FWD Tech Guides '95-'07 Guides/How-To information for FWD Montes 1995-2007

Mod Guide: 3800 - Swap 4T65 to 4T80

Old 09-27-2011, 03:17 AM
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Join Date: Sep 2011
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Default 3800 - Swap 4T65 to 4T80

3800 - Swap 4T65 to 4T80

'96 SSEi with the Twin-Charged 3800 SII.

The first thing that jumps out
is the enormous side cover and general girth of the 4T80
In stock form its rated a conservative 305lbs.ft. torque

There are a few Caddys pushing WAY more than that thru.
I'm sure in stock form it will handle 450hp and 450lbsft

I estimate hard parts to be good for 550-600lbsft
before hard part breakage occurs (using GMs 2:1 margin of safety factor).

I will rebuild it using old transmission tricks of the trade
for shift improvement and clutch life

The 98-up SSEi pcm and program with Caddy shift tables
in place of the 4T65 tables will be used to control it
All inputs and outputs are identical b/t the two transmissions

A custom trans harness
will be needed to add necessary wires and run them to pcm
Of course custom mounts will be needed as will BOTH axles

Both 4T80 axles have a female inner joint
the differential uses an output shaft as well

I will be installing my EP Limited Slip Differential in the transmission
before final assembly

As for fitment
a new tailshaft support bracket will be fabricated
as will front and rear trans mounts

I might use a W-body-style rear mount
and add upper dogbones if it looks like it will be easier.

The rear knock sensor WILL need to be eliminated
and a little grinding necessary for the rear lower bellhousing bolt

The block hits the trans (barely)
and the bolt holes do not line up
I already have a strap/bracket in mind for this issue

Both the block and trans bolt holes will get a helicoil insert
enabling me to bolt the strap/bracket and tie the two holes together.

The block was drilled and tapped
for a 10mmx1.5 bolt to line up with 4T80 bellhousing

I am planning 450+hp at the wheels
don't want to waste 1000's on exotic parts for a 4T65 to make it last.

Pix were missing:

4T80E-note the enourmous girth!
new t.s. bracket required
rear ks might need to be deleted, can't tell til its bolted up all the way
the rear lower bolt holes dont line up... the 4T80 is so big
GM had to move the bolt hole in and up.

A little grinding on both the trans and block will be required for clearance
The fix will be something like this, but in reverse: courtesy Will, Fiero

The rear of the side cover is the exact distance
that the W-body trans mount is from bellhousing face
I might make a frame stand off
and use a side mount like the w-body
or just keep the front/rear mounting config like the H-body uses
I'd almost rather use the W- with its upper dogbone config

One other thing...
the 4T80 centerline is ~.375" wider than the 4T60/4T65 (9.500" vs. 9.125")
so the axles will have a slight rearward slant...
not nearly enough to even give a second thought about

curious to know how
much better the 4T80's hold up vs a modded 4T65e w/LSD

Ya, it does.
I'll take pics comparing 4T65 and 4T80
I know it weighs about 100# more!
And gobbles up more power, too

However, the "new" 3.71 FDR
will more than make up for any additional power absorbtion the 4T80 incurs

I'm really thinking it's a good idea to work out all the trans swap bugs,
with the necessary pcm swap and all, before the turbo kit gets installed

I'll dyno it after the trans swap if I do
(it made 206whp at 5400
with no less than 200 whp from 5200-6000 bone-stock with 148K miles!)

consider the H body core support WILL NOT handle a dogbone mount or mounts...
Nor will the 92-98 GA, but that didn't stop me either...
(my first L67 swap back in 2002-2003)

{Info on SC 3800 in GP
I spread the load across the width of the core support
to the vertical header uprights with a 1/8" steel plate.
These pictures were of the first design...
I went back and revised it a little
(not that the first wasn't strong enough, just looked a little rogue-ish)}

So if you decide to keep the Bonneville torque-axis mount on the pass/side
Will the tranny clear the other side of the engine bay?

Is that d/s cover even going to fit in the engine bay?
Or are you going to have to shift the engine over to the p/s side?

YES!!!! can you believe it?
With the early engine mount, the cv axles are dead-on equa-distant
(the 4T80 uses equal length half-shafts, both female, too,
same part left/right)

The rear of the side cover
is the exact distance that the W-body trans mount
is from the bellhousing face.

I might make a frame stand off
and use a side mount like the w-body
or just keep the front/rear mounting config like the H-body uses
I'd almost rather use the W- with it's upper dogbone config.

