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Transmissions and Rear Ends Three on the tree or four in the floor? Shift it all here.

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  #11  
Old March 10th, 2017, 02:43 AM
arepoff arepoff is offline
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Default Re: 478 to SM420

So I stopped by my machinest tonight, you can imagine what he said about the V6. Something about "sorry". His biggest issue was the lack of parts availability. He has been a machinist for 40 years, he took me in the back and showed me he had an early 305 tore down, headed to the junk yard because he couldn't get the parts or the cost was too much to rebuild. He also stated the top end wasn't the problem but finding the parts for the rotating assembly, which I knew already.

Anyway, he didn't have the ability to balance the 478. Don't know what to do at this point, I don't have a lot of options for machine work on this side of the state.
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  #12  
Old March 10th, 2017, 02:53 AM
AZKen AZKen is online now
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Default Re: 478 to SM420

Go with the Chevy LS motor or stay stock 305. Balance the whole rotating assembly? Custom flywheel? Even the good old 454 will blow the doors off a 478 dump truck motor. You can't turn the beautiful GMC motors into anything but what they are. Nice, dependable, powerful, unique. new and used parts are not real easy/cheap to find, and get shipped to you, and get machined and so on.
Stay original or make life easy.

Last edited by AZKen; March 10th, 2017 at 02:58 AM.
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  #13  
Old March 10th, 2017, 02:56 AM
arepoff arepoff is offline
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Default Re: 478 to SM420

Thanks AZKen, that is the way I am leaning at this point. This truck will be with me rest of my life and handed down to my boys so I want it to last. Plus I want to be able to drive it.
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  #14  
Old March 10th, 2017, 03:02 AM
AZKen AZKen is online now
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Default Re: 478 to SM420

Why can't you drive it with the 305E motor? Talk about lasting.........
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  #15  
Old March 10th, 2017, 03:31 AM
arepoff arepoff is offline
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Default Re: 478 to SM420

It may. It runs but I see blue smoke. At best I need to take a compression test, hopefully it is just the valve stem seals, then I would just need to get the heads done and have hardened seats installed. Compression test will be next. I may have a line on a good running 401m, might go that way.
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  #16  
Old March 10th, 2017, 03:35 AM
bigblockv6 bigblockv6 is offline
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Default Re: 478 to SM420

If you go with the 401M you can still get pistons these engines and if the 401M has the 6 bolt crankshaft flange which will allow you to use the 305E flywheel and bellhousing, it is an internal balanced engine so there is no weight on the balancer or flywheel.
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  #17  
Old March 10th, 2017, 03:40 AM
arepoff arepoff is offline
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Default Re: 478 to SM420

yeah, I just had big inch dreams (don't tell my wife!). Looks like the 401 is still a pretty good gain on power compared to the 305 I have. 68hp and 90ftlb difference and it is a bolt in.
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  #18  
Old March 10th, 2017, 03:59 AM
bigblockv6 bigblockv6 is offline
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Default Re: 478 to SM420

A few mods like custom ground cam which I have specs for, a 4bbl carb, HEI and good dual exhaust should do good for the 401M.
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  #19  
Old March 10th, 2017, 04:15 AM
arepoff arepoff is offline
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Default Re: 478 to SM420

that sounds good! I was planning HEI, FiTech fuel injection and dual exhaust already. Who grinds the cam?
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  #20  
Old March 10th, 2017, 04:19 AM
bigblockv6 bigblockv6 is offline
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Default Re: 478 to SM420

Fuel injection sounds good! Anyone who custom grinds cams can do it. I have sent out the specs to quite a few members and they were all able to get the cams ground to those specs. Just get online and search for Custom Cam grinders.
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