Shifting very late

[Supercharged111]

Completely normal for a 4L80E truck with 3.73s.

xc_hide_links_from_guests_guests_error_hide_media

Thank you. Not only is the 4L80 geared taller, but in the stock tune the HD trucks upshift at 5100 RPM vs 5000 for the half tons which is splitting hairs. My 4.10 geared half ton doesn't leave 2nd until 77mph. Those legs come in real handy when you hit a nasty hill at 70+ with a heavy ass trailer out back.

 

[L31MaxExpress]

I was thinking more like 3.42s but yeah, that sounds about right for a 4L80E. They have a really long first gear. My '97 C1500 with 3.42s shifts into second right around there at wide open throttle.

EDIT - According to the ChevelleStuff gear calculator a 4L80E truck with 3.42s and an 80E will hit 52MPH in first at 5133RPM, assuming 235/75/R15 tires. 3.73s would put you at 5599RPM at the same wheel speed.

https://chevellestuff.net/tools/rpm_calculator.htm

The heavier trucks have taller/wider tires. LT245/75R16 if I remember correctly is the factory size.

 

[L31MaxExpress]

Thank you. Not only is the 4L80 geared taller, but in the stock tune the HD trucks upshift at 5100 RPM vs 5000 for the half tons which is splitting hairs. My 4.10 geared half ton doesn't leave 2nd until 77mph. Those legs come in real handy when you hit a nasty hill at 70+ with a heavy ass trailer out back.

They are also nice when you get stuck behind someone running 55-60 on a two lane road.

FWIW the 0411 PCM I used from an 02 van was programmed for 5,200.

 

[Supercharged111]

Like my drive to work every day? Yeah, it's great with the blower.

 

[df2x4]

The heavier trucks have taller/wider tires. LT245/75R16 if I remember correctly is the factory size.

Correct, that's what size my '97 K1500 Suburban came with. That larger tire only equates to 268RPM of difference in the calculations, though.

 

[L31MaxExpress]

Like my drive to work every day? Yeah, it's great with the blower.

My 2nd gear is great for that now with 5.13 gears, LT265/75R16s and the 6,500 rpm capable 383. I get 45 mph out of first with 200 rpm converter slippage shifting at 6,200 rpm. 2nd gear I get 77 mph @ 6,200 with the converter locking about 4,500 rpm. Turns 2,850 @ 70. It will accelerate and pull grades in lean cruise with nearly no load on the engine. I have seen 17 mpg on a recent road trip and it is not tuned as well as I would like it to be yet. My timing map is ultra conservative because of the 11:1 compression ratio and small cam with Rhoads lifters making the cam effectively even smaller and I am only running at 16:1 air fuel ratio. I ran the old 350 closer to 17.5:1 without misfire thanks to the coil per cylinder ignition.

The Tahoe is geared pretty well for me too. Marine cammed 8.1 that makes about 450 hp @ 5,100 rpm. 4L80E and 3.42 geared 9.5 14 bolt. Has 32" tall P305/50R20s. Shifting at 5,200 rpm I get 55 mph out of first with about 150 rpm slip in the stock B82 converter and 98 mph out of 2nd. I lock the converter about 65 mph or 3,500 rpm in 2nd. The 8.1 does not seem to mind pulling against the tall gear since it makes something like 400 ft/lbs @ 1,200 rpm and 550 tq @ 3,500. The 8.1 turns about 1,850 rpm @ 70 and stays in lean cruise with the empty Tahoe. I have gotten nearly 18 mpg on a long trip. As crappy as the combustion chamber is, thanks to the low compression ratio and the larger marine cam it has no issue running at 16.5:1 air/fuel mixture and 42* timing at 1,850 rpm on 87 octane. I am thinking of pulling the intake and swapping out the lifters for a set of Rhoads lifters to recover some of the low-end torque the 8.1 loses from the marine cam as well as some of the intake vacuum. Making the cam effectively smaller should make the mileage 1-2 mpg better.

