Thanks guys,
The MKII is moving along. The engine fired for the first time about a month ago. It is still on a run stand. The car sat on all four wheels for the first time about a month ago as well. We are still a long way off, but over the hump. We'll put pictures on here when it is all done.
I have just one set of headers left in the basement. I haven't heard of anyone actually getting them on a car. Ted Baird is probably the closest. We did put them on 1032. They fit fine. I'm glad to say that my welding and header fabrication has come a long way since those MKII pipes. I was lucky enough to learn from Wayne Church, RYRE's header fabricator.
Ron,
Please understand that I can't talk about work much. But we can play bench racer just for fun. The 4V mod was respectable for its time, circa 1996. It basically suffered from lack of development, as did most U.S. products during that decade.
The Mach I variant was a nice engine I thought. It had the power of the earlier cobras, but also had great torque.
About this time the company was occupied with launching the 3V. I feel this was also a decent engine for the time. It had a power curve very similar to the Mach I, but with two less cams and 8 less valves. Of course the mustang variants were all aluminum with mag cam covers and a plastic intake. The engine was pretty light given it's dimensions. It was also the first modular with cam phasers.
Please, let me make this clear... VCT, particularly TiVCT, is the single greatest advancement in IC engines since electronic fuel injection. I could write a book about the benefits. It is good for NVH, emissionis, fuel economy, torque, AND power. Very few technologies can say that. We owe a debt of gratitude to the 3V for the path that it blazed.
Ron, I am a pushrod man as well. Well I am a split personality. Pushrod at home, DOHC at work. Hobby and work are two very different things. When you are racing it is all about weight, power, and simplicity. Production engines are all about fuel consumption at part load, NVH, and emissions.
I'll just talk about some of the tradeoffs between 2V pushrod and 4V DOHC. There really isn't a right answer. It just depends on what your objectives are, and what you currently have available.
4V heads have more valve area for a given bore diameter
2V heads have higher discharge coefficients, meaning they flow more for a given valve area
4V heads have smaller valves that weigh less, and therefore you can lift them higher (in therms of lift/diameter) than 2V for a given RPM. Basically, 4V heads can have a more aggressive lift profile than 2V heads with equivalent valve area.
2V only needs one cam and one timing chain without a tensioner, reducing friction.
OHC enables a stiffer valvetrain with less moving mass. This enables the engine to spin higher for a given lift profile.
Pushrod valvetrains are not stiff at all. Stability at high speed is a serious issue. Pushrod engines can deactivate cylinders very cheaply however.
4V enables TiVCT, while 2V is generally limited to DeVCT, save for the Viper. The biggest advantage of TiVCT over DeVCT is broadness of the torque curve. You can set the DeVCT up for peak torque or peak power, but not both. This is because the valve overlap is fixed.
A big bore helps power because you can fit a larger valve in it. A long stroke does NOTHING for torque. If an engine is under square, that does not mean it is torquey. It simply means it cannot fit enough valve in there to rev as high as an oversquare engine. The over square engine CAN be set up to produce the same torque as the under square engine however, this is rarely done.
A small bore helps emissions because there is less crevis volume. A small bore also helps fuel economy because there is a lower surface/volume ratio. Larger displacement per cylinder is also good for fuel as well though. A 4-cylinder 2.5L will typically do better with fuel than a 2.5L V6 because there is less surface area to transfer heat.
Shorter stroke is good for friction because friction scales with mean piston speed. So you could say that short stroke is good for fuel economy.
That's basically it. So lets compare a hypothetical 5.0L-4V to a 6.2L-2V.
5.0-4V:
Small bore = fuel +, power -, emissions +
OHC = fuel - (friction), power +, emissions neutral
4V = fuel nuetral, power +, emissions neutral
displacement = fuel +, power -, emissions +
TiVCT = fuel +, power +, emissions +
6.2L-2V:
Big bore = fuel -, power +, emissions -
Pushrod = fuel + (friction), power - (RPM), emissions neutral
2V = fuel +, power -, emissions neutral
displacement = fuel -, power +, emissions -
DeVCT = fuel +, power neutral, emissions neutral
Cylinder deactivation = fuel +, power neutral, emissions -
So in the end which is better? Both engines make about the same power and have about the same fuel economy. They both weigh about the same. The 6.2L makes a little more torque, but the 5.0L can rev higher. If geared properly they will both deliver the same torque to the wheels.
What you are seeing is two different ways to skin the same cat. What is more interesting to me is the method of attack. Some general observations.
4V engines will generally have smaller bores because they can get equivalent power out of them. 4V engines will spin higher because their valvetrains can take it, and will therefore have higher specific outputs. For fuel economy, 4V engines need to have smaller displacement to make up for their increased friction.
That's really it.
As far as 5.0L competitors... It really has two competitive sets. One set makes similar power, while the other has similar specific output.
Similar power engines:
GM 6.0 and 6.2's
Mopar 6.1's
Similar specific output:
Lexus 5.0L
Jag 5.0L
You guys decide how they stack up given their content, pricing, and availability.