If the 3-valve 5.4L modular V8 was better than the earlier 2-valve version, why is the new 6.2L V8 offered next year a 2-valve design? Sorry in advance if this is a dumb question.

 

There are no dumb questions, actually that's a very good question. They did have problems with breaking plugs while extracting them but I would think that could be fixed. 3 and 4 valve per cylinder engines do perform better but cost more to make.................good question.

 

The new 6.2 is a 2V motor?

I assumed it was a 3V.

 

The number of valves per cylinder isn't as critical as the CFM flow of the valves. The 3V (and 4V) modular engines were designed to maximize flow compared to the 2V engines, but you have to realize that was using the existing engine platform. Since the 6.2L is a new design, the port flow can be easily optimized for 2 valves.

From Wikipedia: The 6.2 L (379 cu in) V8 is the main variant of the Boss engine. The V8 shares design similarities with the Modular engine family such as a deep-skirt block with cross-bolted main caps, crankshaft driven gerotor oil pump, and overhead camshaft valve train arrangement. In particular, the 6.2 L V8 features a 2-valve per cylinder SOHC valve train with roller-rocker shafts and two spark plugs per cylinder as well as dual-equal variable cam timing. The single most significant departure that the Boss engines make from earlier Modular engines is that they have much wider 115 mm (4.5 in) bore spacing (compared to the Modular's 100 mm (3.9 in)), allowing for the use of larger bore diameters and valves. The 6.2 L V8 specifically has a bore diameter of 102 mm (4.0 in) with a 95 mm (3.7 in) stroke. The 6.2 L V8 has lightweight aluminum cylinder heads and pistons but makes use of a cast iron cylinder block for durability since most applications for the engine will be trucks.[3]

 

Multiple valves per cylinder are done as much for valvetrain control as they are for flow rates. Large (read: heavy) valves are very difficult to control at the top RPM's that the modular engines run.

-blaine

 

So, if I understand correctly, the new 6.2L V8 is able to use larger valves to accomplish the flow rates desired. Something the smaller 5.4L block was not able to do because of cylinder head spacing. However, the larger and heavier valves may pose control problems at higher rpms. In other words, the engine may ultimately receive 3 valves anyway. Is this close?

 

sounds like they went to 2 vavles because all the variable stuff was getting a bit complex. They wanted 2 plugs to make it slightly cleaner burning.

I believe Honda first did a 4 valve head in the 60s for a 250 cc 6 cylinder race bike to keep the valves light enough to survive the 20,000 or so rpm they wound that engine up to. before that, it was assumed that 2 valve heads flowed better. The 6.2 isn't ment to be a top end engine, so it will do just fine with 2 valves

 

And I'll wager there will eventually be a high output 4 valve version! Fitting 2 spark plugs and 4 valves can get a bit tricky but BMW has done it for several years now. So Ford should be able to copy it for the next generation. Or at least go back to 3V.

Others hit the nail on the head - it's not just the number of valves, but how well the combustion chambers and ports are designed. There have been significant developments in these over the last few decades.

Also, the original 2V modular had all the valves in line. I believe the most significant improvements with the 3V came not by adding the extra intake valve, but by moving the intakes to the intake side and the exhaust to the exhaust side, greatly improving port designs and flow. That and much better combustion chamber design.

I'm assuming the new engine retains the better valve positions and ports?