It's funny how things work. My car started off life as a 2.8L V6 NWC T5 car that got a 355 with a WC T5. After I ditched the 355 for a 383 that put out 420HP to the wheels, I had to give up the T5 because it wouldn't hold up under drag racing. So now I have a built 700R4 with a 3600 stall converter. Now I have come to a point where I would like a manual transmission back in the car. I initially thought T56 and did all the searches that one should do. Here is what I have come up with so far...

1. I need the T56 to be able to handle about 800HP. My plans for the 383 now include an ATI Procharger System. After contacting ATI about my setup, they figure that I should make between 750-800 FWHP give or take, at around 12-13 PSI. For the transmission, I was looking into the Transzilla line, namely the Son of Transzilla. Anyone have any good or bad things about it? Got any other companies to recommend?

2. I know that I have to use a flywheel designed for an LT1 with a 2 piece Rear main seal. I am partial to Centerforce, and from what I gather that part number is 700107.
http://www.jegs.com/i/Centerforce/183/700107/10002/-1

3. Along the same lines as #2, I would like to use Centerforce's Dual Friction clutch as well. After some searching at Summit/Jegs I came up with part number DF039020. 1.125 in. 26 spline input shaft w/the 11 in. disc.
http://www.jegs.com/i/Centerforce/183/DF039020/10002/-1
Seems a little expensive to me, but I am new to the T56 world!

4. During my post scouring I came across a tidbit of info regarding the LT1 pressure plate bolts and how they are 'special'. I tried to find ARP pressure plate bolts for the LT1 but can not seem to come up with anything. Can anyone provide a link if they even make them?

5. I know that I will need a new driveshaft due to the fact that the T56 is longer than the T5/700R4.

6. After consideration, I think that the MGW short throw shifter will work best for me.

7. I am genuinely excited that when/if I swap to T56 I will be able to use long tube headers again. I had to swap over to the Dyno Don 1 3/4 primary shorty setup because the long tube wouldn't clear the 700R4. With the shorties and factory style, factory routed y pipe, the car lost its deep, throaty rumble.

8. I also know that I will be better off sourcing a set of factory 4th gen pedals and a pre bled master/slave setup.

9. This is going to be the caveat to all of this. Currently, I am running a Spohn transmission crossmember with a crossmember mounted torque arm. I understand that the T56 will require the use of a different crossmember, which I can get from Spohn, but I am not sure if I can keep the torque arm in the car as well, ie. just bolt the torque arm back up to the T56 swap crossmember. I guess I will end up calling Spohn here in the next couple days, unless anyone know for sure if this will or won't work.

Sorry for the long post. Did I miss anything? Any thoughts or suggestions? I'd like to hear them. Thanks for your time as always!

 

Check with jeremy at RPM Transmission, my motor make just around 750lbs of torque, 900 FWHP, they have a converted t-56 magnum level 6 ( LS1 Style ) that I bought for my setup, also went with Mcleod RXT dual disc that can handle up to 1000 HP. I also with with MGW shifter, what a great little piece, I put a Hurst pistol grip handle on it with line loc button.

I used Hawks crossmember because of how the make it for the exhaust, but it fit like crap and spent a lot of time modifying it to fit

 

572_rat- Thanks for the reply. I will have to look into the RPM transmission place. I was under the assumption that the LS1 style T56 transmissions won't bolt up directly due to a different bellhousing, different input shaft lenght and spline count. I assume that these issue are all corrected with their unit?

On a separate note, how did you need to modify the hawk's crossmember to make everything work?

 

I have no first or direct second hand experience with the Transzillas. I had my T56 built by Tick for much lower HP than you are talking. I do know I was happy with their service and they seemed quite knowledgeable to me. It might be worth a phone call.

No issue there. That part number looks correct from my memory. One thing to check out. I bought a SPEC flywheel for 1pc rms and it was not counter bored for the special LT1 PP bolts. I would recommend calling Centerforce and asking if their's is. I ended up having a machine shop counter bore my SPEC flywheel. SPEC was no help. I would not run an LT1 setup without the counter bore and special bolts.

Are you sure that is a good clutch for you??? I believe that is a street clutch for mid HP cars. I would call Centerforce and see what they recommend for your HP and how you plan to use the car, track.

You are correct, they are special. ARP does not make a suitable replacement. Your ONLY options are OEM or Mcleod pn 1502. I would recommend just buying the Mcleod bolts. For more information see this thread. See my reply (8) for more info and pics.

https://www.thirdgen.org/forums/tran...ate-bolts.html

Do not believe anyone who makes any claim otherwise. I can't stress this enough.

Not true. The driveshaft length is the same for the LT1 T56.

No arguments from me. Very nice shifter. Be aware that when shifting into reverse the aluminum offset block with just barely rub the inside of the console. No big deal. You could machine the block down slightly to avoid this.



No comment, I run shorties.

There is a lot of back and forth on this regarding pedal height and dead zone in the pedal. I use 4th gen pedals with the tick master cylinder. Whatever you choose I would HIGHLY recommend and adjustable clutch pedal rod so you can tune the pedal height.

