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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: olblue2 on December 11, 2009, 11:56:36 pm

Title: big block swap in a 1977 k-20
Post by: olblue2 on December 11, 2009, 11:56:36 pm

ok guys tell me if a big block chevy will fit up in my 1977 k-20 4x4. it has the m-20 muncie 4 speed.  will it fit up with no problems???

Title: Re: big block swap in a 1977 k-20
Post by: Blazin on December 12, 2009, 12:10:06 am

 In line six to a big block are the same bellhousing bolt pattern.

Title: Re: big block swap in a 1977 k-20
Post by: olblue2 on December 12, 2009, 12:11:09 am

Quote from: Blazin on December 12, 2009, 12:10:06 am

In line six to a big block are the same bellhousing bolt pattern.

ok cool but how about the motor mounts? any changes need made?

Title: Re: big block swap in a 1977 k-20
Post by: Engineer on December 12, 2009, 08:32:51 pm

You can use your small block motor mounts, but there are big block specific mounts as well. If you are looking to go with BB motor mounts just ask, and I will post the OE part number. Otherwise use your SB mounts.

The only issue I had using the SB mounts on a BB was the fact that the fan hit the lower portion of the fan shroud, and if you are using Hooker headers, they may hit the frame if using the SB mounts.

All Chevy bell housings use the same bell housing bolt pattern.

If your BB is a 396~427 you can even use your SB flywheel. However, the 400SB, and 454 are extenally balanced, and you should only use those engine's flywheels on those engines specifically.

Also, even though the 400SB, and 454 are both externally balanced, their flywheels will not interchange with each other.

Title: Re: big block swap in a 1977 k-20
Post by: olblue2 on December 13, 2009, 12:46:07 am

Quote from: Engineer on December 12, 2009, 08:32:51 pm

You can use your small block motor mounts, but there are big block specific mounts as well. If you are looking to go with BB motor mounts just ask, and I will post the OE part number. Otherwise use your SB mounts.

The only issue I had using the SB mounts on a BB was the fact that the fan hit the lower portion of the fan shroud, and if you are using Hooker headers, they may hit the frame if using the SB mounts.

All Chevy bell housings use the same bell housing bolt pattern.

If your BB is a 396~427 you can even use your SB flywheel. However, the 400SB, and 454 are extenally balanced, and you should only use those engine's flywheels on those engines specifically.

Also, even though the 400SB, and 454 are both externally balanced, their flywheels will not interchange with each other.

cool , well the fan wont be a problem im running a electric fan, so if i get a new flywheel will i have to get a new clutch and pressure plate?

Title: Re: big block swap in a 1977 k-20
Post by: Irish_Alley on December 13, 2009, 02:06:14 am

you dont have to but you might as well. same some trouble down the road

Title: Re: big block swap in a 1977 k-20
Post by: olblue2 on December 13, 2009, 10:24:17 am

Quote from: Irish_Alley on December 13, 2009, 02:06:14 am

you dont have to but you might as well. same some trouble down the road

clutch, pressure plate and flywheel all are new and have only few miles on em

Title: Re: big block swap in a 1977 k-20
Post by: 1980c10 on December 13, 2009, 10:48:44 am

I have had problems switching to an externally balanced engine due to bell housing clearance, becuase of the increase in flywheel thickness. I'm not sure if it might apply here or not.