[Tucsonas]

I noticed somerging disturbing, while on the highway around 70 or 80 MPH, in 6th gear, I floored it and felt a big thump back by the differential, didn't do it in 5th, felt it slightly in 4th. My 5th gen never did this, anyone notice this? Or could someone try it in 6th gear and let me know own, bringing it it Friday to have it checked regardless, just curious

[FNxR3DNECK]

Yea 6th gear on this transmission is not meant for any WOT... like ever haha

[MatthewAMEL]

LSPI is a thing that kills motors.

Especially using DI. Downshift.

[Ryephile]

Put the pitchforks down guys. LSPI, yes that's true, but this is a low BMEP naturally aspirated lump, LSPI is not exactly a threat here. 70 MPH in 6th is 1662 RPM, which is not lugging it. At that RPM, it's like, oh my goodness, a paltry 140 PSI BMEP. Seriously, not even a concern.

Putting DI in the equation improves LSPI resistance due to the vastly improved chemical quench, FYI.


To to OP: maybe just driveline slack? Is it a new sound, is it repeatable, and do other 1LE's do it?

[Tucsonas]

To the one guy that tried to help

Thank you

[FNxR3DNECK]

I'm not saying he's gonna kill the motor by doing that, just that he's not going to get much acceleration.

[nancygrl]

My ZL1 doesn't like it either if I try to do a quick acceleration in 6th gear doing 70. I did it once and car wasn't happy; if I need to, I downshift the car, it is much happier when I do that.

[unavailablezl1]

In my 2017 ZL1 is the same way, if you press too quickly, it will bog/clunk a bit. The gear is so high it will do it. The 2016 GT350 I had was even worse. Just press slower instead of so fast.

[Ryephile]

Originally Posted by FNxR3DNECK

I'm not saying he's gonna kill the motor by doing that, just that he's not going to get much acceleration.

I will agree that the engine vibrations are undesirable at WOT below 1200 RPM. That said, it doesn't mean it's harming the engine, just that it's resonating with the engine mounts & chassis. Of course, the torque to axle is not good at 6th gear with it's double-overdrive. Acceleration amount does translate to lugging, I think we're on the same page there.

Take a look at this. Here is SAE's official dyno plot for the LT1. It means SAE certifies the engine will make that much power. The low end is 1000 RPM, and the high end is 6k RPM. It's interesting they stopped at 6k, given the ECU redline is 6500, I can only surmise it's because the power drops off and makes the graph less pretty. The important bit is the engine is SAE certified at 1000 RPM at WOT. If you needed proof that 1k RPM isn't lugging the engine, this is it.



Now, just for fun, here's the graph for the LT4. Notice the lower RPM limit is slightly higher, say 1200 RPM. Now I can't say for sure, but it's probable it's because the higher BMEP induces LSPI, and that's why they raised the low RPM certification point. If the engine makes 450 LbFt at 1200 RPM, that means it's BMEP is still a very low 180 PSI, so my money would still not be on LSPI. Also note they went higher RPM to get the power rating, though it still doesn't go to redline.



I hope that sheds some light on the subject.