Question for those with big block 4x4s...

[John Fabris]

Hi All,

I have been reviewing the big block swap threads as I am considering putting my 1971 402 engine in my 67 K20 Suburban.

Right now the suburban has the stock 4 speed in it. The 402 engine has a turbo400 on it.

I do not know what tranny I want to use with the big block and was hoping that those who have already done the swap could tell me thier opinions.

I plan on using the suburban for towing a car trailer, a motorcycle trailer, and a camping trailer (not all at the same time), and for offroad use, I really only would be traveling dirt roads (fire roads and logging roads) during camping and flyfishing trips. I don't do the extreme 4x4 thing...

What do you guys have and what is your preference (auto or stick with a 4x4)?

thanks!!

[Superron21]

hey, i've always preferred the manual trans for several reasons including the fact that if you ever have to, you can compression start a 4 speed! also your
project would be easier without having to change the rest of your running gear. my '68 GMC 3/4 ton 4x4 still has all the original trans/ t-case, drivelines etc.... and it does really well. i much prefer to keep all the old cast iron under my truck rather than the newer aluminum t-cases and transmissions. the old cast iron bellhousing that has the starter bolted to it is much heavier duty than the aluminum nose cone starter set ups and doesnt seem nearly as likely to have heat soak problems that the newer ones do if i were you, i'd definately keep your 4 speed. good luck!!!

[Livrat]

Hi John,
I have done 3 BBC conversion in the 4X4's.. My preference is the Auto..
I got tired of shifting my 68 SWB 4X4 when it had the 327 and 4spd/rockwell in it.. I went to a 402 T350/205 and loved it.. When it came time to build my 68 GMC 3/4 ton 4X4 it got a 060 over 454 and a T350/205.. I have been driving it the last 10years that way.. My 71 suburban has a 454 with the T350/205..
I guess its all in what you prefer.. One thing to note if you stay with your current 4spd/rockwell transfer case.. they do not hold up to big block power real well..(mine went BANG!!)
I would upgrade to the SM465/205 if you want to stay with the manual trans..
There has been alot of talk on the BBC conversion on whether there is firewall clearance issues.. YES there is unless you have a body lift... on my first swap I moved it all forward 3 inches.. a bit too much.. On my 68 GMC I moved it all 2 inches forward which seems to be about perfect..then a V8 2WD fan shroud is a perfect fit.
On my 71 Sub the previous owner had installed the 454 in the stock small block location and he just sliced and beat on the firewall for valve cover and HEI clearance which resulted in and ugly firewall which I am now fixing..
With your Sub I would consider it a tough decision since it is such a rare one..
But all in all I would go with the auto and set aside all the original stuff just in case you wanted to go back at some point in time..
A couple of other things to consider is the closed knuckle drum brake front end.. the stopping power is not real good,I would definately upgrade that to disc brakes.. also the H052 rear end probably has 4:56 or 4:10 gears, Big blocks dont like those ratios for freeway cruising..
Whew... sorry for such a long winded post.. you just happend to remind me of when I was contemplated the swap.. All in all I am glad I have gone thru it.. there is nothing like the torque to set you back in the seat..
The first pic is of my 68 GMC with the motor and trans moved forward 2 inches from the stock small block configuration.. the next two are of the Suburban with the big block in the stock small block location and the firewall butchery..

[4x4Poet]

Thanks for that info, Livrat.

I don't recall noticing anyone in the last year that has posted first hand, specific info on the firewall and radiator clearance issues with each of the three engine positions you mentioned. The 2 inches forward with a 2wd shroud sounds promising. If I go BBC, I'll be using a 73up engine crossmember to facilitate such movements.


Mr. Fabris, I can't help you on manual vs. auto tranny choices since I prefer manuals all the way. I want to swap a BBC in my K20. I'll be installing a modified Lakewood bellhousing mated to an NV5600 6-speed mated to an NP205 via an adapter recently made available. Actually, I'll be using a LoMax transfer case (available EOY 2005) which is a beefy, aftermarket NP205 with a 4:1 low range. Expensive, but I want a 6-speed and super low range xfer case. With them I can keep my 4.11 gearing while running 33s or 35s, so I'll just save up till I can do it. No big hurry involved. Plenty of projects to finish first.

Sorry for the ramble. Sometimes I think if I keep talking about the swap, it keeps the dream alive. Besides, sometimes folks add pointers to what I mention.

