Is it possible to coax 1,000...
Is it possible to coax 1,000 hp from the lowly Two-Valve mod motor?
When talk turns to maximum performance mod motors, the 4.6-liter Two-Valve variant isn't usually part of the discussion. Truth be told, there is a reason the Two-Valve motors take a back seat to the more performance-oriented Three- and Four-Valve combinations. It is a simple matter of valve count, or more accurately, the airflow that accompanies that missing valve.
Both the latest Four- and Three-Valve heads offer exceptional flow compared to the older Two-Valve motors. Sure, Ford improved the situation with the Two-Valve motors by offering the so-called Power Improved version back in 1999, but even the improved version was a far cry from its Three- and Four-Valve cousins. With similar displacement and wild cam timing available for all the mod motors, the thing that differentiates the Two-Valve from the Three- and Four-Valve motors is basically head flow. With little to no aftermarket support (until Trick Flow offers up its new Two-Valve head), the choice is limited to porting the stock castings.
The 5.0-liter displacement...
The 5.0-liter displacement came primarily from the 3.75-inch stroker crank (up from 3.54-inch) from Coast High Performance.
In stock trim there is no comparison, and this trend continues even once ported. Where a fully ported Two-Valve head may reach 245-250 cfm, a ported Four-Valve motor will be a minimum of 50-cfm, better and may actually offer as much as 100 additional cfm per cylinder. That is a big performance obstacle to overcome, and the main reason why the Three and Four-Valve motors will be chosen before the Two-Valve for serious power levels.
With all that buildup, you might assume this is a story on the superiority of the Three- and Four-Valve motors, but nothing could be further from the truth. Despite the valve deficiency, the lesser Two-Valve mod motors can be made to produce some serious power. Just how much you ask? How does an honest 1,000 hp sound? That is a big number in anyone's book, but a serious step for the lowly Two-Valve. Naturally such prodigious power will require the use of forced induction, something that will help us overcome the breathing inefficiency inherent in the Two-Valve motor.
The increased stroke length...
The increased stroke length required a dedicated piston and rod combination. The 13ccc dish pistons were combined with forged connecting rods to produce a reciprocating assembly capable of withstanding the punishment of 1,000 hp.
Another limitation shared by all the mod motors is bore spacing. When you go looking to increase the power output of your modular motor, think displacement. Unfortunately for modern Blue Oval enthusiasts, the basic architecture (actually, bore spacing) of Ford's modular motor limits the available bore size. It is possible to resleeve the blocks, but you'll never see the 4.125-inch or even 4.00-inch bores run on the earlier pushrod motors. With limited bore spacing, additional cubic inches must be obtained through increased stroke length. You can, of course, opt to install a larger 5.4-liter block, but the taller deck height creates hood clearance issues, not to mention the additional weight of the larger motor.
The best route to a powerful turbo motor is to start with an efficient naturally aspirated combination. When it comes to making power, there really is no replacement for displacement. Given the limitations of the bore spacing on the mod motor, the route to increased displacement must come from additional stroke length. By combining an increase in stroke length from 3.54 inches to 3.75 inches with a 0.020 overbore, the result is an increase in displacement from 281 ci (4.6) to 300 ci-the magical 5.0-liter displacement.
Thanks to companies like Coast High Performance, installing the longer 3.75-inch stroker crank into the 4.6-liter block isn't any more difficult than picking up the phone and providing a credit card number. CHP offers 5.0-liter (and 5.1-liter with the maximum allowable bore size of 0.070 over) stoker kits complete with the 3.75-inch stroker crank, forged connecting rods, and forged aluminum pistons. This combination will drop right into your professionally machined 4.6-liter block (iron or aluminum Cobra version) or the kit can be ordered as a dedicated short-block.