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

mathews8pt said:
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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I'm sure it would build way more than that if I didn't back off the throttle, at 2400 its almost impossible to keep it under control. Boost builds super fast at about 2000, no idea how high it would go as I have never tried to launch with more than 20-22. You can see in the colored graph how fast boost builds once I reach about 2000, then essentially following RPM right up to the first shift point. Its probably 70 psi or more in the first 1.5 seconds.

I don't have any boost leaks at those pressures, thats one thing I am super picky about. I slip a plate in at the intake manifold then pressure through the atmospheric turbo to 25-30 psi any time I disturb any of the piping.
 
jlibert said:
did you get the double adjustables the whole way around? How did you decide on the big gun vs. the basic afco double adjustable?
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I did.

The basic afco's aren't rated for the power we are running. (not that I think building a shock based only on HP is the right way to go, that is the main factor they were concerned about)
 
bgreen776 said:
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?
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I based my comment on matching the TPS to boost, from your log. Roll into the throttle slower and smoother will help a bunch. Tuning can also play a big part.
 
paulb said:
I based my comment on matching the TPS to boost, from your log. Roll into the throttle slower and smoother will help a bunch. Tuning can also play a big part.
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Thank you. After I posted that I re-read your comment a few more times, makes sense. I'll talk to John about the UDC tuning aspect. I'm too inexperienced to take that on for myself at this point in my "program".

This is a graph from one of my other runs. It is WAY worse. It looks like I just rolled up to the line and mashed the throttle. Just pure luck that it was one of my fastest runs last year. LOL.

Not to derail my own thread, but look at what happens when my converter finally locks up right as I hit 4th gear. Lots of work to do.

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You aren't locking the converter until OD??? And you still ran an 11.03? Lock it down WAY sooner. Most lock on the second gear shift.
 
I struggled with that all last year. What I have found out, postseason, was that the PCS software has some tables that override the tables I was using to adjust lockup. I didn't realize that there was a WOT table that had been set to shift into 4th gear at 3000 rpm. I ran an 11.26 like that. I changed it to 3900 and pulled the 11.04, but still hadn't found that there was yet another table that was keeping me from commanding lockup until 55 mph. If I hadn't got the flu this week and had nothing better to do, I probably would have never found this out. :doh:

I wont be able to test it for months, but I'm working on a tune that should initiate the lockup at 33 mph, resulting in full lockup just after I hit 2nd gear. Right about the 60' mark.
 
It appears I have omitted critical information. The blue line is gear commanded.

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Looks like you are on the right track. IMO locking up in 4th is way late, and arguably harder on the trans. I lock at 18mph in 1st gear.

There are quite a few things that come into play that can effect spool up when power braking. In a nut shell anything that increases load against the engine makes it harder to spool. For example typically transmission line pressure increases with throttle position. If you have the throttle open more then needed during spool up, you are making extra line pressure. This all depends on how the transmission is setup. You want enough pressure so you don't weld the forward clutches, but to much just makes it harder to spool. Also, you can "flood" the governor pressure solenoid if you try to lockup at the same time it shifts.

The same thing goes with rail pressure. If you tune with a really high rail pressure during spool up, it takes hp to make that pressure. Enough pressure for clean burn is great, just don't go over board. This is especially true with dual CP3s.

Just to be clear all of my comments on spool up, pertain to building boost at the line for drag racing. I am not talking about spool up for towing or street driving. A well written tune will work for both, but some of this will never come into play with street driving. Unless of course every stop light is a drag race. :)

Paul
 
:rockwoot:

11 mph! Are you guys using some sort of microcontroller like the PCS TCU-2000 where you can program the lockup rate?

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you can lock-up anywhere with standard PCS controller, just in the pcs tuning.
 
Im kinda curious at the lock up rate itself. ATS told me to leave the rate alone to keep from breaking things. Of course. But at the rate they suggest it commands the solenoid to take a full second to fully open. On the PCS controller its a pulse width managed circuit, so we can control the rate of clutch engagement, where other people might be using a simple on/off circuit. One second is probably fine, but if I can change it to half a second it might help my 60' substantially. Or just make me blow the tires off. :doh:
 
I was poor and always used a manual switch to hit lock up as soon as I got out of the hole and up in rpm. Only time I ever broke trans parts was acting stupid, not on the track. Get that thing locked up as early as you can without bogging.
 
The logs I'm working with lockup looks like first gear and is not PWM over time other than hydraulic delay. Hits hard any ways.
 
i have a 3200 stall in my truck and i love it both for driving and at the track. it sounds like alot of stall which it is, but it makes spooling a single 475 with a 1.25 exhaust housing super easy. i can say its 8 seconds from idle to full spool.

also it makes driving a heavily fueled p pump on the street a dream, it lights fast it doesnt lock up and billow smoke everywhere. its perfect for what i need it for.

just my $.02
 
Thanks Joesixpack. Thats what I suspected. GreanMeanie: Thats awesome, I've never driven a big single, but if having a higher stall helps keep me from smoking on the street, I definitely want to try it.

I think I will add a little stall since they are willing to do it for free. I can always go forward or backward later if I have to. It would be good for me to experience the difference first hand.

You guys have all been a great help! Thank you. :bow:
 
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GreenMeanie5.9 said:
i have a 3200 stall in my truck and i love it both for driving and at the track. it sounds like alot of stall which it is, but it makes spooling a single 475 with a 1.25 exhaust housing super easy. i can say its 8 seconds from idle to full spool.



also it makes driving a heavily fueled p pump on the street a dream, it lights fast it doesnt lock up and billow smoke everywhere. its perfect for what i need it for.



just my $.02
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I have about the same experience, makes driving with big chargers very manageable and fun. Also with the high stall it smooths out the ultra touchy throttle of a 13mm with 5k springs.

If you plan on bigger chargers anytime soon I would definitely look at the 2-2200 stall range, I've heard good things about those converters, seems to be a sweet spot.
 
bgreen776 said:
I did.

The basic afco's aren't rated for the power we are running. (not that I think building a shock based only on HP is the right way to go, that is the main factor they were concerned about)
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When I looked at the big gun shock, they were only listed for the rear. Did you use the big guns on the front? Do you ever think you'll use them as a coilover?
 
jlibert said:
When I looked at the big gun shock, they were only listed for the rear. Did you use the big guns on the front? Do you ever think you'll use them as a coilover?
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I ordered 7" BG's for the front and 9" BG's for the rear. They don't offer them in a pin mount, so I'll just build my own mounts. Shouldn't be too difficult. Hopefully I can come up with something fairly easy to swap back and forth as I really don't want to tear up $1500 of shocks on the street.

On this truck, its pretty unlikely that I'll ever use them as a coilover, but... ya never know. Its much more likely that I would use them as a coilover in a full blown pro-street build sometime in the future. If I did use them as a coilover on the front, it would save a significant amount of weight.

Dangit, stop giving me ideas!
 
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