4l80e how much can it handle ?

[Olav]

4l80e how much power can it handle in stock form behind a SB ? Is there any years that are better than others ?

Olav

[Olav]

Ttt

[critter]

I have no experience but my research has shown that most agree it will take over 400hp and 500 ft. lb. of torque.

There are 2 schools of thought on the early VS later cores. Some say the later cores are better due to a change in the lubrication circuit. It has to do with rear planetary gears cooking, if I read it right. Most seem to think that this is more an issue with a towing application as opposed to a performance issue.

I hope someone who builds transmissions will jump in here. I'm only passing on what I've read on the internet so we all know that could be a load.

[jakeshoe]

The 4L80E in stock form would be limited by it's direct clutches (3rd gear) and that would be a part that would gradually fail at ~500 HP if raced often but last years on the street at closer to 600 HP/TQ in a passenger car application.

Other than that it would mostly depend on the year model and how it was used. With minor mods 800 HP isn't an issue. Above 800 HP it needs and input shaft and forward clutch hub upgrade and that will make it fairly stout up to over 1000 HP.

The ultimate limiting factor becomes the OD section. 1200 HP is a good number.

I'm working on a fix for the OD section to improve it's strength.

[nightrunner]

a built 4L80e will stay behind a 1000rwhp/1000rwtq turbo'd 408 lsx in a 4500lb. truck, and that is well documented.

a 4L65e will hold up to 500rwhp/500rwtq in the same truck.

and these are heavily drag raced trucks

reason i am giving this info is alot of these muscle crs weigh in at about 3500-4000 lbs and weight and torque is what kills the trans

[Jake's Performance]

There are many factors that kill a trans, weight and torque are two of the main factors but engine RPM is another big one that is overlooked.
Driving style obviously has a big effect too. Manually downshifting an automatic while under hard decel will kill any of them quickly.

[burnoutbruce]

It will handle whatever you throw at it

[DeltaT]

Manually downshifting an automatic while under hard decel will kill any of them quickly.

Does that include using a paddle shifter on the road race course?

Thanks,

Jim

[Jake's Performance]

Does that include using a paddle shifter on the road race course?

Thanks,

Jim

Yes

[Steve Chryssos]

NO!

An all electronic paddle shifter bypasses the manual valve.

[Jake's Performance]

It has nothing to do with whether or not you use the manual valve to shift it or the shift solenoids.

The problem with downshifting during heavy deceleration on an automatic transmission is one of power flow and design. Specifically the sprags used in most common paasenger car and light truck applications.

No matter what you do or how you shift it (manually or electronically) this problem is present.

It's brutal on the sprags to engage them on a downshift under hard decel.
They are designed to carry an upshifting load, where they are being driven by the input end of the trans and driving the output end of the trans.
When decelerating you are reversing the power flow of the trans. The output shaft becomes the input as far as torque.
Under normal operation the sprags over-run in deceleration, except when a gear is manually selected that applies a clutch or band that prevents the over-run of the sprag. (In a 4L80E the low band, intermediate band, and over-run clutches would be examples).
A 3-2 downshift on a 4L80 electronically would actually be worse for the trans than manually because the intermediate band doesn't apply to take some of the load off the sprag.
The problem in either case is that the sprag will lock quicker than the band can come on due to the reversal of input torque.
You control the sprags shock on upshift through the use of accumulators, cushion clutches, and orifice sizing, you lose much of this control on the downshift side, especially on the typical modified transmission.
However even stock trans don't have the accumulation for downshifts because they weren't designed with this in mind.
Heavy truck applications that don't use a sprag but use synchronous clutch shifting (6L80/6L90, Allison) would work better for this type of use.
However the shift quality on upshifts suffers with these units usually.

In reality a manual transmission works better for a road race application. An automatic will work as well but the builder needs to be aware of the intended use, and the customer should be aware that it won't ever live as long as an equivalent drag racing type unit.
Mostly due to the sprags.

If building a 4L80E for this type of application, be sure the builder keeps the accumulators functional.

