TH350 to TURBO 400 CONVERSION - Hot Rod Forum : Hotrodders Bulletin Board
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Old 01-22-2006, 07:39 PM
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TH350 to TURBO 400 CONVERSION

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I'm sure dozens of you guys have done this, but it's a first for me. My 72 Nova now has a fresh 550 HP BB chevy upgrade and I still have the stock TH-350 with stock converter. My engine guy and his tranny buddy tell me I will destroy the TH-350 if I get the car to hook up good and beat on it. They told me to get a Turbo 400. Ok, that's fine but what's involved with installing it other than just buying it? What about driveshaft length, crossmember changeout, yoke, bolting up to the 454 block, etc. I want to know what I am getting into before I dump $800 for a performance rebuilt Turbo 400, only to maybe find out there's a lot more than meets the eye. Also, can I do all this myself in my garage? I've never done this but I am very handy and good with cars. I do everything myself when I can but I won't do something I am not capable of only to try and save a few hundred bucks. If you think I need to bring it to a tranny guy I will.

Thanks.

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Old 01-22-2006, 07:49 PM
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Crossmember has to be further back, output shaft is larger, driveshaft is shorter, and you will need an electric kickdown switch..................piece of cake.
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Old 01-22-2006, 07:52 PM
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The driveshaft will have to be shortened. The yoke is differerent. And the mount is 6-9/16" further back. I know the 1st gen. Camaros had a different crossmember, making the swap a bolt in with the proper driveshaft. That crossmember or possibly one specifically for a Nova would be the way to go. The bell housing bolt pattern is the same. While you have it apart, I would install the appropriate aftermarket flex plate (cheap insurance) and a converter to match your engine and driving application. I think you could build a 350 to stand up to the abuse. The advantage would be quicker et's. The down side would be more frequent refreshing and a greater chance of breakage. The 400 is a tough unit.
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Old 01-22-2006, 09:49 PM
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The early Camaro and Nova share the same trans crossmember. The 350 turbo/stick cars used a rectangular pressed metal crossmember. The 400 turbo cars use a round, tube type, with quite a big rearward loop in it. A Monte or Chevelle 400 yoke will work with most 400's. Check to see if there is a vent hole in the yoke end. A big O-ring on the tailshaft.

I get my d-shafts from a pile at the yard. The last one was actually a Ford, but it fit perfectly.
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Old 01-23-2006, 05:14 AM
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I replaced the original TH350 in my 74 Nova SS 350 cid with a TH400 out of a 67 Impala. That's been several years ago but if I remember right I had to drill those holes for the crossmember to bolt to the frame. I am thinking I used the original Nova crossmember but I may have used the one from the Impala.
And 6-9/16" toward the rear sounds about right.
Yep, an electric actuator switch will need to be installed in order for the kickdown to work without having to downshift manually. I skipped that detail and shifted down manually.
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Old 01-24-2006, 12:09 AM
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You can get the crossmember you need from a Camaro or Nova restoration supplier such as Ricks First Gen. It may still be available from GM, but I'm not sure. It mounts to the same frame holes your current crossmember uses, but like Bob said, it's a totally different shape. It also locates the transmission mount holes about 1/2" farther to the right. This is due to the fact that the Camaro & Nova big-block engines were located farther to the right in the chassis than small-blocks were.

Go to http://rickscamaros.com/cgi-local/So...da8+1138125111 and click on "crossmember & rear mount" (lower left).
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