Can the G20s hold a 454 big block? I plan to add quite a bit of weight to mine and would like some more torque to deal with this. Can anyone tell me what the largest engine the G20s can hold is? Someone told me the only reason the G30s can have the 454 is because they had a slightly larger dog house, if so, is it just the lid to the engine compartment or is the actual bay too small?

 

At some point in production (I forget what model year, maybe 1982-ish) they enlarged the doghouse and engine opening to allow for a big block, or a 6.2/6/5 diesel. The opening is the same on all after that point, be it G10, G20, G30.

The clearance is tight with the 350, but I was able to change exhaust manifolds on one.

If you intend to add weight you probably should add the heavier springs and so forth, the vans are different from pickups - a G20 has the same springs and axles as a half ton pickup

I would measure and see if a Cadillac 472 would fit in there if I was doing one. More torque and a little less thirsty on fuel.