[Steve Chryssos]

I must have over 10,000 downshifts across three in house test vehicles up to 700 horsepower over almost 7 years. No sprag failures or other failures for that matter. One vehicle, my own, has the Sonnax mod for engine braking. I have it on video, in front of witnesses.

I'll be happy to lend you a paddle shifter. What TCU's are you using?

[Jake's Performance]

We've used TCI, Compushift, PCS (new TCI), and full manual on the 4L80Es.

It has nothing to do with what controller you use, it completely mechanical in nature.

Do you understand the function of the sprag in an automatic transmission?

Have you ever looked at one?

Do you know the power flow of a 4L80E? Low sprag locked in low gear, intermediate sprag locked in 2nd gear, overdrive sprag locked in all gears except OD, what clutches and bands are on when?

Have you looked at the surface area of the intermediate band (holding in decel) in a 4L80E compared to the intermediate clutches (holding in accel)?

Over-run clutches that hold in 1st, 2nd, and 3rd? A 4L60E has 2 small clutches here, 4L80E is better but still not the holding capacity of the rest of the transmission.

HP is not applicable here, vehicle weight, rpm, and accumulator function are much more important.
As I stated before the power flow is different in deceleration, the output shaft becomes the power input. The faster the car is traveling, and the heavier it is, the more strain it will cause on a downshift.

You have components spinning at engine speed in 3rd gear or even greater speed in 4th, that will come to a complete stop instantly when the trans shifts to 2nd. Direct drum is about 14 lbs in a 4L80E.

6500 rpm to zero rpm is quite a hit on a rotating component.
Reliability will suffer.

I'm not here to say it can't be done, but that there are more reliable ways to do it. One being a manual transmission. Most of my business is building automatics for high performance vehicles, so it's not in my interest to tell someone a manual is better but I'm also not going to be dishonest about the strengths and weaknesses.

That said,
I have several 4L80Es being used in Pro-Touring type combos. They work well. It is the unit to use because it will take abuse that other unit's won't.

The key is to work with the accumulators in this type of combo, GM did a good job designing them, so eliminating them is moving decades into the past.

[Steve Chryssos]

Now you're being sarcastic and condescending. That's not nice. I tried to be nice. First. I called you last Friday, so we wouldn't do this stupid message board thing. No call back. Then I offered you product for testing. I asked what TCU you guys use, so I could send the right product. I never said the TCU brand makes a difference--even though it does. You responded with condescending sarcasm. Strike two.

The difference, Jake, between Smart and Know-it-All is TESTING. If you take me up on my offer, you will see the flaw on your power flow diagram when comparing electronic shifting (manual valve does not move) with manual shifting. I won't challenge you on that here because I don't do message board pissing matches.

If you're here to "do" pro-touring builds, then you can't get around the downshifting thing because that's what pro-touring cars do. Which is fine because no one downshifts at 6500 rpm and the sprags are taking the load. No sense selling transmissions that just upshift.

Offer still stands. Just let me know what type of computer you're running.

[Jake's Performance]

Steve,
I'm not being condescending, I'm asking seriously if you know the things I asked.

I build the transmissions, I look at the parts day in and day out, I have 3 4L80E's in process in the shop right now. One for a 1200 HP ride that will be built next week when the parts show up, another for a 900-1000 HP ride that is being test fitted to the car, and another for a guy in Kansas that I'm correcting a VB issue from a transbrake vendor who is selling junk.

I'm not here to knock what you are doing with the paddle shifters. I'm simply stating the stresses imposed on the trans when downshifting.

They are a different animal than when upshifting. Upshifting isn't hard to calibrate for. I've been preaching that for years on various message boards and in tech seminars recently.

I did not get your message. What number did you call? I was out of town until Monday afternoon, I checked messages as soon as I got back and didn't get one from you. I'll check with the guys and see if they checked them Friday.

All the cars I'm doing right now are either full manual VB with brake, or the one 1200 HP deal is an auto VB with transbrake (obviously all drag oriented combos).
I have a couple of customers who are probably already running your product or might be interested. One's using the PCS controller and the other is using a Compushift.

