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Companies converting base vehicles for other uses. Like Gruman using GM chassis to make delivery vans and RV manufacturers. My van was upfitted by Advantage Enterprises for example.
Stock 4l80e power
- Thread starter weaponoffreedom
- Start date
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Greetings OP,
Since buying my truck a year ago ('99 C2500/L29/4L80-E) I've been
doing my own research on what is going to happen if I decide to
scratch the mo' power itch. The following is from some of my
crib notes:
* On my vehicle the 4L80-E is rated at 440 ft/lbs. of torque capacity.
* The stock L29 (454) makes only 290hp, but cranks out 410 ft/lbs
of torque @3200 rpm.
* This only gives me room to make ~30 ft/lbs of additional torque
before I get tangled up in the computer's torque-mgmt limits.
* At the same time, both engine & tranny look to be undisturbed/unopened
since it left the assembly line after 220K miles on the odo, so do I want to
defeat the computer safety margins that maximizes the longevity of the
drivetrain if left to it's own devices?
* How about improving the motor and then stuffing a 4L85-E behind it?
Turns out the (non-Duramax) ones from the factory were rated at 460 ft/lbs
- this gives me 50 ft/lbs of torque headroom, which if that's all the more
I make, might be a reasonable solution. (especially if I finesse the associated
computer tables to match.) NOTE: There's plenty of confusion here -- even Wiki
is misleading about the torque rating of the stock 4L85-E, influenced by a
relatively recent Chevy Performance offering we'll be discussing in a bit. (Link)
* What if I selectively upgrade my existing 4L80-E to the 4L85-E spec, and
renew the wear items at the same time, giving me a fresh 460 ft/lb 2024(?)
tranny under my '99 truck?
****
The preceding was just trying to illustrate a few points that I want to make
below. Hopefully you will find the remainder of this helpful.
Showroom salespeople talk about how much horsepower your chariot of fire
will have under the hood. On the other hand, transmission engineers talk
about how much torque their design can handle. Keep in mind that if
you ask them how much torque their baby can handle, any engineer
worth their salt will give themselves some wiggle room. If they claim
440 ft/lbs on paper, there might be a 20% underrating fudge factor.
(Assuming the bean counters haven't cheapened out on his design vision.)
Nice 'Exploded Diagram' of the 4L80-E's internals. Q: Which of the following areas are stronger than needed?
And which areas will fold up under the application of large doses of additional torque?
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If pushed, the engineer will explain that his number allows the transmission
to deliver an expected problem-free service life of 100-150+K miles. If
the design is robust, it will certainly handle more power for short periods
of time...as long as excess heat is not allowed to build up during these
episodes. (ie: typical street use by a enthusiast -- typically you either
use the power you've amassed for short, discrete bursts**...or you end
up running afoul of John Law and are forced to memorize the local public
transportation routes & schedules. :0) **{Think Interstate onramp
merging into traffic cleanly, etc.}
Speaking of design, this is my 1st automatic purchase in 35 years.
I much prefer a standard transmission for several reasons -- one of
which is that if I break it *I* can fix it. I consider almost every automatic
transmission out there as a $3-4K balloon payment that can come due
with very little warning. Don't like driving in fear of $$$$ failure.
The one exception to the above? The Turbo 400. 45 years ago my buddies
and I did dumb stuff to a couple of them. They didn't care. They shrugged
off our feeble attempts to make enough twist to break them. (So that we
could upgrade to a stick shift.) Other automatics? Only took a weekend or
two for them to give up.
And since the 4L80-E is a Turbo 400 with an overdrive (and the implementation
is still as good as the original architecture) I broke my own rule of it has to
be a standard or I'm not interested. No regrets.
So let's talk about 'high horsepower' being applied to the 4L80-E. Using my
290hp L29 as an example, while I *can* make more horsepower on pump gas,
if I want my *stock* 4L80-E to stay reliable, then I must walk the torque tightrope
carefully. Let me explain. Making 1 ft/lb of torque per cubic inch on pump gas
while meeting emissions is a figure of merit. And if I try to make much more
than that then I will certainly wake up the knock sensors in the process.
So, I really can't add more power down low while on pump gas. So, in order to
keep what I have, if I was smart I would size a turbo that wouldn't really
spool up where the engine already shines (lower rpm) ...but when the L29
starts to fade due to the towing-oriented intake design *now* the turbo takes
over & blows this big block to a sparkling finish...to as high an rpm as I can set
up the bottom end & valvetrain to handle. (!)
