SBC or BBC in 1972 K20 project vehicle?

[kabcpapc]

I am getting ready to start on a 1972 Chevrolet K20 Suburban project. It has a 350cid with a TH350 automatic trans which is the originalengine/trans. I have been away from the GM camp since 1989 so I need some tutoring to reclaim my memory about GM engines and transmissions. My dad had a 1972 Chevrolet C20 Suburban with the 400 BBC with automatic which I felt sure was a TH400. My prior memory told me that SBC had the TH350 and the BBC had the TH400. I was contemplating installing a BBC with a TH400 in my K20. In the various threads I have read on the site, a lot of guys reported inadequate firewall clearance when installing a BBC and they had to move the engine forward or cut out more space on the firewall. They also said they reused the SBC motor mounts. Now my dad's 'burb had plenty of firewall clearance with his BBC. According to what I have found out, the BBC used different motor mounts than the SBC.

So to make a long story short, can you install a BBC with a TH400 in a K20 without cutting on the firewall by using the motor mounts that was used on the C20 BBC?

[derotoreut]

IMO I wouldn't mess with putting in a BB. Seems like too many issues to be concerned with. Why not make it easy and put in a SB 383? Check out mine.

[kabcpapc]

Originally Posted by derotoreut

IMO I wouldn't mess with putting in a BB. Seems like too many issues to be concerned with. Why not make it easy and put in a SB 383? Check out mine.

As a matter of fact I have considered putting in a SB. I looked at the HT383/340HP and the ZZ383/425HP. I also looked at the Ram Jet 350/350HP.

Which 383 is yours? Is that the GM drive accessories kit or a custom kit?

What transmission is going behind your 383 and what axle ratios will you be running?

[MARKDTN]

I would put in a fuel injected small block and overdrive trans. A TPI ot LT1 will bolt right in the original mounts. Keep the 700R4 auto from these and move the trans mount back. Or even better a 5.3 with 4L60E swap. No way I put a BB in todays market with fuel what it is and it's only going up. If I had one I might keep it, but if I am going to swap, LS power is the way to go! Power, economy, and reliability all in 1.

[GMCJOE]

Originally Posted by MARKDTN

I would put in a fuel injected small block and overdrive trans. A TPI ot LT1 will bolt right in the original mounts. Keep the 700R4 auto from these and move the trans mount back. Or even better a 5.3 with 4L60E swap. No way I put a BB in todays market with fuel what it is and it's only going up. If I had one I might keep it, but if I am going to swap, LS power is the way to go! Power, economy, and reliability all in 1.

I agree with putting a small block in with todays fuel economy, unless you have no worries about how much fuel this truck is going to eat. Some people don't and are going the route for play reasons. Even if you decided to go with a BBC and TH400 setup, there would be no reason to cut the firewall, some had 402's and 396's. When my truck came to me, it had a 454 with a TH400 with no modification to the firewall. That is long gone, and a 96 LT1 motor sitting on the same motor mounts and stands mated to the TH400.

My suggestion is to choose the route you are going to go with motor and transmission as to what you are going to use the truck for. I choose my route cause I wanted to be more street friendly, though I am still working on getting my transmission.

[mrein3]

Originally Posted by kabcpapc

I am getting ready to start on a 1972 Chevrolet K20 Suburban project. It has a 350cid with a TH350 automatic trans which is the originalengine/trans. I have been away from the GM camp since 1989 so I need some tutoring to reclaim my memory about GM engines and transmissions. My dad had a 1972 Chevrolet C20 Suburban with the 400 BBC with automatic which I felt sure was a TH400. My prior memory told me that SBC had the TH350 and the BBC had the TH400. I was contemplating installing a BBC with a TH400 in my K20. In the various threads I have read on the site, a lot of guys reported inadequate firewall clearance when installing a BBC and they had to move the engine forward or cut out more space on the firewall. They also said they reused the SBC motor mounts. Now my dad's 'burb had plenty of firewall clearance with his BBC. According to what I have found out, the BBC used different motor mounts than the SBC.

So to make a long story short, can you install a BBC with a TH400 in a K20 without cutting on the firewall by using the motor mounts that was used on the C20 BBC?

The problem is GM NEVER put a big block in a K truck through 1972. They made big block 2wd trucks but never a 4wd truck with a big block until after the 1972 body style.

For whatever reason GM has the stock small block in 4x4s sitting pretty far back under the hood compared to 2wd trucks. So far back that the simple points to HEI distributor swap is a tight fit.

If I had to start over, knowing what I know now, I would build the following 4x4:
I'd start with a modern (up to 1999 in pick-ups a little later in Subs) 350. It comes with the roller cam shaft.
I would build it into a 383 and keep the stock, vortec heads.
I would run some kind of fuel injection. TBI, aftermarket, something other than a carb.
I would get a 700r4 setup with the Advanced Adapters output shaft that is made to mate up with the NP205 that came from the factory behind a th350.
I would move the 383 engine cradle forward and mount the longer tranny and stock t-case to the place on the frame that GM did. Then I could use standard driveshafts.
3.73 gears in the diffs.
Standard height tires.

I've heard that a big block will fit with the engine moved forward to compensate for the longer 700r4. Perhaps somebody that has done that swap can weigh in here.

[superduty_59]

If I were going to spend a lot of time and $ on an engine swap it definitely would not be a gasser. I would swap in anything diesel and my engine of choice would be a 5.9 Cummins.

If your mind is made up on sticking with a gasser then I would definitely go for the 6.0L or even the 5.3L with an overdrive.

[derotoreut]

Originally Posted by kabcpapc

As a matter of fact I have considered putting in a SB. I looked at the HT383/340HP and the ZZ383/425HP. I also looked at the Ram Jet 350/350HP.

Which 383 is yours? Is that the GM drive accessories kit or a custom kit?

What transmission is going behind your 383 and what axle ratios will you be running?

My 383 was built by United Racing Engines. It was built to use stock torque converter and makes adequate vacuum to use power brake booster. It was dyno tested at 465 HP/465 TQ.

The accessory drive is made by March, and is their Revolver model.

The transmission is TH350 with 4.10 rear end.