Ported Intake Manifold & Cylinder Heads
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The lower intake manifold below is a stock aluminum casting, #RFE65E 9K461D5 from a mass air fuel-injected Mustang 5.0L engine. The biggest problem with this stock casting is the huge imbalance in flow between runners, with runners no. 1 and 5 far behind the others. While runner 1 is not to difficult to bring up to flow with the rest, runner 5 is a problem. The reason is that the no.5 intake runner has two sharp bends that restrict airflow. The no.1 runner also has two sharp bends but the first bend is at a slightly better angle.
The key to making this intake perform at its best is to balance the airflow of all the runners as much as possible. The no.8 runner is the straightest and has the highest airflow, so the aim is to increase the airflow of the other runners to closely match that of no.8.
Porting the stock intake manifold
No.1: 155 No.5: 151 No.2: 200 No.6: 190 No.3: 186 No.7: 177 No.4: 197 No.8: 207
(cfm at 28"H2O)
Airflow velocity is reduced when it has to change direction, therefore straight intake runners will produce the best airflow. Making the no.1 and no.5 intake runners as straight as possible is a tall order, but this article explains how to make each of the intake runners flow approximately 200cfm:
DIY Porting Mustang 5.0L Lower Intake
To achieve this, the inside radii of the bends of the worst flowing intake runners are cut back to reduce the angle of the bends and give the airflow a straighter shot into the cylinders. The no.3, no.6, and no.7 runners are also worked upon to bring their airflow to within 5% of the no.8 runner.
Porting the stock E7TE heads
A blown cylinder head gasket on the no.1 cylinder caused by a stuck thermostat (aargh!) meant that the intake manifold and heads had to come off. This presented me the opportunity to extract a few more ponies from the 5.0L V8 by porting the heads and lower intake in the comfort of my home. The heads were also shaved 0.010" for flatness adding 0.15 to the compression ratio.
In terms of airflow, the stock heads plain suck. Small 1.78" intake and 1.45" exhaust valves, coupled with tiny 126cc intake ports and 43cc exhaust ports, are good for low/medium rpm torque production but they're also one of the reasons why a stock Mustang 5.0L engine wheezes like a three-pack a day smoker above 4500rpm. Fortunately the aftermarket has blessed us with a large selection of heads that'll cure the engine's asthmatic tendencies, but they come at a price and require other supporting modifications (intake manifold, camshaft, larger injectors, higher-flowing fuel pump, computer tune). None of these are necessary if you merely port the stock heads and the results are better than you might expect.
These two articles are excellent guides to porting your own E7TE heads:
Intake Ports
Exhaust Ports
I performed steps 2-9 and 12-15 on the intake ports, and steps 2-8 and 14-17 on the exhaust ports. The whole exercise took me 10 hours but was it worthwhile?
Absolutely! Even though there's a plethora of aftermarket heads and intake manifolds available that flow much more air than the stock items, it's still possible to extract useful horsepower/torque gains by porting the stock heads and lower intake manifold. Indeed a pair of E7TE heads with a good DIY port job are capable of matching the performance of Cobra GT40 heads.
It cost me only $18 worth of grinding stones to complete the job and I was very happy with the result. The throttle response improved tremendously and there was a noticeable gain in torque across the whole rpm range (estimated 20rwhp gain).
At less than $1 per hp, this was by far the best bang per buck mod on my Mustang. Brilliant!
Crane 1.7 ratio roller rockers
The stock camshaft has an intake/exhaust valve lift of 0.444" when coupled with the factory stamped steel 1.6 ratio rocker arms. Crane pedestal-mount aluminium 1.7 ratio roller rocker arms are a direct, bolt-on replacement and increase valve lift to 0.472" for an easy 4rwhp/3rwtq gain.
Installation instructions.