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| | | | Joined: Mar 2013 Posts: 223 'Bolter | | 'Bolter Joined: Mar 2013 Posts: 223 | I'm currently working on a 270 GMC and fitting a turbo. I have a big port head, so my question is that the 270 exhaust manifold doesn't fit the big port 302 head. With the exhaust mounted to the head it comes right up to the bottom of the intake port covering all but about a 1/16 of the sealing area of the port. I'm thinking a large port head, 302 or 270H has there own exhaust manifold ???
Jay D.
Last edited by Gdads51; 06/09/2025 2:11 PM. Reason: add detail to title
| | | | | Joined: Jan 2019 Posts: 2,243 Herder of Cats, Goats, and Sheep (moderator) | | Herder of Cats, Goats, and Sheep (moderator) Joined: Jan 2019 Posts: 2,243 | Do you have some pictures? That would help make it clear what you are asking. | | | | | Joined: Mar 2013 Posts: 223 'Bolter | | 'Bolter Joined: Mar 2013 Posts: 223 | | | | | | Joined: Jan 2022 Posts: 2,489 'Bolter | | 'Bolter Joined: Jan 2022 Posts: 2,489 | What is the casting number on the exhaust manifold? There are many exhaust manifolds listed for 270/302 engines in the 39-54 and 55-60 GMC Master Parts Books. Sometimes you get lucky and the part number is one digit different than the casting number.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
| | | | | Joined: Mar 2013 Posts: 223 'Bolter | | 'Bolter Joined: Mar 2013 Posts: 223 | thanks for the reply, sadly i ground off the numbers. i was going to have it coated and want it smooth.
Jay D. | | | | | Joined: Feb 2020 Posts: 47 'Bolter | | 'Bolter Joined: Feb 2020 Posts: 47 | You may find that the exhaust manifold isn't lining up correctly with the ports in the head. I have had several manifold and head combinations where this is the case.If you are using the 3 piece intake/exhaust gasket. bolt it to the head, and then tape all 3 peices together. Now lay the gasket on the manifold and see if the ports line up. You may have to elongate the front and back mounting holes. I have also have had to install a spacer between the exhaust and intake manifold where they bolt together for all the ports to line up correctly with the ports in the head.
gmc-is-me
just retired and finally making headway on my project truck. 1940 GMC AC152.
| | | | | Joined: Feb 2004 Posts: 29,871 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,871 | It might be necessary to make snug-fitting wooden plugs in the shape of the exhaust ports and use a die grinder to match the manifold to the head openings. That's a trick we used when porting heads and headers/exhaust manifolds for round track engines. Once the ports are matched up, them tweak the bolt holes to fit.
Jerry
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