And if all the while I keep the maximum torque at/near 460 ft/lbs (assuming
the -85 upgrade bits are in) well, now I have a 'high hp' L29 that can be fed
pump gas AND not excessively shorten the expected service life of the 4L80-E.
In English, right now the L29 pulls strong up up to it's torque peak at 3200rpm,
and then starts to fall off, and by it's peak HP rating at 4200rpm it really starts
to fall off a cliff. (But then the tranny shifts & the process repeats.)
What I tried to describe was leaving the L29 built as a torque monster, but
upgrading the internals so that once we get to 3200 rpm and then apply
boost to overcome the intake/cam design, if I manage all the variables, then
the engine continues to make my 460 ft/lbs of torque all the way up to,
say, 6800 rpm. And since HP is nothing more than torque x rpm, maintaining
the peak torque from 3200 to 6800 (instead of the stock 3200 to 4200)
will give me much improved bragging rights at the show & shine. :0)
****
OK, up 'til now I've been hiding behind my normal bang-for-the-buck
miserly b@st@rd facade. Time to switch into Go Big or Go Home mode:
Don't want to observe the stock torque limit? Would prefer to buy your
way into something that can take a lot more torque yet still comes with
a 12 month warranty? Enter the Chevrolet Performance Supermatic
version of the 4L85-E -- rated at a robust 685 ft/lbs of torque! (Link)
Heck, no more tiptoeing around the stock torque limits!
Now I can do the 496ci upgrade, + the AFR heads, upgrade to
the cam that Chevy should have built the L29 with originally, maybe
add some water/methanol injection indexed off of the MAF to
ward off the knock demons, and have a turbo L29 setup worth
writing home about?
How about price & availability? Here's what Jeg's has to
say about that. (Link)
And of course no product pitch is complete without some
marketeering. Here's a Chevrolet Associate Marketing
Manager doing his job to charm your socks off with
this new 4L85-E Hulk Hogan edition. (Link)
Still not enough? How about a 4L85-E built to handle
a full 1,000 ft/lbs of torque? These guys promise
a lot of capability in exchange for your entire
piggy bank. (full/unbroken. :0) (Link)
NOTE: They offer several flavors, including
LS & LT ones in addition to the BBC/SBC in
the link.
****
OK, back to reality. I know that all of the above
was a lot to slog through, but over the years
I've lived this over & over. Got enough of a
bad taste in my mouth that I quit building
engines for people who wanted to make the
big power under the hood & then, once the
budget was blown, wanted to stuff a tired
700R4 behind it & go to the races. Only
to burn the thing up in a month & then
be completely dissatisfied with the project
and dump it. (And they expected me to
have sympathy about their predicament...
or worse, share in the blame? Uh, no?)
Maybe that explains all of the above. I love to
add power to a car/truck/boat. If some
is good, then more is gooder. But at the
same time I feel bad if I don't first warn
my fellow motorsports enthusiast about
the perils of collateral damage downstream
of the hopped-up powerplant.
****
Alright, it's way past time to wrap this up. In
the real world, any time you are planning
to push up against the limits of an
automatic transmission, you should first
install 2 accurate gauges to monitor
the lifeblood of the transmission -- both
a tranny fluid Temp Gauge as well as
a Line Pressure Gauge. Run those
on a happy, stock transmission setup
until you have the known-good readings
memorized/photographed.
NOW, add the extra power in front of the
transmission, and then all you have to do
is figure out how to keep those temp &
pressure readings the same...and you win!
...but unless you are very lucky, since
extra power = (potentially) extra heat you
may have to add additional cooling capacity
for your transmission fluid.
And when I tell people this, a percentage of
them don't want to bother with the extra
gauges. I simply respond that maybe you
don't have the right mindset to be successful
with this project as a long term self-propelled
toy.
And if this makes them mad, well it's good to
find out before we join together like the Lewis & Clark
dudes did on their expedition on this
doomed-to-disappointment project. :0)
****
So, find out how much torque your
"6.0 Vortec, stroked to 6.6, then supercharged"
setup is actually making, and then the answer
to your question should be easy to pinpoint on
the 4L80-85E transmission torque continuum laid out
above.
Hope the above makes sense. Questions welcome!
Signed,
Been there, broke that.
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If you use a pressure gauge and dial in the pressures with the tune and have a fluid cooler to keep everything cool they will hold up to a fair amount of abuse.
~45,000# gross weight
125psi in rear helper bags
Trailer bags were self leveling and ran roughly 90psi. Very heavy load but the ride was very smooth.