So if you decide to keep the bonneville torque-axis mount on the p/s.
Will the tranny clear the other side of the engine bay?

I'm going to buy a spare k-member later this week for fitment.
I will know more about the mounts then.

Everything inside is MUCH bigger and stronger than the 4T65.
Take a look at the differentials!

Look at the difference
b/t the 4T80 planetary gears and the 4T65 planetary gears!!!!

Ya, it's MUCH stronger!
The 4T80 planet PIN is almost as big as the 4T65 planet GEAR!!

More pics comparing the 4T80 and the 4T65.

Forget billet input shafts and hardened output shafts...
who needs them when these parts are bigger, stronger, and stock!

Look at the ouput shaft!
and the input shaft!
more pics of the differential.
I just finished building a limited slip for a customers 4T80.
I plan one for this, too.

I'll be fabricating a bracket/brace for the tailshaft housing.
Also, the flywheel needs 4 holes instead of 3.
the gear selector lever needs to be relocated to clear the crossover pipe.

How much more horse power does it take
to turn the 4T80 as opposed to the 4T65?

the 4T65 weighs 195# with converter,
the 4T80 weighs 245# with converter.

As for drive losses, I'm sure thee will be some...
but the 3.71FDR will more than make up for any torque losses
vs. the 2.97FDR of the 4T65.
( FDR= Final Drive Ratio )

there are 9 possible FDRs for the 4T65E
based on 3 differential planetary gear sets and 3 chain drive sets.

The most common used FDRs are 2.86 (3400 N- and W-),
3.05 (3800 W-, H-, C-, and E-)
and 3.29 (3400 U-vans and Grand Am GT),
all of which use the 35/35 chain gear set.

The 2.93 is only used in the -HD behind the 3800 S/C
and is derived from using a 3.29.

A 3.42 was used in the '97 Z-34 (3400DOHC) Monte Carlo.

The only GM factory use of the 3.69
is in Buicks destined for China
with the 2.5L 60deg V-6.

there are also 3.52 and 3.76 gear sets available
as well as a 4.0FDR differential
that would change all the ratios based on gear sizes.

I don't know where you got your info,
but I have to respectfully disagree.

According to three aftermarket transmission ID books
and the latest version of ATSG GM Techtran manual,
there are three FDRs available, 2.86, 3.05, and 3.29.

There are also three chain drive gearsets made by GM for the 4T65E,
33/37 (1.12 underdrive),
35/35 (1:1)
37/33 (.89 overdrive).
That means a total of nine possible combinations for us to play with
(listed by base FDR):
2.54, 2.86, and 3.20...2.71, 3.05, and 3.42...2.93, 3.29, and 3.69.

Unless GM has come up with some custom parts for the drag racing program,
that is all there is.

They are available via GM Racing
and come in 800hp and 1200hp chain sets.

They were not a stock production item,
but they are available for our transaxles (4T80).
INTENSE will be offering them for sale soon.

I guess the 4.00 will give 4th gear some action in the 1/4-mile.
What is the combination to achieve the other ratios you (3.52 and 3.76)?

Which all brings me back to the point of my 4T80E swap
The 4T80 in stock form is good for 600+hp
with a basic rebuild and custom clutch packs.
No exotic parts, 300m-this, billet that, welded c.v. shafts

I have a 3.71FDR, huge c.v. shafts
(which are equal length and both female ends),
EP limited slip...

the core trans cost me $150
the kit and parts about $500
and the converter, custom built and furnace brazed, $200

To handle 600+hp,
you need to spend 4 times that much on a 4T65E-HD.

The first thing I'll do is dyno it to see the difference.

The trans is mounted to the engine, flywheel drilled for the Caddy converter
The hard part is going to be mocking it up
I have to have it in the car due to front engine mount in the Bonne
It will be the only locating mount I have to work with
(unless I decide to go W-body mounts
and fab-up a front engine mount pad and rear trans pad,
then I can use all GM mounts.
I will have to build a tubular rad support
so I can run upper dog bones... still mulling that over).

The Final Drive Ratio inherent in the 65 is 3.29,
it's the chain and gearset combination that determines the actual FDR.

3 sets are currently used offering 2.92, 3.29 and 3.69 ratios.
I have a good baseline to compare it to.

this 98 riv has such a large engine compartment

what if any problems have you come across
regarding the rear manifold and/or downpipe clearance
with the larger planetary section of the 80e?

i'm asking since want to get the pacesetter headers,
and i'm curious as to whether i may need to fire up my torch
when the 4T65hd goes and we drop the 4T80e in...

