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T-56 6 Speed


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Silver State Classic


T56 Conversion

Production T56 ratios:

Gear 1st 2nd 3rd 4th 5th 6th
Ratio to 1 2.66 1.78 1.30 1.00 0.74 0.50

Aftermarket ratios: 

Gear 1st 2nd 3rd 4th 5th 6th
Ratio to 1 2.97 1.94 1.35 1.00 0.84 0.62

I purchased the aftermarket T56 from National Drive Train. At the time (1997) this was about the same price as a used factory trans from a salvage yard. This aftermarket has a .62 6th as apposed to the factory T56 which has a .5 6th. But I have been told that the factory will only put up with about 450hp. My bored and stroked and fuel injected 455 (472cid)  is cranking out 520 on the dyno. The other advantage of the aftermarket T56 is that it came with an adapter plate intended to replace a T5 in a Firebird or Camero. The T5 in these cars is mounted at an angle, therefore I was able to drill new holes in the adapter and mount it straight up to the 455. You must (and I cant stress this enough) use an adjustable height pivot ball (available from JEGS 800-345-4545 #720-3855G). You can use a stock through-out Bering (the short one, not the long one). I would recommend using the Centerforce Dual friction clutch and follow there instruction for setting the pivot ball to the letter. You will need to spec a Hayes flywheel (Jegs #490-13-130) and use the Firebird 11" clutch (Jegs #183-DF148552) which has 26 splines as apposed to the stock 13 splines and only a 10.4" clutch. The next unfortunate (if stock) thing you need to do is get a saws-all and cut the trans tunnel between the main floor cross braces. This is the only way I could get it to fit. I have talked to other people who just beat the floor board into submission, but I did not even attempt that on a freshly painted body. Also, I wanted top access to the trans anyway. My dad then fabricated a new flat topped tunnel to go over the hole in the floor. But this made a great place to mount my cup holder, as it's hard to hold your morning coffee while shifting through all those gears. You could also just make about a 2" high frame around the hole and weld the piece you cutout back on, but it's nice to be able to get at the top of the trans. 

My next step was then to get the cross member to work. Bill had a great idea. The mounting holes were actually the same as the factory for the trans mount, but about 2" to high and 10" to far forward. So Bill cut out the mounting pad in the cross member, flipped it over to the other side, made a few adjustments and welded it back on. We then used the last hole in the frame as the front hole for the cross member mounts and drilled a new hole for the rear bolt. We then bolted it in on a polyurethane mount (JEGS #890-952500). The next challenge was the drive line. I called Inland Driveline (Corona CA) here in southern California and gave them the measurements. They fabricated me up an aluminum drive line with heavy duty universal joints and guaranteed it to 10,000RPM. It worked great and slipped right in. I highly recommend doing the same. If you do the math a 3.55 rear at 175mph in 6th is about 8000rpm on the drive line. I would of course also recommend a drive shaft loop just in case. There were some articles I believe in Car Craft about how much HP&torque these transmissions can take. My application is not for drag racing but high speed road racing so I was not to concerned. We just ran the Silver State Classic in the 125mph class. It's a 90 mile race on a public highway. 125 is fun, but for 45 minutes it gets kind of intense. Next Sept we jump up to the 155mph class.



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