Stall Speed data log illustration - should I run a higher stall?

[bgreen776]

Attached is a data log I recorded during my best run last year. It illustrates flash stall and brake stall fairly well, or at least I think it does. (I'm no expert)

The converter is an ATS 5 Star stock stall (1800)
The engine is a stock 5.9 with a 66/484 setup, UDC tuning, and 65lpm injectors. I street drive the truck all year, but I don't haul or tow with it.

It takes me approximately 15 seconds to go from flash stall (if I am reading the log correctly) to needing to let off the throttle to keep under 23 psi. I seem to get my best launches at about 20 psi. That seems like a LONG time to build boost, and AH64ID has already put some effort into the UDC tune to help boost faster.

The two dips in boost, where I let of the throttle, are likely caused by my BOV set too sensitive. A completely different issue and I assume completely unrelated to this discussion. I just pointed it out because it looks odd and wanted to clear it up before hand.

You can see the green line rise rapidly shortly after the two dips, this is where I let off the brake and mash the throttle. The green line is vehicle speed, and the grey like that shoots straight up is TPS value. The purple line is boost. This is where my question lies. As you can see, boost builds VERY slow until I reach about 2200 rpm. Then it climbs so rapidly that I can barely control it. On this run I left the line at 2400 rpm. I have a very hard time not accidentally deep staging or even driving right through the lights.

Should I get the converter re-stalled to say... 2200? 2500? I don't want to raise my 60', but I do want less ET. I would also like to have less lag on the street. I'd also like to not spend ~25 seconds in pre-stage roasting the transmission.

 

[bgreen776]

Time slip and Dyno chart (way low on boost during the dyno run)

 

[IdahoRob]

Are you graphing egt's during the "spool up". What about timing? Timing/fueling can play a large part in spool up. May not need a converter change.

 

[bgreen776]

I can't log timing. Its an '03-04.

By the time I launch I'm at about 1400*F

 

[Joesixpack]

Man that's a pile of time on the converter.

 

[bgreen776]

Ya! Its sickening.

I'm not sure whats wrong with my boost log, but the numbers here are way higher than what I see on the display. Almost like the CTS is adding barometric pressure on top. SO... ignore the boost pressure values.

This graph is a little hard to read, but it does show the EGT's.

 

[Kill]

I think a higher stall would certainly help, I used to have the lowest stall dpc makes and had to roll into the throttle very slowly in order to build boost on the brakes or it would just hit a wall at about 5psi and sit there. This was using a smarty TNTR for tuning though. I now have somewhere closer to stock stall and it is a lot easier to build boost on the brakes. You might be able to get it where you want it with tuning but even so, a higher stall would be a lot more forgiving if your tune wasn't perfect.

 

[bgreen776]

Thank you.

I think a higher stall would help, but I dont know how high to go. My gut tells me to add another 500 rpm, so it would be at full stall right when I launch, but I just don't have the experience to know how high to go. I'd really like to re-stall this converter, but if I do that and I don't like the results, it will take a long time to get it fixed. Shipping is going to be a killer as well, probably $200 each way, and a week or two each way.

I would prefer to just buy a second converter, but man, those suckers aren't cheap!

 

[Big Blue24]

Time slip and Dyno chart (way low on boost during the dyno run)

Ohhh so close to 10's you can taste it!!!! Just a slight bit more power and that run was there!!!

I have a 10.95 time slip with a similar 7.07 1/8th @ 100.8 MPH that ended up 10.957 @ 126.1 MPH. You might be able to find that last 25 HP playing with the wastegate a little.

 

[bgreen776]

Oh. so. close.

I should have it nailed. *fingers crossed* I have since replaced the two blown exhaust gaskets, the one CP3 that was so bad it wouldn't start the truck on its own, bought caltrac bars, ordered double adjustable AFCO Big Gun shocks, and am beefing up the transmission a bit. (I was slipping 3rd pretty bad). I think I'll have a much better transmission tune this year as well. John is going to add some more power to the UDC tune as well.

I hate to admit it, but I haven't touched the wastegate since I first set it on the street months before our first race last season. So many things to do, so little time.

 

[JQmile]

I would get a re-stall for sure, or some nitrous. Converter sounds a lot tighter than stock too.

 

[bgreen776]

I have two stages of nitrous, one on a progressive controller, and one on a momentary. My problem is with the IHRA rules stating that I have to run them both on a WOT switch, so... I've never run either. I don't even carry the bottle anymore.

 

[bgreen776]

Any thoughts on how much to add?

 

[paulb]

It doesn't appear to me that the converter is that far off. My setup is fairly close to yours, and I pre-stage at an idle, build boost, and then fully stage within 8 seconds. I launch at 19psi, and the rpm at that boost is a little less then 2100. It would appear that my converter "stalls" pretty close to yours. I'm at about 900 EGT when staging.

You mentioned blown exhaust gaskets and not having adjusted the waste gate. I would start there. Exhaust leaks, even small ones, can play havoc on spooling while power braking. Also check and make sure that the waste gate pucks are closing when the waste gate is closed. You should also check for intake leaks.

Everyone stages and launches a little differently, and there isn't a right or a wrong. As a suggestion though, you might want to try and match the throttle position closer to the boost. If you get ahead of the boost to much and the boost flairs and you have to bring it back down, you will have a hard time being consistent. I bring it up to 1400 rpm, and then at a smooth pace open the throttle to where I know I will be very close to my launch boost. You can adjust the torque management map and the duration map in UDC to make it easy to hit and hold the desired boost.

Hope this helps...
Paul

 

[IdahoRob]

^ This man is very knowledgeable and arguably the best bracket diesel racer in the country.

 

[bgreen776]

That's great input, thank you!
Would it be possible to raise the flash stall without moving the brake stall too much higher?

 

[bgreen776]

I hadn't considered how the exhaust leak would have effected spool down low. And I certainly could spend some more time working on consistency! How would a guy try to match the TPS to the boost? Just roll into the throttle slower?

 

[khaoskustoms]

I would thank that moving the base stall up will also increase the stall once on boost.

 

[mathews8pt]

Before restalling I would look at your setup for leaks. I am surprised that it takes so much rpm to build that much boost with your CR. I have a 64/80 setup on my p-pumped truck and could easily build more then 25 psi if I took it to 2400 rpm.


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[jlibert]

Oh. so. close.

... ordered double adjustable AFCO Big Gun shocks

did you get the double adjustables the whole way around? How did you decide on the big gun vs. the basic afco double adjustable?