Keep in mind, engines are more complicated than explained below. Lot's of air is good, as long as it can be taken advantage of. To take advantage of it, you need parts that prefer working as a team.
E7TE cylinder heads came equipped on all 5.0L Foxbody Mustangs between the years of 1987-1993. They featured a 1.782" intake valve and a 1.46" exhaust valve, with a combustion chamber size ranging between 60.6-63.6 cc. Factory port volume was 127cc intake and 44cc on the exhaust side with an average air flow of 125 CFM between 0.100" and 0.500" lift.
|Part||Port volume||Valve size||0.100"||0.200"||0.300"||0.400"||0.500"|
|E7TE cylinder head||127cc/44cc||1.78"/1.46"||55 cfm||110 cfm||142 cfm||160 cfm||157 cfm|
E7TE Cylinder Heads - What you need to know
It is common knowledge that a major restriction point, from a power perspective, is found within the factory-cast E7TE heads that originally came equipped with the Foxbodies. If you wish to understand WHY the E7 heads are the restriction, read on.
Essentially, an engine is one massive air pump. Air enters the cylinder chamber, fuel is sprayed in and the combination mixture of oxygen and hydrocarbons is ignited (courtesy of the spark plugs) and resulting explosion drives the piston, which in turn rotates the crankshaft, which in turn spins the flywheel mated to the clutch and transmission...yada yada yada. Gas mixture ignites, engine spins, car moves forward. You get the point. The interesting AND important notion here is that the power output is related to the quantity of air and fuel you can mix. Bigger the boom, more power will be had. Of course, why not just dump in more fuel? Wouldn't that make more power? It seems it would, but actually, no, it won't. As it turns out, there is a maximum threshold for a fuel and air mixture. Meaning, if you have x amount of fuel and y amount of air, there is a ratio between the two (x:y) that results in perfect burning efficiency. If you double fuel (now 2x) but keep air the same, y amount of air can only react with x amount of fuel, thus you have x amount of fuel left over, meaning it is unburned. The ideal stoichiometric ratio between air and fuel, to make maximum power, is 13:1 (13 parts air to 1 part fuel). Fuel, because it is controlled by a pump, can be added or removed at will with no impedances to whatever quantity is necessary. Thus, the limiting reagent is air! Hey, chemistry can be useful!
This means to make the most power, an engine should be optimized to flow the greatest amount of air. Cylinder head airflow is essentially static, determined by the passageways and contours of the head. They have a maximum limit of what they can flow. Fuel, on the other hand, is infinitely variable. Because we cannot control the amount of air (well, a turbo or supercharger does provide some measure of control, but this is a whole other topic) like we can fuel (remember, air is the limiting reagent) it is important to pick parts that flow well and similar to each other. The E7's, compared to modern heads, just don't flow enough. Their casting is just too restrictive. So, to conclude, the reason E7 heads choke the engine, is actually, they literally choke the engine. They just don't flow enough air into the engine. To squeeze some more ponies out of your 'Stang, upgrading the cylinder heads can lead to some substantial results.
Are E7's worth porting?
Quick and dirty, no, stock 87-93 Mustang E7TE cylinder heads are not worth porting. There is power to be had from porting even E7's, no doubt about that, but how much power will come, and at what cost? This is wherein the problem lies. Porting is expensive. A rough estimate would be to pay $500 to have a decent port job done on your E7's. The resulting power gain will probably be no more than 30HP. Of course. 30HP is better than 0HP, but it cost $500 to get it. Basically, E7 heads are not worth the money to pay someone to port.
Porting them yourself, on the other hand, why not? I'm always an advocate for free power. If you want some free HP (minus cost of burrs to port) and have a lot of determination, time and of course a steady hand, you can port E7's yourself. Mind you, porting is tricky business, so you must pay attention. It is entirely possible to reduce performance with a bad port job.
If you want to port E7's yourself, keep in mind 2 things.
A happy alternative for those on a budget is to look at picking up a used set of GT40 or GT40P cylinder heads. Read FiveOhInfo's Ultimate GT40 & GT40P FAQ for all the information you'll need on Ford GT40/GT40P cylinder heads.