The 4T80E was never factory available with
the LS4, but amazingly, it lines up as if GM
was toying with the idea. On this left-hand
side of the block centerline, the transmission
housing boss has to be drilled to access an
existing threaded hole in the block. Brandon
says the resulting four-bolt system clamps
everything together just fine.On the right-hand side, the finger points
to an unused ear in the transmission case.
There’s no meat in the block to accept
a drilled and tapped hole, so Brandon
ignores this fastener location and has had
no trouble.The finger points to where some stiffening
ribs in the LS4 block need^1 ⁄ 8 inch removed
to cure contact with the 4T80E’s case.
Brandon says, “Northstars were plagued
with overheating and blown head gaskets,
which led to premature vehicle scrappage.
None of this hurt the big 4T80E transaxle,
and I can buy them for $150.Even though the 4.6L Northstar DOHC V8
wasn’t a torque monster like Caddy’s old
472/500 pushrod V8s, a fully loaded Seville
extended-wheelbase airport limousine can
nudge 8,000 pounds, so a tough transaxle
was needed. The 4T80E 1-inch drivechain
(shown) is twice as wide as the 4T65 unit.The hands are holding the 4T80E’s
upsized planetary gearset. The 4T65 unit
is generally 30 percent smaller in most
respects. One downside of the stock 4T80E
is a soft 2-3 upshift, but Brandon credits
online friend Jeff Lanitello of Engineered
Performance with a secret solution that
uses all stock parts.If the LS4 block lacks a starter-motor
mounting rail and the Caddy Northstar
recipe put the starter inside the engine’s
“V,” where does the starter go? Seen here
in black, on engine, Brandon’s solution cuts
the LS4 center sump pan to enlarge the
box region. Then he welds mounting lugs to
the pan that accept a compact CVR starter
motor (PN CVR5414). The stock windage
tray is trimmed to work with the revised
pan shape.The LS4 crank is 13mm shorter than other
LS units, 10mm at the snout and 3mm
at the flange. Though LS4 blocks lack
starter-motor mounting pads, they’re all
lightweight aluminum with integral iron
bore liners.The finger points to the LS4’s distinctive
rear-facing throttle-body. The small Metric
transmission bolt pattern is shared with
GM’s 3800 V6. These strikes against the
LS4 are only bad for swapping them into
traditional rear-wheel-drive hot rods. The
LS4’s standard-issue, displacement-on-
demand cylinder-deactivation system is
easily defeated via replacement lifters,
trays, valley cover, and programming.The stock aluminum engine/transaxle
cradle attaches to the body with four
fasteners. By replacing the stock
rubber bushings with solid aluminum
replacements, Brandon moves the engine/
transaxle assembly 1 inch forward to add
steering-rack clearance and 1 inch down to
increase manifold-to-hood clearance.Below: Brandon Furches says: “The stock
4T65 transaxle [left] is OK with the LS4’s
stock 303 hp and 323 lb-ft, but as soon as
you nudge 400 hp, it breaks input shafts,
planetary sets, and stretches chains.” A
much stronger replacement is the 4T80E
from any 1993–1999 front-drive Cadillac
with the Northstar 4.6L V8. The stock
Caddy 10.5-inch converter is retained; the
turbo pushes it to an acceptable
2,300-rpm stall speed.52 CAR CRAFT AUGUST 2019I
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