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Message: <blockquote data-quote="blackfang" data-source="post: 2828" data-attributes="member: 8011">Difference in enginesB/Swirl Port: 96-98 CobraThe first and only production Ford head with two (square primary, round secondary) intake ports per cylinder, these swirl port castings arrived first in the Ã¢â‚¬â„¢93 Lincoln Mark VIII. Aptly named, due to the way they promoted the incoming air to swirl into the combustion chambers, much like water running down the drain of a once full sink.Through the years these heads have proven themselves to be excellent high rpm (8000rpm+) performersÃ¢â‚¬â€mainly in power adder applications--since their tremendous combined intake port cross sectional area and volume (when combined, a full 55cc more than any other 4.6L head design) provide for exceptional power production in the upper regions of the tach. Ironically, itÃ¢â‚¬â„¢s those same big, beautiful, twin ports that also prove to be the B headÃ¢â‚¬â„¢s largest inherent design flaw. The extra intake port size has a tendency to kill low/mid rpm intake port velocity and power productionÃ¢â‚¬â€hence the use of FordÃ¢â‚¬â„¢s first IMRC (intake manifold runner control) intake on the 96-98 Cobra. By allowing air to reach only one of a B headÃ¢â‚¬â„¢s twin intake valves, velocity, and therefore low/mid range torque production was restored in situations under 3250rpm. Later head designs are clearly superior in this regard, which happens to be the one of the most important considerations for those wanting a stout street motor.There is also some controversy over the single fuel injector/dual intake port setup. Some claim insufficient air/fuel mixing because of the compromised design, however, others contest that the ability to make 1000+rwhp with only minor porting and some form of power adder is testament to the contrary. Whoever you believe, there is little doubt that even after as little as 8,000 miles, carbon and other deposits tend to form on the secondary ports, causing a major airflow impedance, as there is no fuel present to clean them. B heads feature a somewhat small stock exhaust port that really hinders flow in power adder applications. Major gains from porting come with a quality valve job, some pocket and lots of exhaust work. There really isnÃ¢â‚¬â„¢t a lot of material to remove from the intake ports themselves.The Bottom Line: B heads arenÃ¢â‚¬â„¢t the best choice for a naturally aspirated street motor. In order to really shine, they need to be paired with a power adder and a short block that can sustain high horsepower and rpm levels. These, the oldest heads, may still be a great choice for full race applications.Stock Intake Choices: Ã¢â‚¬Ëœ96-98 Cobra.Aftermarket/Modified Stock Intake Choices: HCI, SSR, PHP.B head dimensions: Combustion Chamber: 52cc, Intake Port Vol.: 107cc primary (square), 115cc secondary (round). Intake Port Entrance: 1.500x1.300Ã¢â‚¬Â primary (square), 1.660x1.400Ã¢â‚¬Â secondary (round), Valves: 37mm Int., 30mm Exh.C/Tumble Port: 99/01 Cobra, These second-generation Ford DOHC heads feature a single intake port per cylinder with a smaller cross sectional area that boosts incoming airflow velocity compared to previous years. To understand how C heads earn their Ã¢â‚¬Å“tumble portÃ¢â‚¬Â designation, try to imagine an Olympic high diver doing repetitive front somersaults before cleanly entering a pool at the bottom. This controlled tumble allows for better air/fuel mixing than in the earlier swirl port heads. The new port design allowed for both substantial increases in midrange torque, and superior horsepower production under 8000rpm when compared with earlier heads. Combustion chamber size is also up 2cc.The design downfall of C heads, and their larger (5.4L Navigator) cousins, is the relatively flat floor and utter lack of a short turn radius in the throat of the intake port. As such, the incoming air tends to overshoot the valves, making the port think the valves are smaller than they actually are. Some Ã¢â‚¬Ëœ99/Ã¢â‚¬â„¢01 Cobra owners reported a Ã¢â‚¬Å“ticking/pingingÃ¢â‚¬Â noise coming from the drivers side head of their cars. This is due to insufficient cooling around the #6, 7, and 8 cylinders that allowed the valves to overheat and therefore seat improperly. Ford remedied the situation by issuing a TSB to remove and replace the affected heads with a version that featured altered coolant flow.C heads feature a small exhaust port much like FordÃ¢â‚¬â„¢s earlier swirl port heads, but unlike in B heads, both the intake (throat region) and exhaust ports can see extensive porting work. However, removing too much material from the intake port (mouth region) of a tumble port head will kill velocity very quickly, so make sure your head porter knows what they are doing!The Bottom Line: C heads remain a viable performance upgrade for those looking for more punch in their street driven 4.6L four valve, without having to pay new part prices for the Ã¢â‚¬â„¢03 DOHC or FR500 versions. The increased midrange torque production and greater overall area under the power curve (when compared to swirl port heads) will enhance the performance of a street/strip driven (8,000rpm and under) modular regardless of application.Stock Intake Choices: Ã¢â‚¬Ëœ99/Ã¢â‚¬â„¢01 Cobra, Ã¢â‚¬Ëœ03/Ã¢â‚¬â„¢04 Mach 1 & Aviator, Ã¢â‚¬â„¢03 Marauder, FR500.Aftermarket/Modified Stock Intake Choices: Al Papitto short runner/ported Ã¢â‚¬Ëœ99/Ã¢â‚¬â„¢01 Cobra, Sullivan, Aviator, '03/'04 Mach 1C head dimensions: Combustion Chamber: 54cc, Intake Port Vol.: 177cc, Intake Port Entrance: 1.960Ã¢â‚¬Âx1.350Ã¢â‚Â, Valves: 37mm Int., 30mm Exh. Also the 99+ Cobra went with a IRS rear axle verse the solid axle of the 96-98 Cobra. Here is a good link for some different links on each car<a href="http://scoa.org/legacy/" target="_blank">http://scoa.org/legacy/</a></blockquote>