oneblackgsx

So I have been trying to find someone else that has done this. Most people in the forums talk about getting a doner car or a transmission out of a chevy. I have a chance to buy my friends wrecked 84 Pontiac Firebird and was wondering if that would make it any easier?

I have a 78 Trans Am. I found a 455 in a junk yard and had it rebuilt along with a new TH350 trans mission about 7 years ago. My car had gotten a blown head gasket, so I pulled the engine and picked up some new 6x heads. I would really like to put the manual 5-speed out of my friends Pontiac in my car.

Basically, I have read that some people have had bolt on issues when switching to a manual transmission. I know having the whole car as a doner car would make it easier for all the parts I need like the pedal, linkage, etc.

I really would like a 4th gear. The third gear in my TH350 is too long for "racing." It feels like I have no power in the bottom half of the gear. My major problem is my car is maxing out at at 90MPH. I don;t want to go with a lower rear end gear, because I think that would make my third gear even longer. I looked and the gear ratios for the TH350 and came up with 1st:2.52 2nd: 1.52 3rd 1:1. I may have gotten them wrong. I believe I have the 3.23 posi rear in in my TA. When I put it in to the calculator I found here:

http://ultimategto.com/art29.htm?eng...eed+Calculator

I find I should have a higher top speed. Which brings me to the conclusion I need a 5-speed!

shoebox

Something is not right if you car cannot go over 90 MPH with your current setup. Likely, the 5 speed will not hold up under the torque of the 455. They are not all that strong.

oneblackgsx

How much torque can I 5-speed hold? I thought it was somewhere in the range of 500-600? I was thinking for the price of building up another transmission I would rather put my money into a 5-speed instead of another automatic...

jmd

you could put the 5 speed in with the understanding that you better save up for a stronger, different trans. than a T5.

oneblackgsx

I think that is the best Idea. Atleast I would be all set up to put a new manual in. My buddy has a wrecked 84 Pontiac firebird I am going to use for parts. How much horsepower/torque can a stock manual hold?

oneblackgsx

So I looked and a stock t-5 will hold about 300-350 ft/lbs of torque. On carcraft they had an 11/12 second car running a stock t-5 and they said it has held up so far. So I guess aslong as I am not beating up the transmission it will hold with a 455.... I also looked and a t-56 will hold about 450 lbs of torque. So maybe a six speed might be a better choice for me.

jmd

It certainly would. One thing about doing a modification you know will be temporary will be whether parts will swap from the interim trans. to the one after that.

With the overdrives of the T56, the 3.23 rear won't be a good match for it. A carbureted car doesn't pull 3.42s and 6th like an EFI car will and that's assuming the engine isn't cammed and otherwise built for a high rpm powerband.

One way to do the T56 in a BOP is BOP bellhousing (like for a Muncie) to match the car, an adapter plate and an LS_ style T56. The pilot bearing that fits farther out in the crank where a torque converter normally seats should be close to where it should be. Shifter position varies depending on which trans. you use.

Lots of details beyond that. But figure out what you're going to have for goals instead of "Hai Guys, I got this trans for cheep!" and then picking up pieces after.

oneblackgsx

Ok, so I am going to go with a T56. I have started looking for 93-02 Camaro or similiar car I can use as a parts car. I think I still might buy my buddies car... I have a Chevelle I think could use the disk brakes off of it. But that is another subject...

Why is the 3.23 rear end not good for a T56? I do have a cam in my car and make pretty good power throughout my powerband. I do not have a high rpm though, my redline is around 5000-5500.
I don't know what you mean by, "A carbureted car doesn't pull 3.42s and 6th." Do you mean it will be "sluggish" in the overdrive gears?

oneblackgsx

Does anyone know of a link to someone who has actually done this? I have found a bunch of people wanting to do it. But I have no Idea if they have ever followed it through. I also read somewhere that a LS1 or the LT1 T56 works better. But I can not find the page again. Does anyone know which one is the better application? Also, I that the stck cross member for the th350 will work and bolt on to a T10. Is the bolt pattern close to the same for the T56?

jmd

carburated engines don't pull low rpm like EFI engines do.
3.42 is the bare minimum rear axle to run with an EFI engine and the 2.66 first gear / .50 sixth gear. Running any less than 3.73 with a carb and those ratios is just going to make 6th less tractable than desired.

The reason the LS1 T56 is commonly used in non-Chevy apps is what I said above. It's a longer style input shaft so an adapter plate spacing it away from a BOP bellhousing takes up some of that length, then the large o.d. pilot bearing is going to be close to ideally located for the pilot end of the input.

The LT1 T56 is adaptable but with it's relatively shorter input shaft and unique o.d. throwout bearing sleeve, it has further problems with pilot bearing depth, finding an appropriate throwout bearing and retaining proper input to disc spline engagement.
Though it won't be quite like yours you could read up what people have done with their swaps on nastyz28 for ideas on shifter position. And frankly, some guys use the adapter plate method to put an LS T56 behind SBC and rats with Muncie pattern bellhousings which is your most likely plan of attack.

MILLER8338

Oneblack,
you should seriously consider a 200-R4 transmission. They have 4 gears with a better low gear, more even spacing and an overdrive. They come with a dual bell housing pattern which allows direct bolt up to chevy or BOP blocks. They seem to have a reputation for being weak but, that may stem from the earlier TH200 or improper setup of the "downshift" cable. They were used in late 80's Trans Ams, buick GN Turbos and 4 ton caddys. They fit where a TH350 was with the addition of a TH400 crossmember. You can switch out your shifter detent pattern and use all the rest of your current shifter. and you can get a system that allows the transmission to lock up in overdrive.