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Is my tune causing this slow RPM build? Or is it the torque converter?
I'm having a frustrating issue. From a dead stop and going WOT - RPMs jump up to 2500rpm, then it takes forever (approx. 3 seconds) to climb to around 3500rpm, which boost takes over and finally has the car accelerating decently quick.
I thought it was caused by a 'too tight / street friendly' torque converter, so I spent a lot of money and got a 3700 RPM converter from the same company I got the 'street friendly' converter from. After installing the new converter..the car still does the lag around 2500rpm.. I'm pretty disappointed after spending the money and doing the install to have no change.. I'm hoping it is tune related.. just so I don't have to change this converter again..
I've messed with the fueling PE tables, had them ramp in slowly and come in later - it still does this slow rpm climb from 2500 to 3500. I've matched up my spark advanced tables to others that have a similar setup and they are roughly the same. I've also matched my PE enable values to match similar setups. I have a slight issue where the engine bogs down when I got WOT from a dead stop, you can see this in the screen shot, I don't believe it is causing this issue though - as once it catches up the issue then starts..idk maybe I'm wrong. Not sure how to fix that one.
Any tips? Could the company I am using for torque converters just manufacture them way too 'tight'? I can't even brake flash the converter above 2800 rpm without it pushing through the brakes, this is supposed to be a 3700RPM converter
I attached my tune, log, channel config (is this needed?), a screen shot of the scan (notice the red RPM line how it shoots up and then levels out), and a youtube video. Note on the video that my tachometer is off by 500 rpm (so it looks like it only jumps up to 2k.
LQ4
VSR Next Gen 7875 Billet - 1.25ar Divided T4
Around 14 psi (though this issue occurs before it reaches 5psi)
Texas Speed Cam 3726/3730 115+4; 232/240 .595/.609 115 LSA 111 ICL
FIC BOSCH 60 LB 650 CC for LS. 750 cc/min – 4.0 BAR (58.0 psi)
Stock 4L80E
4L80 PRO SERIES SINGLE 258MM 3700RPM stall
3.31 gears
12 bolt
id give them a call then, they might have just set it up conservatively on the tight side rather than on the loose side.
when i got my first FTI it was for my truck and i told them the combo and that i wanted to tow. the converter came in super tight. i talked to them and told them what it was doing and they restalled it free and hit it perfectly on that one.
usually a new custom converter comes with 1 free restall.
I don't think it has anything to do with the converter.
The partial throttle opening when you go WOT looks like the issue to me.
but, once it goes 100% throttle open, that's when it slowly climbs through the RPMs. So it seems the partial throttle opening isn't tied to the slow RPM climb, unless I'm missing something
id give them a call then, they might have just set it up conservatively on the tight side rather than on the loose side.
when i got my first FTI it was for my truck and i told them the combo and that i wanted to tow. the converter came in super tight. i talked to them and told them what it was doing and they restalled it free and hit it perfectly on that one.
usually a new custom converter comes with 1 free restall.
Well.. I emailed the converter company thinking they would help me out and point me in a direction that can solve this issue. Converter company just told me "No other converter option will work for this combo"...???.. It's the only converter that will work for my setup?? They told me to think about get a transbrake. Not really happy with that answer
I messed around with the tuning. I got rid of the initial hesitation going WOT. So that definitely is not the issue, as it still does this RPM jump. The only thing I'm thinking it could be now is just too low of timing, but from what I've seen.. I'm running proper timing.
You're giving up some torque with the spark. But its not a magic bullet. You're experiencing turbo lag. Nothing is going to make the the torque the turbo makes...until the turbo comes and makes it. Unless you have nitrous. Then that gets rid of this problem entirely.
I would run NA timing until 2-3psi and set PE to come on a bit later. The Rich AFR and Low timing are not helping the turbo light off. Not saying this will be a cure but it should help the lag which I believe that is all the issue is as mentioned above.
Edit*
Looking through your last log and yea it supports what I mentioned above. You are 10 degrees timing @ 3800 rpm but the turbo is not making any boost yet. You have the engine timed like it's running a PD supercharger not a Turbo. I edited your high octane table and took a screenshot of it. Basically added 5 degrees where you need it which is probably still conservative.
I would run NA timing until 2-3psi and set PE to come on a bit later. The Rich AFR and Low timing are not helping the turbo light off. Not saying this will be a cure but it should help the lag which I believe that is all the issue is as mentioned above.
Edit*
Looking through your last log and yea it supports what I mentioned above. You are 10 degrees timing @ 3800 rpm but the turbo is not making any boost yet. You have the engine timed like it's running a PD supercharger not a Turbo. I edited your high octane table and took a screenshot of it. Basically added 5 degrees where you need it which is probably still conservative.
Thanks! I'll make these changes
Originally Posted by smokeshow
You're giving up some torque with the spark. But its not a magic bullet. You're experiencing turbo lag. Nothing is going to make the the torque the turbo makes...until the turbo comes and makes it. Unless you have nitrous. Then that gets rid of this problem entirely.
Great point. I just figured the converter would allow it to flash up to 3k+ without needing much power. This would explain why both the 'street friendly' converter and the 'pro series' converter are both flashing up to the same exact point. Hmm... I wonder how I can test this.. pull the turbo off, NA tune and see how the converter acts? lol
Reading your mod list again, I didn't realize how large the cam was. That makes what kinglt-1 even more spot on. Bigger cams need more spark where the combustion suffers on the low end under load. This is the spark difference between stock and my calibration on a slightly smaller cam, 227/234 in an LS6. Notice how much more spark it wants/takes down low. The lower compression on the LQ4 will want more. At the very least, the extra spark should help drag the car through that area a little quicker and get the turbo online slightly sooner.
12.8 and slowly ramp in fuel with boost and ramp timing out. As soon as your in boost it was commanding .75 lambda (11.0 AFR) and timing is like 15 degs.
I uploaded the tune and went for a drive. The issue is still there, taking off from a stop hits a wall at 2500rpm. Though, my throttle response is much better while cruising. I have attached a log and screen shot.
I'll adjust the fueling to get a 12.8 AFR before boost, but looks like my issue might not be the tune (unless I should add even more timing in the 2500rpm range..??)
Still SUPER rich! Went in the 10's AFR. What rpm does the converter flash to?
I agree, super rich near the end of the WOT phase (which I def need to work on) - but AFRs were pretty good during the problem area where the RPMs stall and slowly climb, I'm just trying to get this slow RPM figured out
Converter barely flashes above 2500 RPM on brake, before the brakes start getting pushed through or rear tires start spinning
Thats a pretty tight converter and wth your cam you probably not in your power band yet. You could try a little more timing down low to see if makes any difference but I bet it doesnt help much.
12-09-2021, 09:51 PM
Is my tune causing this slow RPM build? Or is it the torque converter? 