A custom rear manifold will be required.
I plan to build a tubular log anyway since I am turbocharging.

Worse than that is the shift linkage.

The shift shaft on the 4T80 is right
where the 3800 crossover pipe
starts to turn toward the back of the engine

I hate the pwm converter lock-up.
I'd rather just use a on-off switch or program the pcm to lock it up as such.

may i ask why your going to a lower stall speed?
who needs alot of converter when you have a 3.71FDR
and the engine is twin-charged? (turbo-supercharged)

God was watching me when I bought the 4T80E...
I bought it as a high-mileage core for 150 bucks.

Well, it's just been rebuilt!
I bet it doesn;t have 5K miles on it.

I went thru and did a couple shift mods.
I firmed-up the accumulators,
removed the cushion spring on the 4th band apply servo (shimmed it solid).
I was going to add clutches to 2nd and 3rd clutch packs,
but when you see the pics, you'll know why I didn't.

All I did was remove the 2nd wave plate
to give the pack real clearance (and a hard hit 1-2 shift).
I also removed 4-of-12 3rd piston return springs
and a few 2nd piston return springs, too.

So, I guess I'm going thru with the swap... now it's fabrication time!

Pix were missing:
chain drive gear
2nd clutch, about 8" diameter x 5 frictions
3rd clutch drum, 6" diameter x 4 frictions, front planetary, 2nd clutches
rear planetary, forward clutches behind (didn't change anything past this point)
1" drive chain and driven gear
huge roller bearing supports each chain gear
(4T65E uses a needle bearing cage about 1/2 the diameter)

The 3.71 came in the STS and ETC with the 300hp engine.
I thought there were only two FDRs,
but found out there are like 8 from 2.7x up to 3.71.

I thought there was a 4.10,
but couldn't find anything about it.
There's a 3.48, 3.05, 3.11, and more.

Dacco says they pin the stock N* viscous clutch
so it's always locked on engagement.
I would like a real clutch, too.

Who have you talked to??? Midwest Converters? Contact info?

Pix were missing:
Some engine build-up pics:
ported blower:
prototype intercooler (not going in right now):
Harland Sharp rocker arms, LS6 springs, ARP head studs
(GM graphite h.g.), Manley chromemoly pushrods:
custom rear Turbo manifold:

how much power are you expecting to make?

450-500whp. on 5-6psi blower and 8-10psi turbo.
The idea is neither will be making any heat
due to the low boost levels (both will be intercooled anyway).

The transmission and engine are ONE!!!!

I had to:
re-drill the flexplate,
which required notching the counterweight and adding weight back;

drill and tap the rear lower hole in the block
to line up with the bellhousing;

make a tailshaft support bracket;
drill out a blank bellhousing hole (middle, on the front side of the engine);
notch the rear lower block boss and grind a little off the bellhousing;

relocate the rear knock sensor
(dont forget to plug the hole... it's in the water jacket!);

and the rear manifold will need more work... it hits the transmission.
I'm going to build a new one using the stock flange,
this way I can make it clear the shifter linkage and trans position switch

Pictures were missing:

Pics explain themselves
LSD installed:

ZZP sells a similar log for the front, for 109-bucks

The engine/trans are "in" the k-member.
I had to notch the front crossmember about 6x2 inches
to clear the gargantuan transmission pan.
Everything else is going to clear fine.

I am looking at the possibility of using a 87-91 Vin L front engine mount
to put the 3800 where it needs to be in the frame.

It's going to be way too hard to put the engine in the car
with the stock front mount
and make trans mounts with the frame and all up in the car.

The '96 Bonne has unused engine mount holes in the frame right
beside the a/c comp where the older 3800 Series I used a front mount.

I am confused about something, though.

The '87-'91 Vin C 3800 uses a front "hanging" mount just like the '96 Bonne.

What is the L engine?
Both it and the Vin C came in a H-body Lesabre and Park as well as the Bonne,
but why do the Vin C and Vin L have different mounting
when installed inthe same chassis?
They are both 3800's!

Pictures were Missing:
big notch (will recieve an angle-iron reinforcement on the inside)

clears everything, even the steering rack (not shown)

Here's where the 87-91 Vin L front engine mount should go...
(I'll have to modify it for use with the late-style a/c compressor bracketry.)

This is the bracketry for the mount I am thinking of:
Pix missing:

Hard to believe you can't fab something a lot simpler than that.
Ya, it is huge..
I will probably need to move the ABS to clear the huge side cover,
or get rid of the ABS altogether... (nah, I'll just move it)

The goal was to test the feasibility of a 4T80E swap
in the H- and W-bodied L67 cars.

