Mustange 5.0

Lower intake

Mustang 5.0L

Lower Intake

Your standard issue Mustang 5.0L Mass Air Lower intake.

Runner No.	1	2	3	4	5	6	7	8
Stock CFM	155	200	186	197	151	190	177	207
Percent of highest	75%	97%	90%	95%	73%	92%	86%	100%

Measured stock flow rates CFM calculated to 28"H2O

Flow testing equipment by Flow Performance

Porting an intake is a great way to really improve the breathing capability of most any engine. The stock castings usually have some sharp bends or corners that will benifit greatly from just a little grinding and blending.

The intake manifold above is a stock aluminum casting, #RFE65E 9K461D5. It came from a mustang 5.0 liter Mass Air induction. I bought it, along with an upper, on Ebay for $55.00 delivered.

The biggest problem with this stock casting appears to be the huge imbalance in flow with runners No. 5 and 1. While runner 1 is not to difficult to bring up to flow with the rest, runner 5 is a problem. So, the following will concentrate on runner 5.

The runners were flow tested using a clay radius on the flange that the upper manifold bolts to. Air was drawn from the flange that bolts to the head through a Flow Performance 2" mini receptacle and FE2.0 flow element in a hand-held configuration connected to a 4.5hp Shop Vac (R). While the test pressure was not controlled, using a Flow Performance FP1 electronic flow rate processor the flow rates were corrected to 28" of water test pressure. While this type of flow testing may seem over-simplified, the as-cast test results did show the slight difference in flow rates between runners 8 and 2. Runner number 8 and 2 are almost identical in size and shape, but runner 2 does have a very slight bend. Other flow data I have seen tend to show these two ports flowing the same.

Since the number 5 runner is the biggest problem, I will concentrate on it to try to bring it up to the flow rates of the other runners. The best areas to find some air was the inside radiuses of the turns that the runner makes.

At the flange that bolts to the head, there is a sharp turn indicated by the white arrow. While this radius had to be increased drasticly, it was the area of highest flow improvement. The notch at the top of the port is a relief for the fuel injector nozzel.

While a bit of material can be removed here to match the stock gasket, no improvement in flow was detected by doing so.

At the upper flange, runner 5 takes a sharp turn and twist. This was the second best place to find some air. Most of this area must be reached with a 6" carbide ball from the head flange. A lot of material has to be removed for any gains to be seen.

The floor was lowered to near the gasket line to gain about 3 cfm.

Cutting the outside wall back to near the gasket line and blending it back into the runner gained a few more cfm.

Cutting the inside radius wall back to near the gasket line did not produce any detecatable improvement in flow.

Stock CFM	151
Percent of highest	73%

Ported CFM	197
Percent of highest	95%

After all the work I put into runner 5, 197 cfm is the best I could do. This brings runner 5 to within 95% of the flow of runner 8, which is the highest flowing port at 207 cfm stock.

The other ports are not nearly as difficult to bring up to near 100% flow, and using the Flow Performance system a perfect balance is easy to achieve between all runners without over-shooting the 100% flow mark established by runner 8. Just carefully increasing the inside radiuses goes a long way to improving flow on runners 1 and 7.

Nothing beats the velvet-growl sound of a well balanced breathing engine.

I did not remove any material from the roof since I saw no pratical way of blending it back into the runner without leaving a dip in the roof at some point.

Runner 5 Review

Runner No.	1	2	3	4	5	6	7	8
Stock CFM	197	190	185	196	195	187	194	191
% of best	100%	96%	94%	99%	99%	95%	98%	97%

Here are the flow rates for the upper manifold. Notice the number 6 and 3 runners closest to the throttle body have the lower the flow rates. This is because of the sharp turn the air must make to flow from the throttle body runner to the individual cylinder runners 6 and 3.

Flow testing equipment by Flow Performance

207

151

155

200

186

197

190

177