[jasonct]

Thanks for the explanation!

[ChadFarr]

Great Answer and clarification!

[Battlezone580]

The LT4 is rated at 650hp @ 6,400 rpm. 5200rpms seems way too soon to shift, you wouldn't be hitting your peak power.

Looking at a hp chart of the LT4, shifting at 5200rpms would put you at about the 550hp range .

[vtirocz]

Originally Posted by Battlezone580

The LT4 is rated at 650hp @ 6,400 rpm. 5200rpms seems way too soon to shift, you wouldn't be hitting your peak power.

Looking at a hp chart of the LT4, shifting at 5200rpms would put you at about the 550hp range .

I think you've misinterpreted the table. For your ZL1, you can shift wherever you want above 5000 rpm but once you execute the shift the feature will adjust spark timing and fuel to target an engine speed of 5200rpm, all while keeping the intake throttle open. So if you execute the shift at 6450rpm, once you push the clutch pedal engine speed will target 5200rpm.

The idea is to keep the throttle open, so intake manifold pressure stays high during the shift so then you can have full power immediately as soon as clutch pedal is released.

[mlee]

Originally Posted by vtirocz

I think you've misinterpreted the table. For your ZL1, you can shift wherever you want above 5000 rpm but once you execute the shift the feature will adjust spark timing and fuel to target an engine of 5200rpm, all while keeping the intake throttle open. So if you execute the shift at 6450rpm, once you push the clutch pedal engine speed will target 5200rpm.

The idea is to keep the throttle open, so intake manifold pressure stays high during the shift so then you can have full power immediately as soon as clutch pedal is released.

[SS 1LE]

Originally Posted by mjk3888

Not really. It's more optimized for drag racing to help lurch the car into the next gear without loss of acceleration in the standard SS. The SS 1LE however, is clearly set to promote smooth NLS gear changes so it won't upset the car mid turn on track. Makes sense. Track calibration for the track pack car.

Then why is the ZL1 around the same range? I think there is more too it then that as having it hold at 6400 is past the power peak of the engine, and right by the limiter...and on top that after your shift point. So that really wouldn't be a "help" drag racing. Dunno...

[vtirocz]

Originally Posted by SS 1LE

Then why is the ZL1 around the same range? I think there is more too it then that as having it hold at 6400 is past the power peak of the engine, and right by the limiter...and on top that after your shift point. So that really wouldn't be a "help" drag racing. Dunno...

Based on this power curve on the lt1, I think shifting as close to redline as possible will result in the best time. This can be calculated as well to confirm the best shift point for each gear. I'll do that and report back.

https://www.edmunds.com/car-reviews/...dyno-test.html

[Russell James]

Does a 5th gen LS3 have no lift shift? i.e. '15 1LE?

[mlee]

Originally Posted by Russell James

Does a 5th gen LS3 have no lift shift? i.e. '15 1LE?

No, it came 1st with the 2012 ZL1

[Norm Peterson]

Originally Posted by vtirocz

Based on this power curve on the lt1, I think shifting as close to redline as possible will result in the best time. This can be calculated as well to confirm the best shift point for each gear. I'll do that and report back.

Best time comes when you maximize the "area under the HP curve" between the (higher) rpm you shift at (in the lower gear) and the (lower) rpm you end up in, in the next gear.

This happens when the HP at the rpm you shift at is essentially equal to the HP at the rpm you end up in . . . assuming that you have enough headroom above peak power rpm before encountering any rev limit to do so. If there is an rpm limit getting in the way of the above, just under that rpm limit would be your optimum shift point.

Keep in mind that the best shift point for one of your shifts won't necessarily be the best shift point for any of the others; best shift point varies a bit as the spacings between transmission gear ratios varies. Wide gear spacing will want you to run the lower gear out to a higher rpm than close gear spacing. Rev limits permitting.


Norm

[vtirocz]

I used the feature several times now on my 2017 SS manual and it works exactly as advertised. I look forward to testing this out at the track next year to see what kind of gains I will see.

Thanks again, Al, for the detailed explanation! The 6400 RPM target speed was so close to the 6500 RPM redline that I thought it might not be working as intended. I'm happy to see I was wrong. In future, I would definitely recommend putting this level of detail in the owners manual or performance supplement so more owners will take advantage of existing features.

[Macaro]

I’m psyched to try this next season at the track, may be good for another tenth or two...

[SS 1LE]

Originally Posted by Macaro

I’m psyched to try this next season at the track, may be good for another tenth or two...

No real gains, as it cuts a tad bit of timing on the shift. Mainly just easier and more consistent.

[vtirocz]

Originally Posted by SS 1LE

No real gains, as it cuts a tad bit of timing on the shift. Mainly just easier and more consistent.

There will be a benefit in how quickly full power returns after a shift since intake manifold pressure won't drop as much (since intake throttle remains full open). I'd like to datalog this to quantify the difference.

I'd expect a small difference in the naturally aspirated engines and a bigger difference in the boosted engines.