RPM 4L80e ?

[graf101]

So I have an RPM Stage 5 4L80e swapped into my 2015 1LE, and I was wondering what gear /rpm you other 4L80e and th400 guys are shifting into at the 1/4 stripe? Mine is at 6400 rpm in 3rd gear when almost crossing at the stripe, and I have been manually shifting into 4th (overdrive)before the stripe. I was told to leave it in 3rd gear. Thoughts or suggestions?

[bct10985]

I shift around 7k. It shifts into 4th right before the line. But im also going 145mph.

[acammer]

Originally Posted by graf101

So I have an RPM Stage 5 4L80e swapped into my 2015 1LE, and I was wondering what gear /rpm you other 4L80e and th400 guys are shifting into at the 1/4 stripe? Mine is at 6400 rpm in 3rd gear when almost crossing at the stripe, and I have been manually shifting into 4th (overdrive)before the stripe. I was told to leave it in 3rd gear. Thoughts or suggestions?

Definitely leave it in third.

The common misconception on shift points is that you want to shift at peak HP. That's bogus. You want to shift (assuming your car can tolerate the RPM) at whatever RPM puts you're next gear's rpm at a point where you generate the highest average HP throughout the gear.

Let's take a look at a dyno chart of my car as an example. Let's assume for this discussion I have a 4L80. If I shift from 2rd to 3th at 6500 where I make peak power that would drop me back down to 4390 rpm in 3th (yellow lines). Compare that to riding 2nd out to 7000rpm which drops you back to 4730 (green lines) and look at how much average power you gain. When you shift at peak power you fall back to an RPM with less power - 350hp vs. 375hp in this example. You do roll past peak power and HP begins to decline, but it's nowhere near the difference you get with the earlier shift - the average power is up significantly with the later shift.

With a car that really lays over after it peaks there comes a point where you're just revving but power has dropped off so much you're no longer effective. With even the stock cam in an LS3, they pull well past their peak and still deliver strong power right to the factory rev limiter at 6600. This dyno graph doesn't show it, but we pulled this cam all the way out to 7400rpm and it was barely rolling over - the dip on the end of this graph is just where the dyno operator lifted. For me, I'm comfortable taking the valve-train to 7200 regularly, so that's where we put the limiter, and I target shifts in the 7000-7100 range.

For you - definitely stay in third, the shift costs you time, and puts you at a lower horsepower output at the end of the track, where you need every pony you can get.

What's the rest of the setup on the car?

[graf101]

Car is a 2015 1LE, RPM stage 5 4L80e swapped, Vigilante 3400 single disc converter, 3.91's, LSA blower, meth, full bolt ons, ADM stage 2 PD cam. Car made 700whp as a manual and I am not sure what it makes now as an automatic. I am adding a 3.73 zl1 diff and e85 now.

[acammer]

Originally Posted by graf101

Car is a 2015 1LE, RPM stage 5 4L80e swapped, Vigilante 3400 single disc converter, 3.91's, LSA blower, meth, full bolt ons, ADM stage 2 PD cam. Car made 700whp as a manual and I am not sure what it makes now as an automatic. I am adding a 3.73 zl1 diff and e85 now.

Yea - I wouldn't go to 4th. When it dyno'd it probably peaked at what, 6400rpm? And I'm sure it doesn't just lay over after that. I'd probably shift at 6800-7000 - whatever you're comfortable with. The 4L80 has quite a bit of space between gears, the converter helps some, but you want all the RPM you can tolerate. 3.73 is gonna work well with that combo.

[graf101]

Thank you for the detailed information, acammer! I will report back with drag strip results soon!

[jrob56]

Can just close this thread down, couldnt ask for a better answer and not how I had ever looked at shift points, good info!

[Devcon 7]

What did this run with the auto?

[RaiderSS]

I have a very similar build:
LS3 416, ECS Ysi, Vengeance Cam, Tsp 2" longtubes, AGP Tripple pumps, Id1650x, ProMeth quad nozzle plenum injection...

Jakes stageIII 4L80e, FTI 3600, ZL1 3.23 diff...

BMR suspension, 17" weld rts 4.5" Hoosier skinnies front, carlyle racing 15" conversion mt 275 et street R


How does the 3.23 rear diff change the pass and where it should shift?

[acammer]

Originally Posted by RaiderSS

I have a very similar build:
LS3 416, ECS Ysi, Vengeance Cam, Tsp 2" longtubes, AGP Tripple pumps, Id1650x, ProMeth quad nozzle plenum injection...

Jakes stageIII 4L80e, FTI 3600, ZL1 3.23 diff...

BMR suspension, 17" weld rts 4.5" Hoosier skinnies front, carlyle racing 15" conversion mt 275 et street R


How does the 3.23 rear diff change the pass and where it should shift?

So - I would think you'd still have a similar shift point, somewhere around 6800rpm depending on how the car dynos. You can usually comfortably figure you want to run out at least 500rpm past where peak power occurred - maybe even more depending on the curve.

With the 3.23 you're going to have plenty of gear in 3rd. There are some guesses here (26" tire, 5% converter slip) but it should be able to go about 155mph at the top of third. It sounds like you've got a lot of power there to get up close to that, but I'd think you've got enough. If you've got a lock-up on the converter the 3.23 would bring you out to 163mph in third (on a 26" tire) @ 6800rpm.

This is a really nice calculator for digging into this kind of stuff. Only thing missing is converter slip, but you can figure that out yourself pretty easily.

https://www.blocklayer.com/rpm-geareng.aspx

[Juiced1]

A good rule of thumb is to shift around 10% over peak power or as close as your valvetrain will allow you to get to that number. You want that shift to stay in the power band.

[RaiderSS]

Originally Posted by acammer

With the 3.23 you're going to have plenty of gear in 3rd. There are some guesses here (26" tire, 5% converter slip) but it should be able to go about 155mph at the top of third. It sounds like you've got a lot of power there to get up close to that, but I'd think you've got enough. If you've got a lock-up on the converter the 3.23 would bring you out to 163mph in third (on a 26" tire) @ 6800rpm.

This is a really nice calculator for digging into this kind of stuff. Only thing missing is converter slip, but you can figure that out yourself pretty easily.

https://www.blocklayer.com/rpm-geareng.aspx

3600 Tripple disc lock up
Mickey Thompson P275/60R15

Havent dynoed yet so all shifts at 6700...

When should converter get locked to bring me up to +160?

[acammer]

Originally Posted by RaiderSS

3600 Tripple disc lock up
Mickey Thompson P275/60R15

Havent dynoed yet so all shifts at 6700...

When should converter get locked to bring me up to +160?

When to lock the converter really depends on the curve of the motor. On a 28" tire it's gonna go 173mph at 6700rpm in third locked, I'd guess that you'll want to let it rev till it's about 200rpm beyond where-ever it makes peak power and then lock the converter to finish out.

I wonder if a 3.45 ratio would work nicer - that would go 162mph locked at 6700 on that tire...

[RaiderSS]

Originally Posted by acammer

I wonder if a 3.45 ratio would work nicer - that would go 162mph locked at 6700 on that tire...

Thanks for the knowledge


ZL1 diff has 2 options that Im aware of and i chose the 3.23 because it gave me more top end speed for half miles than the 3.7x