The PCS is in a '68 Camaro, I'll check and see if they want to try it.

[critter]

Jake, I'm going to be running Steve's Shrifter product. Steve, I sourced my converter through Jake. I've talked to you both and I think you're both professionals. You can probably help each other. It's not unusual to see experts with a passion for the hobby have different points of view. There's nothing wrong with that. I hope you two can work together to understand the difference of opinions and why. Perhaps you can teach each other something in the exchange.

[DeltaT]

So you are basically saying, Jake, that you need to be almost done with your heavy deccel (via braking) before you downshift, and not to expect to use any engine braking? I guess that's how I'd generally be driving anyway.

Jim

[Jake's Performance]

Yes,
The slower the car is going and the lower the rpm the less stress the trans will see.

The OEM's simply didn't intend for the transmissions to see hard decel downshifts often. The intermediate band in a late model 4L80E is larger than the earlier 4L80Es and Th400s, however it still doesn't have even half the surface area of the intermediate frictions that hold on the upshift.

A 4L60E doesn't have a intermediate sprag to get damaged, and the 2nd band is holds both accel and decel, so it is better off BUT, it has a known weak forward sprag and very small over-run clutches.

[Steve Chryssos]

Jake, I'm going to be running Steve's Shrifter product. Steve, I sourced my converter through Jake. I've talked to you both and I think you're both professionals. You can probably help each other. It's not unusual to see experts with a passion for the hobby have different points of view. There's nothing wrong with that. I hope you two can work together to understand the difference of opinions and why. Perhaps you can teach each other something in the exchange.

I'll start here:

Thanks Chris. I'm okay. I've had this conversation with dozens of transmission professionals. So I'm used to working thru it. My relationship with Compushift even started out this way. We worked thru it. Twist is a CNC job shop that makes shifters. So I defer to the transmission professionals. Jake isn't wrong about the abuse. I just put it in the same context as increased wear from a burnout. I take it out of the context of a nuclear meltdown.

Think of a chassis dyno run. Only keep collecting data after snapping off the throttle. The rollers are decelerating gradually. The rear wheels are decelerating at the same rate, but the graph does not show load decreasing gradually. It falls off a cliff. Load on decel for an automatic transmission is very different than that of a manual transmission with a clutch. Barring circumstances outside of normal shifting, load on decel for an automatic--with its semi viscous coupling--is way fractional.

Watch the following video in its entirety (sorry, I've posted it a million times) and as Jim has stated, I decelerate without downshifting. I tap down each and every time just before getting back in the throttle. In that sense, we use the paddle shifter for kickdown purposes--not to pretend that I have 3 pedals. All we're really doing is telling the TCU that I want to be in 2nd gear when coming out of the turn. Don't think about it, don't hunt around--2nd gear. Listen for the engine braking and shifts.



So:
-Mechanical shifter in "3" (not OD)
-TCU in S3
-Dive into turn on brakes
-Turn
-Start straightening out steering wheel and
-Tap down to 2
-Accelerate

That driving scheme is very different than a 3 pedal car. Many people insist that we provide an exact duplicate of manual transmission / clutch function. The answer is always NO. We're selling an improved automatic driving experience--not mechatronic manuals.

According to Sonnax, the modified HD 2-3 shift valve in my 4L65RR trans adds support to the input sprag and the forward clutch on decel. We also increase line pressure at 0% throttle angle. The technology is not there yet for the 80's. Or at least it hasn't been fully tested yet. But then again, I was applying the driving scheme described above with 60's before the mod was available. And we're doing it now with 80's Looking back, the trans I started with was junk--and with a stock power flow diagram. Even then, there were no failures.

If I were a transmission builder, maybe I would have been too wise to try this seven years ago. But I'm not. So I did.

[Steve Chryssos]

....
I did not get your message. What number did you call? I was out of town until Monday afternoon, I checked messages as soon as I got back and didn't get one from you. I'll check with the guys and see if they checked them Friday....

Jake,
I spoke to Tommy (I think). Things are bananas here, too. Call me when you get a chance.
/Steve