turbo 400 core for rebuilding to handle 650 rwhp?

[GNVAIR]

I understand the short tail/long tail. I also understand the switch pitch and the BOP vs Chevy. I would like to know if there are preferred
cores. I have found some that are from the late 70's. I even found one out of a 1990 truck. Are there any that are better than others?
I also would like to know what I need to do to upgrade to the 34 element sprag. Do I need the early drum or is there an aftermarket one that I should buy.
Basically I would like to hear recommendations of what I need in order to support 650 rwhp on a street/strip car, Any help is greatly appreciated. TIA! :smile:

 

[jakeshoe]

You need either an early drum or a 4L80E drum and the 34 element sprag.

Any year core will work. On the BOP stuff, watch out for the ones with no speedo hole machined. Early stuff 66-67 models.

If you get an early core, it will probably have the drum.

I would get the later model unit because it has the better center support and fretting ring and put a 4L80E or early drum in it.

The late 70's early 80s style 1 ton Chevy truck cores VB's are preferred by some builders.

Otherwise, the 400 isn't too picky, any of them can be made to handle 650 HP.

 

[GNVAIR]

Thanks Jake for the quick response. I appreciate the info!
Is it possible to build something decent without having to upgrade a bunch of hard parts? What about the oem valve bodies. I wouldnt mind having it shift on its own if possible.

 

[jakeshoe]

THe TH400 isn't picky about VB's like a 200-4R. Any of the transmissions from 1970- newer have a decent VB, some of the early SP400's had a vb that idn't have the 3-2 kickdown valvetrain and they are usually avoided.

You can take TH400 from a 1970 LS6 Chevelle or a 1986 1 ton Chevy truck and both will work equally as well.

Governor modifications are much easier to do and don't have the negative effects on part throttle shifts like the 200-4R governor mods can do.

You don't need all the fancy billet parts. The early (or 4l80) direct drum and the 34 element sprag are the only "fancy" parts you need. They aren't even fancy, the sprags are about $50 and are stock in the late model 4L80Es as well as the drums are stock pieces just not used in 1972-up TH400s (usually).

I have the drums and sprags if you need them.

The truck output shafts are different and require a counterbored yoke or you lose a bit of yoke travel.
I don't feel this is an issue with a retrofit, but if you intend to install a TH400 in place of a stock passenger car TH400, you must use the passenger car output shaft.

You can retain automatic function. The people who recommend full manual VB's for any kind of power are usually the ones who have no real knowledge of the hydraulics and have to use a VB to keep their junk alive.

I have TH400s with automatic VB's at ~900 flywheel HP and ~3 years on one like that so far.

Video of one customers twin turbo'd Chevelle. 720 to the wheels at the time of the dyno run, 9 psi on a 358 SBC combo.

http://www.chevelles.com/cgi-bin/video/dirwrap.cgi?rt=count&path=video//dynoday2.wmv

 

[GNVAIR]

I found a 400 out of a 1990 2wd truck. I know you said there is an issue with the output shaft. Should I pass on this one or is a counter bored yoke readily available? I have been looking, but most places sell a standard 400 yoke. What should I do in this situation?

 

[jakeshoe]

Grab the core,
and just buy a passenger car shaft before you rebuild it and replace it.

I have the shafts and I'm sure any of the vendors here can get you one also.

Spicer makes the counterbored yoke and Denny's sells it, but it's a 1310 series, if you want a 1350 you'll probably have to have a machine shop counterbore it.

 

[GNVAIR]

Are you familiar with any companies that make a 32 spline yoke for a 1330 joint? The reason I ask is because the car the trans is going into has 1330 series joints.

 

[jakeshoe]

Spicer does.

 

[GNVAIR]

Awesome! Thanks for the info!

 

[chris718]

Most of the 8 bolt pump cores will have the 8 or 16 element sprag direct drum.Just update the sprag with the 36 element sprag.The down side to the early cores is they dont have heat treated pump stator tubes.These are identified by black splines instead of plain metal finish.Only the late 6 bolt pumps came with this (895 castings).

 

[GNVAIR]

Good info Chris! Thanks for the tip!

 

[Jay Wicks]

Some of the eight bolt pump cores had a "thick case". These were usually found in Cadillacs and for Chevrolet, the 1 ton step vans.

 

[GNVAIR]

I just picked up a good core removed from a 1990 Chevy 3500 step van for $25! The guy said it still worked and was removed because of a delayed engagement problem.

 

[BadAssGN]

Some of the eight bolt pump cores had a "thick case". These were usually found in Cadillacs and for Chevrolet, the 1 ton step vans.

I have a trasnmission from a cadillac, it has all the hardened parts Chris is talking about. how do you tell if this is a "Thick Case?"

And Chris, I have to upgrade the Sprag Drum with the sprag right??


Thanks

 

[chris718]

Correct