Classic Restorations tech Scott Hand lowers the Turbo 400 trans from the SD-455 T/A as the
As you learned reading Part I of this story in the last issue, our plan is to install GM Performance Parts' (GMPP) new 4L85-E SuperMatic four-speed Overdrive (OD) transmission (PN 19154550) and its included lockup converter (approximately 1,800-to-2,000-rpm stall speed) in HPP contributor Melvin Benzaquen's street/strip '74 SD-455 Trans Am. Many of the advantages of this new transmission over the original Turbo 400 and the previous GM O.D. boxes like the 200-4R, 700-R4, 4L60-E, 4L65-E, 4L70-E, and 4L80-E were discussed in Part I, so here is a very brief review.
The 4L80-E shares its forward gear ratios of 2.48:1, 1.48:1 and 1:1 with the vintage Turbo 400, but the newer trans added an Overdrive gear of 0.75:1 and electronic control, among other upgrades. It's rated to handle 440 lb-ft of torque. GM's 4L85-E is a heavier-duty version of the 4L80-E and incorporates a five-pinion planetary design, torque-converter upgrades, a 34-element intermediate sprag, an induction hardened input shaft, and a hardened forward hub, all to increase durability and its torque rating to 460 lb-ft. GMPP's new 4L85-E SuperMatic was conceived to hold up behind the ZZ572/720 crate engine package. This trans features more clutch plates with upgraded materials in the intermediate, direct, and forward clutches, an improved overrun roller, and selective-fit intermediate sprag outer race. Mods to the direct-clutch housing prevent centrifugal apply at high rpm, fluid pressure was increased, and revisions were made to the valvebody to further firm up the shifts. The torque rating for this trans is 685 lb-ft.
With that step up in torque rating, the SuperMatic can be purchased and bolted in behind most potent Pontiacs without the worry of grenading it. Also, the Overdrive gear and lockup converter will allow Melvin to replace the 3.08:1 rear gears for a more aggressive setup to improve dragstrip performance, without losing highway cruiseability due to high rpm. And finally, a major advantage of having electronic control over the transmission's functions is tuneability via GMPP's transmission controller (PN 1249736). Part- and full-throttle shift points can be programmed, as can parameters for downshifting, line pressure, converter lockup, engine braking, slapstick-type shifter operation, pressure curves for each gear, and more.
If these attributes sound like what you are looking for in an automatic Overdrive transmission, then read on to see how it was installed at Classic Restorations. For this installment, we will deal with the hardware. In the next issue, we will delve into the electronics, and cooling aspects. First, let's address questions and concerns you may have pertaining to this swap.
Midway up the driver's side of the SuperMatic are black connectors for the transmission in
On the factory Turbo 400's driver's side, we see the electrical connector for the 12-volt
Note the Chevy-only bellhousing bolt pattern on the SuperMatic (left) as compared to the B
Frequently Asked Questions
Regarding Bolting In A
Late-Model Od Transmission
Q: Will the SuperMatic bolt right in with the existing Pontiac block bolt pattern?
A: No, an adapter plate will be required. We used one from Trans Dapt.
Q: Will the floor have to be cut or hammered to fit the SuperMatic?
A: Not in our case, as the '74 T/A had ample floor clearance.
Q: Will I need to modify the crossmember to install the transmission?
A: Yes, the crossmember mounting point on the SuperMatic is approximately 31/4 inches further back than the Turbo 400. (Included in the measurement is the 5/16-inch thick adapter plate used with the SuperMatic.) Be sure to take your own measurements for your swap.
Q: Will the trans mount have to be changed?
A: Yes, the bolt spacing on the trans is 41/4 inches for the Turbo 400 and 33/4 inches for the SuperMatic. The Turbo 400 mounts to the crossmember via two bolts and the SuperMatic with a single stud and nut.
Q: Will the driveshaft have to be shortened?
A: Yes, because the SuperMatic is longer than the Turbo 400. Our driveshaft needed to be shortened approximately 35/8 inches. Take your own measurements on your Pontiac before you have the shaft cut.
The passenger side of the SuperMatic simply has the two ports for the cooling lines (shown
In comparison, the Turbo 400 cooling lines use typical NPT fittings and are positioned dif
The flexplate was replaced for this project but not because the stock one won't work with
Scott employed an old shop trick, which is to weld a nut onto the end of the dowel; then s