478 Diesel vs Gas?

[farmdreamer]

I have some updating since it’s been a while. I just came across someone selling a 305 out of a pickup for $250. It’s stuck, but thought it might be useful for my swap. The bellhousing in particular was of interest to me since mine are out of unis with a sae housing set up for hydrostats.

I found that you need a 16” flywheel to fit in the truck bellhousing. Then, I noticed my flywheels are different sizes between the gas and diesel. The gas one is a 16” flywheel. Then, I went looking for the stamping on the gas and see it’s a 401, not a 478. I think this might be good in that it doesn’t require an externally balanced flywheel and I could swap the whole setup over from the 305 to the 401 without looking for a balanced flywheel. Still a big power upgrade from my current 250. But, not a 478.

I know in my reading that the 478 gas requires a balanced flywheel. Does anyone know if the 478 toroflow does as well?

Thanks!

[BobBray]

Good question! The 478 Toroflow had a balance shaft in the left block skirt and a large harmonic balancer, but I am not sure about the flywheel. I will check some old shop manuals I have.

[bigblockv6]

I know in my reading that the 478 gas requires a balanced flywheel. Does anyone know if the 478 toroflow does as well?

Thanks![/QUOTE]

A shop that I worked at did a conversion like the one you're talking about. Basically started by someone else giving up on the project. My boss told me he took over the conversion in the early 70's, the ToroFlow was replaced with a brand new 401M in a School bus. When he received it there was the ToroFlow flywheel attached to the 401M and the engine could not run above idle so he had to get the correct flywheel for the 401M. So yes there is balancing on the Diesel version flywheel, Does your 401M have the 6 bolt pattern crank flange or 8 bolt pattern? If you have the 6 bolt pattern the 305 flywheel will work. When I did my 478M conversion I had a custom flywheel built from Tilton Engineering, the basically made me a zero balance flywheel so when the bottom end was balanced considerable weight was added to the flywheel.

[farmdreamer]

Thank you for the replies. I didn’t know what was behind the hydrostat adapters on the flywheels, so I took them off yesterday. The cast center of the hydrostat adapters have balance drill holes in both of them, but I assume that is for the coupler itself.

The 401 has a 6 bolt flywheel, the toroflow has an 8 bolt. I didn’t take the flywheels off yet. I assume if there was any balancing work on them to match the engine, it would be on the back side, so I can’t tell for sure yet. Attached are some pictures in case anyone else gets curious about uni engines as well.

As much as I’d like to use the diesel, it sounds like the 401 would be a pretty easy swap if I buy that stuck 305 for the bellhousing/ flywheel/ clutch assembly.

Another question, you referred to the 401 as a 401M. I don’t have an M stamped on my block. Were all 401 engines magnums, and they just didn’t stamp them?

[bigblockv6]

Your 401 then is a 1960-65 if there is no M stamped. Magnum engines were introduced in 1966. Only replacement 401 engines for older trucks may have not been Magnums after that. You should be good on the 401 conversion provided you have a 305 flywheel and bellhousing from a pickup truck.