4l80e questions for the Dyno
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From: Worcester, Mass
4l80e questions for the Dyno Hi guys. I'm going to be heading to the dyno in about 2-3 weeks to finally get some numbers on the budget build and do some fine tuning. It's an lq4/4l80e, stock cam, stock converter. I've got a few questions about the way to lock the trans and converter (if that's a good idea) while I'm on the dyno. I am going to tune this myself so I'm just renting dyno time. I have no idea about the guys or the shop I'm going to so I can't say how helpful or knowledgeable they will be. I've got the car feeling good on a street tune at 7psi from the few times I've been able to bury the throttle.
First question, what gear should I tune in? I've been reading and I'm seeing third gear with the converter locked. Does that sound right?
Second question. If third, I would manually shift into third and then use HP Tuners to hold 3rd and possibly lock the converter with the VCM scanner? I've only done this once on the street and I was a little confused about how it worked. It didn't seem like it wanted to let go of third once I activated it. I pulled over, stopped, put it in park and only when I closed my scanner did it seem to go back to normal. Maybe I didn't do it right. Any input would be much appreciated. Thanks.
First question, what gear should I tune in? I've been reading and I'm seeing third gear with the converter locked. Does that sound right?
Second question. If third, I would manually shift into third and then use HP Tuners to hold 3rd and possibly lock the converter with the VCM scanner? I've only done this once on the street and I was a little confused about how it worked. It didn't seem like it wanted to let go of third once I activated it. I pulled over, stopped, put it in park and only when I closed my scanner did it seem to go back to normal. Maybe I didn't do it right. Any input would be much appreciated. Thanks.
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Third depending on gearing. If you have a 2.56 rear gear and a 29" tire, you're not going to want to go 230 mph on the dyno.
Put the shifter in 3rd, and use the scanner to shift from 1st, to 2nd, and then to 3rd, and then lock the converter.
If you try to force 3rd right away while its in first gear, it might still try to downshift on you.
Put the shifter in 3rd, and use the scanner to shift from 1st, to 2nd, and then to 3rd, and then lock the converter.
If you try to force 3rd right away while its in first gear, it might still try to downshift on you.
Thread Starter
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Joined: Apr 2017
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From: Worcester, Mass
Third depending on gearing. If you have a 2.56 rear gear and a 29" tire, you're not going to want to go 230 mph on the dyno.
Put the shifter in 3rd, and use the scanner to shift from 1st, to 2nd, and then to 3rd, and then lock the converter.
If you try to force 3rd right away while its in first gear, it might still try to downshift on you.
Put the shifter in 3rd, and use the scanner to shift from 1st, to 2nd, and then to 3rd, and then lock the converter.
If you try to force 3rd right away while its in first gear, it might still try to downshift on you.
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From: Ohio
I've had half a dozen cars downshift into 2nd on the dyno when commanding 3rd in the scanner. So when I'm ready to roll, I put the shifter in 3rd and then use the scanner to shift through the gears. No issues.
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From: Worcester, Mass
I've read that about them trying to downshift which is what I'm trying to avoid. I also didn't want to mess with the shift tables much just to dyno it, and the scanner seemed to work fine for me. And you say to definitely lock the converter? I seem to read mixed reviews on this too. Stock converter I forget if I mentioned that.
We just change the trans tune to make it shift into 3rd and stay. Using the scanner is hit or miss when holding in gear on some vehicles, the tune always works. We also dont lock single disc or stock converters 99% of the time.
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So no to the converter. Do I need to tell the converter to stay unlocked when I go WOT in third? I do not have blue pin 33 hooked up at all so it's just defaulting to a speed when it locks the converter as of right now. Everything worked fine like that so I never changed it.
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Third depending on gearing. If you have a 2.56 rear gear and a 29" tire, you're not going to want to go 230 mph on the dyno.
Put the shifter in 3rd, and use the scanner to shift from 1st, to 2nd, and then to 3rd, and then lock the converter.
If you try to force 3rd right away while its in first gear, it might still try to downshift on you.
Put the shifter in 3rd, and use the scanner to shift from 1st, to 2nd, and then to 3rd, and then lock the converter.
If you try to force 3rd right away while its in first gear, it might still try to downshift on you.
Launching!
Joined: Jan 2018
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So no to the converter. Do I need to tell the converter to stay unlocked when I go WOT in third? I do not have blue pin 33 hooked up at all so it's just defaulting to a speed when it locks the converter as of right now. Everything worked fine like that so I never changed it.
in your TCC section of the trans go into all of your apply and release speed tables for cruise and full throttle. select a speed that is unreachable like 455km/h and put that value in every apply column. then populate every release column with a value slightly less such as 448km/h.
your converter will never engage the lock up clutch then and the extra torque from the boost wont burn it out.
if you wish just do one power run using the scanner to lock the converter before you go full throttle and start the run so its not trying to lock while you're applying heaps of torque.
generally a stock converter is tight enough that it will have minimal slip without lockup even with the extra torque
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From: Worcester, Mass
I wouldn't be trying to lock a stock converter with boost.
in your TCC section of the trans go into all of your apply and release speed tables for cruise and full throttle. select a speed that is unreachable like 455km/h and put that value in every apply column. then populate every release column with a value slightly less such as 448km/h.
your converter will never engage the lock up clutch then and the extra torque from the boost wont burn it out.
if you wish just do one power run using the scanner to lock the converter before you go full throttle and start the run so its not trying to lock while you're applying heaps of torque.
generally a stock converter is tight enough that it will have minimal slip without lockup even with the extra torque
in your TCC section of the trans go into all of your apply and release speed tables for cruise and full throttle. select a speed that is unreachable like 455km/h and put that value in every apply column. then populate every release column with a value slightly less such as 448km/h.
your converter will never engage the lock up clutch then and the extra torque from the boost wont burn it out.
if you wish just do one power run using the scanner to lock the converter before you go full throttle and start the run so its not trying to lock while you're applying heaps of torque.
generally a stock converter is tight enough that it will have minimal slip without lockup even with the extra torque
Just want to thank everyone for all the advice. I finally got the car to the dyno and I ran it 3rd gear, locked converter on 8.5psi and the car made 403rwhp 479rwtq. I've never tuned anything before the car felt pretty good and everything worked like i'd hoped. Just had a few questions maybe you guys could help me out.
