T56 Trial Fitment

The mockup motor and T56 are trial fitted into the '71 Mustang. Modifications to the transmission tunnel and mounts are necessary.

With all the parts now present and accounted for it was time to test fit the engine and T56 in the car. With the factory motor mounts in place a hoist was used to lower the assembly into the chassis. Using an engine leveler and rolling the car forward a bit at a time, the T56 could be angled down into the tunnel. The short throw shifter would have to come off to make the turn under the car. By supporting the tailhousing with a floor jack it was easy to see how poorly the T56 would fit in the 71's transmission tunnel. The transmission was pointing down almost 10 degrees in the stock location.

This was when the engine setback idea really began to make sense. The shifter tower was hitting the tunnel brace and it was at least two inches under the factory shifter hole. By moving the engine back a 1.75" inches the shifter tower would come up in the factory location and the T56 case would better clear the tunnel bracing. This would improve drive shaft angles dramatically alleviating driveline vibration issues.

Setbacks
Moving the engine and transmission in a car certainly sounds like a daunting task, but taken methodically it can often be done quite easily. Obviously you must be comfortable in the decision to cut and modify the vehicle. The factory's choices in engine location have as much to do with speedy assembly and future serviceability as it does with performance considerations. Having the chance to reconsider where the largest and heaviest set components fit in a car can create real opportunities for improvement. The most obvious benefits were moving almost 900 lbs of engine and transmission back in an already nose heavy car and getting a lower center of gravity with the drop. Another advantage would be added under hood clearance for a single plane intake.

Setting the engine back 1.75" and down .75" mandated a change in the engine and transmission mount configuration, addressing oil pan to cross brace clearance, and making exhaust system adjustments. The engine mounts were easy, as .75" of setback was obtained simply by swapping the mounts side for side, as they are offset in stock form. The remaining 1" was added by cutting the flanges off the chassis pads and welding them to .25" plate. The plate was then drilled to get the inch setback. To drop the engine .75" the pads were sectioned. Incidentally, .75" was the most possible with the factory steering link in place.

Dropping the motor down resulted in interference with the deep-sump oil pan and under engine cross brace. Unlike earlier Mustangs, the '71's cross brace is a spot welded permanent structure. I had removed this some years earlier to facilitate a pan swap without having to remove the engine. For the new engine location I fabricated a new bolt-in member to allow for rearward pan clearance and to allow pan removal in the car.

Note the height of the motor mount bracket. Cutting a section out of the middle will achieve the desired 3/4" drop. Unbolting it from the chassis and then welding on new plate re-drilled 1" back gets the motor .75" closer to the desired setback. Photo courtesy: 429mustangcougarinfo.50megs.com	Shown is the chopped and 1" setback motor mount bracket. The stock rubber mounts are used on the opposite sides, which gains the additional .75" set back.
A fabricated under engine cross-brace (top) allows for oil-pan clearance due to the engine relocation. The original crossmember was a welded in unit.	The new cross member is bolted in place between the motor mount pads.
The custom brace clears the 460-strokers deep sump and winged oil pan.

Tunneling Through
The large dimensions of the T56 case requires the transmission tunnel to be modified. As with all early Mustangs, the transmission tunnel is wrapped with a brace which also serves as the mounting locations for the the transmission crossmember. Since the T56 would not clear this bracing, and knowing a new crossmember had to be fabbed due to the T56's mount being 6" further back than the C6 location, I cut out a section of the stock bracing. This enabled the T56 to clear the tunnel and remain at a relatively level angle.

The transmission tunnel brace is cut to offer better clearance for the T56.

The shifter hole in the tunnel is also modified to allow shifter clearance.

Fabricating a new transmission crossmember also required taking into consideration exhaust system routing and clearance. There needed to be clearance for the header collectors, 3.5" exhaust tubing, and the new 3.5" driveshaft. As everything comes together in a 10.5" wide space under the car, a simple crossmember spanning between the frame rails wouldn't work. Besides clearance problems with the bulging T56, a mount of this type would also put an excessive twisting load on the sheet metal mount points that had already been compromised by the cuts made to clear the top of the trans. The new crossmember had to have additional structural bracing.

The solution ended up being an integrated transmission crossmember and driveshaft safety loop. The crossmember would bolt to the original mounting location, except using two bolts per side rather than the stock single through bolt. 1" x 2" by .125" thick rectangular tube was welded to form the unit and angles back to the T56 mount location. The driveshaft loop was positioned within 6" of the u-joint to meet NHRA rules and secured to the frame rails with four bolts per side. A set of braces, made from aero-shaped chrome moly obtained from a scrap metal dealer, tie the loop and crossmember together to form a rigid assembly.

Due to the T56 mount being 6" behind the stock C6 location, a new crossmember has to be fabricated.	The one piece crossmember and driveshaft loop assembly weighs 18 lbs. and provides a fully supported location for the back of the engine and transmission.
With downward pressure of over 150 lbs. at the mount, plus the torque under load, the custom brace adds considerable piece of mind and will help keep the unibody in one piece a bit longer.	This mockup verifies proper clearances around the 3.5" x-pipe, driveshaft and transmission crossmember assembly.