1974 2.7 CIS Heads?

[Flying356]

Gentleman, Can the intakes on 74 only heads be opened up from 32mm to the later 35 or 36 mm? Also, are the intake and exhaust valves the same as the later 2.7 heads?
My engine is a 73 1/2 T 2.4 with 74' 2.7 heads. I am currently planning on installing the PMO intake manifolds but they are the 36 not the 32's. Instead of selling these and buying the 32's, I was just planning on matching the ports to the intake manifolds. Currently has the CIS cams but I will swap those at a later date.
Thank you in advance for the assistance,
Christian

[4sd911]

I asked a machine shop about this, they can do it. It was suggested that they would open it up and I could finish it, I assume polish the port. Did not follow up on this. You must have the '74 T heads (non '74 S type).

[Walt Fricke]

Christian

Plenty of meat there to open up your ports. My race 2.7 heads were opened up to 38 each (not that I am suggesting you do this - ports which are too large are a problem as bad as having ones which are too small, especially for a street motor where good low RPM performance is essential).

Valve sizes in all of these heads the same.

The suggestion from a shop that the customer could finish a porting job most likely means that the shop was going to bore out the holes down to, say, the start of the valve guide boss. Then the customer could use a die grinder to smooth out the transition into the bowl. Because that is a labor intensive hand operation, and machine shops charge a lot of $ per hour. Sounds like a good shop with which to do business - looking out for the customer's pocket book.

Polishing intake ports is generally seen as something you don't want to do - a slightly rough surface apparently helps hold a boundary layer of air, and that acts to reduce wall friction for the main air flow. Something like that. Polishing exhaust ports gets better reports, though I don't think it is worth the effort for most of us. Going to carbon up soon enough anyway, isn't it? Yes, I grew up reading about "port and polish." But not everything you heard about in kindergarten turns out to be so.

[Flying356]

Thank you both for the info., I really appreciate it.
Christian