Revision as of 08:04, 1 January 2017

Head porting means to re-shape the cylinder head inlets/outlets for better flow. Either to smooth out the original castings for improved power, or to enlarge them for higher RPM.

See also: CCing

1 Overview
2 Flow
- 2.1 Example 1
- 2.2 Example 2
3 Profile
4 Photo Index

Overview

Album 1777

Quote by sagemanone:
Port and polish will yeild power gains and 3 or 5 angle valve grinds help also hand grinding the sharp lips in the valve pocket helps the flow into the combustion chamber. Any reputable high performance machine shop should be able to do any of the work to your head you ask them to do if you ask them for spacific items to be done. If they seem puzzled or can't answer ALL your questions real easily take your head and run the other way. Don't be discouraged and don't be afraid to try to be creative . I heard of guys cutting down L16 valves after modifying the ports and installing the matching seats in an A14 to get marvelous increases in flow .So let your pocket book and imagination guide you.
One other thing ,Look for the factory goodies like the GX option stuff that could be ordered like the GX duel SU intake ( Iam looking for one myself) And NISMO still has some neat stuff they sell right out of a catalog . Iam hoping to put a list togather that will be on My web page as to the sources for all the places for the parts we Datsun A/nuts need . I hope to Launch that web page soon and you will all be invited!!!

All Datsun A-series engines come from the factory with a 3-angle valve job (even though most V8s didn't have this good feature). So certainly don't do anything less!

Ports	Size (mm)	Exhaust	Raised	Note
round	28	27x26	no	1971 A12
round	28	?	lowered	1977 GFU
Oval - Small	28x30	?	no	1973 A13
Oval - Medium	28x32	28x26	no	A14E, A15E
Oval - Regular	28x34	28x26	no	Many A14s
Oval - Large (GX)	30x35 - 36	27x29 or 28x26	Yes	A12GX (1971-1973)

Quote by azza_bijan:
Go for the high comp. head (not dished out). These have 9.5:1 compression. A15s in AUS are mainly high comp Don't enlarge the ports matching to the inlet, they are already large enough. Enlarge around the exhaust valve area and out and get some cut down 1600 valves to fit. The exhaust porting hugely boosts better flow and power. If you are rich or race, do the inlets. I got my head done for $300AUS. Then get good manifolds (handmade steel inlets $200AUS are as cheap as new aluminiums but are port matched to the head and work heaps better).

"high comp" means closed chamber heads, which yields maximum HP. The "dished out" heads are the open chamber type, which reduce emissions with the downside of slightly lower HP and more temperamental timing issues (including dieseling run-on problems). Either type can be used with high compression.

Closed Chamber (heart-shaped) VS Open Chamber
Album 26426

9.5:1 compression is achieved by using lesser dish in the piston, which the H89 engine uses. Datsun also used closed chamber heads on 8.5:1 engines, by fitting pistons with a larger dish. See Compression Ratio for more information.

Flow

Professional porters use a Flow Bench to measure the airflow of the unmodified cylinder head, then after smoothing or enlarging the port, measure the flow again. This is to ensure the modifications actually work. Not only should the airflow improve, but the air/fuel charge swirl must not be retained.

It is entirely possible to enlarge the ports, yet ruin the airflow of the head

Example 1

dattoman's cylinder head

measured at 25" water pressure
A14 regular oval port head with 38/33 (oversize) valves

UNMODIFIED PORTS w/oversize valves
LIFT(inch) .100  .200  .300  .400  .500  .600
INTAKE CFM 52.89 91.62 118.3 118.6 124   126.8
EXAUST CFM 43.03 71.71  93.5 111.1 124.2 129.6

AFTER MODIFICATION
LIFT(inch) .100  .200  .300  .400  .500  .600
INTAKE CFM 59.14 103.3 129.7 135   140.6 141.2
EXAUST CFM 52.37 80.92 103.4 122.8 129.2 130.9