25" intake and exhuast port sizes needed

[Ajgkirkwood]

Hi there. I was wondering if anyone know the shape and size of the intake and exhaust ports on the 25" block. Block is question is a 265 from 54 but im assuming the 25" blocks all had the same port sizes and shape?

Im getting an intake and dual exhaust for my engine but i plan to make my own intake and exhaust header. What i like to know is the size and shape of the ports on the block so i can use measurement from the intake and exhaust header im getting put know the diameter/shape of thr engine ports to match them as close as possible together. I dont want to remove the intake off my car just yet to keep it mobile till i get closer to be done it

Edited December 1, 2017 by Ajgkirkwood

[Brad47]

Adam h just posted about making his own for a 230 , maybe you could ask him ? He looks like he knows what he’s doing they turned out mint !!

[martybose]

Just buy a gasket set and use the manifold gasket as a guide.

Marty

[Ajgkirkwood]

2 minutes ago, Brad47 said:

Adam h just posted about making his own for a 230 , maybe you could ask him ? He looks like he knows what he’s doing they turned out mint !!

I just sent him a msg so ill hear back from him hopefully

[Ajgkirkwood]

3 minutes ago, martybose said:

Just buy a gasket set and use the manifold gasket as a guide.

Marty

Haha i didnt think of that. Do the gasket set sizes match up to the motor? I guess if i was even bigger then the gasket diameters. The gasket size would restrict it

[dpollo]

The gasket holes match the manifolds.  The block's ports are a little smaller .  I use the gasket as a template to enlarge the block's intake  ports so they match the manifold.

The 25 inch engine has larger ports than the 23.

[Matt Wilson]

I went out to the garage just now, where I have a bare 251 block, which I'm going to convert into a 265.  I used calipers to measure a couple of intake ports and a couple of exhaust ports.  The intakes are 1.375" or very close to it. The exhausts are 1.310" or very close to it (probably actually 1-5/16).  I also took two measurements of each port, 90 degrees apart from each other, and got the same numbers, so they are circular in shape.

Edited December 1, 2017 by Matt Wilson

[Matt Wilson]

I also have a 230 block (23" block, of course), so out of curiosity, I measured its ports, and the intakes are 1.312" (probably actually 1-5/16), and the exhausts are 1.25".

[Adam H P15 D30]

Funny, my 230's ports were all 1.25. I'll remeasure when I get back into town. 

The gaskets were larger and if I didn't have a freshly rebuilt engine I would have matched the portsto the gaskets also. 

The headers I used were the small primary tubed SBC headers, I think 1 5/8 and they were plenty big for my 230  

Adam  

[Ajgkirkwood]

1 hour ago, Matt Wilson said:

I went out to the garage just now, where I have a bare 251 block, which I'm going to convert into a 265.  I used calipers to measure a couple of intake ports and a couple of exhaust ports.  The intakes are 1.375" or very close to it. The exhausts are 1.310" or very close to it (probably actually 1-5/16).  I also took two measurements of each port, 90 degrees apart from each other, and got the same numbers, so they are circular in shape.

Wow thank you for measuring it out! Everyone replying thank you. Looks like i sparked some interest in the sizes for others too. Glad to know they are just round circles. Gonna make things alot easier. If the gaskets are alittle bigger then the ports then i could round the corners of the ports to smooth the air flow on them