Is this turbo lag or something else? Video
Is this turbo lag or something else? Video Trying to fight an issue I'm having. When I take off from a dead stop the RPMS jump up and then hit a wall at 2500RPM and ssssllloooowwwlllyy climb up to 3500RPM, which then boost kits in and it finally takes off.
I've never ran a diff turbo on this vehicle, I just installed a 3700 RPM stall (thinking that would fix the issue - but it DID NOT, feels exactly the same as it did w/ a street tight 2800RPM converter). So I have no idea if this is tied to the turbo being too big or something else. We have been playing w/ my tune in the PCM section of the forum, and timing/fuel is pretty good during the slow RPM areas, so that doesn't seem to be the issue.
Is this turbo lag? I have never been in another turbo vehicle.. so I have no clue..Please go easy on me lol
1970 Chevelle
Vehicle weight approx. 3,700lb
3.31 gears
Stock 2005 4L80E
Circle D 05D-12-05-2D-P 4L80 PRO SERIES SINGLE 258MM 2D-P 3700RPM
All stock LQ4 besides Texas Speed Cam 3726/3730 115+4; 232/240 .595/.609 115 LSA 111 ICL
VSR Next Gen 7875 Billet - 1.25ar Divided T4 14psi
Note: My tachometer is off by 500RPM, that's why it looks like it starts at 2k RPM
I've never ran a diff turbo on this vehicle, I just installed a 3700 RPM stall (thinking that would fix the issue - but it DID NOT, feels exactly the same as it did w/ a street tight 2800RPM converter). So I have no idea if this is tied to the turbo being too big or something else. We have been playing w/ my tune in the PCM section of the forum, and timing/fuel is pretty good during the slow RPM areas, so that doesn't seem to be the issue.
Is this turbo lag? I have never been in another turbo vehicle.. so I have no clue..Please go easy on me lol
1970 Chevelle
Vehicle weight approx. 3,700lb
3.31 gears
Stock 2005 4L80E
Circle D 05D-12-05-2D-P 4L80 PRO SERIES SINGLE 258MM 2D-P 3700RPM
All stock LQ4 besides Texas Speed Cam 3726/3730 115+4; 232/240 .595/.609 115 LSA 111 ICL
VSR Next Gen 7875 Billet - 1.25ar Divided T4 14psi
Note: My tachometer is off by 500RPM, that's why it looks like it starts at 2k RPM
4L80E controlled by P59 PCM, whenever I log I track transmission gear - shows it being in first gear during these WOT from stop take offs. I'll manually put it into 1st gear though and see if there is a change, thanks!
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Yeah. I almost feel like I need to remove the turbo just to see if the converter will flash up higher NA lol if it does.. 100% need a smaller turbo (I would think at least). This isn't a track car, it's for fun driving around town whenever I do get to drive it. I don't really care for more than 650 rwhp, which reading can be done w/ a TC76 which I'm hoping would spool way faster.
Last edited by TXjeepTJ; Dec 14, 2021 at 10:26 AM.
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TECH Addict
Joined: Dec 2004
Posts: 2,177
Likes: 627
From: Florida
whats your compression? isnt it pretty low? you should be throwing quite a bit of timing at it below 3-4psi. i always leave full timing until 6 on my 5.3s.
have you overlaid logs with timing changes and its actually no change, or is it just minimal change? when i had a 4.8 with twin 72s my converter was too tight and it didnt matter how long i stood on the converter it just wouldnt get them spinning without getting some rpm in it. as soon as i had my converter loosened up a little it made all the difference.
i think you just have a mismatched combo, tune inclusive to that mismatch.
have you overlaid logs with timing changes and its actually no change, or is it just minimal change? when i had a 4.8 with twin 72s my converter was too tight and it didnt matter how long i stood on the converter it just wouldnt get them spinning without getting some rpm in it. as soon as i had my converter loosened up a little it made all the difference.
i think you just have a mismatched combo, tune inclusive to that mismatch.
TECH Enthusiast
Joined: Feb 2020
Posts: 734
Likes: 209
What is your AFR and timing in that 2500-3500 range ?
are you logging the KR ? it's possible it's sensing knock on the initial stomp , pulling a bunch (8°) of timing and then ramping it back in over 6 sec or so. Unless you've already sped up the recovery rate.
are you logging the KR ? it's possible it's sensing knock on the initial stomp , pulling a bunch (8°) of timing and then ramping it back in over 6 sec or so. Unless you've already sped up the recovery rate.
I'm leaning towards this suggestion.
Looks like adjust my timing DID do the trick. It shoots up to 3k rpm now, hits a wall - but I'm pretty sure that it is turbo lag now. Drives ways better than it did before. Thanks everyone for the help!
I have 6.0 w/78/75 (although .96a/r) with tighter converter than you listed, in heavier car, and never see/feel any lag, unless I'm simply going too slow for the gear, or something, or I am running on wastegate, which is 4# on my car.
.
My son's car is a tad lighter than yours, with a little 4.8, and similar "advertised stall speed', and same exact turbo you have (even the 1.25a/r), and also has pretty much zero lag, unless boost is turned way down.
FWIW, when I first got my car, the transmission was fresh, had a Jake's 4L80E, and installer had plugged wrong connectors up, input and output shaft speed sensors were reversed, so the car drove and shifted very weird, until I realized (& figured out why) the speedometer was showing 10-15mph, at idle, in gear. It would take off, then immediately be in 2nd, and I thought car was just a turd, since it had quite a few other issues as well....Just something else to ponder
