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Discussion Starter · #1 ·
I have been pretty confused on heads , and wanted your help to explain some figures.

1. Intake runner? What is this number telling me? I have seen 180cc...190cc , 230cc ect....what is the advantages/disadvantages to lower or higher numbers?

2. Combustion chamber volume: I have seen #'s in the 40's to the 70's (cc's). If the number is lower, expect higher C.R. numbers but lower flow right?

3. Straight vs angles spark plugs just help with header clearance right?

4. Bigger valves = better flow?

5. 12 degree, 24 degree, what is that? The angle of the outside of the head or how it matches to the intake on the inside?

Thanks , I appreciate your time helping me out

Premium Member
22,122 Posts
1. the physical volume of the intake runner, like if you filled it with water. Useful for comparing heads for the same type of engine, as in small block chevy. higher volume ports flow more air, but it's not that simple as the actual airflow requirements of the motor need to be taken into acount. Too big is as bad as too small.

2. same as above but relating to the combustion chanber. lower volume = higher compression ratio

3. Angle plug heads point the plug toward the exhaust valve, and are (debatably) better at getting the fire lit. Often actually worse for header clearance, depending on the header.

3. yes

4. the valve angle refers to the relationship between the valve stem and the cylinder bore (or the valve head and the deck, same angle) The standard angle for gen1 small blocks is 23 degrees. Many race heads are at 18 degrees. LS2 heads are much shallower, down in the 13 degree range.
I'm not real sure what difference this makes, other than the obvoius, as the chamber gets "flatter" it gets smaller, so higher compression, there is more to it tho.

21,341 Posts
The deal w/ flattening out the valve angles is that as you do so, the valves "windows" at lift become true cylinders w/ respect to the centerline's of the cylinder bores.

Instead of angled.

The only problem is when going to flat like the old 348/309's were is that even tho they were still angled 16 degree's vs 23, w/ the chambers being in the now slanted block decks, the ports were still very flat in relation to the valves themselves. What I mean by flat is that they still made like a 90 degree turn in the bowl to exit into the cylinder.

They really need to be stood up so they get a straighter shot at the valve head, but then we get into head "packaging" problems. And this was done way back then when they created the Z-11 427 "W" engine!!! Some say their heads flowed better than any of the standard BB heads even today for what they are..

And fwiw, there are old English car engines that have zero valve angles and only perimeter quench rings and deep dished piston's that end up actually being the chambers!! And if you look closely at their heads, both valves ports tend to stand up very tall until they have to curve either into the exhaust manifold or coming out the intake..

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