[Livrat]

A couple of other issues I forgot about you mentioned using your 71 402.. as long as its out of a Truck or Chevelle you will be okay.. But if its out of an Impala.. it will have pan to engine crossmember interference.. unless you use the 73 up 4X4 engine crossmember which does have much better mounting system.. or change the oil pan to what is commonly refered to as "The chevelle pan"
Also if your is choice it to go with the manual and you move the engine/trans/tcase assembly forward.. you will have to move the clutch linkage "Z-bar" mount on the frame forward too. Then fabricate the rod from the clutch pedal to "Z-bar".. One thing to keep in mind here is that the rod is made from "hardened steel". I have not done that one yet.. As the older I get the less shifting I like to do.. To me there is just something about Putting it in "D" (for dummy) and pushing on the long skinny pedal and it pinning me into the back of the seat..
4X4Poet.. Using the 73 up cross member is cool.. much better mounts..
It sounds like you have been thinking about it for a while? Keep rambling you wont regret it in the long run..
Livrat

[4x4Poet]

Originally Posted by Livrat

...Also if your is choice it to go with the manual and you move the engine/trans/tcase assembly forward.. you will have to move the clutch linkage "Z-bar" mount on the frame forward too. Then fabricate the rod from the clutch pedal to "Z-bar".. One thing to keep in mind here is that the rod is made from "hardened steel"....

I've read on other BBC-into-4x4s threads that one must use a 73up Z-bar and clutch pedal rod. Maybe the 73up Z-bar to clutch fork threaded rod, as well. Any knowledge on that?

Reading your last post made me wonder if the 73up BBC clutch lingage assy would work without mods on BBCs moved foward in 67-72 4x4s. The 73up clutch linkage assy might only be needed for BBCs in the 4x4 small block position since the BBC's Z-bar boss is farther back from the motor mounts than a SBC's Z-bar boss. I think it is, anyway. Still researching [rambling]

[Livrat]

Hmmmmmm, good point, Unfortunately I have no knowledge on the 73 up Z-bar and rods since I alway removed the manuals and went with the auto setup in the 4X4's.. Not sure if the small block/big block Z bar bosses are in different locations.. I do remember some of the 67/72 manual small blocks in trucks I have parted out having a 5 or 6 inch long metal bracket with the Z bar pivot "ball" mounted in the middle of it.. but to be honest I do not remember if that was from 2WD's or 4X4's... Anyone have any more insite??

[John Fabris]

Good Info!!

I am guessing that I will put my 402/T400 combo (came out of a 71 Longhorn) into the burb. I was looking into how to covert the manual steering into powersteering, but there does not seem to be an easy way to do that without just swapping out the 67 running gear for a later set.

Have seen several mid 70s to mid 80s 3/4 ton 4x4 burbs with no engine or tranny for sale pretty cheap.....
Keep the great info coming!!!!!!!!!!!!!

[454_72_4X4]

I agree with 4x4Poet on the manual vs auto debate.
Ideally would be the NV5600, but the NV4500 5 speed is what I'm gonna have to settle for. (I'm hoping to swap the SM465 for a NV4500 this winter.)

The 73-up crossmember is the way to go for a BB swap also. I used the original and it's tough to find exhaust manifolds that fit.

Just my opinion here, but I'd never move an engine forward. I did the firewall "massage" on mine for valve cover clearance but I didn't have to do anything for the distributer, (large cap HEI).

[OLDCHEV4X4]

I am trying to do the th400/205 swap and am having problems finding a 205 that is for the th400. It is a one of a kind transfercase. They do make kits to convert one, but i was hoping to just find one in the junkyard and do the swap. You might want to keep this in mind. Military trucks had them and desiel pick-ups too. But no luck yet.

Anybody else have this problem?

[454_72_4X4]

Originally Posted by OLDCHEV4X4

I am trying to do the th400/205 swap and am having problems finding a 205 that is for the th400. It is a one of a kind transfercase. They do make kits to convert one, but i was hoping to just find one in the junkyard and do the swap. You might want to keep this in mind. Military trucks had them and desiel pick-ups too. But no luck yet.

Anybody else have this problem?

Actually, I think there's two different 205s for a TH400. The newer? version has a round 6 bolt pattern and the older version has the "figure 8" 8 bolt pattern.
I've never seen one with the round pattern yet.

My wife's 1980 K20 has a "figure 8" pattern 205 behind a TH400.
(I'm gonna steal it for my NV4500 swap into my 72 ) Shh, Don't tell her that! LOL Hahaha
I think in 81 they went to the round pattern. That's just a guess though.

[OLDCHEV4X4]

yea, your right. Forgot about the newer one.

