Picking a New Full Race Stall Speed

[Alky V6]

Had some good runs today. The larger shot size was not an improvement. After a little work on the fuel table, I was able to at least match the performance of the previous shot size. I will be going back to the 364 shot.
Now that the limit of what the nitrous could do for me has been found, it's time to work on the boost control curve. There's a little work still to be done there.
With the tire pressure at 10.25 psi, the car smoked the tires from the 330 ft mark to the 660 finish line. The car did not lose complete traction, but tire shake was felt as I crossed the finish line, and when I checked the rearview mirror, tire smoke. Watchers also confirmed this.
With no changes to the boost control, I dropped the tire pressure to 9.0 psi on the last run and picked up one mph and the car felt much more stable.

The rpm drop on the 1-2 shift was 900-1200 rpm, depending on the shift point rpm, 6950 or 7250 rpm. This was at a leveled boost pressure of 200 kPa.
The rpm drop on the 2-3 shift was 650 rpm. Boost pressure during the 2-3 shift was 274 kPa.
Rpm across the finish (660 foot mark) was 7350 at a boost pressure of 280 kPa. The slip across the finish is much higher than the previous TC where I was crossing the finish at around 6700-6800 rpm.

 

[Alky V6]

That's a good range for the rpm drop on the 1-2 shift, but I don't have a clear range for the 2-3 shift yet. After I get more data together I'll post up a more concrete range for the rpm drop on the 2-3 shift. It looks like the range may be 350-650 rpm depending on the shift point, but I'll wait until I have more data before I commit to that.

 

[Alky V6]

We got Chad's car on the dyno and pulled a 463 rwhp out of the hat on the first and only pull. An oil leak caused us to shut down the session early.
After we get the oil leak fixed, we'll be de-tuning the sucker!

 

[charlief1]

Why you goona cut the power Donnie? That sounds like it will be a nice ride.

 

[Alky V6]

Why you goona cut the power Donnie? That sounds like it will be a nice ride.

Stock crank, rods, heads, hyper pistons. He can't afford to be hurting something.

 

[Alky V6]

Latest stats on the new TC.
1-2 shift rpm drop, 7059 to 6188 at 211 kPa. 871 rpm drop.
2-3 shift rpm drop, 7274 to 6717 at 276 kPa. 557 rpm drop.

At the tail end of the pass the rpm flattened for the last .7 second. The rpm slightly peaked at 7311 .2 sec before the end of the pass and then dropped slightly to 7267 by the end of the pass. A steady 280 kPa by the finish of the pass. This must be where the TC is coupling.

So far, it doesn't appear that there's been any loss in performance on the top end with the TC change up to this point (1/8 mile). Pre-spooling at the line is still set on the conservative side. .902 second.

 

[Alky V6]

After doing some analysis of the latest data on the car, it appears that the TC is stalling on the low side. Depending on atm conditions, the stall on the nitrous system is between 4550-4700 rpm.
With some new dialing-in of the drag simulator with the new data, it appears there is the chance to better the 60 foot by .12 of a second by having the stall changed to 5200. That would mean a 1.30-1.32 60 foot. This is a 60 foot that gives a nice controlled launch with this car with some carrying of the front tires.
According to the drag simulator, with just a small increase in the stall speed to just 4900 would yield the largest drop in the 60 foot, with less and less of a drop in the 60 foot being encountered as the stall is stepped up from there.
From a consistency point of view, increasing the stall beyond 5200 rpm for the launch could introduce traction issues that could make good 60 foot and ET consistency less likely.
As is well known with matching a torque converter to a turbocharged V6, it's easy to reach a point as you increase the stall speed for a happy launch to end up with a TC that is too loose on the top end, also known as blowing through the torque converter. The trick is to find that happy medium between enough stall to get as close as possible to obtaining the best 60 foot possible, but not so loose that the engine, when on full boost at the top end of the track, ends up blowing through the torque converter.
RPM drop during the shift, and TC slippage (the difference between engine rpm and driveshaft rpm) are good ways of gauging whether the TC is being blown through or how close you are to that point.

 

[Alky V6]

I just finished going over some past datalogs and realized that this torque converter/nitrous shot size combination had stalled to over 4800 on the evening when the car had performed a 1.37 60' about a month ago. The fueling was 3% leaner for the 1.37 than it was during this last testing session in a critical section of the fuel map. Also, the buzz around the track was that the air was pretty bad during the last test and tune.
I think I'll do more testing before I decide whether to send the TC out for a re-stall or not.

 

[Alky V6]

Slip percentage appears to be 19% at the 660' mark, with the slippage at the end of the quarter projected to be 10%. Tire growth of 6% taken into account.

 

[Alky V6]

With some new increases in the performance level of the car this last weekend, I recalculated the TC slippage at the 1/8 mile and came up with 18%. 10% is still the projected slippage at the 1/4 mile mark.
Still have a little more tune to throw at her.

 

[Alky V6]

Update

It's a good thing I didn't go for loosening the torque converter anymore. I've found a tuneup that is pushing this 3200 stall TC (off the nitrous) to over 5,550 rpm. It would have gone much higher, but I got off the throttle and ended the test. This is going to leave me with more than enough power for a good launch.

 

[Dusty Bradford]

Sounds like that 300 shot is finally working like it's supposed to.

 

[Otto J]

It's a good thing I didn't go for loosening the torque converter anymore. I've found a tuneup that is pushing this 3200 stall TC (off the nitrous) to over 5,550 rpm. It would have gone much higher, but I got off the throttle and ended the test. This is going to leave me with more than enough power for a good launch.

Very nice,now lets see the efficiency numbers this convertor has on the big end.

 

[Alky V6]

Sounds like that 300 shot is finally working like it's supposed to.

A little more complicated than that.
http://www.turbobuick.com/forums/al...ous-methanol-anti-lag-system-afterburner.html

 

[Alky V6]

Very nice,now lets see the efficiency numbers this convertor has on the big end.

Slippage at the 1/8 mile mark is 18-19 percent. I'm projecting it will be 10 percent at the 1/4.

 

[dank GN]

rock on don