350/350 out, 454/400 in

[Bluegoose972]

Just bought the blazer and I have always wanted a big block, so rather than spend any money on the existing combo, I want to swap it out for the engine I really want.

Looking to swap out my 350/350 combo and install a 454 with a 400 trans. This is going to be on a 71 Blazer 4x4. My understanding is that the 400 is a little longer than the 350. Is there a special adapter that is required in order to keep the transfer case from shifting back?

Who has completed a swap like this?

[Mike C]

The 400 to stock NP205 requires an adapter from advance adapters. It is expensive, something like $450. The factory 400/205 setup has a different spline count inside the 205. MOST cost effective way to do this is to buy a complete single wheel 4x4 one ton with a 454/400/205 combo and swap. Beauty of that is it should be a Dana 60 front/14 bolt combo as well with 40" spring centers on the 14 bolt only requiring new shock mounts. You should be able to find one in the $2000 range, which looks better and better all the time when you price even the OEM 400 to 205 adapter, since you have to buy the t-case or at least the input gear as well.

The big block/400 combo will be TIGHT, requiring motor relocation, firewall dimpling, and usually a body lift as well.

I came to the conclusion on my Jimmy I was way ahead to build a big small block and save many headaches...

[jeffspower]

unless you have the big $ to do the 400 trans swap, go thru the 350 trans. with quality parts & complete freshing up. Unless you are building a super stout 454, it will handle a big block fine. My original 72 K20 350 trans was rebuilt about nine years ago. Held up to farm abuse behind the 350 motor just fine. Then, about six years ago, i put in a 500 Cad. I have been abusing the crap out of it ever since at mud drags & truck pulls. I thought I would probably kill the 350 trans the first year, but it is still going strong. I haven't done anything but change the fluid twice since it was installed. It has only logged about 11,000 miles- but most of them have been with roosters flying in the mud or the pulling sled lugging it down to a stop at WOT.

[Bluegoose972]

Good info guys.

I figured that there would be more to the story that I just hadn't discovered yet.

Unfortunately, having a small population to draw from, things are a little more expensive. The local wrecking yards are wanting $1100 for a 454 and 1 ton 2WD trucks with 454/400 combos go for $2500, unless the engine is bad. 4WD 1 tons are rare.

I guess I may need to back my way into this, starting with trying to locate a 400/205 combo first. Is the 400/205 combo the same length as the 350/205 combo? I'm assuming they are and that just the tail shaft is just shorter on the 400 to make up for the longer case length. Is this wrong?

[jeffspower]

The 400/205 setup is longer than the 350/205 setup. I have both so i will try to get some measurements & post them this weekend.

[72SWB4X4]

you will be happy but as the reply above me said use the 350/205 unit it will work fine i have a big block with turbo 350 and 205 and it all works well and has for many years

[jeffspower]

Here are the measurements-

th350/205 in my '72: From bellhousing to rear (t-case) mounting face of installed adapter, 25-1/4"

th400/205 in my '80: From bellhousing to rear (t-case) mounting face of installed adapter, 28-1/4"

My conclusion: the 400 setup is 3" longer. Keep in mind that most 205's off th400's have a slip-yoke style rear output which makes the joint-to-joint measurement much shorter than the fixed flange style. with much lift on a Blazer, you will run into angle problems & possible slip-yoke slip-OUT on full axle droop. My longbox is stock height & STIFF springs- it shows about 2-1/2" to 3" in/out travel on the slipyoke from normal driving. It's u-joints are about as straight running as you could ask for.