Swapped The 350 For A 454

[79GMCChris]

Hi Fellas-

Like the subject line states, I just swapped out my 350 engine for a 454 engine.

Here’s the story, I also need help with one issue.

I bought the 1979 GMC K25, 4x4, long bed, 350 hydro transmission, about 3 months ago.

The original owner (I’m the 2nd owner) bought the truck new and it came with a 400 CID.  When the 400 wore out the owner put in a 350 CID.

I bought the truck and the 350 was pretty tired and  decided to swap out for a rebuilt 454.  I got a 454 engine from a crashed, what I believed was a, 1976 Chev or GMC 1 ton truck 2WD.  Got it with the a/c (which I wanted to keep) and all the 454 brackets still attached to the engine (for me, a good find).

I disassembled the 454 and had the machine shop do all the needed (and a little extra) machine work.  I won’t go into what all I had done unless someone asks specifics.

The swap was pretty much a directly match bolt up.  Few issues and headaches with motor mounts, but got it all worked out.

Oil pressure is good, no surprises during break-in.  Hopefully I’ll be using the truck for many years towing our 5th wheel, towing our trailer with firewood, and using it as I think a truck should be used.

Now for the help needed……As many of you know it is not uncommon with the 350/454 swap to end up with the bottom of the radiator fan hitting the bottom of the shroud.  I trimmed the bottom of the fan shroud away from the vibration damper, and also the forward edges of the alternator and power steering pump.  Most of the shroud is still in undisturbed and I’d say about 90 % of the shroud still covers the fan.

I have not had any overheating issues, but we have not yet gotten into the warm weather and I haven’t yet towed anything with it.  I’m concerned about future overheating issues, and would like to get a replacement fan shroud that would completely encircle (is that really a word ) the fan.  The fan is a stock clutch type fan.

I have been told a fan shroud from a 1981-1987 truck, with a 454, would be a good replacement.

The radiator is a 3 core (I hope a got that right).  I had the radiator serviced by a radiator shop during the rebuild and they said it was in good shape and they felt it would suffice for cooling the 454.

Any help would really be appreciated.

Thanks in advance,
Chris (in Idaho)

[VileZambonie]

Did you use new mounts? Are you sure they're bolted up correctly? Drop the crossmember down an inch and see what happens.

[79GMCChris]

Hi Vile, thanks for the reply.  I always look forward to your input, no matter what the subject.

Yes, I used new mounts.  The clam shells were on the 454 when I got it, and I used those on the install.  I wanted to use 454 frame mounts, but they were to long for the frame, and would have allowed only two bolts to be installed on each mount.  So I went with 350 mounts.  I compared the 350 frame mounts to the 454 mounts, and the 454 mounts looked to be maybe 1/2" taller.  Maybe that had something to do with the engine sitting lower.

I'm pretty sure they are bolted up correctly.  The new 350 frame mounts used the exact same attaching holes that the removed 350 had used (I hope that made sense).

I'm not following you when you suggested "drop the crossmember down an inch".  Are you referring to the crossmember that attaches to the frame mounts?  Wouldn't that add to the engine already being mounted to low, with the bottom of the fan already contacting the bottom of the fan shroud?

Sorry if I'm missing something.

Thanks again Vile for your help.

[VileZambonie]

The trans crossmember. It sounds like the problem is in the motor mounts though. Is your truck lifted at all?

[Captkaos]

Do you have a gap at the top of the opening?

[Engineer]

You used the 454 clam shells, that is good. The rubber mounts should be bought for a 454 as well. I'm not sure why only two holes lined up, I've never encountered that.

The donor truck should have had a fan shroud for the BB.

On the swaps I have done if you use the 454 mounts, and the 454 shroud, all is good. GM used the same shroud for the 454 engined trucks from 73~87. The only time I had a fan rub was when I tried using SB clamshells on the BB.

[79GMCChris]

Thanks to all who responded to my post.

As mentioned by Engineer I'll be looking for a BB fan shroud to replace the "cut" SB shroud.

Thanks again fellas !!!!