Mercury, I see the potential in the motor. It doesn't have any pushrods to deal with. So that opens up huge possiblities in head design. As far as I can see the only thing that has to remain the same is the intake port flange? Valve angles, spacing, etc are wide open ( upto the limits of the bore) along with the shape and contour of the ports themselves. That means big improvements in cylinderhead flow. What I don't care for is the overall external dimensions of the motor. A Y-block is nice and so is a super long connecting rod, but I think they could have gotten by with a regular block design and shorter rods. This could have trimmed some inches off the motor. Theres no cam in the block so deck height could have been shortened, etc. I think the big reason for the big little engine is NVH stuff for the most part, emmissions on the second. This can be seen in the smallish 3.550 bore and 3.550 stroke. Its designed for hi-speed low octane operation and low emmissions.
3.550 bore = reduced crevice volume (emmisions), reduced surface area minimizes thermal transfer and, the amount of ign timing, as well as controling the flame front better. This is why SB's can get away with more compression. It also reduces frictional loses.
On the downside the smallish bore does need a OHC cylinder head because valve area is limited by it's confines which means a much more efficent port is needed to get the same amount of air through to the cylinder (better discharge coefficent from the valve)
Cobra guys have it easier, but the 2 valve motors with the FRRP heads and no porting are stuck around 450 hp (naturally aspirated) which is 1.6 hp per cubic inch. BTW a 5.0 making 1.6 hp is 483 hp. To do that N/A on a 5.0 takes a little work. So its the same with a 4.6 at 450 hp. And for the BB guys a 460 is making 736 hp. All things being equal all three motors are producing the same amount of work relative to thier bore sizes. To get 500 hp N/A they are gonna have to do some fancy work to get about 243 cfm out of the ports on a 4.6. Good luck anybody who wants to try
|