Thoughts on compression ratio.

[Dumpling]

On a very large displacement engine, with very large intake ports, would something like the old 351C Weiand dual port make sense? Especially at lower rpms, in a heavy vehicle?

[gt350hr]

    Offenhauser made them. The problem is too much surface area. In the day , we "cut back" the separator from the flange almost three inches and it helped allot.

[Dumpling]

    Offenhauser made them. The problem is too much surface area. In the day , we "cut back" the separator from the flange almost three inches and it helped allot.

Helped how? Higher rpms?

They cut back the shared runners on the old Chrysler 300 long Rams, to help high rpm performance.

[Gaugster]

The cross section area and low RPM port velocity was my initial concern. Jay addressed that (in theory) way back for me. Good to see this topic come up again with more discussion. A 390, 428 or 427 based project is still up in the air for me. Depends on what the actual power is vs. available engine blocks/strength.

Another point is to recall that the cross ram intake is under development as well. Generally these have the butterflies lower which reduces the relative air volume on the vacuum side i.e. valve to butterfly. Another bonus for throttle response and and low RPM manners. Should complement the heads well. Again in theory.

[Joey120373]

I fully intend to use the cross ram intake, it’s what pushed me over the edge on using the heads.

Jay can chime in with more detailed specs, but to answer some questions I think I know the answer to,

The port cross section is only slightly larger than a stock MR, the port volume is larger but that is because it is a longer port, not because it is a bigger port. The heads flow something like 417cfm on the intake, so it’s not just a little better than current offerings, it’s a LOT better.

[jayb]

The port volume is bigger not just because of the added length, but also because of the valve size.  When you go to a larger diameter valve, you need a larger diameter bowl under the valve.  Plus, the more tulip shaped the valve is, the taller the bowl needs to be.  When I do the smaller valve version, the port volume will shrink up some.  All those dimensions are kind of designed to work together.  Part of the theory is to ramp the port velocity up along the intake tract to the choke point in the port, and then slow it down so it can negotiate it's way around the short turn and the valve while keeping the fuel in suspension.  I don't claim to know everything about this, and people like Blair or Joe who spend lots of time on the flow bench probably know more, but I know enough to get the port design into the right ballpark.  I think that has been born out with the flow numbers, and hopefully will be confirmed with the dyno testing.  But again the really big advantage of my heads is to throw off the basic FE architecture that all the other heads out there use, and improve the design with a raised, straightened intake port.