After building and re-building "budget" 4T65E transmissions for people
(and fixing "other companies" broken transmssions)
I am tired of wasting time with them.

I bought this used 4T80E for 150 bucks.
Lucky for me, it had just been rebuilt,
but even if not, it would cost about 500.00 in parts and another 700.00 labor (mine)
to build it for a customer.

Compared to a $3000.00 4T65E build!

The extra labor to swap so far has not been bad at all.
Next I will look at the W-bodies

You got an LSD in that thing?!?!?
Nope, with an open diff
it won't last long if you keep doin that!
You can't tell, but the wheels are definately turning different speeds.
The pin is screaming "HELLLLP!"

Compare: this looks exactly like what I need:
pix missing

My first thought is how much power
this big transmission is going to siphon off

IT FITS!!!!!!!!!!!!!!!!!!!!!!

That transmission should have been in our cars in the first place!

I used the front mount from a 90 LeSabre
and it put the engine right where it is supposed to be!
(I was able to check it referencing the original torque axis mount
and it is in the exact same spot in relation to the body!)

The transmission actually clears everything under the hood.
i was afraid the large girth would hit the inner fender, but it clears like it was made to fit!

The only thing I have to do
is move the ABS brake lines closer to the fender
by removing the clips that separate the lines and keep them still,
then anchor them directly to fender using some good old steel line clamps.

I also have to move the ABS unit 2 inches forward
to clear the transmission fill/dipstick.

Pix were Missing
It's a tight squeeze, no question!
The front notch
A second notch in the left rear

The steering rack hits a little rib on the back of the transmission.
I will remove the rib. (no pic)

I wanted to see what is was going to do in the car...
now I will remove the k-member and build three transmission mounts.

The engine will sit on three Energy Suspensions urethane GM transmission mounts in custom brackets (as long as they fit...)
and the stock GM front engine mount.

I will consider using a single top dogbone as a torque strap
IF it moves around too much, but I really don't think it will.

I went back and measured again the other day...
the 4T80 and the 4T65 both have the same input/output cL.
So with the engine where it should be, the axles are, too!

Good Work!
That transmission should have been in our cars in the first place!

Actually, the 4T60E in the '92-'96 is a superior transmission
when compared to the trouble-prone 4T65E that replaced it in '97.

The 4T80E is probably overkill for a stock 3800 n/a.
But the S/C engine should have gotten the 4T80E from the start
instead of the aforementioned POS 4T65E
(the only thing different about the 4T65E-HD is the diff, anyway)

To use an upper dogbone on a H-body,
you will have to reinforce the radiator core support.
It's been done, IIRC.

Yes, I would run a piece of .062" steel plate,
contoured to the core support,
all the way across,
bolted to every hole available, as a reinforcement.

The dogbone doesn't really do much,
esp. if I have four mounts on the eng/trans.

talked to a buddy and he suggested them they can do anything
he said there was a good chance they can machine a setup
similar to the aftermarket double and triple disk (TD truck) TCC assembly
and fit it in the 4T80e converter...

he suggested i bring em a core converter
and a couple of guys will cut it open and tinker with it
(who knows if the LS4 equipped W bodies
have the 4T80E with the viscous clutch? )
they are always looking for new products to sell
besides depending on what they can do we'll be buying two

Im thinking to switch the converter to a 6 lug arangment

what are your thoughts on
the differences in the 4L80E and the 4T80E (internals wise)
i have rebuilt a L not long ago?

give em a call they are right next to rt20 in rockford
(they did a couple of converters for me
when i worked at Wayne's World a TH400 and 4l80e)

Midwest Racing Converters
"Good Enough...isnt Good Enough"
3535 Kishwaukee St
Rockford IL 61109
(815) 229-9808
fax (815) 229-9874

I bought a converter from Transmission Crafters in Albany, GA.
They built a Allante converter (B23)
that uses a conventional clutch, not the viscous.

All the 4T80 converters are furnace braized,
so they can't tweak the fins at all (more stall).

I called Midwest, they wanted 195.00.
I paid 110.00 for the Allante converter.

I built the rear header to clear the shifter and switch

It was hard enough to get the 4-bolt drilled into the 3800 flywheel.
I had to notch the counterweight in two places
and add back the weight with the mig welder (see the pics)

My next is to buy a junk 97-up W-body k-member
and try the 3800/4T80 in it.
I'd like to sell a package to the hi-hp GTP guys, with LSD.