The 4l80 is mostly stock with some sonnax valves and such. Nothing special. Spent a few minutes dialing in the pressures with a gauge and adjusting the tune. TruCool 40k cooler, trans Temps would rise to about 175 getting the load up to speed. Lock TCC in 2nd, 3rd, and 4th. Trans Temps settled back down to 125-130 for the rest of the trip.
8.6mpg was all it got so I was happy.
I'm not scared to put 800ftlb thru a 4l80. My next setup will be a turbo 370ci in this truck and all I'll do is change converter, fluid and filter.
~45,000# gross weight
125psi in rear helper bags
Trailer bags were self leveling and ran roughly 90psi. Very heavy load but the ride was very smooth.
The 4l80 is mostly stock with some sonnax valves and such. Nothing special. Spent a few minutes dialing in the pressures with a gauge and adjusting the tune. TruCool 40k cooler, trans Temps would rise to about 175 getting the load up to speed. Lock TCC in 2nd, 3rd, and 4th. Trans Temps settled back down to 125-130 for the rest of the trip.
8.6mpg was all it got so I was happy.
I'm not scared to put 800ftlb thru a 4l80. My next setup will be a turbo 370ci in this truck and all I'll do is change converter, fluid and filter.
Attachments
D@mn, that's a mighty fine photo of a hard-working rig!
I honestly hope that anyone who worked the 4L80-85E line at Ypsilanti
gets an opportunity to see that photo & take pride in what they
accomplished/we can accomplish when left alone to do the right thing.
'Murica!
Some factors not mentioned:
1. How is torque rated? Buick 455 in '70 had a torque rating of 510 ft/lbs. I don't doubt the 400 used behind it had some extra clutches in the clutch packs. And given the trans fluid limitations at the time, the trans was probably done in a hundred-thousand miles. Still...510 ft/lbs isn't bad.
Cadillac 500 in '70 was rated even higher. 550, I think.
But all of this is GROSS rating. The "real" torque produced was less. Even today, engines have torque management during shifts, where the timing is retarded to kill the torque as the clutches/bands engage and disengage. So during the most-crucial trans operation, the engine torque drops like a paralyzed falcon. A non-computer-controlled engine--or one with torque management disabled--doesn't have this.
2. How is the transmission rated? Just like engines, the SAE procedure, or the GM Durability Testing may be totally different from aftermarket testing protocol, or "real life" use.
I'm thinking that if GM rates that trans at 440 ft/lbs, it'll take 440 ft/lbs day and night for a week straight using torque management during shifts. Maybe longer. Which tests the ability of the clutches and bands to not slip, but also tests the gears for wear under stress, the case for twist under stress, the bushings and shafts for twist and wear...etc. But that's not how we use these vehicles. We're using intermittent power; "long term" power is measured in minutes not days. We need pieces to not break, we need the frictions to not slip...but long-term wear is not something folks think about when stuffing a bigass engine under the hood. That is just kinda accepted.
For the record, 440 ft/lbs at the engine flexplate is going to be multiplied by something like 2:1 by the torque converter (880+ ft/lbs to the transmission input shaft) and then by 2.48 by 4L80E low gear (2182+ ft/lbs at the trans output shaft, not counting losses within the transmission--driving the pump, friction, etc.) You put the transfer case in "Low", but don't engage the front axle disconnect for another 2:1 or more torque multiplication (4364-ish ft/lbs of torque at the rear driveshaft (You see why they don't offer 2WD low-range?) and then the rear axle has 3.73: 1 ring 'n' pinion gears (maybe higher numerical) and that poor differential case is getting something like 16,000+ ft/lbs of torque to divide between two axle shafts, assuming the tires aren't on fire by now. I've tried to be conservative on some of the torque multiplication, because I don't know how much is lost due to friction, pump losses, etc.
The "factory" rating for torque capacity on these transmissions is a figure that a) allows bragging rights, b) allows an ability to deny warranty claims if the engine is modified, c) is not really applicable to ordinary use, since the rating comes from a genuinely-artificial testing protocol.
Ya pays your money, and ya takes your chances.
1. How is torque rated? Buick 455 in '70 had a torque rating of 510 ft/lbs. I don't doubt the 400 used behind it had some extra clutches in the clutch packs. And given the trans fluid limitations at the time, the trans was probably done in a hundred-thousand miles. Still...510 ft/lbs isn't bad.
Cadillac 500 in '70 was rated even higher. 550, I think.
But all of this is GROSS rating. The "real" torque produced was less. Even today, engines have torque management during shifts, where the timing is retarded to kill the torque as the clutches/bands engage and disengage. So during the most-crucial trans operation, the engine torque drops like a paralyzed falcon. A non-computer-controlled engine--or one with torque management disabled--doesn't have this.
