Why Port an EFI Lower or a Carb Intake?

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Why Port an EFI Lower or a Carb Intake?

Unread postby Tmoss » Tue Jan 21, 2014 2:52 pm

EFI and Carb Intakes
We have ported most commercially available past and present intakes. Ford, Chevy, MoPar, Edlebrock, Holley, Canfield, Offenhauser, Saleen, Trick Flow, Weiand, etc. We have pictures and flow data on almost all the intakes we have done in the last 8 years since setting up an Audie Flow Quick digital flow bench. Just contact us and we can discuss your needs and we can share our data and recommendations. Thanks,

Stock Ford HO Lower Intake
The stock intake has runner cross sections (square inches = cross section) that vary through the runner length. The upper intake runners have a cross section of ~1.7 square inches. The runner is an extended oval shape that can be measured by converting the area to one hole (one half at each end of the rectangle) and one rectangle and calculating the square inches of area. The area of a circle is pi (3.14) x radius squared. The radius = one half the circle diameter. For example, the Cobra has a 1.625 round hole for the upper runner. Its area is 1.625/2 = .8125 radius, so .8125 x .8125 x 3.14 = 2.07 square inches. For a rectangle just multiply the length times width. So, a stock upper intake has a cross section 21% smaller than the Cobra. a significant difference for rpms above 4,500.

The stock lower transitions that oval upper runner shape to a rectangular shape just below the interface of the upper-to-lower intake. There it becomes an area of very close to or at 2.0 square inches. The catch is, it narrows down to a cross section of 1.2 square inches where the lower intake runner opening meets the head intake runner opening. That cross section is only 71% of the stock upper and 58% of the Cobra. That is a significant difference and is the one of the primary reasons the stock engine stops making power over 5,000 rpm (assuming the valve springs are capable of those rpms). The stock lower small cross section sets up an inertial block at about the 5,000 rpm point for a 302 engine. The inertia block varies by cross section, runner length and cubic inch displacement.

Porting the stock lower to a 1.9-2.0 square inch size while reshaping the runner short side radius (just as important as enlarging the intake-to-head opening cross section) can provide substantial increases in the ability of the stock intake to make power. Essentially you are removing the inertia block of the lower intake and making the 1.7 square inch cross section of the upper intake the limiting inertia block. This moves the critical upper usable rpm range from 5,000 rpm up to about 5,400-5,600 rpm and pushes the inertia block up to ~6,000 rpm (near the stock rev limiter). The Cobra cross section will carry flow to 5,550 rpm in stock form but ~7,500 rpm before hitting the inertia block for a 302 engine when ported. It takes the right cam to get power above ~5,500 rpm though.

ported HO lowers for use with a 302-306 engine will gain a significant difference in the usable power band their engines makes and will run 13s to mid 12s depending on weight and gain. 10-15+ horsepower and 20-25 lb-ft. However, this is NOT a race intake modification. It will work very well with stock or mildly ported E7, Gt40 or GT40P, Windsor Jr, or any head that flows up to 200cfm on the intake side and engine speeds up to 6,000 rpm. You will experience very good torque through the usable rpm, good power and it will be a FUN car to drive on the street. Power should be somewhere between 260-300HP at the flywheel (230-270 RWHP) depending on your head/cam combination and maybe a little more if you get a custom ground cam supplier to do a custom grind cam for you. With good transmission, gears, chassis, and 60 foot times you're into the 13s or 12s depending on weight and driving skill. For the money, it's hard to beat

Follow my guide on porting your own stock lower intake (http://tmoss.efidynotuning.com/ or http://tmoss.efidynotuning.com/) or let me do it and get rid of that factory power limiting intake port design.

Cobra/GT40/Explorer Intake
The Cobra intake has average flow of 205-210cfm. This is adequate for ported E7 heads or stock GT40/GT40P heads. If you use this intake with heads that flow more than 210cfm, then you will benefit from porting the lower intake. Just like the stock intake, the restriction in these intakes is in the lower. They can be ported to support a 250cfm flow rate head without welding the lower runners. My customers have made over 305RWHP/340RWTQ - 325RWHP/350RWTQ on 302-331 ci engines with ported Cobra style intakes.

Edelbrock Performer
The Performer flows about 210-215cfm in stock form and can also benefit from porting for heads that flow more - up to about 260 cfm. A customer that used my ported Performer lower on a 306 with AFR 165 heads made 332RWHP and 348RWTQ.
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Aerodynamic Engineer
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