My Tunnel Ram

FortFun said:

I made a tunnel ram .......

Click to expand...

Hey FortFun.... I have enjoying what you have been sharing since you got here!!!!

Especially about the work you have been doing with your "unique" intake manifolds.

But...... I am really "scratching my head" about the "Offy CrossRam"????? I do remember "Offy" offering crossram.... similar to the Edelbrock I have (that hopefully I will be able to get on the Opel over the Winter).....


....... BUT NOT a Offy CrossRam with staggered carbs mounting at different heights??????

Is the "Offy" an off-the shelf-model or have you also re-designed it like what you did with your "Tunnel Ram" ??????

And again...... welcome to the forum.

I am also "new here" & have been really enjoying the "forum-chatter", interesting & informative topics & lots of GREAT pictures posted by a great bunch of fellow hot rodders who also "love" gassers like I do.

The Offenhauser cross-ram I have is not modified. I became a dealer for them in 2004 and must have sold 80-100 of them over the next four years, through an E-bay store. The Offy cross-ram is a close copy of the GM piece made for the Z28 cars in the Trans Am series. There are long runners underneath the lid. The performance characteristics are just like a vertical ram. I put it on the Vette because I was tired of my engine looking like all the other old Vettes. With my 4.11 gears, wide ratio Muncie, big cam, and headers, the whole thing works fine. I don't really need low-end torque with my gearing and a 3200-lb car. You can get the Offy for about $500 new still. I quit selling them when we had some medical stuff going on in the family and I didn't have time to mess with the side business for awhile. Then Summit started selling them and I figured there was no way to compete with them. My big advice is to use 390CFM carbs. This is key because it gives you the best possible venturi velocity. You still have plenty of airflow available through the carbs, since it is a giant single plane. The Z28s used 585CFM carbs, but I think Holley didn't have anything smaller available at the time. The 390CFM was developed for restricted carburetion in NASCAR at Daytona, not sure when. Mine are double pumpers, but I might switch over to the vacuum secondary versions, so it will be more responsive at low RPM if you punch the throttle.

From what I've read, the side-by-side cross-rams with two separate plenums are pretty quirky. You have an uneven-firing situation in each of the plenums, combined with a tough fuel distribution problem due to where the runners attach to the plenum relative to where the carb is. The cylinders on the ends tend to run lean. Offenhauser made this type as well as the Z28-style. If you are not worried about ultimate power you can probably get it to run OK though. I would use 390CFM Holleys, and an MSD multi-spark box, and a lot of initial timing.

The Elco is awesome. It is so eager and responsive. Really a joy to drive. Gotta get some pictures up!