Stall speed question.

[Turbo6Smackdown]

Dusty, Brian, Bison, and any other 10 second and faster guys chime in at any time.
Odd question. For those of you who spend most of your time on the track, vs. the street.. If you're on a well prepped track, and have your suspension dialed in, so that you car hooks great, and utilize a trans brake or line lock, does this tempt you guys to go for slightly less stall speed, knowing that you can build tons of boost on the line and launch hard, not needing those few rpms you shaved off, to build boost?
I was thinking, that if I needed for example, a 2800 stall for a good match between spooling and top end slippage, but could build a solid 10 psi on the line, with zero wheel spin upon take off, could I get away with a 2400 rpm stall, knowing that I already have a good amount of rpm's built up, and won't slip a bit when I let 'er go? Will that combination of high launch psi & a perfect hook make up for a tight converter?

I was thinking of this, as I'm still afraid of having zero traction in the street, when I flatten the accelerator. I'm going thru different scenarios in my mind every 5 seconds.. "Maybe I could use a tight converter to control wheel spin when accelerating, but if I need a good launch, I'll just build a lot of boost on the line next time"
How far off am I? I was hoping for the best of both worlds.

 

[bison]

For the most part we arent worried about how fast it is going to come in on the line. With the 9.5" PTC converters and BB turbos with a good tune and some CR they come up very fast. The converter is spec'd to work down low and couple up top. The advertised stall speeds you read about dont reveal anything about the coupling efficiency. You need it to spool easy and couple which is a hard thing to do with a small ci engine that has very little torque without boost and a lot under full boost. Converters will work very different on different combos. An example i can give is the 9.5" i have tried between 2 different engines. Both examples were on aggressive tunes down low with high octane fuel to maximize the stall speeds. With the old iron headed, 212/212, 8.5:1 stock shortblock engine the converter stalled to 3100 on the t-brake @ zero boost/vacuum and flashed to 5100 @ 28.5psi. With the 9.3:1 GN1 headed, 218/224 engine it stalled to 2800 @ zero boost/vaccum and flashed to 5500@26 psi. Same converter. With the iron headed engine i was at about 2.5-3% slip @134mph with the latest engine it was at about 4% at 140mph. As you can see the new engine has a lot less torque down low but has a lot more up top even though the boost is almost 3 psi less. Same turbo too. Both engines are within 2 ci of each other. So what has to happen for the converter to work optimally is it has to be spec'd based on the combo and how hard you are going to run it. What you are thinking about comparing the two converters in your post will work but it will just make it laggy on the street and require you to work it harder on the line. Its easier to get the correct converter spec'd that will work on the lone and up top.

 

[Dusty Bradford]

Dusty, Brian, Bison, and any other 10 second and faster guys chime in at any time.
Odd question. For those of you who spend most of your time on the track, vs. the street.. If you're on a well prepped track, and have your suspension dialed in, so that you car hooks great, and utilize a trans brake or line lock, does this tempt you guys to go for slightly less stall speed, knowing that you can build tons of boost on the line and launch hard, not needing those few rpms you shaved off, to build boost?
I was thinking, that if I needed for example, a 2800 stall for a good match between spooling and top end slippage, but could build a solid 10 psi on the line, with zero wheel spin upon take off, could I get away with a 2400 rpm stall, knowing that I already have a good amount of rpm's built up, and won't slip a bit when I let 'er go? Will that combination of high launch psi & a perfect hook make up for a tight converter?

I was thinking of this, as I'm still afraid of having zero traction in the street, when I flatten the accelerator. I'm going thru different scenarios in my mind every 5 seconds.. "Maybe I could use a tight converter to control wheel spin when accelerating, but if I need a good launch, I'll just build a lot of boost on the line next time"
How far off am I? I was hoping for the best of both worlds.

I do take transbrake use in consideration when spec'ing a converter. I look at the entire combo. In some cases it make no difference but if a car has a turbo on the larger side for a given engine size and rpm range, I tend to lean towards the tighter side if the customer uses a transbrake.

The car with the transbrake can get away with a little lower stall speed but it depends on the combo whether a tighter converter can help or not.

 

[Turbo6Smackdown]

I see I see. Thank you both! Do you guys think I can get away with a 24 or 2600 with the future combo in my sig? Or is 28 optimal. And then, what will change, if I add a 62mm tb/plenum, 2.75" up pipe, and ported stock heads? How will those mods affect my current TC?

 

[Dusty Bradford]

I see I see. Thank you both! Do you guys think I can get away with a 24 or 2600 with the future combo in my sig? Or is 28 optimal.

With a Ta-61 and a transbrake........2400 without a doubt if we're talking the 10" converter.

With a 9.5 non lock you can run a 2800 and still run more mph from better efficiency. Different converters have different characterisitcs. Clear as mud

 

[bison]

Keep in mind that PTC's stall ratings are more accurate than other brands.

 

[Turbo6Smackdown]

Huhh??? 2800 with more efficiency than a 24? I'm lost again lol.

 

[Dusty Bradford]

Huhh??? 2800 with more efficiency than a 24? I'm lost again lol.

Yes. When talking different sized converters.

If your talking the 10" converter like you have. A 2400 will be more efficient than the 2800.

When you start talking custom converters like my 9.5 converter. I can build a 2800 stall 9.5 that will be more efficient than a 2400 stall 10". Different sized cores or housings have different characteristics.