Explain to me how to "read" head numbers---

[alwayscode390]

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 ---

 

[dgoodhue]

Re: Explain to me how to "read" head numbers---

My quick cliff notes, soem of it might be generalizations so don't hang me.

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?

Volume of the intake runner. Larger volume have the ability to flow more but too large of a volume cut down on air flow velocity. Too little velocity will create an engine that isn't responsive. On a 4.3L 230cc is more towards a race port.

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?

Yes its the volume and small chamber lead to higher CR. The chamber size has little to do with air flow though. Sizing can play some with quench area./detonation, but its a little more complex.

Straight vs angles spark plugs just help with header clearance right

Yeah basically, I Imagine it can have some logistical placement advantages.

4. Bigger valves = better flow?

Yeah in general. Too big of valve can affect port velocities and it also assume the rust of the port and valve seat is properly sized. Port shape and valve seats play a really big roll as well.

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?

Angle of the valves. The stock heads and SBC are usually 23 degrees. The 18 Degrees heads have some inherent advantages. I not 100% up on them because they are out of my price range, but I think port entry angle of the 18 degree heads is advantageous in term of air flow. I think it has less of entry angle behind the valves. Someone correct me if I am wrong.

 

[alwayscode390]

Re: Explain to me how to "read" head numbers---

Thanks a BUNCH, I really appreciate your response. I feel like I know alot more now ---

 

[turbodig]

Re: Explain to me how to "read" head numbers---

There aren't any real hard and fast guidelines when it comes to any of these parameters, to some extent, there are trade-offs involved in all of them.

My quick cliff notes, soem of it might be generalizations so don't hang me.



Volume of the intake runner. Larger volume have the ability to flow more but too large of a volume cut down on air flow velocity. Too little velocity will create an engine that isn't responsive. On a 4.3L 230cc is more towards a race port.

Very much towards a race port. Hard to make a port that big have decent velocity at low RPM.

Yes its the volume and small chamber lead to higher CR. The chamber size has little to do with air flow though. Sizing can play some with quench area./detonation, but its a little more complex.

There can be a small penalty in flow with smaller chambers, as the edges of the chambers get too close to the valves at lower lifts ("Shrouding"). It depends on how the chamber is
designed as to how bad the shrouding is.

Yeah basically, I Imagine it can have some logistical placement advantages.

You don't move plugs to fit headers. Plug position relates to the shape of the chamber, and the dome of the piston, and the flame propagation during combustion. The goal is better, more complete combustion.

Yeah in general. Too big of valve can affect port velocities and it also assume the rust of the port and valve seat is properly sized. Port shape and valve seats play a really big roll as well.

Shrouding becomes a concern at a certain point... also, the amount of margin between the intake and exhaust- a prime location for cracks.

The effects a larger valve will have will depend greatly on the seat, the port, and the chamber. Generally, the effects are positive, but not always.

Angle of the valves. The stock heads and SBC are usually 23 degrees. The 18 Degrees heads have some inherent advantages. I not 100% up on them because they are out of my price range, but I think port entry angle of the 18 degree heads is advantageous in term of air flow. I think it has less of entry angle behind the valves. Someone correct me if I am wrong.

That's a pretty good general description. The different angle allows different port shapes, and can minimize shrouding due to the valve opening more to the center of the cylinder.