2. How is the transmission rated? Just like engines, the SAE procedure, or the GM Durability Testing may be totally different from aftermarket testing protocol, or "real life" use.
I'm thinking that if GM rates that trans at 440 ft/lbs, it'll take 440 ft/lbs day and night for a week straight using torque management during shifts. Maybe longer. Which tests the ability of the clutches and bands to not slip, but also tests the gears for wear under stress, the case for twist under stress, the bushings and shafts for twist and wear...etc. But that's not how we use these vehicles. We're using intermittent power; "long term" power is measured in minutes not days. We need pieces to not break, we need the frictions to not slip...but long-term wear is not something folks think about when stuffing a bigass engine under the hood. That is just kinda accepted.
For the record, 440 ft/lbs at the engine flexplate is going to be multiplied by something like 2:1 by the torque converter (880+ ft/lbs to the transmission input shaft) and then by 2.48 by 4L80E low gear (2182+ ft/lbs at the trans output shaft, not counting losses within the transmission--driving the pump, friction, etc.) You put the transfer case in "Low", but don't engage the front axle disconnect for another 2:1 or more torque multiplication (4364-ish ft/lbs of torque at the rear driveshaft (You see why they don't offer 2WD low-range?) and then the rear axle has 3.73: 1 ring 'n' pinion gears (maybe higher numerical) and that poor differential case is getting something like 16,000+ ft/lbs of torque to divide between two axle shafts, assuming the tires aren't on fire by now. I've tried to be conservative on some of the torque multiplication, because I don't know how much is lost due to friction, pump losses, etc.
The "factory" rating for torque capacity on these transmissions is a figure that a) allows bragging rights, b) allows an ability to deny warranty claims if the engine is modified, c) is not really applicable to ordinary use, since the rating comes from a genuinely-artificial testing protocol.
Ya pays your money, and ya takes your chances.
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Exactly. Duty cycle is a major variable when it comes to predicting the
useful service life of something as precise & complex that is forced
to deal with this level of heat + stress.
****
Speaking of which, there are 2 different ways to break an automatic.
The first is shock loading, especially real knuckle-dragger tricks
like full-throttle neutral slams. :-( Education is the only solution,
for there are some people who can break whatever they are given
without breaking a sweat.
The second is smooth, intelligent, adult-owned operation...but they
are driving a full-sized RV across the Continental Divide...without
transmission gauges. And despite all the smooth kindness that they treat
the tall pedal on the right with, they are unaware that the clutches
are slipping/burning up on the steep grade they are climbing until
they smell that sharp $$$$ smell with their noses.
And then there's people like RDF1 and his rig. He knows exactly
what he's asking of his transmission, and furthermore, if you
ask him what transmission fluid temps he is experiencing...he
can absolutely tell you, during each phase of his journey.
And he also knows that tranny fluid pressures are paramount
to being able to work at/near capacity reliably. Now of
course if he was running a Metric 200 from the bad old
daze even his extra cooling + monitoring those gauges
wouldn't be all that much help. You gotta have the
correct foundation to build upon. There is a lot to be
said for the right architecture that people have analyzed,
evolved, & supported continuously since the mid-'60s. (!)
Rebuilding one of these is on my motorhead bucket list. (And afterwards I'll paint a little fresco on the living room ceiling ala the Sistine Chapel... ;0)
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Anyway, if the OP were to follow RDF1's lead
then I think he will end up in a reliable space.
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Companies who buy cab and chassis trucks and add bodies/beds. Ambulances, campers, rollbacks, etc.
weaponoffreedom
OBS Enthusiast
That is a heavy load. What engine? 6.0?
weaponoffreedom
OBS Enthusiast
So the reason for the post is i am thinking about having my 04 Burb tranny rebuilt and getting a reman from Kodiak Truck np246........and local guys dont want to touch the thing due to engine work. Thanks for the replies fellas, reaffirmed what I already thought. I have used the 4l80e in severe conditions for 20+ years and never had a failure due to overloading, but never had a stoked 6.0 with a supercharger either. Trans temps stay below 180 even when 100 out, normal driving. Havent towed with it yet.
Yea poor lil 6.0 with 364,000 miles on it.
Ive had more bushing wear/failures in 4l80Es than i have had planetarys and clutch failures. Sure anything is possible but the things are strong with a few simple upgrades.
Simple things like this zip valve for TCC engagement.
TCC Regulator Valve Kit - 34994-01K
GM vehicles equipped with 4L80-E and 4L85-E transmissions may exhibit problems such as TCC shudder, burnt converter linings, TCC apply and release concerns a
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