 

[L31MaxExpress]

Correct, that's what size my '97 K1500 Suburban came with. That larger tire only equates to 268RPM of difference in the calculations, though.

Redo those calculations with a 2.48 vs 3.06 1st gear and 1.48 vs 1.63 gear for 2nd gear. The 4L80E transmission makes the bigger difference in the 8 lug stuff. One other thing is the OD is shallower in the 80E too. With 30.5" tall tires and 3.73s I gained 200 rpm @ 70 with the 4L85E compared to the 4L60E in the Express van and 150 rpm in the Tahoe with 3.42s & 32" tall tires. The 305/4L60E used to pull the Tahoe down the road at 70 mph @ 1,700 rpm.

 

[df2x4]

Redo those calculations with a 2.48 vs 3.06 1st gear and 1.48 vs 1.63 gear for 2nd gear. The 4L80E transmission makes the bigger difference in the 8 lug stuff. One other thing is the OD is shallower in the 80E too. With 30.5" tall tires and 3.73s I gained 200 rpm @ 70 with the 4L85E compared to the 4L60E in the Express van and 150 rpm in the Tahoe with 3.42s & 32" tall tires. The 305/4L60E used to pull the Tahoe down the road at 70 mph @ 1,700 rpm.

Yup. I had the same experience in OD after the 80E swap in my '97 4.3L C1500. It cruises at 70 right around 2100RPM now as opposed to 1900RPM when it had the 60E. Which actually made it a lot more pleasant to drive on the highway, it doesn't want to downshift on every little incline now.

 

[L31MaxExpress]

Yup. I had the same experience in OD after the 80E swap in my '97 4.3L C1500. It cruises at 70 right around 2100RPM now as opposed to 1900RPM when it had the 60E. Which actually made it a lot more pleasant to drive on the highway, it doesn't want to downshift on every little incline now.

I noticed the same improvement. I noticed even more improvement in the ability to climb grades when the Thorley Tri-Ys went on. To the point it would hold overdrive on long grades that were 6% or more. There is one long grade a little west of me that it would downshift to 3rd on and still easily run up at 75+ mph that I would usually have to take it off cruise and slow down because other cars can't keep their speed up on. With the 5.13s even with the 350 it holds overdrive on that grade. The 350 would pull my 6,000 lbs travel trailer up that grade at 70 mph in 3rd at about 3,500 rpm with 1/2 pedal to spare. Have not climbed it yet with the 383.

I wonder if the 4.3 S10 long tubes would fit your chassis? Would definately wake up the little 4.3. Especially if you fabricated a 2.25" to single 3" exhaust to go behind them with a thunderbolt 3" high flow cat. I also know the 4.3 CPI "W" cam wakes the 4.3s up and is more aggressive than a F/Y car LT1 cam.

 

[df2x4]

I wonder if the 4.3 S10 long tubes would fit your chassis? Would definately wake up the little 4.3. Especially if you fabricated a 2.25" to single 3" exhaust to go behind them with a thunderbolt 3" high flow cat. I also know the 4.3 CPI "W" cam wakes the 4.3s up and is more aggressive than a F/Y car LT1 cam.

Not sure about the S10 headers, I looked around a little on that subject when I redid the exhaust years ago but I never did find a definitive answer. I ended up going with some Pacesetter shorties (garbage, flanges machined in a way that interferes with the CTS) with a Magnaflow Y-pipe/cats and Gibson single 3" cat back system. It seemed like a decent improvement overall, not as noticeable as the tune but maybe that's because I had it tuned after the exhaust mods.

Interesting thought about the cam, I'll keep that in mind. I've thought about building the V6 in the past but for the money invested to get the power I'd like it seems more logical to just drop in a V8 if and when the V6 ever gives me problems. I've got my eyes on an LQ4, or maybe one of the newer LT V8s if that stuff comes down in price a little by the time I need one.