some of you can educate me on the other way of picking the TC before you know what the engine combination can do first. I'm eager to learn that method.
It was just last weekend that I found the limit of what the nitrous system can do for me. In other words, I've pretty much maxed out the tuneup on the engine, as far as the launch goes. So,... that means that I've changed my focus to the torque converter stall for a total of 'X' hours? After one night of studying datalogs from last weekend, and figuring out that there is no more to explore with the engine tune, I decided that night where my new stall speed needed to be. That doesn't seem to me to be a very long time burning brain cells on deciding on a TC change. And, on top of that, because of all the time I spent on the fuel table, I know exactly where that stall speed needs to be and how a different stall speed may change the performance of the car.
With the engine tune limits well understood, picking the right TC stall is a breeze.

OK. Now tell me how you pick a TC before you understand the performance potential of an uncommon engine combination??? I really want to read the answer to this one. Come on. Show us all how it's done.

 

[BadAssGN]

Don

I really think this is a simple case of all these guys having incredible faith in
Dusty's ability to spec out what you need.

The might have delivered the message a little smoother but I think the are trying to say you are missing out.

I have seen results first hand of an optimized engine tune and a popular bolt together unit they worked with for years get blown out of the water by a unit spec'd by dusty fresh out of the box. it truly was a sight to see.