[qksilver]

Going thru all the replies, one question. I am going to do the bb swap into a 68 SWB. I have all the cross members out of a 87 3/4 burb but small block engine stands. Can i use the small block engine stands? If I need to use bb stands, are the 4x4 and 2 wheel drive the same?
Thanks,
Steve

[67-72williso]

IF you really want options use a divorced 205 transfer case. The engine can be moved around and the front driveshaft longer and more transmissions. It not just a plug in job.
Later Willis

[b454rat]

Just FYI, but the military trucks didn't come with the 205s, they both had the alum 208. (trucks and K-5s). As far as converting, Off Road Design has the input stuff to convert to 400, it's $200. I know where there are 2 400/205 combos, one mid 70s and the other 87 or 88. I think I'm gonna snag the mid 70s one, it's all there and that's what I need. You can run a div 205, I have one that I'm gonna get rid of hopefully soon. Only pain about these is you have to be sure that it is inline with the whole drivetrain. When I put mine in, I couldn't tell if it was inline or not, and after I got it in, I found out that it's not. Has a good vibe from a dead stop, or under power. I have 1350s on all 6 joints, so I don't think they are gonna blow, but it's annoying. I was contemplating stick or auto for my 4wd 62 burban. Auto's will go bad, even under normal driving and good maintenace. But a standard will last alout longer under the same conditions. Every vehicle I own is auto, now I want to bang some gears. I think my burban will be a blast to drive with an alum head'd 468 and a 4 speed, and some nice highway friendly 3:08s. Just my .02.

[OLDCHEV4X4]

The older military trucks (pre 208) had th400/205 set ups. Seen them. Whish i had one.

[b454rat]

Hmm, only older military trucks that I've seen where Dodges. Learn something new everyday. I just went to get a 400/205, and turns out that its a 350/205. Still know where there is one, so I think I'm gonna snag it while the snagging is still good.

[454_72_4X4]

Originally Posted by qksilver

Going thru all the replies, one question. I am going to do the bb swap into a 68 SWB. I have all the cross members out of a 87 3/4 burb but small block engine stands. Can i use the small block engine stands? If I need to use bb stands, are the 4x4 and 2 wheel drive the same?
Thanks,
Steve

There shouldn't be any difference in BB and SB engine mounts, (87 burb). Chevy used the same "clamshell" type mount from 73-86 truck, 87-91 Blazer/Burb, (and probably newer, not sure).

BB and SB share the same mounting boss dimensions so basically where one was the other will bolt in. Don't get me wrong here, there's still other clearance issues to deal with, but the engine mounts are the same.

There are two different "clamshell" heights though. Some trucks used the taller ones and some used the shorter ones. I think the ones with the shorter version had the plates between the clamshell and the engine block for the braces that attached to the trans.

I'd use the setup that was on the burb x-member myself.
I wish I'd used a 73-up x-member.

[qksilver]

Thanks............you brought up something I did think about. The braces......I have been picking up pieces for more than a year. Are they for manual trans also?
I was going to use what i had 4 speed and transfer case out of a 72 chassis for the time being, I would like to find a good 7004 and transfer case but that will have to wait.
I will save exhaust questions for down the road! After I get the engine/trans/case/crossmembers etc installed. A lot of Nascar guys around here, one guy said he would do custon equal length headers in trade for one of my bb cores.
Thanks,
Steve

[b454rat]

I can confirm the mounts being the same. I had an 84 3/4 ton 4wd that was originally a SBC. I traded the motor for a 454, used the clamshells off the SBC, got a set of headers, and bolted the motor in. Didn't do nothing. Wish I still had the truck.....Did the same to my car too....

[qksilver]

Thanks,
Steve
each day a little closer, 68 SWB 3/4 bb stepside

[kwmech]

One thing I do not quite understand. These trucks came factory with big blocks. What is the big issue with one going into a 4wd? Are you guys trying to avoid doing drivelines? Or putting later model 454s in with the longer water pump? Reason I ask is I am going to pull the 6.2 turbo setup out of my 68 4wd and put a 454tbi in after the holidays. I do not want to get into lifting the body and/or pounding the firewall for clearance.

[b454rat]

Factory 2wd BBC, but not 4wd BBC.

[kwmech]

Originally Posted by b454rat

Factory 2wd BBC, but not 4wd BBC.

That is my point, a big block fits under the hood without doing a body lift or pounding sheetmetal with a short waterpump.

[454_72_4X4]

In the factory BBC 2wd trucks the engine sits farther forward than the SB 4x4 trucks.
With a 4x4 you either have to massage the firewall or move the motor forward to the 2wd mounting location.