On the dyno graph the graph does this very odd circle where it appears that the rpm goes back and then forward again. The guy running the dyno said oh that must be where the converter was locking so I said ok I'll look at it later. Cleaned up my fueling and left happy. I haven't looked at the logs until just now and the log shows that the car literally loses rpm around 4450 looks like its stumbling there for a second goes down to around 4350 and does some strange stuff there then starts climbing again. Continued picking up mph the whole time just did this odd thing. Also I should mention my boost pressure is dropping during this until it gets to what my mbc is set to. Prior to this it is spiking to around 10 or so. Just a cheesy mbc that bleeds pressure not sure if that has anything to do with it. I've posted my log if you guys want to let me know what you think I'd appreciate it. Btw, stock gen 3 lq4, stock cam, 243 heads with stock yellow springs, stock 4l80e, stock converter. Thanks.
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From: Worcester, Mass
Rev limiter was 6200 and yes I tagged it. I didn't get another run to clean up my AFR but car sounded good I'll have to sort that out when I get back. Did you see the weird RPM thing around 4400 though? It's a funny little circle on the dyno graph which is what made me look at the log. Any thoughts on that part?
Launching!
Joined: Jan 2018
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that is the boost spiking until the gate cracks and relieves some gas to reduce turbo speed and in turn boost pressure. that spike will go away if you add duty cycle to a boost controller or fit a shorter spring of the same tension. that spike is simply the extra boost generated until the gate can initially open maintaining boost.
stall speed increases exponentially in a coupled relation ship with torque. more torque applied to the same converter the greater the stall speed and flash RPM will be. your log shows the lock up clutch unlock as you stand on the throttle and then lock up again at 4400RPM ish. the drop in RPM in the log it the lock up clutch going from a fluid coupling with slip to a fixed coupling with matched input and output speed. (input speed is impeller RPM and output speed is Turbine RPM) its easier to bog the engine than slow the driveline to match speeds so when the clutch engages it pulls the engine RPM down to match the converter output speed.
given your relatively low power and boost, a decent converter should have very close input and output speeds by 4400RPM. the engine bogging tells you your converter is slipping. if you keep locking the clutch when the input and output speeds aren't nearly the same you'll destroy the clutch. either get a better converter or simply run it unlocked under power all the time.
stall speed increases exponentially in a coupled relation ship with torque. more torque applied to the same converter the greater the stall speed and flash RPM will be. your log shows the lock up clutch unlock as you stand on the throttle and then lock up again at 4400RPM ish. the drop in RPM in the log it the lock up clutch going from a fluid coupling with slip to a fixed coupling with matched input and output speed. (input speed is impeller RPM and output speed is Turbine RPM) its easier to bog the engine than slow the driveline to match speeds so when the clutch engages it pulls the engine RPM down to match the converter output speed.
given your relatively low power and boost, a decent converter should have very close input and output speeds by 4400RPM. the engine bogging tells you your converter is slipping. if you keep locking the clutch when the input and output speeds aren't nearly the same you'll destroy the clutch. either get a better converter or simply run it unlocked under power all the time.
Thread Starter
TECH Regular
Joined: Apr 2017
Posts: 424
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From: Worcester, Mass
that is the boost spiking until the gate cracks and relieves some gas to reduce turbo speed and in turn boost pressure. that spike will go away if you add duty cycle to a boost controller or fit a shorter spring of the same tension. that spike is simply the extra boost generated until the gate can initially open maintaining boost.
stall speed increases exponentially in a coupled relation ship with torque. more torque applied to the same converter the greater the stall speed and flash RPM will be. your log shows the lock up clutch unlock as you stand on the throttle and then lock up again at 4400RPM ish. the drop in RPM in the log it the lock up clutch going from a fluid coupling with slip to a fixed coupling with matched input and output speed. (input speed is impeller RPM and output speed is Turbine RPM) its easier to bog the engine than slow the driveline to match speeds so when the clutch engages it pulls the engine RPM down to match the converter output speed.
given your relatively low power and boost, a decent converter should have very close input and output speeds by 4400RPM. the engine bogging tells you your converter is slipping. if you keep locking the clutch when the input and output speeds aren't nearly the same you'll destroy the clutch. either get a better converter or simply run it unlocked under power all the time.
stall speed increases exponentially in a coupled relation ship with torque. more torque applied to the same converter the greater the stall speed and flash RPM will be. your log shows the lock up clutch unlock as you stand on the throttle and then lock up again at 4400RPM ish. the drop in RPM in the log it the lock up clutch going from a fluid coupling with slip to a fixed coupling with matched input and output speed. (input speed is impeller RPM and output speed is Turbine RPM) its easier to bog the engine than slow the driveline to match speeds so when the clutch engages it pulls the engine RPM down to match the converter output speed.
given your relatively low power and boost, a decent converter should have very close input and output speeds by 4400RPM. the engine bogging tells you your converter is slipping. if you keep locking the clutch when the input and output speeds aren't nearly the same you'll destroy the clutch. either get a better converter or simply run it unlocked under power all the time.