The LS4 W-bodies use a new 4T65E-HD
with 5-pinion planetaries and beefed-up internals,
GM billet input shaft, output shaft, etc.

I finished the left rear transmission mount today.

I butchered the stock Bonneville 4T60/65E trans mount
and welded a huge bracket to it
that bolts across the back of the 4T80
and around the left side
using two side cover bolts (replaced the bolts with studs).

Sorry, no pic yet.
I have two more rubber mounts coming in the morning
to build the left front and right rear.

I will likely run one upper dogbone
using the right side w-body dogbone bracket (engine)
and an early (88-96) w-body core support bracket.

The short one from a 3400DOHC car
and the appropriate length bone to fit.
I always replace the rubber with urethane.

The engine and transmission are mounted to frame using four motor mounts.

Stock 87-91 front engine mount and modified engine brkt (remove a/c part)
modified stock left rear trans mount with custom transmission bracket,
BMW engine "puck" mount in the left front and right rear positions
with custom transmission ans frame mounting.

The engine sits perfectly level, side to side,
and a is about a 1/4" lower in the rear
(most every GM FWD car i have ever worked on,
the transmission pan has a slight rearward tilt).

The transmission output shafts are dead-on parallel to the LBJ
and equi-distant from the hubs (w/in 1/16").

It took alot of moving around until I was satisfied with the location.
I slotted the holes in the right front engine mount (about 1/2")
to move the engine away from the steering rack a tad.
I think it would still line up perfect with the stock torque-axis mount.

The guy who works with me said
I should retain the t-a mount as a "dogbone"
instead of adding the upper dogbone,
but I hate the thing
- makes putting belts on the engine a real PITA.

I have yet to scrub and paint the k-member
before I mount the engine for the final time.
Then it's in the car tomorrow.

All I have to do is make a wiring harness for the 97 pcm to the trans plug.
I already have the 97 program modified to run the engine and transmission

Well, the drivetrain is installed in the car! All the wiring is hooked up.
I made a transmission harness with wires from a GTP harness.
The stock Eldo-Seville axles worked perfect!
The 4-mount system is going to work fine, I still might use the single GTP r.s. dogbone (see bracket in the pics)

I relocated the computer to the battery side.
I will build a small box to enclose it.
The wiring harness reached all the way over with no mods at all!
A couple wire-ties will hold it secure.
I need to extend about 4 wires
I made too short for the trans harness so it will reach, too.

what pcm are you using, and which programmer?

It's a '96 4T60E car,
so I have to use the '97 4T65E pcm to run the 4T80E.
if it doesnt work for some reason,
i will use the diesel truck 4L80E stand-alone tcm to run the trans.
DHP Powertuner.

SO, it runs!
I need to do a CASE learn on it b/c it only cranks right up every third time.
When it does crank, it cranks hard.... but I have worse issues.

Besides the shift solenoid problem
with the second output being reversed
are there are any other issues
that won't allow the stock L67/4T65E PCM to control the 4T80E??

the goal was to test the feasibility of a 4T80E swap
in the H- and W-bodied L67 cars.

After building and re-building "budget" 4T65E transmissions for people
(and fixing "other companies" broken transmssions)
I am tired of wasting time with them.

I bought this used 4T80E for 150 bucks.
Lucky for me, it had just been rebuilt,
even if not, it would cost about 500.00 in parts & another $700 labor (mine)to build it for a customer.

Compared to a $3000.00 4T65E build!

The extra labor to swap so far has not been bad at all.
Next I will look at the W-bodies

You got an LSD in that thing?
Nope, an open diff
it won't last long if you keep doin that!
You can't tell, but the wheels are definately turning different speeds.
The pin is screaming "HELLLLP!"

Compare: this looks exactly like what I need:
Pix missing

this is the man who put a 3800 and 4T80 together

Jeff Ianitello/Engineered Performance
Atlanta, GA.
Engineered Performance
1988 Grand Am SE 2.0 Turbo
1996 Bonneville SSEi Twin-Charged

More found here
4T80E/Turbo-S/C... TIME FOR A NEW THREAD? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat

Old 09-27-2011, 06:17 AM
mrl390's Avatar

Monte Of The Month -- December 2009
5 Year Member
Join Date: Oct 2007
Location: Canonsburg, PA
Posts: 3,604

Thanks for posting this. Ive always wished that the 4t80e was used in these cars, even tho it would rob more power stock. Especially the 06-07 SS montes should have used the 4t80e. Ive never really heard of anyone killing that trans, tho most of the time the cars that use it were owned by people who didnt abuse their cars anyway.
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