The torque arm is the same. All you need is the new cross member.

Have you thought about how you are planning to deal with the reverse lockout solenoid?

Do you street drive this car? Cruise control?

John

 

87350IROC- Thanks for taking the time to respond as in depth as you did. It is greatly appreciated! I definitely took some notes down and will be researching more intensively with companies like Centerforce, Tick, RPM transmission etc.

Seeing as how I am utterly unfamiliar with the LT1 world, could you explain, or possibly give a link or picture, of this counter bore that you mentioned? From the way you explained it, I am picturing the pressure plate bolt to be a shouldered bolt of some sort, and the hole in the flywheel needs to be bigger to allow the should to fit in. Would this be a correct assumption?

I am very happy to know that the Denny's Custom driveshaft that I had custom made, good for 1000HP, will still be able to work. I paid a pretty penny for that one.

As far as the dual friction clutch, when I was doing my reading I came across a chart on the centerforce website on how to select your clutch. I chose to focus on street/strip and drag racing, and the 2 best options seem to be either the dual friction or the DFX. I had a dual friction behind my 383 and it was awesome to use with the T5. pedal felt great, clutch held full throttle with no slipping and engagement was butter. From what I have read thought, the DFX clutch is more like an on/off switch. Even though I am upping to power to 700+HP, I still think it will see more street duty than anything else...basically highway cruising.

Regarding the 'dead zone' in the pedal, I don't know what to think about it. From what people have said, I think the pedal in my 06 GTO is similar. Once i let the clutch up to about halfway, the car starts to creep forward. Full engagement is about 3 inches from the top of the pedal travel. I actually like it because I only have to press the clutch pedal in 1/2 way to totally disengage the clutch. If the pedal feels similiar to that with the 4th gen pedals and LT1 slave, I'm all for it.

I actually called Spohn yesterday and confirmed that the crossmember mounted torque arm WILL work with the T56 swap crossmember, but I have to order a special one with the pivot bushing/bracket. T56taxm was the part# i think.

Reverse lockout solenoid...I think I read that you have to splice one of the wires into the brake light switch so the reverse lockout disengages when your foot is on the brake pedal.

And to answer you last questions, yes I will street drive the car and no I don't have cruise control.

Thanks again!

 

Rockland puts together a stout trans., but their pricing is higher than others who put together a nearly identical trans.

A 383 is usually going to be balanced like a 400 or a 2pc RMS 350. If the latter, then yes. If the former, then no.

There is a new PN but I need to verify it.

Depends on how it's built. If you're sticking to a stock bellhousing depth, GM front plate, and F/GTO tailhousing, then no it's not.

There's no magic to pre-bled. If you own a modified car, you should know a little bit about it, including the method to properly bleed the clutch.

Good for you!

 

There are pictures in the link I shared. The bolts indeed have a square shoulder that goes through the pressure plate and into the flywheel. The flywheel needs the counterbore to allow the shoulder to fit. The shoulder is a larger diameter than the major diameter of the threads. Some companies like SPEC feel you can use any old bolt without the shoulder and therefore the counterbore is not required. This is very dangerous thinking IMO. GM does not develop a special bolt for no reason. And that is on a stock vehicle making stock HP. The fit between the shoulder and counterbore is quite tight. I imagine the joint was designed so the bolt can take sheer force between the pressure plate and flywheel in the event the friction created by tightening torque is overcome. You never want to load a normal bolt in shear. Remember the PP bolts do not get torqued very tight. 37 ft-lbs if memory serves me correctly.





I would just call and make sure. I have heard of pro touring guys having problems with that clutch in high HP applications. I don't blame you for wanting a nice clutch for the street though.

See that kind of dead zone is not my style. I have my pedal tuned so the clutch starts grabbing within 1/2" of letting the clutch out. Basically there is no wasted motion. The clutch pedal need to bottom out to fully release the clutch. So my total possible pedal stroke is much longer. This also eliminates the possibility of over stroking the slave. But feel would certainly be a personal preference issue.

I think it depends on the style of torque arm you own. If it is their kind with the rotator in the front, then of course you will need the new crossmember to match. When I switched there was nothing special about the crossmember, it was straight out of the catalog.

There are a few options for this. What you describe is likely the most common. It depends how much convenience you want and how much you are will to pay. I don't have my foot on the brake when shifting into reverse, so for me that method is not ideal. I went with the Samoco box that emulate the stock functionality where it will only allow you to shift into reverse under ~10mph.

http://www.samocoind.com/T56MODULE.html

 

So, I just got off the phone with Centerforce regarding my clutch situation. In applications over 700HP they recommend thier DYAD dual friction disc system to give the best blend of streetability and clamping power. The only problem is this...the DYAD will not work with a pull style clutch, which is what the LT1 setup is. That being said, I believe that the LS1 style T56 uses a push type clutch, so now I may have to research this a little further. Anyone have any insight?

 

Mcleod makes a dual if that's your goal.

A push dual is do-able, but there are so many ways to do it, it's not worth going into when there's an off-the-shelf like McLeod available.